A SET OF SUGGESTED AIR QUALITY FOR CANADA
INDICES
H. INHX~ER Science Policy Branch. Department of the Environment. Ottawa. Canada KIA OH3 (Firsrreceiced15 July 1974 andinjnaljortn
19 Seprernber1971)
Abstract-An approach to producing air quality indices over a wide area is discussed. The proposed indices cover aspects of pollution in cities around cities, and in rural areas. Data are shown on a local and regional basis, and the production of national indices is attempted. Lack of comprehensive data makes detailed evaluation difficult. Views expressed are not necessarily those of the Department.
Over the last few years, environmental monitoring in many countries has produced mountains of data on many aspects of the atmosphere. However, not as many conclusions based on these data as could be desired have been effectively transmitted to environmental planners and laymen. One way of transforming these data into useful information is by means of environmental indicators or indices. These indices could let the planner or layman (a) compare the local quality of the environment, which he knows, to.others in the region or nation, and point out areas and frequencies of potentially dangerous problems. (b) evaluate the changes in environmental quality over time, both locally and nationally. (c) relate government efforts in money and manpower to these changes, and (d) point out gaps in environmental monitoring in time. space and pollutant. From these and similar lines of reasoning was born the Environmental Quality Index (EQI) (Inhaber, in press), and as part of it, the Air Quality Index. The EQI, or similar indices, can be used to serve any or all of the four purposes mentioned. The philosophy of the EQI has been described in detail elsewhere (Inhaber, in press). At present, most information available on the Canadian environment has been collected for specific, relatively narrow purposes. and not to give an overall picture. The main problem in constructing the EQI is the combination and evaluation of this information. By nature, an index is an average of conditions, and environmental situations potentially dangerous to human health should not be considered on the basis of indices. An index can be defined as a unitless number, which ranges from zero, for the best possible environmental condition, through increasing numbers for progressively worse environmental quality. Data used in its calculation should (a) be numerical rather than descriptive, (b) be national and comprehensive, (c) relate to a consistent time period, and (d) be comparable to some standard, objective or status level. Much environmental data does not fully meet all these requirements. To avoid subjective opinion, about sixty scientists, engineers and administrators were consulted in the course of the work on the entire EQI. While individual viewpoints differ somewhat on the meaning of results, there was a fairly solid core of understanding on the index scales used. 353
It is virtually impossible to reach a value of zero for some indices. no matter n-hat the degree of government or private action. For example. there is always a certain amount of dust and other matter in the air due to kvinds. active volcanoes. etc. As a result. an inde\ for suspended particulate matter can never become zero. Standards (or objectives) have been set for some air pollutants. but have not been (and are unlikely to be) set for others. To allow the construction of indices. temporary standards were set by using national averages in some cases. Because absolute consistency teas not possible in the selection of standards, a value judgement based on any combination of indices should be highly cautious. For illustrative purposes. several sub-indices can be combined to give a larger overvieu of the state of the environment. The root-mean-square method was used to amalgamate sub-indices. Since an EQI could function in part as an alerting service for deteriorating environmental conditions. the mathematics of combination had to accentuate relativelq high values of sub-indices. Other more complicated mathematical schemes for combination have been discussed (Bisselle rr nl., 1972). The problems of constructing air quality indices have been evaluated before (Bisselle et al.. 1972: Leblanc and Rao. 1972; McNeeley er nl.. 1973; Porch. 1971; Shenfield. 1970a.b. 1971: Thomas rr al.. 1971: Thomas. 1972). Most considered only one or a Fe\\, aspects of constructing an overall air quality index. For example, Bisselle rr al. (1972). as well as Shenfield (1970a. b, 1971) considered only certain pollutants, as did Thomas rt trl. (1971). The data they used were generally insufficient in scope to construct a national air quality index. Figure I shows the structure of the Air Quality Index. The hierarchical structure is designed to take account of three major aspects of air quality. The Index of Specific Pollutants is derived from physical measurements of particular pollutants like sulphur dioxide. carbon monoxide. and so on. in many large urban areas. The air quality around urban areas can be described by an Index of Inter-Urban Air Quality. One way of obtaining this type of index is by measuring the visibility at airports. which are generally located some distance from the centre of cities. The visibility is a rough measure of the effect on air quality of a number of air pollutants. Finally. we consider the air quality in areas far from urban centres. and especiaHy in the vicinity of large industries. For this aspect. we evaluate the effect on surrounding vege-
Fig. I. Schematic
diagram
of air qualit)
index.
A set of proposed tlir quality indices for Canada
355
tation. soil. water and wildlife in the countryside. Because physical measurements often are not made in these areas, an Index of Industrial Emissions was calculated. based on estimates ofemissions ofparticular air pollutants (Babcock. 1970. 1972f. Because of the different types of data. the indices are presented in varying formats. For example. when there was a considerable amount of data for maps. contours were drawn for equal values of an index. The index contours do not necessarily imply that every area between two contours is within the same range of the index. Because of the relatively small amount of data for some parts of the Air Quality Index. these data are put into the form of tables.
