Atmosphrric
Encironmrnr
Vol. 10. pp. 181-194.
Pergamon
Press 1976. Prmted in Great
Brltaln.
MEASUREMENTS OF ATMOSPHERIC POLLUTANTS IN THE ST. LOUIS AREA R. J. BREEI)ISC;*.H. B. KLOKIS~.J. P. L~Dc;E. JR.:. J. B. PA&. D. C. SHEESLEY~.T. R. ESGLERT,Iand D. R. S~;ARS’ National Center for Atmospheric Research.** Boulder. CO 80303. U.S.A.
Abstract-Measurements of the concentrations of trace gases and particles have been made in the plume from metropolitan St. Louis at 80 and 120 km from the urban center. The concentrations of SO1, N&, NO, NHJ, H2S, aldehydes, CO, total hydrocarbons, and CFCI, were determined. The concentrations of many of these gases were found lo be significantly higher in the plume than outside the plume at these distances. Measurements were made near the ground and from an aircraft. The width of the plume was usually between 20’ and 30’. which is less than had been expected. By comparing the concentrations measured at 80 km from the city with those measured at 120 km from the city. and using the decrease of conservative trace gases to account for loss through physical process. we have arrived at preliminary estimates of the decay rates for a few trace gases. The evidence is most compelling for sulfur dioxide. and it appears that. at LX. 100 km from the city. the overall half-life of SO2 is between 2 and 8 h. INTRODUflIOS
The Fate of Atmospheric Pollutants Study (FAPS), conducted by the National Center for Atmospheric Research (NCAR), was an attempt to find out what happened to some of the most common atmospheric pollutants after they left their urban source areas. The general method was to measure the concentrations of a number of gaseous and particulate species and to use the ratio method to discover the in situ rates of reaction. The ratio method depends on determining the ratio of the concentrations of reactive to nonreactive species at different distances from the source area. The decrease of the concentration of the nonreactive species with distance enables one to account for the loss of urban effluents through physical processes such as dilution and diffusion. The more rapid decrease in the concentration of the reactive species is due to these physical processes plus chemical transformations. The reaction rate may be calculated from the change of the ratio with distance and the time it takes the air parcel to move from one sampling location to the other. If there were several competing removal mechanisms operating simultaneously. this
* Present address: Energy, Inc.. P.O. Box 736. Idaho Fall, ID 83401. U.S.A. + Present address: Terran Resource Management Associates, Inc., P.O. Box 572. Addison. TX 75001. U.S.A. : Present address: Consultant in Atmospheric Chemistry. 385 Broadwav. Boulder. CO 80303. U.S.A. 9:Present address:. Ambient Analysis. Inc.. P.O. Box 4056. Boulder, CO 80302, U.S.A. ,I Present address: Colorado Department of Health,
Dirango, CO 81301, U.S.A. . P Present address: College of Engineering, West Virginia University, Morgantown. WV 26506. U.S.A. ** National Center for Atmospheric Research is sponsored
by the National
Science
Foundation.
method would give only the overall loss rate or an effective removal rate due to all of the processes, unless the increase rate of the individual products of each mechanism could be determined. In these preliminary field tests, ground and air measurements were made on arcs of 80- and l20-km radius around St. Louis, MO. The center of the St. Louis metropolitan area was taken to be the Arch (Gateway Arch, Jefferson Expansion National Memorial). which is a conspicuous feature on the Mississippi River near the commercial center of the city. In the past several years persistent winds have brought the plume into the quadrant north of St. Louis more frequently than they did into any other quadrant. so most of our measurements were made in this quadrant. Most sampling was done in the afternoon when vertical mixing was most vigorous. but one sampling period was in the early morning under stable conditions. Figure I shows the major rivers and cities of the area around St. Louis. In the October 1972 field test. the sites where a measuring station might be set up were located 18’ apart on the l2@km arc. and there was only one site (Hamburg) on the 8O-km arc. (On the 120-km arc, I8 = 37.6km). This spacing proved to be too coarse, so for the April 1973 test, the sites were located 9’ apart on both arcs. The sampling sites were usually fallow fields as far removed as practicable from main highways and occupied houses. A number of instruments, including gas chromatographs. which required line electricity and which were too delicate to move frequently were located at the Glasgow site. I06 km from the Arch. In addition to making continuous measurements during the sampling episodes, these instruments were used to analyze samples collected field station.
in bags or syringes
at the regular
182
R. J.BREEDING
et al.
80kmt
_:-. 1120km
Fig. 1. Map of the St. Louis area showing the 80- and 120-km arcs and the site locations. Two aircraft were used in both field tests. The NCAR Queen Air was equipped to take bubbler and bag samples and was equipped with a condensation nucleus (CN) counter. In April 1973, a nephelometer and an oxidant monitor were added. The primary mission of the Queen Air was to fly back and forth within the plume to measure concentrations aloft in the plume. The other plane, a Bonanza flown by Prof. J. F. Stampfer, Jr. (University of Missouri at Rolla) had the location and delineation of the plume as its primary mission; most of the Bonanza flights were therefore made prior to the more extensive sampling. The Bonanza was equipped with a light-scattering instrument which measured the number of particles in two adjacent size ranges. Both aircraft had temperature, dew-point temperature, and pressure recorders. Although these field tests were designed to be preliminary experiments, this program was terminated sooner than originally planned. Thus, the data reported here may be fragmentary since the “preli-
minary” field tests became in fact the “final study” only after they were completed. The purpose of this paper is primarily to report the results of the reactive gas measurements. The results which more directly concern meteorology, the prediction of the plume’s position, and the measurements of the continuously operating instruments aboard the aircraft, have been reported elsewhere (Stampfer, 1972; Stampfer and Anderson, 1974; Breeding et al., 1975; Haagenson and Morris, 1974). We use certain information from these papers as to the plume’s position, width, and behavior without explicit reference. Heights are given in meters above mean sea level. Times are reported in Central Daylight Time for the October 1972 field test, and in Central Standard Time for the April 1973 field test. Positions along the arcs of radius 80 or 120 km about the Gateway Arch in St. Louis are given in degrees: positive (clockwise) from north and negative (counterclockwise) from north.
Atmospheric pollutants in the St. Louis area MEASUREMENT
TECHNIQUES
At about 100 km from the center of an urban area, concentrations of the common pollutants in the plume are not far above the background concentrations. We were not able to find any real-time instruments which were sufficiently accurate, reliable, and inexpensive to be used at all the ground stations. Thus. we relied on methods which were quite accurate but required 45-60 min to take a sample. Sulfur dioxide (SO,), nitrogen dioxide (NO,), nitric oxide (NO), ammonia (NH,), and aldehydes ‘(ECHO) were removed from the air by wet scrubbing (bubbling) for about an hour; the scrubbing solutions were analyzed by standard calorimetric analytical methods. To remove hydrogen sulfide (H,S), the air was drawn through a sensitized filter at the same time that the air was being drawn through the bubblers (Natusch rt al., 1972). The analytic methods, sensitivities, and accuracies for all of these methods (except the NO method) have been described in Breeding et al. (1973). These five methods were not changed from October 1972 to April 1973. Although NO was measured in October 1972, the method used then was inadequate and we have not reported any NO concentrations from that field test. The method has been improved and we are confident of the NO levels we report for the April 1973 field test. The improved method for NO is essentially that given in Methods of Atmospheric Analysis (Intersociety Committee, 1972). The air is first passed through ground firebrick which has been soaked in triethanolamine to absorb the NO2 and then through ground firebrick which has been soaked in chromium oxide to oxidize the NO to NO*. Tests showed the absorption of NO, and the oxidation of NO to be nearly 100 per cent efficient under the conditions in which this method was used. When five or six bubblers were operated side by side at the Glasgow site on 15 April 1973, the following concentrations and S.D. were obtained: Concentraton Gas SO* NO, NO
NH, RCHO
‘K’;’ 2.54 0.29 4.00 2.46
SD. 0.23 0.08 0.1 I 0.59 0.46
Carbon monoxide (CO), methane (CH,), and total hydrocarbon (THC) were measured by a Beckman 6800 gas chromatograph. To determine the CO concentration, the CO is first reduced to CH4 using hydrogen and a nickel catalyst. Samples were taken in Mylar bags at the ground stations and aboard the Queen Air, and later analyzed by the chromatograph at the Glasgow site. The concentration of fluorocarbon-11 (CFCl,) was determined by taking syringe samples at the site and later injecting them into a * The transport vector is defined as the wind vector averaged throughout the ground-based layer. Usually a mixed layer, this would be an inversion layer if a normal nighttime
period
were being discussed.
183
gas chromatograph. (A description of this instrument is not yet available in the literature, but similar measurements are described in Simmonds et al. (1974). This substance is hereafter referred to as “freon” for convenience; it does not imply any particular manufacturer. The concentration of nitrous oxide (N,O) was determined by the method of LaHue
et al. (1973). The instrumentation of the Bonanza and its use. in determining the location of urban plumes at distances on the order of 100 km have been described by Stampfer (1972) and by Stampfer and Anderson (1974). The instrumentation of the Queen Air and a comparison between the plume indicators aboard the two aircraft are contained in Breeding et al. (1975).
October 1972 jield test On 20 October 1972 ground stations were set up at the Hamburg, Bowling Green, Summer Hill, Glasgow and Orleans sites. Sampling took place from 13 : 00 to 17 : 00 h. Aircraft and radiosonde ascents indicated that the air was well mixed from the ground (which varied from 150 to 220 m above sea level in the sampling area) up to the inversion base at 800m MSL. Skies were overcast during the sampling episode and light rain fell at some of the stations. From IO:00 to 17:OO h on this date, the transport vector* varied from 140” to 150” at 7 m s- ‘. The results of the sampling on 20 October 1972 are shown in Fig. 2. Every indication from the first sample is that the plume was centered over Hamburg and Summer Hill at -32”. The results from the four outer stations in the second sample show that the plume center was still near -32”. but the low values for SO2 and NO, concentrations at the four outer stations again show the plume at -32” and again the Hamburg concentrations are much lower than those at Summer Hill. However, the third-sample CO values indicate the plume center may have been west of -32“ while the freon values indicate it was likely to have been east of -32”. The plume’s position as determined from the reactive gas concentrations at the four outer stations is in good agreement with the transport vectors calculated from the meteorological data alone. The data from the aircraft traverses indicated that the plume center was slowly changing from about -35” at the beginning of sampling at 13:00 h to about -45” or - 50” at the end of sampling at 17:00 h and that it was only 15”-20” wide. Of the third-sample gas data, only the methane and CO data support a shift this far west. The reason for the low SO, and NO, values at Hamburg is not known. The flow continued from the south so another sampling episode was conducted between 03:OO and 07:OO h on 21 October 1972. The southerly flow brought moist air up from the Gulf of Mexico and prevented the usual ground-based nighttime inversion from forming, although mixing during the sampling episode was certainly not vigorous. This situ-
R. J.
184
BREEDINGet al.
ation caused light rain to fall steadily at almost all the ground stations. The transport vector was estimated to have come from 175” to 185” during the sampling at 9-10m s-r. The results of this sampling episode are shown in Fig. 3. Of the four outer stations, the SO, and NO, concentrations were highest at the Glasgow site during each of the three sampling periods, indicating that the plume centerline near the ground was probably around - 15”. Estimates of plume width from particle
Fig. 2(c). Fig. 2. Variation of trace gas concentrations with position on 20 October 1972. The first air sample was taken at 960m MSL between -6’ and -58” on the 120-km arc. The second air sample was taken at 450m MSL between -6” and -55” on the 120-km arc. The third air sample was taken at 450 m MSL between - 17” and -60” on the 80-km arc. The midpoint times for the ground samples were 13:30, 15:OOand 16:30h.