I. INDEX
OF SPECIFIC
POLLUTANTS
An -ideal” index for specific pollutants might include indices on sulphur dioxide. SUSpended particulate matter, carbon monoxide, total oxidants. and oxides of nitrogen. Since a large amount of data on the coefficient of haze (CQH) has been and is being gathered. it was decided to include this information in this section as well. The coefficient of haze is also a measure of the amount of particulate matter in the air. For each of these six pollutants, objectives (or standards) were chosen. The first four were published in the Carrad~ Gn~erre (Part 1) on 16 December 1972, and are designed to protect public health and welfare by setting limits on levels of pollution in the air. (Some revisions. not considered to be substantive, have been made in these objectives. as announced in the Canada Gazette, 30 March 1971). They are: (i) S~rlplrrlrdioxide: averaged over 1 y. O*O:!ppm: averaged over 1 day. 0.11 ppm. (ii) Suspended particrrfare u~mer: averaged over 1 y, 70 itrn- ‘. This standard was to be computed as the geometric mean. Averaged over 1 day, 120 jrrne3. (iii) Carhori r~rioltitlr: averaged over 8 h, 13 ppm: averaged over L h. 30 ppm. (iv) arcs o.~~da~zrs: averaged over 1 y, @015 ppm: averaged over I day. 0.025 ppm; averaged over 1 h, 0.08 ppm. (v) CoeSJicient oj’hax: since no objectives had been set for this pollutant, the Ontario objectives were adopted (Shenfield, 1970a, b, 1971). Ontario Regulation 15/70 states that the criteria are 0.45 COW units for a 1 y average, and 1.0 unit daily. (vi) Oxides ofmbogen: since no objective had been set for this pollutant, the Ontario objectives were adopted (Shenfield, 197Oa,b, 1971). Ontario Regulation 15/70 states that the criteria are 0.10 ppm averaged over I day: 0.20 ppm averaged over 1 h. In terms of availability, the data may be broken down into two groups. The first group are data that have been compiled by the Environmental Protection Service of Environment Canada from 237 sampling instruments in 37 cities (as of January 1972). These data include measurements of sulphur dioxide. suspended particulate matter, and coefficient of haze. The second group comprises measurements on carbon monoxide. total oxidants and oxides of nitrogen. These data are considerably less in volume than that of the first group. The majority of the data are from the same time period (1971) as that of the first group. The exact dates of each data recording are on file. The second group is less comprehensive in its degree of geographical coverage than the first group. However. because the measurement network for these pollutants is being expanded, these data were included. They are shown in the form of tables rather than maps. The numbers quoted in criteria (i-iv) were the “maximum acceptable objectives’*, designed to provide adequate protection against effects on soil, water, vegetation, etc. and represent the realistic objectives for all parts of Canada. They fit well with the Ontario
356
H.
ISH.ABEK
objectives for coethcient of haze and oxides of nitrogen. criteria (v and vi). since the latter were based on a maximum acceptable level. In general. the problem in calculation of the indices was taking account of the daily (or more frequent) variations in the level of a given pollutant while comparing the annual av’erage to the annual (or other long-term) objective. la. First group oj‘specijc
polhtmts
The index for suspended particulate governmental specifications: Isp,, =;
matter. Isp,,,
(C, x C? x C, x
was
calculated as f~310w,
based on
.C,,) 70
(11
where n is the number of weekly readings per station in a month. and the Cs are the weekl! concentrations in pm- 3. Data were available only on a weekly basis. The arithmetic average of the monthly average indices of equation (1) was taken as the yearly average. The yearly suspended particulate matter indices for each station in a multiple-station city were then averaged. To produce a national average of I sp,,, the city averages were weighted according to their metropolitan populations. National and yearly averages for subsequent specific pollutants were calculated in the same way. Results are shown in Fig. 2 and Table 1. The highest regions are in southern Ontario, with high regions also in Quebec. Alberta and British Columbia. Levels of I sp,, in the Maritimes and most of the Prairies tend to
__
MlkI 0
200
402
16
Fig. 2. Suspended particulate matter index I sp,,. Highest regions of the index ar: in southern Ontario. with high regions also in Quebec, Alberta and British Columbia. Points arc shaded onl? over land.
A ~lt of proposed air quality indices for Canada
351
Table I. National air quality indicer 1971
index ISPU
[SO: [COti [co
I OX fN0,
I SP I t.Y
National average
Number of stations
Number cities
1.33 1.61
59 26
33 13
I.11
2-l
1-l
0.41 1.69 0.63 1.23 0.59
30 13 15
12 I1 I1 36 96
0r
Combined population 11400000 526Oooo s 78Oooo
8700000 6-MXMOO 5900000 llj~~ 10s00000
For both sulphur dioxide and coefficient of haze, the indices had to be calculated in a somewhat more detailed marmer, since daily as well as yearly data exist. Data are not available for hourly readings. An attempt was made to consider high daily readings separately as well as averaging them yearly. There are a number of mathematical methods for doing this. For example, the MITRE Corporation in the U.S., as reported in the Tkirn Annual Report of the U.S. Council on Environmental Quality (1972),used a step function, which had a value of zero if criteria were not exceeded, in combining the daily and yearly objectives. A problem with this method was that only the maximum daily concentration for the year was used. In other words. solely the worst episode was used in the calculations, and all others were disregarded. If a city had one extremely high reading of a pollutant, perhaps due to unusual weather conditions, it could have a fairly high yearly index. On the other hand, a city whose daily readings approached but never quite exceeded a daily standard might have a considerably lower index. To take account of this problem, the following general formula was developed for the five remaining pollutants:
Here I is the specific pollutant index. C, is the annual average concentration, S, is the annual objective+C,, is the daily concentration, and II is the number of readings in a month. The factor 2 in the denominator indicates we are considering two average concentrations, annual and daily. The second term in brackets deals with the daily variation in concentration. The two terms in brackets were approximately of the same size, indicating that annual and daily contributions had about the same weight. Results for sulphur dioxide are shown in Table 1. Most of the cities in eastern Canada had relatively high values of the index, as compared to those in western Canada. The prime exceptions were London and Ottawa, which are relatively unindustrialized. The information is not shown in map form. since this is available elsewhere (Inhaber, in press). Quantities used in the calculation of the index of coefficient of haze are as described after equation (2). Results are shown in Tables 1 and 2. Although it is difficult to make a comparison on the basis of this table from city to city (for the reasons cited at its foot), the data have sufficiently wide coverage to allow the computation of a national index &-on.
35s
H.
Table 2. Cit)-wide
I\H.ABER
averages of specific pollutants
Province
Cirb
(COH
Nova
C&cc Ba) Skdnc) Hull Montreal Hamilton London Ottawa Sarnia Sudbury Toronto Windsor Cornwall Simcoe Winnipeg Calgary Edmonton Vancoucer
0.45
Scotia
Quebec Ontario
Manitoba Alberta British Columbia
I(0
I 0,
0.73 0.28 0.13 0.18 0.27 0.10 0.35 0.45 0.13 0.23
2.9 I I.53 1.X 1 :? ;:;; I.73 I .98 2.19
ILO
I 4: 0.68 I .6S I..71 0.47 O.-M O.$O 0.57 0.96 I.37
0.85 0.51 0.47
0.1 I 0.10
0.57 I.51 I .6.:
0.36 0.40 0.26 0.19 0.76 0.5.; 0.29 0.18 0.47 0.33 023
Note: Caution should be used in the comparison of these indices from one city to another. The exact placement of measuring instruments with respect to areas of air poltution the results of which these indices are based on. varies from city to city. In the case of coetlicient of haze. the cotour of the particles on which the measurement is based also varies.
1b. Second group of specific pollutatzrs The three pollutants in the second group had considerably less data available. The index for carbon monoxide was calculated by substituting the annual objective of equation (2) by the 8-h objective. the daily concentration by the hourly concentration. and II by the number of readings in a month or year. Results for carbon monoxide are shown in Tables 1 and 2. Again, while it is difficult to make city-to-city comparisons, the data are adequate to compute the national average. The index for total oxidants. I,,. was calculated by means of equation (Z), except that the l-h concentrations were substituted for the daily concentrations. Results are shown in Tables 1 and 2. Finally, the index for oxides of nitrogen. l,V,swas computed, using equation (2) and substituting the daily objective for the annual objective and the hourly for the dail!- concentrations. Table 1 shows that the index for oxidants had the highest national average, and that for carbon monoxide the lowest. Because of the variability of temporal and spatial coverage, these results must be considered as only tentative. To produce an overall index of specific pollutants I sP, the six sub-indices were combined by means of the root-mean-square method discussed above. Since the coefficient of haze is also a measure of the amount of particulate matter, each of these two indices was given half weight compared to the other four. Because comparatively few cities had data on all six pollutants, this index is not shown on a map. lc. 7ittv cariatiott of specific polhrranrs
The levels of the indices for specific pollutants vary in time as well. The national level for each of the first group was calculated for each month of 1971, using population weight-
.A set of proposed air quality indices for Canada
359
. .. .. . : : 3,....:
:
; :
Fig. 3. National indices of sulphur dioxide, coefficient of haze and suspended particulate matter for 1971. The sulphur dioxide index has by far the largest maxima, which occur in the winter months. The other two indices have smaller seasonal swings.
ing. Results for suspended particulate matter, sulphur dioxide, and coefficients of haze are shown in Fig. 3. In contrast to the other two following curves, we see comparatively little change in the index of suspended particulate matter from month to month. The largest values are in spring, and may be due in part to natural conditions of spring air dust. The index of sulphur dioxide is very high in the first two months of the year, but decreases quickly to a minimum in July and August. This change may be due to (a) the fact that the bulk of industrial and home-heating uses of sulphur-containing fuels occurs in the winter months, or (b) changes in mixing depths. The index of coefficient of haze is similar to that for sulphur dioxide, except that the values are not as high. The index has a maximum of around 1.3-1.5 in the fall and winter months, and then declines to about 0.75 in the summer. This is apparently due to heating effects in the winter months. In order to study the scatter from year to year, the three indices of Fig 3 were recomputed for 1972 in Fig. 4. Because of changes in the siting of some monitoring stations, the opening and closing of others during the course of the two years, and other factors, the two graphs are not as comparable in coverage as might be desired. However, some simiiarities can be seen. The curves for the indices of coefficient of haze and suspended particulate matter are close in shape for the years 197 1 and 1972. For the former index, the 1972 maximum came in May rather than April, as expected on the basis of the 1971 results, but the two curves AX.