Fig. 2(a).
measurements made from the aircraft in the early hours of 21 October vary from 20” to 3.5”. Sampling from the aircraft occurred south of St. Louis on 24 October 1972. On this date there was very little directional shear with height and the unstable conditions extended up to 630 m. The transport wind was from 350” at 7m s-l. The first flight was certainly in the well-mixed portion of the plume at 480m, but the last two samples were taken too close to the top of the mixed layer to be definitely representative of the plume. Sampling results are given in Table 1. Table 1 also contains the results of early morning and afternoon sampling flights on 26 October to the north of St. Louis. The morning flights took place in a wind situation that made it difficult to ascertain the plume’s location. The samples were taken just above or near the top of the inversion layer. By the time of the afternoon flight on 26 October, the air was apparently well mixed up to 630m, and directional shear with height was considerably reduced. The transport vector came from 17W180 at 5-6 m s- 1 during the sampling period. All flights were well below the top of the mixed layer and particle measurements obtained from the aircraft indicated that the plume maximum was near +5” and the plume width was about 25”.
Atmospheric pollutants in the St. Louis area April 1973jeld
185
test
During April 1973 three sampling episodes took place in the quadrant north of St. Louis. Both aircraft and ground measurements were made during each episode. During the October 1972 field test the plume width often appeared to be of the same order as our station spacing (18”), so for this field test the spacing between sites was reduced to 9”. Because equipment for only six ground stations was available. and put-
Fig. 3(c). Fig. 3. Variation of trace gas concentrations with position on 21 October 1972. The first air sample was taken at 810m MSL between - 17” and 0” on the 120-km arc. The second air sample was taken at 450 m MSL between - 28” and + 19” on the 120-km arc. The third air sample was taken at 450 m MSL between - 17” and + 18” on the 80km arc. The midpoint times for the ground samples were 03:30. 05:OO and 06:30h.
Fig. 3(a).
*ZIM”TH, 21 OCTOBER
degrees
1972,SECONO SAMPLE
Fig. 3(b).
ting three stations on each arc would cover only 18” of arc, it was decided to attempt this arrangement of ground stations only once. For the other two sampling episodes all six stations were placed on the 120km arc. On 11 April stations were set up at the three easternmost sites on each arc, with sampling to begin at 13:OOh on the 80-km arc and at 14:4Oh on the 120-km arc. The lOO-min delay was approximately the time required for pollutants to travel the 40km between the sampling stations. The skies became increasingly overcast as the sampling continued, so mixing was probably not vigorous at the end of the sampling period. At the beginning of the sampling, the transport wind was from 225” at 9 m s-l, and the lapse rate was approximately dry adiabatic up to 1000 m. By the end of sampling at 19: 00 h, the top of the mixed layer was down to 600m and the lapse rate was considerably less than dry adiabatic. The transport wind at 19:00 h was from 215” at 8 m s- ‘. The results of the sampling on 11 April 1973 are given in Fig. 4. During the April 1973 field test, the Queen Air gas samples were taken while the plane flew a Z-shaped path through the plume, so no single height can be assigned to the aircraft samples. The purpose of this flight pattern was to obtain a more representative
R. J.
186
BREEDING et al.
Table 1. Concentration of trace gases measured from an aircraft in the St. Louis area on 24 and 26 October 1972. The rows with FBA in the time column contain the average of the field blanks for that site. The concentrations have been corrected for this field blank value Gas ConcenCrarion
h-b) site
Time
H2S
1402
0.25
FBA 1510 1623
0.15 0.20
so2
NO*
NH3
RCHO
co
CR4
a-eon
442
1600
1.29
471
1570
1.07
444 591
1560 1690
435
1630
580
1710
24 October
Air 80-km arc 480 m Air lZO-km arc 570 m
26 October Air 80-km arc 360 m 540 m Air 1*0-!a arc 390 m 540 m 360 m
15.3 0.0
-0.3
AVG
0.24 0.23
9.4 13.1 24.2
0400 1340
0.12 0.24
25.0 23.5
4.4
0.14 0.16 0.13 0.12 0.25 0.24
0.0 0.0 22.3 13.5 15.7 16.1
0.0
FBA (am) FBA (pm) 0516 0631 1453 1606
of the plume. The first traverse was a few hundred meters below the top of the mixed layer; during the second traverse the plane descended from that height to a few hundred meters above ground level. The ground station data do not indicate conclusively the location of the plume on 11 April. Since they covered only 18” of arc, this was not unexpected. Particle concentrations measured aboard the Bonanza along the 120-km arc indicated that the plume was about 30” wide, and that the plume center at 500 m was near 45”. Plume curvature on this date, and the lag of plume behind the transport vector when the wind direction is changing have been discussed by Haagenson and Morris (1974). On 14 April sampling took place from 1l:OO to 15:30 h at six stations set up on adjacent sites on the 120-km arc from Summer Hill (-32”) to Loami (+ 13”). All the meteorological measurements indicate that the air up to 9WlOOOm was well mixed during the sampling period. The transport vector for this layer was from 160” at 10m s- ’ during the entire sampling period. Light stratus were present when the sampling started, and by the end of the last sampling period all of the sky was covered by heavy stratus. Figure 5 presents the results of the 14 April measurements. In spite of wind and mixing conditions which should have been ideal for producing a welldefined urban plume, the locations of the plume maximum and plume edges are not clear from the measurements either near the ground or aloft. The mixing was vigorous up to 700m by IO:00 h, and the transport vector had been from 160” since 08:OOh so the plume center should have been near -20”. This location agrees with that indicated by the aircraft particle measurements at 300m made near 13:30. On 14 April the correlation spectrometer of Environmental Measurements, Inc., was operating in this area; the results of four traverses along roads sample
3.4
0.0 0.1
4.5 10.2 7.4
-0.2 1.0 0.4
6.6
3.4
-0.3
-0.7
5.5 7.8
3.0 3.3
5.4 3.6
approximating the 80- and 120-km arcs are shown in Fig. 6. Overburden is the integral of concentration with height. The concentrations labeled “SO, ground” were actually measured with a Melloy flame photometric total sulfur analyzer amd may overestimate the sulfur dioxide concentration, but the trend is significant. Unfortunately, two of the traverses occurred after the sampling at our ground stations had been completed, but it certainly does appear that the plume center was near - 12” at 15: 30 h on the 80-km arc. The long traverse of the 120-km arc took 3 h, and we cannot be certain that the plume did not change during that time. Nonetheless, a maximum was found in the -20” to - lo” region where the plume would have been expected to be from the meteorological data alone. The NOz peak at -38” is probably related to a fertilizer plant just south of the 120-km arc near Louisiana, Missouri. The peak at +28” is very likely due to a large coal-burning electrical generating station near Coffeen, Illinois. On 17 April the speed of the transport vector remained close to 6m s-’ throughout the day, but its direction varied due to the weakening stationary front. It was from 140” at 08:OOh, from 165” at 12:00, h, and from 180” at 16:OOh. Sampling took place at the six westernmost sites on the 120-km arc from 12: 30 to 17:O0. The results are shown in Fig. 7. Skies varied from a 50 per cent cover of scattered cumulus to clear. The top of the mixing layer was at or above 700m during the sampling. Ground station data show that the plume was relatively broad, but all the concentrations of both reactive and nonreactive species agree as to the location of the plume near the ground. It seems clear that the plume was centered between - 50 and - 40” during the first sampling period, was near -35” during the second sampling period, and was around -27” during the third sampling period. A Bonanza flight starting at 12:22 on the 80-km arc and another flight
II APRIL
ICI
io
4.0
5ii ll APRIL
10
1973,
30
40
AZIMUTH, degrees SECOND SAMPLE
20
II APRIL
10 1973,
THIRD
$0 SAMPLE
AZIMUTH,
io
Fig. 4. Variation of trace gas concentrations with position on 11 April 1973. The air samples were taken during a Z-shaped flight which took the plane from a few hundred meters below the top of the mixed layer to within a few hundred meters of the ground and from one edge of the plume to the other. The gas sampling took place between i-28. and +67’ on the 80-km flights and between -1-24” and t-49’ on the 120-km flights. The midpoint times for the samples were 13:26. 15:07 and 17:07 h on the 80-km arc, and 15:02, 16:47 and 18:47 on the 120-km arc.
degrees AZIMUTH, 1973, FIRST SAMPLE
?o
40 degrees
.-.
degrees
t.
120 km orc-
20
-;o
14 APRIL
AZIMUTH, 1973, SECOND SAMPLE
; degrees
lb
?b
t
L 14 APRIL
40
0
40
0
-a
I?
16
;.a 04
.._ 0.8 0.
-20
-10
AZIMUTH, 1973, THIRD SAMPLE
-30
A
Fig, 5. Variations of trace gas concentrations with position on 14 April 1973. The air samples were taken during a Z-shaped flight which took the plane from a few hundred meters below the top of the mixed layer to within a few hundred meters of the ground and from one edge of the plume to the other. The gas sampling took place between -2” and -40” on the 80-km flight and between +6” and -39” on the 120-km flights. The midpoint times for the ground samples were 11:22, 13:07 and 15:07 h.
AZIMUTH, 14 APRIL 1973, FIRST SAMPLE
.
-
0
0
degrees
0
10
20
AIR VALUES
189
Atmospheric pollutants in the St. Louis area
c
“Q SOz 20
0
120 km
100
0
”
_._.-._J I
-40
100
I\
“-.-_._._./’
I
I
I
I
I
-30
-20
-10
0
IO
AZIMUTH,
‘.L__j I
I
/
20
30
40
0
degrees
Fig. 6. Variation of SO2 and NO2 overburdens and surface SO2 concentrations with position on 14 April 1974.
commencing at 13: 19 -on the 120-km arc both found maximum particle concentrations near -40”. The plume width appears to be 20” or less, but the data are somewhat ambiguous. In spite of the rotation of the wind vector, the plume was well defined on 17 April 1973. The location of the plume center as a function of time has been discussed by Haagenson and Morris (1974).
TRACE GAS CONCENTRATIONS
Although the measurements of trace gases that were made during these field tests did not always succeed in unmistakably locating the center and edges of the plume, on every occasion that we expected to be close to the plume, we succeeded in finding concentrations of many gases which were much higher than the background values in this region (Breeding et al., 1973). We take this as evidence of the presence of a plume from the St. Louis area or from other anthropogenic sources. While small local sources cannot be ruled out completely, the location of the large sources outside the metropolitan St. Louis area and outside the Alton-Wood River area are well known. Sulfur dioxide is certainly one of the most ubiquitous effluents in a city like St. Louis where coal is a major source of energy. The highest SO, concentration we measured was 42ppb at Summer Hill on 20 October 1972. Except for this date, no sulfur dioxide concentrations near the ground exceeded 20ppb, but on every sampling date at least one
station recorded values of 15 ppb or higher. Aircraft values exceeded 15 ppb only on 20 and 26 October 1972, and generally were in the range from 10 to 15 ppb when we expected the plane to have been in the plume. We did not expect that the NOz concentrations would be as high as the SO, concentrations, since the St. Louis metropolitan area emits less NOz than SO2 (Venezia and Ozolins, 1966). Further, NOz is largely produced by automobiles and therefore the NO* sources are more widespread spatially, but more variable in time. NOz concentrations as high as 20ppb were measured in the morning of 21 October 1972 and as high as 15 ppb on the afternoon of 20 October, but in April 1973 the high value at the ground stations each day was between 7 and 10 ppb. The NO, concentrations found from the aircraft were mostly between 5 and 9 ppb. The measured concentrations of NO were approximately a factor of 5 lower than the NOz concentrations. The highest values measured were 5.6 ppb at Summer Hill and 4.3 ppb at Louisiana on 17 April. The concentrations aloft (3.3, 2.4 and 2.3 ppb) were also higher on this date than during the two previous sampling episodes. The ratio of the NO1 concentration to the NO concentration shows interesting variations (Fig. 8). From our measurements in April 1973, this ratio is seen to vary between 0.8 and 14.3. The value of this ratio for the ground stations was calculated using only those stations which we felt were within the plume. (For comparison, for St. Louis County, this ratio was between 0.3 and 1.0 for the period 08:0&13: 00 h on 20 October 1972 and between 1.0 and 3.0 for the period from 22:00 h, 20 October to 03 :OO,21 October 1972). It appears that the variation of the NOz:NO ratio may be about 180” out of phase with the diurnal variation in ozone concentration. Since NO is produced fom NO, mainly by the reaction NO, + hv+NO
+ 0,
the rate of which depends on the intensity of light in the near ultraviolet region, and since most of the sampling sessions ended in the late afternoon or at dusk, the rise of the NO,:NO ratio is to be expected. Ammonia is a ubiquitous trace gas in rural regions and. as expected, its concentrations did not appear to correlate with the plume’s presence or with the concentrations of other gases of primarily anthropogenie origin. And no reduction in the ammonia concentration was noted when the aircraft sample was taken above the mixed layer (e.g. the sample taken from the Queer] Air at 14:08 on 20 October 1972). Although aldehydes are known to be common reaction products of metropolitan effluents, we found no correlation of RCHO values with the plume location. The maximum concentration of 11 ppb was measured on 14 April 1973. There was some correlation of aldehyde concentration with the amount of solar radiation reaching the ground, however. On 14 and 17
.q ~~:91 pue LE:PI ‘~S:ZT aIaM safdtues puno~8 ay3 JOJ sawg tu!odp!ur ay& wf%f~ UT-0~1 ayl uo .fj~- pm .gz-- UaaMlaq pue ]q8!y ury-08 ay$ liluy~p .~p- pun ,p[ - uaamlaq acm[d 7001 Buqdms sa% ayJ_ ‘Jaylo aql 01 amnld aq] JO aspa auo mOlJ puv punoZ3 aql JO walam palpunq MaJ e mqI!M 01 sIadv+ pax!m aql Jo doI aql MOpq slajam paJpunq MaJ e U~OJJ autqd aql ~00, q3!qM )q%y padeqs-z 8 8uynp ua?el aJaM saldmes .I!= aqL ‘~~61 Iydv ~1 uo uoy!sod q$!M suoyJluawo3 stz?8aDwl JO suo!~epe~ ‘L %,J
Atmospheric pollutants in the St. Louis area I
I
I
I
I
I
I
a whole were significantly lower than the October 1972 concentrations. Scatter or correlation plots were examined for all the combinations of the concentrations of SOZ, NOz, NO, aldehydes, NHa, and HIS. The concentrations of SOZ, NO*, and NO showed a definite tendency to be correlated with each other, but the other three gas concentrations showed no correlation with any other concentration.
I
I6 -
e
0 GROUND
120 km
16-
+ GROUND
80 km
14-
A AIR 0 AIR
,2 _ lo-
--.-.-. -
120 km 80 km
,
II APRIL 14 APRIL I7 APRIL
0
/
/
/
/
/O-
/’
-
,’ h
191
6RATIOS AND HALF-LIVES
642 c/
t 01 1000
1
I
I
I
I
1200
14 00
1600
1FJ:00
TIME,
I
h
Fig. 8. The change of the ratio of the concentration of NO2 to the concentration of NO with time. The ground station values were averaged before the ratios were formed. On 14 April, the data from the Orleans and Loami sites has been excluded, and on 17 April the data from the Lynnville site has been excluded, because these sites were not clearly on the plume. On 11 April the results from the Taylorville station were not used since the NO concentrations were unreasonably low.
April 1973, with clear to partly cloudy skies, the average aldehyde concentrations were about 6ppb. But on 20 October with heavy overcast and some rain, and on 21 October 1972 when the measurements were made before dawn, the RCHO concentrations averaged about 1.5 ppb. Carbon monoxide is largely produced by automobiles. On most days we found maximum values between 540 and 630 ppb both near the ground and aloft. On 11 April, however, the maximum value found aloft was only 360ppb. On 14 April, although values aloft were between 500 and 530ppb, values were over 700ppb at every ground station but one. The maximum of 930ppb was measured at the Detroit site. Hydrogen sulfide does not seem to be obviously related to the urban plume. Although it is given off in some industrial operations, such as the sulfite process used by a paper board factor in Alton, Illinois, a major source is suspected to be the decay of vegetation in rural areas. Maximum values during each episode ranged from 0.28 to 044ppb on the ground and from 0.11 to 0.33 ppb aloft. The concentration of fluorocarbon-11 (CFCl,) was found to be a fairly reliable indicator of the plume from metropolitan St. Louis, although not as trustworthy as SO,. The concentrations were of the same order as measured by other studies (e.g. Simmonds et al., 1974). The maximum for each episode except 14 and 17 April was between 3 and 4 ppb. These last two episodes had significantly lower freon values than the other days, and the April 1973 values as
The ratio method of determining the rate of increase or decrease of a substance is based on the assumption that the fluid being sampled is well mixed and that diffusion will affect both reactive and nonreactive species alike. Thus the decrease in concentration of the nonreactive species between two points of measurement can be laid to diffusion and a similar amount of diffusive loss can be expected for the reactive species. Let C,(x) and C,(x) be the concentrations of the nonreactive and reactive species, respectively, at distance x from the source. And let B, and B, be the background concentrations for the two species, respectively, that is, the concentrations one would expect to measure in the same area where no large sources were upwind. The ratio of ratios, Q, is defined:
Q=
C,(l2Okm) - B, CJ120km) - B, -I C,(8Okm) - B, >( C,(80 km) - B, > .
If it takes time, t, in min, for the material to travel the 40 km between the two measuring arcs we used, then the half-life, in hours, can be derived from Q:
A negative half-life means that the reactive species was increasing and the negative of the half-life (which is positive in this case) may be interpreted as the doubling time. Figure 9 represents plots of Q versus time for SOZ, NOz, NO and ozone. Although there are very few ozone values, these have been included because they group very well. The instrument used to measure the ozone concentrations is a Komhyr-type instrument built by Wartburg of NCAR (Komhyr, 1969). Strictly speaking, this instrument measures total oxidant. Since by far the bulk of the oxidant measured is ozone, however, it has been referred to as ozone throughout this paper. The ozone level for each flight is an average of the values measured during the Z-shaped traverse through the plume, and should be roughly representative of the plume as a whole. At the ground stations the nonreactive species whose concentrations were measured were carbon monoxide (CO), total hydrocarbons (THC). and freon. The integration time for the CO and THC samples was about the same as for the bubblers since
R. J.
192 10.0 I_
- (a)
’ so2
0.1
I 30
0
10.0
I 120
0.1 0
IS0
0.1
0
I
1
I
I
I
I
60
90
120
10.0 _
I
I
%
30
min ’
- (d)
I
I50
min
1
I
I
03
I
I
30
60 TRAVEL
’
TRAVEL TIME,
1
NO
-(b)
NO2
I 90
I 60
’
al.