9 3-l
H. INHALER
360
... .
z.#!&W
Di
-
Caffkki
-
elpnM
.f
fko
fbemdm
MERI
Fig. 4. Nat&tat indices of sulphur dioxide, coeflicient of haze and suspended particulate matter for 1972.The shape of the curves is similar to those of Fig. 3. However, the maxima for the sulphur dioxidi index are lower than those of 1971.
both have theii high points in thespring. For the latter index, a fiat rn~~urn is reached in both years in the summer months, with maxima in February. Both sets of indices are similar in mag&ude for cornpar&& months in the two years. The maximum of the suiphur dioxide index, while still in February, decreased considerabfy in 1972as compared to 1971.This decrease he-id in most months, making the values of this index in 1972 similar to those of the other twu indices. The overaII shape of the curve in 1972was aImost the same as in 1971, with strong maxima in the winter months. 2. INDEX
OF
INTER-URBAN
AIR
QUALITY
This index, designed to give an indication of air quality in the regions around urban at Canadirtn .airports. Hourly readings m which precentrcs, is based on booty cipit&ori or fog were not& luded. The quantity chosen asan indicator was the average visibility for each hour. The visibilities were summed.and divided by the number of hours with precipitation. The year 1971 was USed em@loyingthe avenge vie&iEty fsr all 365 &ys. There are many f~etora,~~~ the relati~nahip of visibility-and air polhtion, such as wind direction and v&city, types of ~~~~~~ and distancea frum cities to airports (Larsen, 1969; Miller er ai., 1972; Munn, 1973).Due to lack of knowledge of these factors pmdble to &dceaccount of them in the cakulations. s for visi&iWes have been or are likely to be set, the average visibility of 14.6 miles, the mean for the years 1953-1971at two far northern stations, Yel-
A set of proposed air quality indices for
Can3d3
361
lowknife and Whitehorse, was taken as a baseline measure. It was assumed that since these stations were ‘so small and distant from major urban areas they would be little affected by air pollution. Because the average visibility was a function of the overall density of air pollutants in the vicinity. the index of visibility had to be approximately numerically comparable to the index lsP derived from the specific pollutant data. It was found after computation that this could be accomplished by dividing the ratio of far northern visibilities to visibility at other airports by a factor of two. The index of inter-urban air quality then became:
where f,,, is the index of inter-urban (or regional) air quality, C$, is the average visibility for the two far northern stations, and V’, is the average visibility for other airports. An airport fidving the same average visibility as the far northern stations had Irvg = 0.5. Results of the computation are shown in Fig. 5. Because of the large amount of data available. the information was contoured. Regions of highest value are in extreme southern Ontario, with indices in that region at least 20
Fig. 5. Index of inter-urbsnair quality, I,,. Extreme southern Ontario has the highest values of this index. Values decrease towards the north. The southern parts of British Columbia, Alberta and Saskatchewan have relatively low values of the index. as does western Alberta. Sampiing stations within a given shade lie within that range of values of the index. This arrangement does not imply that all areas in a particular shade have the same range of values
per cent higher than in most other areas. The entire industrialized region from there to mid-Quebec tends to have higher indices than western Canada, although part of this ma> be due to natural conditions (Hare, 19731. The region of high indices also extends into the Maritimes, with the southern Maritimes tending to have higher indices than the north. In western Canada, there is a ridge of extremely low indices with values less than 0.5 running along the southern extremes of British Columbia, Alberta and Saskatchewan. The indes rises farther north. but it stiI1 remains low and comparable to the average for the far northern stations. Southwest British Columbia has an index comparable to that of au average eastern station, but considerably Iess than southern Ontario. X national index of regional air quality was computed b, population weighting. and results are shown in Table I. 3. iNOES
OF
fNDt;‘STRIAL
EMISSIONS
The third and finat component of the Air Quality Tndex was the index of industrial emissions Ii,. designed to give a measure of air quality outside urban areas. Use was made of the Xatiotwitiu Incmtor!~ of’ Air Pollutam Emissions. published by Environment Canada. This listed the estimated weight of emissions for major point and area sources, defined as those emitting more than 5000 tons of a particuIar pollutant per Fear. The estimates are based on the level of production of various commodities. the type of emission controls installed, and other factors. Although emission estimates were made for more than two pollutants, only sulphur dioxide and suspended particulate matter were considered for the AQf. They were chosen because they were in the first group of pollutants mentioned in Section I-tise_for which extensive physica measurements have been made. The emission data could be grouped into two sections. The first j~~~~ tba~e locations where physical measuremenfs of air qality have been made; t&se*-wer@&me& “urban”. A11other locations were termed “industrial”. A small prop&& of the emiakms in those areas were non-industrial in origin. The index of industrial emit&ons was defined as
where 15, is the sum of the industrial emissions. for a given pollutstnt for a county. and P, is the population of that county. Ei is the sum of the industrial emissions for a given pollutant for all of Canada, and P,,, is the population of Ci@tia. In this way. we can take account of the r&&e ~~~~ibu~ns ofeach: of the countis, both compared to each other rd” ofa Canadian average was chosen because and to the Canadian a~~~~~ no others were available. Counties ate used as crude surrogates for airsheds because the boundaries of the latter are often not well-defined. For the sulphur dioxide index, 31 industrial sources in 9 provinces Lvere noted. The total emissions for all Canada were 6222000 tons. of which 5363000 tons were emitted from industrial sites. The county indices are shown in Fig. 6. Because the data are relatively scattered, it is difEcult to draw national conclusions. However, British Columbia has the Iargest number of areas with relatively high values of the index. Manitoba. Ontario and Quebec are the only other provinces with areas with values of the index in the highest category. To compute a national index for industrial emissions of sulphur dioxide. the
h set of proposed air quality indices for Canada
.363
Fig. 6. Index of industrial emissions of sulphur dioxide, I,,,,_.