%
TRAVEL TIME,
-_ (4
et
10.0 _
I
1
f
BREEDING
%l so
TIME,
I
0.1 120
150
min
0
-30
1 -60
TRAVEL TIME,
I
I -120
-90
-150
min
Fig. 9. Q as a function of travel time for four trace gases. The nonreactive species used in the calculation are identified by the following symbols: . for CN, 0 for CO, 0 for THS, + for the nephelometer, and A for fluorocarbon-l 1. The subscript g identifies Q’s derived from averaged ground measurements. All the other values are derived from aircraft data.
the sample was slowly pumped into a large bag over approximately the same period as that for which the bubblers were sampling. The freon concentration, however, was determined from a lO-cm3 sample taken approximately in the center of the bubbler sampling period, and thus is not time-integrated at all. In addition to these nonreactive species, aboard the Queen Air we were able to measure the concentration of condensation nuclei (CN) and to determine a measure of the particle density by means of a nephelometer (Neph). The CN and mephelometer values used in the ratio calculation are averaged across the Z-shaped flight path, and the averaging period is approximately the same period during which the bubblers were operating and during which the sample analyzed for CO and THC was being obtained. The syringe of air analyzed for freon concentrations was filled about midway in the downward slanting portion of the Z-shaped path. Each time we had the concentration of a reactive gas at both 80 and 120km from the city, the Q and half-life for this gas were calculated using all the non-
reactive gases whose concentrations were also known for the same times and places. Although these determinations of the half-life of a reactive gas using different nonreactive gas indicators are not statistically independent in any way, they provide a check on the reliability of the concentrations of the nonreactive indicators. In Fig. 9 the values marked with a “g” are derived rom the average of the concentrations at the three ground stations on each arc. With regard to the aircraft data, for each combination of a reactive and a nonreactive species two values of Q and the half-life have been calculated. These values use different measured concentrations on the 120-km arc, but must use the same values of 80km since we were only able to make one sampling traverse of the 80-km arc. Thus the two aircraft values for Q and half-life are not independent. The data for SO, are clearly indicative of a half-life in the range of 2-8 h. Of the ten values less than 0.5, one is a small positive value, and of the nine negative values, three more are due to the aircraft samples on 11 April. In view of the diverse nature
193
Atmospheric pollutants in the St. Louis area of the conditions under which the measurements were made, the half-lives group quite well. The half-life of SO, in the atmosphere is probably affected by the temperature, humidity, and hydrocarbon concentration, and possibly by other factors. McKay (1971) has calculated the rate of sulfate formation in cloud water droplets at 15 and 25”C, and he found a negative temperature dependence because of the greater solubility of gases in the liquid phase at the lower temperature. Stephens and McCaldin (1971) studied the oxidation of sulfur dioxide in power plant plumes and found a very marked dependence on the relative humidity (r.h.). They found the half-life to be 70 min at 80 per cent r.h., 144 min at 4G55 per cent r.h., and no apparent decay when the r.h. was below 40 per cent. They made only the three measurements, however, and their conclusions are not in complete agreement with another study they quote, that of Dennis rt a!. (1969), which found a half-life near 50 min for 35-52 per cent r.h. But many other factors have not been taken into account in these studies, such as temperature, the presence of other species, and light. Recently Smith and Urone (1974) found enhanced photochemical reaction of SO2 in the presence of NOz and propylene. Looking at our data more closely to see if there is a photochemical effect, we restrict ourselves to the half-lives derived from the aircraft data and which used carbon monoxide as the nonreactive species. The longest half-life in this set was found before dawn on 26 October 1972 when no photochemical reactions would have been taking place. The shortest half-life, 2.4 h, was measured on 14 April 1973 between 11:45 and 14:45 h. The average temperature during this flight was 9.8”C and the average r.h. was 42 per cent. We can calculate the concentration of nonmethane hydrocarbons (NMHC) by subtracting the methane concentration from the total hydrocarbon concentration. The NMHC concentration found on this flight was one of the highest we recorded-750ppb. In Fig. 10 the half-life of SO2 is plotted as a function of the NMHC concentration for the data from 14 and 17 April 1973. The trend is unmistakable. While the data are too scanty to be conclusive, it appears likely that a photochemical reaction involving some reactive hydrocarbons may explain part of the variation in the removal rates of sulfur dioxide. The nitrogen dioxide half-life data are ambiguous. There are slightly more negative half-lives than positive ones, so it seems likely that NO* is being formed as well as removed in the plume and that the concentration depends on the net effect of the various processes involved. There is no obvious grouping of the data by date or weather conditions, but there is a very slight indication that the half-lives may be positive on sunny days and negative on cloud days. The concentrations of the oxides of nitrogen and ozone are linked through the reaction: NO + O,+
NO,
+ 0,
=
6
0
AIR
n
GROUND
k
i I 4 !!I 4 -1 N2
2
0 0
A
t 0’
400
I
I
I
I
500
600
700
800
NMHC
CONCENTRATION.
900
ppb
Fig. 10. Half-life of sulfur dioxide as a function of the concentration of non-methane hydrocarbon (NMHC) concentration. Only those values which used carbon monoxide as the nonreactive specie are plotted. The ground values are taken from the averaged ground station data from 1 I April 1973. The anomalous NMHC value foumd at Glenarm has been excluded in calculating an average NMHC value. The air data are from 14 and 17 April 1973.
which may be the dominant removal mechanism for nitric oxide. Our data indicate that the half-life for NO may be between 2 and 4 h, and that the doubling time for ozone may be of the same order. Even though our data are few, and the instrument used measured total oxidant. of which the major fraction is certainly ozone. the fact that these data indicate that the NO half-life is close to the oxidant doubling time is very suggestive. It is well known from studies in Los Angeles and other cities with photochemical smog problems, that the early morning increase of NO concentrations due to automobile exhausts begins to decrease with the buildup of ozone formed by the sun’s U.V. radiation.
CONCLUSIONS
When measuring the concentration of trace gases near the ground and aloft at 80 and 120 km from the center city in areas where the effluents from the St. Louis metropolitan area would be expected to have been transported by the winds at that time, we invariably found that the concentration of SO1, NO, and NO were considerably higher than the background levels in Illinois and Missouri, although we were sometimes not able to be certain about the location of the center or edges of the plume. There was no evident association of high concentrations of NH3, aldehydes, or H2S with the presence of the plume. Among the nonreactive trace gases, CO. CH,, CFCl,, and total hydrocarbons all showed definite associations with the plume at 80 and 120 km from St. Louis. CO and total hydrocarbon concentrations were somewhat more reliable than methane and CFC&. While the urban plume was always detectable at 80 or 120 km from the metropolitan center when the
194
R. J. BREEDING et al.
wind speeds were more than a few meters per second. the plume structure was often complex. and in some cases the more reliable indicators did not agree as to the location of the plume centerline. When the plume was well defined, it was usually found to be between 20” and 30” wide. This may be due to the fact that the reduction of concentrations at the edges of the plume with distance renders an increasingly large section of the plume undetectable (Stampfer and Anderson, 1974). Although the data are not numerous. the ratio method has been applied to obtain preliminary indications of the half-lives of some of these reactive gases about 100 km and a few hours away from their source. We have the most data for SO2 and N02: the half-life for SO2 appears to fall in the range of 2-8 h, but the results for NO, are inconclusive. The NO half-lives show a surprising grouping in the range of 24 h, but there are only a few measurements. There are even fewer measurements of the total oxidant level. but most of them show the total oxidant level to be doubling in 24 h. Acknowledgements-We acknowledge the help and cooperation of C. Kanatzer, B. Campbell, and the Chemistry Department of MacMurray College, Jacksonville, Illinois; the Springfield, Illinois, Office of the National Weather Service; J. F. Stampfer, Jr., of the University of Missouri at Rolla; the owners of the land on which our sites were located; and the county agents who assisted us in locating these sites. We also acknowledge the assistance of the following NCAR personnel: E. Ackerman, J. A. Anderson. B. W. Gandrud. P. L. Haagenson, M. D. LaHue, A. L. Lazrus, R. B. McBeth. A. L. Morris, R. Pogue. W. Pritchett, G. Sturdy. A. F. Wartburg and J. Wood.
REFERENCES
Breeding R. J., Haagenson P. L. . Anderson J. A.. Lodge J. P., Jr. and Stampfer J. F., Jr. (1975) The urban plume as seen at 80 and 120 km by five different sensors. J. uppl. Meteor. 14, 204 216.
Breeding R. J.. Lodge J. P., Jr.. Pate J. B.. Sheesley D. C.. Klonis H. B.. Fogle B.. Anderson J. A., Englert T. R.. Haagenson P. L.. McBeth R. B., Morris A. L.. Poguc R. and Wartburg A. F. (1973) Background trace gas concentrations in the Central IJnited States. J. guoph~~ Res. 78, 7057-7064. Dennis R.. Billings C. E.. Record F. A., Warneck P. and Arin M. L. (1969) Measurements of sulfur dioxide losses from stack plumes. Paper No. 69 156. 62nd Annual Meeting of the Air Pollution Control Assoc.. New York. Haagenson P. L. and Morris A. L. (1974) Forecasting the behavior of the St. Louis, Missouri, pollutant plume J. appl. Meteor. 13. 901 909. Intersociety Committee (1972) Methods of Air Sumpliny und .4ncdysis. American Public Health Association. Method No. 402. pp. 325 328. Komhyr W. D. (1969) Electrochemical concentration cells for gas analysis. Ann. Geophys. 35. 203-210. LaHue M. D.. Axelrod H. D. and Lodge J. P.. Jr. (1973) Direct measurement of atmospheric nitrous oxide in a stored air volume using thermal conductivity gas chromatography. J. Chror&og. Sci. 11, 585-587. McKay H. A. C. (1971) The atmospheric oxidation of sulfur dioxide in water droplets in presence of ammonia. Atmospheric Encironnlent 5. 7-14. Natusch D. F. S.. Klonis H. B.. Axelrod H. D.. Teck R. J. and Lodge J. P. Jr. (1972) Sensitive method for measurement of atmospheric hydrogen sulfide. .4&. Chem. 44. 2067. Simmonds P. G., Kerrin S. L., Lovelock J. E. and Shair F. H. (1974) Distribution of atmospheric halocarbons in the air over the Los Angeles basin. Arnlosphcric Encironment
8. 209-216.
Smith J. P. and Urone P. (1974) Static studies of sulfur dioxide reactions. Environ. Sci. Techno/. 8, 742.-746. Stephens T. N. and McCaldin R. 0. (1971) Attenuation of power station plumes as determined hy instrumented aircraft. Enciron. Sci. Technol. 5. 615621. Stampfer J. F.. Jr. (1972) An aircraft. aerosol sampling program: Some preliminary results. Afmospheric Emironmrnt 6. 743 -757. Stampfer J. F.. Jr. and Anderson J. A. (1975) Lmting the St. Louis urban plume at X0 and I20 km and some of its characteristics. Atmospheric Enrironmenr 9, 301-313. Venezia R. and Ozolins G. (1969) Inrersturc, Air Pollution Study. Phase II Project Report. Vol. II Air Pollurunr Emission Imvntory. Publ. U.S. Dept. of Health. Education SC Welfarc. Public Health Service. Cincinatti. OH.
Encironmrnr
Vol. 10. pp. 181-194.
Pergamon
Press 1976. Prmted in Great
Brltaln.
MEASUREMENTS OF ATMOSPHERIC POLLUTANTS IN THE ST. LOUIS AREA R. J. BREEI)ISC;*.H. B. KLOKIS~.J. P. L~Dc;E. JR.:. J. B. PA&. D. C. SHEESLEY~.T. R. ESGLERT,Iand D. R. S~;ARS’ National Center for Atmospheric Research.** Boulder. CO 80303. U.S.A.
Abstract-Measurements of the concentrations of trace gases and particles have been made in the plume from metropolitan St. Louis at 80 and 120 km from the urban center. The concentrations of SO1, N&, NO, NHJ, H2S, aldehydes, CO, total hydrocarbons, and CFCI, were determined. The concentrations of many of these gases were found lo be significantly higher in the plume than outside the plume at these distances. Measurements were made near the ground and from an aircraft. The width of the plume was usually between 20’ and 30’. which is less than had been expected. By comparing the concentrations measured at 80 km from the city with those measured at 120 km from the city. and using the decrease of conservative trace gases to account for loss through physical process. we have arrived at preliminary estimates of the decay rates for a few trace gases. The evidence is most compelling for sulfur dioxide. and it appears that. at LX. 100 km from the city. the overall half-life of SO2 is between 2 and 8 h. INTRODUflIOS
The Fate of Atmospheric Pollutants Study (FAPS), conducted by the National Center for Atmospheric Research (NCAR), was an attempt to find out what happened to some of the most common atmospheric pollutants after they left their urban source areas. The general method was to measure the concentrations of a number of gaseous and particulate species and to use the ratio method to discover the in situ rates of reaction. The ratio method depends on determining the ratio of the concentrations of reactive to nonreactive species at different distances from the source area. The decrease of the concentration of the nonreactive species with distance enables one to account for the loss of urban effluents through physical processes such as dilution and diffusion. The more rapid decrease in the concentration of the reactive species is due to these physical processes plus chemical transformations. The reaction rate may be calculated from the change of the ratio with distance and the time it takes the air parcel to move from one sampling location to the other. If there were several competing removal mechanisms operating simultaneously. this
* Present address: Energy, Inc.. P.O. Box 736. Idaho Fall, ID 83401. U.S.A. + Present address: Terran Resource Management Associates, Inc., P.O. Box 572. Addison. TX 75001. U.S.A. : Present address: Consultant in Atmospheric Chemistry. 385 Broadwav. Boulder. CO 80303. U.S.A. 9:Present address:. Ambient Analysis. Inc.. P.O. Box 4056. Boulder, CO 80302, U.S.A. ,I Present address: Colorado Department of Health,
Dirango, CO 81301, U.S.A. . P Present address: College of Engineering, West Virginia University, Morgantown. WV 26506. U.S.A. ** National Center for Atmospheric Research is sponsored
by the National
Science
Foundation.
method would give only the overall loss rate or an effective removal rate due to all of the processes, unless the increase rate of the individual products of each mechanism could be determined. In these preliminary field tests, ground and air measurements were made on arcs of 80- and l20-km radius around St. Louis, MO. The center of the St. Louis metropolitan area was taken to be the Arch (Gateway Arch, Jefferson Expansion National Memorial). which is a conspicuous feature on the Mississippi River near the commercial center of the city. In the past several years persistent winds have brought the plume into the quadrant north of St. Louis more frequently than they did into any other quadrant. so most of our measurements were made in this quadrant. Most sampling was done in the afternoon when vertical mixing was most vigorous. but one sampling period was in the early morning under stable conditions. Figure I shows the major rivers and cities of the area around St. Louis. In the October 1972 field test. the sites where a measuring station might be set up were located 18’ apart on the l2@km arc. and there was only one site (Hamburg) on the 8O-km arc. (On the 120-km arc, I8 = 37.6km). This spacing proved to be too coarse, so for the April 1973 test, the sites were located 9’ apart on both arcs. The sampling sites were usually fallow fields as far removed as practicable from main highways and occupied houses. A number of instruments, including gas chromatographs. which required line electricity and which were too delicate to move frequently were located at the Glasgow site. I06 km from the Arch. In addition to making continuous measurements during the sampling episodes, these instruments were used to analyze samples collected field station.
in bags or syringes
at the regular
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R. J.BREEDING
et al.
80kmt
_:-. 1120km
Fig. 1. Map of the St. Louis area showing the 80- and 120-km arcs and the site locations. Two aircraft were used in both field tests. The NCAR Queen Air was equipped to take bubbler and bag samples and was equipped with a condensation nucleus (CN) counter. In April 1973, a nephelometer and an oxidant monitor were added. The primary mission of the Queen Air was to fly back and forth within the plume to measure concentrations aloft in the plume. The other plane, a Bonanza flown by Prof. J. F. Stampfer, Jr. (University of Missouri at Rolla) had the location and delineation of the plume as its primary mission; most of the Bonanza flights were therefore made prior to the more extensive sampling. The Bonanza was equipped with a light-scattering instrument which measured the number of particles in two adjacent size ranges. Both aircraft had temperature, dew-point temperature, and pressure recorders. Although these field tests were designed to be preliminary experiments, this program was terminated sooner than originally planned. Thus, the data reported here may be fragmentary since the “preli-
minary” field tests became in fact the “final study” only after they were completed. The purpose of this paper is primarily to report the results of the reactive gas measurements. The results which more directly concern meteorology, the prediction of the plume’s position, and the measurements of the continuously operating instruments aboard the aircraft, have been reported elsewhere (Stampfer, 1972; Stampfer and Anderson, 1974; Breeding et al., 1975; Haagenson and Morris, 1974). We use certain information from these papers as to the plume’s position, width, and behavior without explicit reference. Heights are given in meters above mean sea level. Times are reported in Central Daylight Time for the October 1972 field test, and in Central Standard Time for the April 1973 field test. Positions along the arcs of radius 80 or 120 km about the Gateway Arch in St. Louis are given in degrees: positive (clockwise) from north and negative (counterclockwise) from north.
Atmospheric pollutants in the St. Louis area MEASUREMENT
TECHNIQUES
At about 100 km from the center of an urban area, concentrations of the common pollutants in the plume are not far above the background concentrations. We were not able to find any real-time instruments which were sufficiently accurate, reliable, and inexpensive to be used at all the ground stations. Thus. we relied on methods which were quite accurate but required 45-60 min to take a sample. Sulfur dioxide (SO,), nitrogen dioxide (NO,), nitric oxide (NO), ammonia (NH,), and aldehydes ‘(ECHO) were removed from the air by wet scrubbing (bubbling) for about an hour; the scrubbing solutions were analyzed by standard calorimetric analytical methods. To remove hydrogen sulfide (H,S), the air was drawn through a sensitized filter at the same time that the air was being drawn through the bubblers (Natusch rt al., 1972). The analytic methods, sensitivities, and accuracies for all of these methods (except the NO method) have been described in Breeding et al. (1973). These five methods were not changed from October 1972 to April 1973. Although NO was measured in October 1972, the method used then was inadequate and we have not reported any NO concentrations from that field test. The method has been improved and we are confident of the NO levels we report for the April 1973 field test. The improved method for NO is essentially that given in Methods of Atmospheric Analysis (Intersociety Committee, 1972). The air is first passed through ground firebrick which has been soaked in triethanolamine to absorb the NO2 and then through ground firebrick which has been soaked in chromium oxide to oxidize the NO to NO*. Tests showed the absorption of NO, and the oxidation of NO to be nearly 100 per cent efficient under the conditions in which this method was used. When five or six bubblers were operated side by side at the Glasgow site on 15 April 1973, the following concentrations and S.D. were obtained: Concentraton Gas SO* NO, NO
NH, RCHO
‘K’;’ 2.54 0.29 4.00 2.46
SD. 0.23 0.08 0.1 I 0.59 0.46
Carbon monoxide (CO), methane (CH,), and total hydrocarbon (THC) were measured by a Beckman 6800 gas chromatograph. To determine the CO concentration, the CO is first reduced to CH4 using hydrogen and a nickel catalyst. Samples were taken in Mylar bags at the ground stations and aboard the Queen Air, and later analyzed by the chromatograph at the Glasgow site. The concentration of fluorocarbon-11 (CFCl,) was determined by taking syringe samples at the site and later injecting them into a * The transport vector is defined as the wind vector averaged throughout the ground-based layer. Usually a mixed layer, this would be an inversion layer if a normal nighttime
period
were being discussed.
183
gas chromatograph. (A description of this instrument is not yet available in the literature, but similar measurements are described in Simmonds et al. (1974). This substance is hereafter referred to as “freon” for convenience; it does not imply any particular manufacturer. The concentration of nitrous oxide (N,O) was determined by the method of LaHue
et al. (1973). The instrumentation of the Bonanza and its use. in determining the location of urban plumes at distances on the order of 100 km have been described by Stampfer (1972) and by Stampfer and Anderson (1974). The instrumentation of the Queen Air and a comparison between the plume indicators aboard the two aircraft are contained in Breeding et al. (1975).
October 1972 jield test On 20 October 1972 ground stations were set up at the Hamburg, Bowling Green, Summer Hill, Glasgow and Orleans sites. Sampling took place from 13 : 00 to 17 : 00 h. Aircraft and radiosonde ascents indicated that the air was well mixed from the ground (which varied from 150 to 220 m above sea level in the sampling area) up to the inversion base at 800m MSL. Skies were overcast during the sampling episode and light rain fell at some of the stations. From IO:00 to 17:OO h on this date, the transport vector* varied from 140” to 150” at 7 m s- ‘. The results of the sampling on 20 October 1972 are shown in Fig. 2. Every indication from the first sample is that the plume was centered over Hamburg and Summer Hill at -32”. The results from the four outer stations in the second sample show that the plume center was still near -32”. but the low values for SO2 and NO, concentrations at the four outer stations again show the plume at -32” and again the Hamburg concentrations are much lower than those at Summer Hill. However, the third-sample CO values indicate the plume center may have been west of -32“ while the freon values indicate it was likely to have been east of -32”. The plume’s position as determined from the reactive gas concentrations at the four outer stations is in good agreement with the transport vectors calculated from the meteorological data alone. The data from the aircraft traverses indicated that the plume center was slowly changing from about -35” at the beginning of sampling at 13:00 h to about -45” or - 50” at the end of sampling at 17:00 h and that it was only 15”-20” wide. Of the third-sample gas data, only the methane and CO data support a shift this far west. The reason for the low SO, and NO, values at Hamburg is not known. The flow continued from the south so another sampling episode was conducted between 03:OO and 07:OO h on 21 October 1972. The southerly flow brought moist air up from the Gulf of Mexico and prevented the usual ground-based nighttime inversion from forming, although mixing during the sampling episode was certainly not vigorous. This situ-
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ation caused light rain to fall steadily at almost all the ground stations. The transport vector was estimated to have come from 175” to 185” during the sampling at 9-10m s-r. The results of this sampling episode are shown in Fig. 3. Of the four outer stations, the SO, and NO, concentrations were highest at the Glasgow site during each of the three sampling periods, indicating that the plume centerline near the ground was probably around - 15”. Estimates of plume width from particle
Fig. 2(c). Fig. 2. Variation of trace gas concentrations with position on 20 October 1972. The first air sample was taken at 960m MSL between -6’ and -58” on the 120-km arc. The second air sample was taken at 450m MSL between -6” and -55” on the 120-km arc. The third air sample was taken at 450 m MSL between - 17” and -60” on the 80-km arc. The midpoint times for the ground samples were 13:30, 15:OOand 16:30h.