county averages were weighted according to county populations. The index had a value
of 0.87. The same method was used to compute the index of industrial emissions of suspended particulate matter. For this index, 28 industrial sources in 9 provinces were noted. The total emission was 758000 tons, of which 566000 tons were emitted from industrial sites. Because the graphical presentation is available elsewhere (Inhaber, in press), it is not shown here. All provinces except Manitoba, New 3runswick and Prince Edward Island have at least one area with a relatively high value of the index. Quebec and Ontario have the largest number of areas with relatively high values. To compute a national index for industrial emissions of suspended particulate matter, the county averages were weighted according to county populations. The index had a value of 0.75. The root-mean square equation used to calculate the overall index of industrial emissions is
When sufficient physical measurements of air quality are available for other specific pollutants, this equation can be modified appropriately. Using the values for the two components noted above, Ii, = 0.81.
364
H. 1. COiMBINED
ISHABER
AIR
QUALITY
INDEX
The three components of the combined air quality index. dealing with specific pollutants, regional air quality. and industrial emissions, can be combined by the root-meansquare technique. Weights of 5, 3 and 2 were respectively assigned to the three components. These weights were suggested to reflect the approximate contributions of each index to the overall Canadian air quality index. The overall air quality index then is: ,
= ‘\ (5(I&
i
y’
+ :!u,‘.)‘i
(6)
where the denominator is, as usual. the sum of the weights. Using equation (6), we have I,i, = 0.99. Because of the relatively small amount of data available for many areas. it was not possible to compile an overall air quality index for specific cities and provinces. Acknowledgements-Mike Kwizak and Ted Munn supplied wise suggestions and informed counsel. I protited by conversations with Dr. S. 0. Winthrop and B. C. Newbury. Without the help of Kristina Przednowek. this work would have been impossible. Rob MacKay and Susan Vadeboncoeur also supplied clerical and typing assistance. Ken Hare and Peter Meyboom gave me much encouragement. REFERENCES Babcock L. R. (1970) Combined pollution index for measurement of total air pollution. J. .-tir Pollrtr. Courrol Ass. 20 (IO). 653-659. Babcock L. R. and Nagda N. L. (1972) Indices of air quality. Indicarors of Enrironr~rrnal Qualify (Edited by Thomas W. A.) pp. 183-198. Plenum, New York. Bisselle C. A., Lubore S. H. and Pikul R. R. ( 1972) !b’ntioml encirowtlentul iruficrs: Air yrrulity ad odoor r~‘ow~tion. MITRE Corp.. Washington. Hare F. K. (1973) Private Communication. Inhaber H. Science. (In press). Larsen R. I. (1969) A new mathematical model of air pollutant concentration averaging time and frequency. J. Air Pollur. Control Ass. 19 (I ). 24-30. Leblanc F. and Rao D. N. (1972) Indices of atmospheric purity and fluoride pollution pattern in Arvida, Quebec. Can. J. Rot. 50 (5). 99 l-998. McNeely M. D., Nechay M. W. and Sunderman F. u’. (1972) Measurements of nickel in serum and urine as indicators of environmental exposure to nickel. Clirt. Chem. 18 (9). 992-995. Miller M. E., Canfield N. L., Ritter T. A. and Weaver C. R. (1972) Visibility changes in Ohio. Kentucky and Tennessee from 1962 to 1969. Monthly Weather Rec. 100 (I ). 67-7 I. Munn R. E. (19721Secular increases in summer haziness in the Atlantic Provinces. Arrtxwhere 11 (41 156-161. Porch W. M.~(1971)Visibility of Mount Rainier as an index of background pollution. Titan;. Am. Geophp. L’nion 52; 430. Shenfield L. (1970s) Ontario’s air pollution index. War. Pollrtt. Control 10s (I I), 55-58. Shenfield L. (197Ob) Ontario’s air pollution index and alert system. J. Air Pollut. Connol Ass. 20 (9). 612. Shettfteld L. (1971) Ontario’s air quality monitoring network and air pollution index. Presented at American Industrial Hygiene Conference, Toronto, 2128 May 1971. Thomas W. A., Babcock L. R. and Shults W. D. (1971) Oak Ridge air quality index. Report NO. ORNL-NSF-EP8. Oak Ridge National Laboratory, Oak Ridge, Term. Thomas W. A. (Editor) (1972) Indicators ofEncironmer& Quality. Ptenum. New York. This is probably the best collection of articles relating to environmental indices.
INDICES
H. INHX~ER Science Policy Branch. Department of the Environment. Ottawa. Canada KIA OH3 (Firsrreceiced15 July 1974 andinjnaljortn
19 Seprernber1971)
Abstract-An approach to producing air quality indices over a wide area is discussed. The proposed indices cover aspects of pollution in cities around cities, and in rural areas. Data are shown on a local and regional basis, and the production of national indices is attempted. Lack of comprehensive data makes detailed evaluation difficult. Views expressed are not necessarily those of the Department.