Fig. 2(a).
measurements made from the aircraft in the early hours of 21 October vary from 20” to 3.5”. Sampling from the aircraft occurred south of St. Louis on 24 October 1972. On this date there was very little directional shear with height and the unstable conditions extended up to 630 m. The transport wind was from 350” at 7m s-l. The first flight was certainly in the well-mixed portion of the plume at 480m, but the last two samples were taken too close to the top of the mixed layer to be definitely representative of the plume. Sampling results are given in Table 1. Table 1 also contains the results of early morning and afternoon sampling flights on 26 October to the north of St. Louis. The morning flights took place in a wind situation that made it difficult to ascertain the plume’s location. The samples were taken just above or near the top of the inversion layer. By the time of the afternoon flight on 26 October, the air was apparently well mixed up to 630m, and directional shear with height was considerably reduced. The transport vector came from 17W180 at 5-6 m s- 1 during the sampling period. All flights were well below the top of the mixed layer and particle measurements obtained from the aircraft indicated that the plume maximum was near +5” and the plume width was about 25”.
Atmospheric pollutants in the St. Louis area April 1973jeld
185
test
During April 1973 three sampling episodes took place in the quadrant north of St. Louis. Both aircraft and ground measurements were made during each episode. During the October 1972 field test the plume width often appeared to be of the same order as our station spacing (18”), so for this field test the spacing between sites was reduced to 9”. Because equipment for only six ground stations was available. and put-
Fig. 3(c). Fig. 3. Variation of trace gas concentrations with position on 21 October 1972. The first air sample was taken at 810m MSL between - 17” and 0” on the 120-km arc. The second air sample was taken at 450 m MSL between - 28” and + 19” on the 120-km arc. The third air sample was taken at 450 m MSL between - 17” and + 18” on the 80km arc. The midpoint times for the ground samples were 03:30. 05:OO and 06:30h.
Fig. 3(a).
*ZIM”TH, 21 OCTOBER
degrees
1972,SECONO SAMPLE
Fig. 3(b).
ting three stations on each arc would cover only 18” of arc, it was decided to attempt this arrangement of ground stations only once. For the other two sampling episodes all six stations were placed on the 120km arc. On 11 April stations were set up at the three easternmost sites on each arc, with sampling to begin at 13:OOh on the 80-km arc and at 14:4Oh on the 120-km arc. The lOO-min delay was approximately the time required for pollutants to travel the 40km between the sampling stations. The skies became increasingly overcast as the sampling continued, so mixing was probably not vigorous at the end of the sampling period. At the beginning of the sampling, the transport wind was from 225” at 9 m s-l, and the lapse rate was approximately dry adiabatic up to 1000 m. By the end of sampling at 19: 00 h, the top of the mixed layer was down to 600m and the lapse rate was considerably less than dry adiabatic. The transport wind at 19:00 h was from 215” at 8 m s- ‘. The results of the sampling on 11 April 1973 are given in Fig. 4. During the April 1973 field test, the Queen Air gas samples were taken while the plane flew a Z-shaped path through the plume, so no single height can be assigned to the aircraft samples. The purpose of this flight pattern was to obtain a more representative
R. J.
186
BREEDING et al.
Table 1. Concentration of trace gases measured from an aircraft in the St. Louis area on 24 and 26 October 1972. The rows with FBA in the time column contain the average of the field blanks for that site. The concentrations have been corrected for this field blank value Gas ConcenCrarion
h-b) site
Time
H2S
1402
0.25
FBA 1510 1623
0.15 0.20
so2
NO*
NH3
RCHO
co
CR4
a-eon
442
1600
1.29
471
1570
1.07
444 591
1560 1690
435
1630
580
1710
24 October
Air 80-km arc 480 m Air lZO-km arc 570 m
26 October Air 80-km arc 360 m 540 m Air 1*0-!a arc 390 m 540 m 360 m
15.3 0.0
-0.3
AVG
0.24 0.23
9.4 13.1 24.2
0400 1340
0.12 0.24
25.0 23.5
4.4
0.14 0.16 0.13 0.12 0.25 0.24
0.0 0.0 22.3 13.5 15.7 16.1
0.0
FBA (am) FBA (pm) 0516 0631 1453 1606
of the plume. The first traverse was a few hundred meters below the top of the mixed layer; during the second traverse the plane descended from that height to a few hundred meters above ground level. The ground station data do not indicate conclusively the location of the plume on 11 April. Since they covered only 18” of arc, this was not unexpected. Particle concentrations measured aboard the Bonanza along the 120-km arc indicated that the plume was about 30” wide, and that the plume center at 500 m was near 45”. Plume curvature on this date, and the lag of plume behind the transport vector when the wind direction is changing have been discussed by Haagenson and Morris (1974). On 14 April sampling took place from 1l:OO to 15:30 h at six stations set up on adjacent sites on the 120-km arc from Summer Hill (-32”) to Loami (+ 13”). All the meteorological measurements indicate that the air up to 9WlOOOm was well mixed during the sampling period. The transport vector for this layer was from 160” at 10m s- ’ during the entire sampling period. Light stratus were present when the sampling started, and by the end of the last sampling period all of the sky was covered by heavy stratus. Figure 5 presents the results of the 14 April measurements. In spite of wind and mixing conditions which should have been ideal for producing a welldefined urban plume, the locations of the plume maximum and plume edges are not clear from the measurements either near the ground or aloft. The mixing was vigorous up to 700m by IO:00 h, and the transport vector had been from 160” since 08:OOh so the plume center should have been near -20”. This location agrees with that indicated by the aircraft particle measurements at 300m made near 13:30. On 14 April the correlation spectrometer of Environmental Measurements, Inc., was operating in this area; the results of four traverses along roads sample
3.4
0.0 0.1
4.5 10.2 7.4
-0.2 1.0 0.4
6.6
3.4
-0.3
-0.7
5.5 7.8
3.0 3.3
5.4 3.6
approximating the 80- and 120-km arcs are shown in Fig. 6. Overburden is the integral of concentration with height. The concentrations labeled “SO, ground” were actually measured with a Melloy flame photometric total sulfur analyzer amd may overestimate the sulfur dioxide concentration, but the trend is significant. Unfortunately, two of the traverses occurred after the sampling at our ground stations had been completed, but it certainly does appear that the plume center was near - 12” at 15: 30 h on the 80-km arc. The long traverse of the 120-km arc took 3 h, and we cannot be certain that the plume did not change during that time. Nonetheless, a maximum was found in the -20” to - lo” region where the plume would have been expected to be from the meteorological data alone. The NOz peak at -38” is probably related to a fertilizer plant just south of the 120-km arc near Louisiana, Missouri. The peak at +28” is very likely due to a large coal-burning electrical generating station near Coffeen, Illinois. On 17 April the speed of the transport vector remained close to 6m s-’ throughout the day, but its direction varied due to the weakening stationary front. It was from 140” at 08:OOh, from 165” at 12:00, h, and from 180” at 16:OOh. Sampling took place at the six westernmost sites on the 120-km arc from 12: 30 to 17:O0. The results are shown in Fig. 7. Skies varied from a 50 per cent cover of scattered cumulus to clear. The top of the mixing layer was at or above 700m during the sampling. Ground station data show that the plume was relatively broad, but all the concentrations of both reactive and nonreactive species agree as to the location of the plume near the ground. It seems clear that the plume was centered between - 50 and - 40” during the first sampling period, was near -35” during the second sampling period, and was around -27” during the third sampling period. A Bonanza flight starting at 12:22 on the 80-km arc and another flight
II APRIL
ICI
io
4.0
5ii ll APRIL
10
1973,
30
40
AZIMUTH, degrees SECOND SAMPLE
20
II APRIL
10 1973,
THIRD
$0 SAMPLE
AZIMUTH,
io
Fig. 4. Variation of trace gas concentrations with position on 11 April 1973. The air samples were taken during a Z-shaped flight which took the plane from a few hundred meters below the top of the mixed layer to within a few hundred meters of the ground and from one edge of the plume to the other. The gas sampling took place between i-28. and +67’ on the 80-km flights and between -1-24” and t-49’ on the 120-km flights. The midpoint times for the samples were 13:26. 15:07 and 17:07 h on the 80-km arc, and 15:02, 16:47 and 18:47 on the 120-km arc.
degrees AZIMUTH, 1973, FIRST SAMPLE
?o
40 degrees
.-.
degrees
t.
120 km orc-
20
-;o
14 APRIL
AZIMUTH, 1973, SECOND SAMPLE
; degrees
lb
?b
t
L 14 APRIL
40
0
40
0
-a
I?
16
;.a 04
.._ 0.8 0.
-20
-10
AZIMUTH, 1973, THIRD SAMPLE
-30
A
Fig, 5. Variations of trace gas concentrations with position on 14 April 1973. The air samples were taken during a Z-shaped flight which took the plane from a few hundred meters below the top of the mixed layer to within a few hundred meters of the ground and from one edge of the plume to the other. The gas sampling took place between -2” and -40” on the 80-km flight and between +6” and -39” on the 120-km flights. The midpoint times for the ground samples were 11:22, 13:07 and 15:07 h.
AZIMUTH, 14 APRIL 1973, FIRST SAMPLE
.