Over the last few years, environmental monitoring in many countries has produced mountains of data on many aspects of the atmosphere. However, not as many conclusions based on these data as could be desired have been effectively transmitted to environmental planners and laymen. One way of transforming these data into useful information is by means of environmental indicators or indices. These indices could let the planner or layman (a) compare the local quality of the environment, which he knows, to.others in the region or nation, and point out areas and frequencies of potentially dangerous problems. (b) evaluate the changes in environmental quality over time, both locally and nationally. (c) relate government efforts in money and manpower to these changes, and (d) point out gaps in environmental monitoring in time. space and pollutant. From these and similar lines of reasoning was born the Environmental Quality Index (EQI) (Inhaber, in press), and as part of it, the Air Quality Index. The EQI, or similar indices, can be used to serve any or all of the four purposes mentioned. The philosophy of the EQI has been described in detail elsewhere (Inhaber, in press). At present, most information available on the Canadian environment has been collected for specific, relatively narrow purposes. and not to give an overall picture. The main problem in constructing the EQI is the combination and evaluation of this information. By nature, an index is an average of conditions, and environmental situations potentially dangerous to human health should not be considered on the basis of indices. An index can be defined as a unitless number, which ranges from zero, for the best possible environmental condition, through increasing numbers for progressively worse environmental quality. Data used in its calculation should (a) be numerical rather than descriptive, (b) be national and comprehensive, (c) relate to a consistent time period, and (d) be comparable to some standard, objective or status level. Much environmental data does not fully meet all these requirements. To avoid subjective opinion, about sixty scientists, engineers and administrators were consulted in the course of the work on the entire EQI. While individual viewpoints differ somewhat on the meaning of results, there was a fairly solid core of understanding on the index scales used. 353
It is virtually impossible to reach a value of zero for some indices. no matter n-hat the degree of government or private action. For example. there is always a certain amount of dust and other matter in the air due to kvinds. active volcanoes. etc. As a result. an inde\ for suspended particulate matter can never become zero. Standards (or objectives) have been set for some air pollutants. but have not been (and are unlikely to be) set for others. To allow the construction of indices. temporary standards were set by using national averages in some cases. Because absolute consistency teas not possible in the selection of standards, a value judgement based on any combination of indices should be highly cautious. For illustrative purposes. several sub-indices can be combined to give a larger overvieu of the state of the environment. The root-mean-square method was used to amalgamate sub-indices. Since an EQI could function in part as an alerting service for deteriorating environmental conditions. the mathematics of combination had to accentuate relativelq high values of sub-indices. Other more complicated mathematical schemes for combination have been discussed (Bisselle rr nl., 1972). The problems of constructing air quality indices have been evaluated before (Bisselle et al.. 1972: Leblanc and Rao. 1972; McNeeley er nl.. 1973; Porch. 1971; Shenfield. 1970a.b. 1971: Thomas rr al.. 1971: Thomas. 1972). Most considered only one or a Fe\\, aspects of constructing an overall air quality index. For example, Bisselle rr al. (1972). as well as Shenfield (1970a. b, 1971) considered only certain pollutants, as did Thomas rt trl. (1971). The data they used were generally insufficient in scope to construct a national air quality index. Figure I shows the structure of the Air Quality Index. The hierarchical structure is designed to take account of three major aspects of air quality. The Index of Specific Pollutants is derived from physical measurements of particular pollutants like sulphur dioxide. carbon monoxide. and so on. in many large urban areas. The air quality around urban areas can be described by an Index of Inter-Urban Air Quality. One way of obtaining this type of index is by measuring the visibility at airports. which are generally located some distance from the centre of cities. The visibility is a rough measure of the effect on air quality of a number of air pollutants. Finally. we consider the air quality in areas far from urban centres. and especiaHy in the vicinity of large industries. For this aspect. we evaluate the effect on surrounding vege-
Fig. I. Schematic
diagram
of air qualit)
index.
A set of proposed tlir quality indices for Canada
355
tation. soil. water and wildlife in the countryside. Because physical measurements often are not made in these areas, an Index of Industrial Emissions was calculated. based on estimates ofemissions ofparticular air pollutants (Babcock. 1970. 1972f. Because of the different types of data. the indices are presented in varying formats. For example. when there was a considerable amount of data for maps. contours were drawn for equal values of an index. The index contours do not necessarily imply that every area between two contours is within the same range of the index. Because of the relatively small amount of data for some parts of the Air Quality Index. these data are put into the form of tables.
I. INDEX
OF SPECIFIC
POLLUTANTS
An -ideal” index for specific pollutants might include indices on sulphur dioxide. SUSpended particulate matter, carbon monoxide, total oxidants. and oxides of nitrogen. Since a large amount of data on the coefficient of haze (CQH) has been and is being gathered. it was decided to include this information in this section as well. The coefficient of haze is also a measure of the amount of particulate matter in the air. For each of these six pollutants, objectives (or standards) were chosen. The first four were published in the Carrad~ Gn~erre (Part 1) on 16 December 1972, and are designed to protect public health and welfare by setting limits on levels of pollution in the air. (Some revisions. not considered to be substantive, have been made in these objectives. as announced in the Canada Gazette, 30 March 1971). They are: (i) S~rlplrrlrdioxide: averaged over 1 y. O*O:!ppm: averaged over 1 day. 0.11 ppm. (ii) Suspended particrrfare u~mer: averaged over 1 y, 70 itrn- ‘. This standard was to be computed as the geometric mean. Averaged over 1 day, 120 jrrne3. (iii) Carhori r~rioltitlr: averaged over 8 h, 13 ppm: averaged over L h. 30 ppm. (iv) arcs o.~~da~zrs: averaged over 1 y, @015 ppm: averaged over I day. 0.025 ppm; averaged over 1 h, 0.08 ppm. (v) CoeSJicient oj’hax: since no objectives had been set for this pollutant, the Ontario objectives were adopted (Shenfield, 1970a, b, 1971). Ontario Regulation 15/70 states that the criteria are 0.45 COW units for a 1 y average, and 1.0 unit daily. (vi) Oxides ofmbogen: since no objective had been set for this pollutant, the Ontario objectives were adopted (Shenfield, 197Oa,b, 1971). Ontario Regulation 15/70 states that the criteria are 0.10 ppm averaged over I day: 0.20 ppm averaged over 1 h. In terms of availability, the data may be broken down into two groups. The first group are data that have been compiled by the Environmental Protection Service of Environment Canada from 237 sampling instruments in 37 cities (as of January 1972). These data include measurements of sulphur dioxide. suspended particulate matter, and coefficient of haze. The second group comprises measurements on carbon monoxide. total oxidants and oxides of nitrogen. These data are considerably less in volume than that of the first group. The majority of the data are from the same time period (1971) as that of the first group. The exact dates of each data recording are on file. The second group is less comprehensive in its degree of geographical coverage than the first group. However. because the measurement network for these pollutants is being expanded, these data were included. They are shown in the form of tables rather than maps. The numbers quoted in criteria (i-iv) were the “maximum acceptable objectives’*, designed to provide adequate protection against effects on soil, water, vegetation, etc. and represent the realistic objectives for all parts of Canada. They fit well with the Ontario
356
H.
ISH.ABEK
objectives for coethcient of haze and oxides of nitrogen. criteria (v and vi). since the latter were based on a maximum acceptable level. In general. the problem in calculation of the indices was taking account of the daily (or more frequent) variations in the level of a given pollutant while comparing the annual av’erage to the annual (or other long-term) objective. la. First group oj‘specijc
polhtmts
The index for suspended particulate governmental specifications: Isp,, =;
matter. Isp,,,
(C, x C? x C, x
was
calculated as f~310w,
based on
.C,,) 70
(11
where n is the number of weekly readings per station in a month. and the Cs are the weekl! concentrations in pm- 3. Data were available only on a weekly basis. The arithmetic average of the monthly average indices of equation (1) was taken as the yearly average. The yearly suspended particulate matter indices for each station in a multiple-station city were then averaged. To produce a national average of I sp,,, the city averages were weighted according to their metropolitan populations. National and yearly averages for subsequent specific pollutants were calculated in the same way. Results are shown in Fig. 2 and Table 1. The highest regions are in southern Ontario, with high regions also in Quebec. Alberta and British Columbia. Levels of I sp,, in the Maritimes and most of the Prairies tend to
__
MlkI 0
200
402
16
Fig. 2. Suspended particulate matter index I sp,,. Highest regions of the index ar: in southern Ontario. with high regions also in Quebec, Alberta and British Columbia. Points arc shaded onl? over land.
A ~lt of proposed air quality indices for Canada
351
Table I. National air quality indicer 1971
index ISPU
[SO: [COti [co
I OX fN0,
I SP I t.Y
National average
Number of stations
Number cities
1.33 1.61
59 26
33 13
I.11
2-l
1-l
0.41 1.69 0.63 1.23 0.59
30 13 15
12 I1 I1 36 96
0r
Combined population 11400000 526Oooo s 78Oooo
8700000 6-MXMOO 5900000 llj~~ 10s00000
For both sulphur dioxide and coefficient of haze, the indices had to be calculated in a somewhat more detailed marmer, since daily as well as yearly data exist. Data are not available for hourly readings. An attempt was made to consider high daily readings separately as well as averaging them yearly. There are a number of mathematical methods for doing this. For example, the MITRE Corporation in the U.S., as reported in the Tkirn Annual Report of the U.S. Council on Environmental Quality (1972),used a step function, which had a value of zero if criteria were not exceeded, in combining the daily and yearly objectives. A problem with this method was that only the maximum daily concentration for the year was used. In other words. solely the worst episode was used in the calculations, and all others were disregarded. If a city had one extremely high reading of a pollutant, perhaps due to unusual weather conditions, it could have a fairly high yearly index. On the other hand, a city whose daily readings approached but never quite exceeded a daily standard might have a considerably lower index. To take account of this problem, the following general formula was developed for the five remaining pollutants:
Here I is the specific pollutant index. C, is the annual average concentration, S, is the annual objective+C,, is the daily concentration, and II is the number of readings in a month. The factor 2 in the denominator indicates we are considering two average concentrations, annual and daily. The second term in brackets deals with the daily variation in concentration. The two terms in brackets were approximately of the same size, indicating that annual and daily contributions had about the same weight. Results for sulphur dioxide are shown in Table 1. Most of the cities in eastern Canada had relatively high values of the index, as compared to those in western Canada. The prime exceptions were London and Ottawa, which are relatively unindustrialized. The information is not shown in map form. since this is available elsewhere (Inhaber, in press). Quantities used in the calculation of the index of coefficient of haze are as described after equation (2). Results are shown in Tables 1 and 2. Although it is difficult to make a comparison on the basis of this table from city to city (for the reasons cited at its foot), the data have sufficiently wide coverage to allow the computation of a national index &-on.