-
0
0
degrees
0
10
20
AIR VALUES
189
Atmospheric pollutants in the St. Louis area
c
“Q SOz 20
0
120 km
100
0
”
_._.-._J I
-40
100
I\
“-.-_._._./’
I
I
I
I
I
-30
-20
-10
0
IO
AZIMUTH,
‘.L__j I
I
/
20
30
40
0
degrees
Fig. 6. Variation of SO2 and NO2 overburdens and surface SO2 concentrations with position on 14 April 1974.
commencing at 13: 19 -on the 120-km arc both found maximum particle concentrations near -40”. The plume width appears to be 20” or less, but the data are somewhat ambiguous. In spite of the rotation of the wind vector, the plume was well defined on 17 April 1973. The location of the plume center as a function of time has been discussed by Haagenson and Morris (1974).
TRACE GAS CONCENTRATIONS
Although the measurements of trace gases that were made during these field tests did not always succeed in unmistakably locating the center and edges of the plume, on every occasion that we expected to be close to the plume, we succeeded in finding concentrations of many gases which were much higher than the background values in this region (Breeding et al., 1973). We take this as evidence of the presence of a plume from the St. Louis area or from other anthropogenic sources. While small local sources cannot be ruled out completely, the location of the large sources outside the metropolitan St. Louis area and outside the Alton-Wood River area are well known. Sulfur dioxide is certainly one of the most ubiquitous effluents in a city like St. Louis where coal is a major source of energy. The highest SO, concentration we measured was 42ppb at Summer Hill on 20 October 1972. Except for this date, no sulfur dioxide concentrations near the ground exceeded 20ppb, but on every sampling date at least one
station recorded values of 15 ppb or higher. Aircraft values exceeded 15 ppb only on 20 and 26 October 1972, and generally were in the range from 10 to 15 ppb when we expected the plane to have been in the plume. We did not expect that the NOz concentrations would be as high as the SO, concentrations, since the St. Louis metropolitan area emits less NOz than SO2 (Venezia and Ozolins, 1966). Further, NOz is largely produced by automobiles and therefore the NO* sources are more widespread spatially, but more variable in time. NOz concentrations as high as 20ppb were measured in the morning of 21 October 1972 and as high as 15 ppb on the afternoon of 20 October, but in April 1973 the high value at the ground stations each day was between 7 and 10 ppb. The NO, concentrations found from the aircraft were mostly between 5 and 9 ppb. The measured concentrations of NO were approximately a factor of 5 lower than the NOz concentrations. The highest values measured were 5.6 ppb at Summer Hill and 4.3 ppb at Louisiana on 17 April. The concentrations aloft (3.3, 2.4 and 2.3 ppb) were also higher on this date than during the two previous sampling episodes. The ratio of the NO1 concentration to the NO concentration shows interesting variations (Fig. 8). From our measurements in April 1973, this ratio is seen to vary between 0.8 and 14.3. The value of this ratio for the ground stations was calculated using only those stations which we felt were within the plume. (For comparison, for St. Louis County, this ratio was between 0.3 and 1.0 for the period 08:0&13: 00 h on 20 October 1972 and between 1.0 and 3.0 for the period from 22:00 h, 20 October to 03 :OO,21 October 1972). It appears that the variation of the NOz:NO ratio may be about 180” out of phase with the diurnal variation in ozone concentration. Since NO is produced fom NO, mainly by the reaction NO, + hv+NO
+ 0,
the rate of which depends on the intensity of light in the near ultraviolet region, and since most of the sampling sessions ended in the late afternoon or at dusk, the rise of the NO,:NO ratio is to be expected. Ammonia is a ubiquitous trace gas in rural regions and. as expected, its concentrations did not appear to correlate with the plume’s presence or with the concentrations of other gases of primarily anthropogenie origin. And no reduction in the ammonia concentration was noted when the aircraft sample was taken above the mixed layer (e.g. the sample taken from the Queer] Air at 14:08 on 20 October 1972). Although aldehydes are known to be common reaction products of metropolitan effluents, we found no correlation of RCHO values with the plume location. The maximum concentration of 11 ppb was measured on 14 April 1973. There was some correlation of aldehyde concentration with the amount of solar radiation reaching the ground, however. On 14 and 17
.q ~~:91 pue LE:PI ‘~S:ZT aIaM safdtues puno~8 ay3 JOJ sawg tu!odp!ur ay& wf%f~ UT-0~1 ayl uo .fj~- pm .gz-- UaaMlaq pue ]q8!y ury-08 ay$ liluy~p .~p- pun ,p[ - uaamlaq acm[d 7001 Buqdms sa% ayJ_ ‘Jaylo aql 01 amnld aq] JO aspa auo mOlJ puv punoZ3 aql JO walam palpunq MaJ e mqI!M 01 sIadv+ pax!m aql Jo doI aql MOpq slajam paJpunq MaJ e U~OJJ autqd aql ~00, q3!qM )q%y padeqs-z 8 8uynp ua?el aJaM saldmes .I!= aqL ‘~~61 Iydv ~1 uo uoy!sod q$!M suoyJluawo3 stz?8aDwl JO suo!~epe~ ‘L %,J
Atmospheric pollutants in the St. Louis area I
I
I
I
I
I
I
a whole were significantly lower than the October 1972 concentrations. Scatter or correlation plots were examined for all the combinations of the concentrations of SOZ, NOz, NO, aldehydes, NHa, and HIS. The concentrations of SOZ, NO*, and NO showed a definite tendency to be correlated with each other, but the other three gas concentrations showed no correlation with any other concentration.
I
I6 -
e
0 GROUND
120 km
16-
+ GROUND
80 km
14-
A AIR 0 AIR
,2 _ lo-
--.-.-. -
120 km 80 km
,
II APRIL 14 APRIL I7 APRIL
0
/
/
/
/
/O-
/’
-
,’ h
191
6RATIOS AND HALF-LIVES
642 c/
t 01 1000
1
I
I
I
I
1200
14 00
1600
1FJ:00
TIME,
I
h
Fig. 8. The change of the ratio of the concentration of NO2 to the concentration of NO with time. The ground station values were averaged before the ratios were formed. On 14 April, the data from the Orleans and Loami sites has been excluded, and on 17 April the data from the Lynnville site has been excluded, because these sites were not clearly on the plume. On 11 April the results from the Taylorville station were not used since the NO concentrations were unreasonably low.
April 1973, with clear to partly cloudy skies, the average aldehyde concentrations were about 6ppb. But on 20 October with heavy overcast and some rain, and on 21 October 1972 when the measurements were made before dawn, the RCHO concentrations averaged about 1.5 ppb. Carbon monoxide is largely produced by automobiles. On most days we found maximum values between 540 and 630 ppb both near the ground and aloft. On 11 April, however, the maximum value found aloft was only 360ppb. On 14 April, although values aloft were between 500 and 530ppb, values were over 700ppb at every ground station but one. The maximum of 930ppb was measured at the Detroit site. Hydrogen sulfide does not seem to be obviously related to the urban plume. Although it is given off in some industrial operations, such as the sulfite process used by a paper board factor in Alton, Illinois, a major source is suspected to be the decay of vegetation in rural areas. Maximum values during each episode ranged from 0.28 to 044ppb on the ground and from 0.11 to 0.33 ppb aloft. The concentration of fluorocarbon-11 (CFCl,) was found to be a fairly reliable indicator of the plume from metropolitan St. Louis, although not as trustworthy as SO,. The concentrations were of the same order as measured by other studies (e.g. Simmonds et al., 1974). The maximum for each episode except 14 and 17 April was between 3 and 4 ppb. These last two episodes had significantly lower freon values than the other days, and the April 1973 values as
The ratio method of determining the rate of increase or decrease of a substance is based on the assumption that the fluid being sampled is well mixed and that diffusion will affect both reactive and nonreactive species alike. Thus the decrease in concentration of the nonreactive species between two points of measurement can be laid to diffusion and a similar amount of diffusive loss can be expected for the reactive species. Let C,(x) and C,(x) be the concentrations of the nonreactive and reactive species, respectively, at distance x from the source. And let B, and B, be the background concentrations for the two species, respectively, that is, the concentrations one would expect to measure in the same area where no large sources were upwind. The ratio of ratios, Q, is defined:
Q=
C,(l2Okm) - B, CJ120km) - B, -I C,(8Okm) - B, >( C,(80 km) - B, > .
If it takes time, t, in min, for the material to travel the 40 km between the two measuring arcs we used, then the half-life, in hours, can be derived from Q:
A negative half-life means that the reactive species was increasing and the negative of the half-life (which is positive in this case) may be interpreted as the doubling time. Figure 9 represents plots of Q versus time for SOZ, NOz, NO and ozone. Although there are very few ozone values, these have been included because they group very well. The instrument used to measure the ozone concentrations is a Komhyr-type instrument built by Wartburg of NCAR (Komhyr, 1969). Strictly speaking, this instrument measures total oxidant. Since by far the bulk of the oxidant measured is ozone, however, it has been referred to as ozone throughout this paper. The ozone level for each flight is an average of the values measured during the Z-shaped traverse through the plume, and should be roughly representative of the plume as a whole. At the ground stations the nonreactive species whose concentrations were measured were carbon monoxide (CO), total hydrocarbons (THC). and freon. The integration time for the CO and THC samples was about the same as for the bubblers since
R. J.
192 10.0 I_
- (a)
’ so2
0.1
I 30
0
10.0
I 120
0.1 0
IS0
0.1
0
I
1
I
I
I
I
60
90
120
10.0 _
I
I
%
30
min ’
- (d)
I
I50
min
1
I
I
03
I
I
30
60 TRAVEL
’
TRAVEL TIME,
1
NO
-(b)
NO2
I 90
I 60
’
al.
%
TRAVEL TIME,
-_ (4
et
10.0 _
I
1
f
BREEDING
%l so
TIME,
I
0.1 120
150
min
0
-30
1 -60
TRAVEL TIME,
I
I -120
-90
-150
min
Fig. 9. Q as a function of travel time for four trace gases. The nonreactive species used in the calculation are identified by the following symbols: . for CN, 0 for CO, 0 for THS, + for the nephelometer, and A for fluorocarbon-l 1. The subscript g identifies Q’s derived from averaged ground measurements. All the other values are derived from aircraft data.
the sample was slowly pumped into a large bag over approximately the same period as that for which the bubblers were sampling. The freon concentration, however, was determined from a lO-cm3 sample taken approximately in the center of the bubbler sampling period, and thus is not time-integrated at all. In addition to these nonreactive species, aboard the Queen Air we were able to measure the concentration of condensation nuclei (CN) and to determine a measure of the particle density by means of a nephelometer (Neph). The CN and mephelometer values used in the ratio calculation are averaged across the Z-shaped flight path, and the averaging period is approximately the same period during which the bubblers were operating and during which the sample analyzed for CO and THC was being obtained. The syringe of air analyzed for freon concentrations was filled about midway in the downward slanting portion of the Z-shaped path. Each time we had the concentration of a reactive gas at both 80 and 120km from the city, the Q and half-life for this gas were calculated using all the non-
reactive gases whose concentrations were also known for the same times and places. Although these determinations of the half-life of a reactive gas using different nonreactive gas indicators are not statistically independent in any way, they provide a check on the reliability of the concentrations of the nonreactive indicators. In Fig. 9 the values marked with a “g” are derived rom the average of the concentrations at the three ground stations on each arc. With regard to the aircraft data, for each combination of a reactive and a nonreactive species two values of Q and the half-life have been calculated. These values use different measured concentrations on the 120-km arc, but must use the same values of 80km since we were only able to make one sampling traverse of the 80-km arc. Thus the two aircraft values for Q and half-life are not independent. The data for SO, are clearly indicative of a half-life in the range of 2-8 h. Of the ten values less than 0.5, one is a small positive value, and of the nine negative values, three more are due to the aircraft samples on 11 April. In view of the diverse nature
193
Atmospheric pollutants in the St. Louis area of the conditions under which the measurements were made, the half-lives group quite well. The half-life of SO, in the atmosphere is probably affected by the temperature, humidity, and hydrocarbon concentration, and possibly by other factors. McKay (1971) has calculated the rate of sulfate formation in cloud water droplets at 15 and 25”C, and he found a negative temperature dependence because of the greater solubility of gases in the liquid phase at the lower temperature. Stephens and McCaldin (1971) studied the oxidation of sulfur dioxide in power plant plumes and found a very marked dependence on the relative humidity (r.h.). They found the half-life to be 70 min at 80 per cent r.h., 144 min at 4G55 per cent r.h., and no apparent decay when the r.h. was below 40 per cent. They made only the three measurements, however, and their conclusions are not in complete agreement with another study they quote, that of Dennis rt a!. (1969), which found a half-life near 50 min for 35-52 per cent r.h. But many other factors have not been taken into account in these studies, such as temperature, the presence of other species, and light. Recently Smith and Urone (1974) found enhanced photochemical reaction of SO2 in the presence of NOz and propylene. Looking at our data more closely to see if there is a photochemical effect, we restrict ourselves to the half-lives derived from the aircraft data and which used carbon monoxide as the nonreactive species. The longest half-life in this set was found before dawn on 26 October 1972 when no photochemical reactions would have been taking place. The shortest half-life, 2.4 h, was measured on 14 April 1973 between 11:45 and 14:45 h. The average temperature during this flight was 9.8”C and the average r.h. was 42 per cent. We can calculate the concentration of nonmethane hydrocarbons (NMHC) by subtracting the methane concentration from the total hydrocarbon concentration. The NMHC concentration found on this flight was one of the highest we recorded-750ppb. In Fig. 10 the half-life of SO2 is plotted as a function of the NMHC concentration for the data from 14 and 17 April 1973. The trend is unmistakable. While the data are too scanty to be conclusive, it appears likely that a photochemical reaction involving some reactive hydrocarbons may explain part of the variation in the removal rates of sulfur dioxide. The nitrogen dioxide half-life data are ambiguous. There are slightly more negative half-lives than positive ones, so it seems likely that NO* is being formed as well as removed in the plume and that the concentration depends on the net effect of the various processes involved. There is no obvious grouping of the data by date or weather conditions, but there is a very slight indication that the half-lives may be positive on sunny days and negative on cloud days. The concentrations of the oxides of nitrogen and ozone are linked through the reaction: NO + O,+
NO,
+ 0,
=
6
0
AIR
n
GROUND
k
i I 4 !!I 4 -1 N2
2
0 0
A
t 0’
400
I
I
I
I
500
600
700
800
NMHC
CONCENTRATION.
900
ppb
Fig. 10. Half-life of sulfur dioxide as a function of the concentration of non-methane hydrocarbon (NMHC) concentration. Only those values which used carbon monoxide as the nonreactive specie are plotted. The ground values are taken from the averaged ground station data from 1 I April 1973. The anomalous NMHC value foumd at Glenarm has been excluded in calculating an average NMHC value. The air data are from 14 and 17 April 1973.
which may be the dominant removal mechanism for nitric oxide. Our data indicate that the half-life for NO may be between 2 and 4 h, and that the doubling time for ozone may be of the same order. Even though our data are few, and the instrument used measured total oxidant. of which the major fraction is certainly ozone. the fact that these data indicate that the NO half-life is close to the oxidant doubling time is very suggestive. It is well known from studies in Los Angeles and other cities with photochemical smog problems, that the early morning increase of NO concentrations due to automobile exhausts begins to decrease with the buildup of ozone formed by the sun’s U.V. radiation.
CONCLUSIONS
When measuring the concentration of trace gases near the ground and aloft at 80 and 120 km from the center city in areas where the effluents from the St. Louis metropolitan area would be expected to have been transported by the winds at that time, we invariably found that the concentration of SO1, NO, and NO were considerably higher than the background levels in Illinois and Missouri, although we were sometimes not able to be certain about the location of the center or edges of the plume. There was no evident association of high concentrations of NH3, aldehydes, or H2S with the presence of the plume. Among the nonreactive trace gases, CO. CH,, CFCl,, and total hydrocarbons all showed definite associations with the plume at 80 and 120 km from St. Louis. CO and total hydrocarbon concentrations were somewhat more reliable than methane and CFC&. While the urban plume was always detectable at 80 or 120 km from the metropolitan center when the
194
R. J. BREEDING et al.
wind speeds were more than a few meters per second. the plume structure was often complex. and in some cases the more reliable indicators did not agree as to the location of the plume centerline. When the plume was well defined, it was usually found to be between 20” and 30” wide. This may be due to the fact that the reduction of concentrations at the edges of the plume with distance renders an increasingly large section of the plume undetectable (Stampfer and Anderson, 1974). Although the data are not numerous. the ratio method has been applied to obtain preliminary indications of the half-lives of some of these reactive gases about 100 km and a few hours away from their source. We have the most data for SO2 and N02: the half-life for SO2 appears to fall in the range of 2-8 h, but the results for NO, are inconclusive. The NO half-lives show a surprising grouping in the range of 24 h, but there are only a few measurements. There are even fewer measurements of the total oxidant level. but most of them show the total oxidant level to be doubling in 24 h. Acknowledgements-We acknowledge the help and cooperation of C. Kanatzer, B. Campbell, and the Chemistry Department of MacMurray College, Jacksonville, Illinois; the Springfield, Illinois, Office of the National Weather Service; J. F. Stampfer, Jr., of the University of Missouri at Rolla; the owners of the land on which our sites were located; and the county agents who assisted us in locating these sites. We also acknowledge the assistance of the following NCAR personnel: E. Ackerman, J. A. Anderson. B. W. Gandrud. P. L. Haagenson, M. D. LaHue, A. L. Lazrus, R. B. McBeth. A. L. Morris, R. Pogue. W. Pritchett, G. Sturdy. A. F. Wartburg and J. Wood.
REFERENCES
Breeding R. J., Haagenson P. L. . Anderson J. A.. Lodge J. P., Jr. and Stampfer J. F., Jr. (1975) The urban plume as seen at 80 and 120 km by five different sensors. J. uppl. Meteor. 14, 204 216.
Breeding R. J.. Lodge J. P., Jr.. Pate J. B.. Sheesley D. C.. Klonis H. B.. Fogle B.. Anderson J. A., Englert T. R.. Haagenson P. L.. McBeth R. B., Morris A. L.. Poguc R. and Wartburg A. F. (1973) Background trace gas concentrations in the Central IJnited States. J. guoph~~ Res. 78, 7057-7064. Dennis R.. Billings C. E.. Record F. A., Warneck P. and Arin M. L. (1969) Measurements of sulfur dioxide losses from stack plumes. Paper No. 69 156. 62nd Annual Meeting of the Air Pollution Control Assoc.. New York. Haagenson P. L. and Morris A. L. (1974) Forecasting the behavior of the St. Louis, Missouri, pollutant plume J. appl. Meteor. 13. 901 909. Intersociety Committee (1972) Methods of Air Sumpliny und .4ncdysis. American Public Health Association. Method No. 402. pp. 325 328. Komhyr W. D. (1969) Electrochemical concentration cells for gas analysis. Ann. Geophys. 35. 203-210. LaHue M. D.. Axelrod H. D. and Lodge J. P.. Jr. (1973) Direct measurement of atmospheric nitrous oxide in a stored air volume using thermal conductivity gas chromatography. J. Chror&og. Sci. 11, 585-587. McKay H. A. C. (1971) The atmospheric oxidation of sulfur dioxide in water droplets in presence of ammonia. Atmospheric Encironnlent 5. 7-14. Natusch D. F. S.. Klonis H. B.. Axelrod H. D.. Teck R. J. and Lodge J. P. Jr. (1972) Sensitive method for measurement of atmospheric hydrogen sulfide. .4&. Chem. 44. 2067. Simmonds P. G., Kerrin S. L., Lovelock J. E. and Shair F. H. (1974) Distribution of atmospheric halocarbons in the air over the Los Angeles basin. Arnlosphcric Encironment
8. 209-216.
Smith J. P. and Urone P. (1974) Static studies of sulfur dioxide reactions. Environ. Sci. Techno/. 8, 742.-746. Stephens T. N. and McCaldin R. 0. (1971) Attenuation of power station plumes as determined hy instrumented aircraft. Enciron. Sci. Technol. 5. 615621. Stampfer J. F.. Jr. (1972) An aircraft. aerosol sampling program: Some preliminary results. Afmospheric Emironmrnt 6. 743 -757. Stampfer J. F.. Jr. and Anderson J. A. (1975) Lmting the St. Louis urban plume at X0 and I20 km and some of its characteristics. Atmospheric Enrironmenr 9, 301-313. Venezia R. and Ozolins G. (1969) Inrersturc, Air Pollution Study. Phase II Project Report. Vol. II Air Pollurunr Emission Imvntory. Publ. U.S. Dept. of Health. Education SC Welfarc. Public Health Service. Cincinatti. OH.