35s
H.
Table 2. Cit)-wide
I\H.ABER
averages of specific pollutants
Province
Cirb
(COH
Nova
C&cc Ba) Skdnc) Hull Montreal Hamilton London Ottawa Sarnia Sudbury Toronto Windsor Cornwall Simcoe Winnipeg Calgary Edmonton Vancoucer
0.45
Scotia
Quebec Ontario
Manitoba Alberta British Columbia
I(0
I 0,
0.73 0.28 0.13 0.18 0.27 0.10 0.35 0.45 0.13 0.23
2.9 I I.53 1.X 1 :? ;:;; I.73 I .98 2.19
ILO
I 4: 0.68 I .6S I..71 0.47 O.-M O.$O 0.57 0.96 I.37
0.85 0.51 0.47
0.1 I 0.10
0.57 I.51 I .6.:
0.36 0.40 0.26 0.19 0.76 0.5.; 0.29 0.18 0.47 0.33 023
Note: Caution should be used in the comparison of these indices from one city to another. The exact placement of measuring instruments with respect to areas of air poltution the results of which these indices are based on. varies from city to city. In the case of coetlicient of haze. the cotour of the particles on which the measurement is based also varies.
1b. Second group of specific pollutatzrs The three pollutants in the second group had considerably less data available. The index for carbon monoxide was calculated by substituting the annual objective of equation (2) by the 8-h objective. the daily concentration by the hourly concentration. and II by the number of readings in a month or year. Results for carbon monoxide are shown in Tables 1 and 2. Again, while it is difficult to make city-to-city comparisons, the data are adequate to compute the national average. The index for total oxidants. I,,. was calculated by means of equation (Z), except that the l-h concentrations were substituted for the daily concentrations. Results are shown in Tables 1 and 2. Finally, the index for oxides of nitrogen. l,V,swas computed, using equation (2) and substituting the daily objective for the annual objective and the hourly for the dail!- concentrations. Table 1 shows that the index for oxidants had the highest national average, and that for carbon monoxide the lowest. Because of the variability of temporal and spatial coverage, these results must be considered as only tentative. To produce an overall index of specific pollutants I sP, the six sub-indices were combined by means of the root-mean-square method discussed above. Since the coefficient of haze is also a measure of the amount of particulate matter, each of these two indices was given half weight compared to the other four. Because comparatively few cities had data on all six pollutants, this index is not shown on a map. lc. 7ittv cariatiott of specific polhrranrs
The levels of the indices for specific pollutants vary in time as well. The national level for each of the first group was calculated for each month of 1971, using population weight-
.A set of proposed air quality indices for Canada
359
. .. .. . : : 3,....:
:
; :
Fig. 3. National indices of sulphur dioxide, coefficient of haze and suspended particulate matter for 1971. The sulphur dioxide index has by far the largest maxima, which occur in the winter months. The other two indices have smaller seasonal swings.
ing. Results for suspended particulate matter, sulphur dioxide, and coefficients of haze are shown in Fig. 3. In contrast to the other two following curves, we see comparatively little change in the index of suspended particulate matter from month to month. The largest values are in spring, and may be due in part to natural conditions of spring air dust. The index of sulphur dioxide is very high in the first two months of the year, but decreases quickly to a minimum in July and August. This change may be due to (a) the fact that the bulk of industrial and home-heating uses of sulphur-containing fuels occurs in the winter months, or (b) changes in mixing depths. The index of coefficient of haze is similar to that for sulphur dioxide, except that the values are not as high. The index has a maximum of around 1.3-1.5 in the fall and winter months, and then declines to about 0.75 in the summer. This is apparently due to heating effects in the winter months. In order to study the scatter from year to year, the three indices of Fig 3 were recomputed for 1972 in Fig. 4. Because of changes in the siting of some monitoring stations, the opening and closing of others during the course of the two years, and other factors, the two graphs are not as comparable in coverage as might be desired. However, some simiiarities can be seen. The curves for the indices of coefficient of haze and suspended particulate matter are close in shape for the years 197 1 and 1972. For the former index, the 1972 maximum came in May rather than April, as expected on the basis of the 1971 results, but the two curves AX.
9 3-l
H. INHALER
360
... .
z.#!&W
Di
-
Caffkki
-
elpnM
.f
fko
fbemdm
MERI
Fig. 4. Nat&tat indices of sulphur dioxide, coeflicient of haze and suspended particulate matter for 1972.The shape of the curves is similar to those of Fig. 3. However, the maxima for the sulphur dioxidi index are lower than those of 1971.
both have theii high points in thespring. For the latter index, a fiat rn~~urn is reached in both years in the summer months, with maxima in February. Both sets of indices are similar in mag&ude for cornpar&& months in the two years. The maximum of the suiphur dioxide index, while still in February, decreased considerabfy in 1972as compared to 1971.This decrease he-id in most months, making the values of this index in 1972 similar to those of the other twu indices. The overaII shape of the curve in 1972was aImost the same as in 1971, with strong maxima in the winter months. 2. INDEX
OF
INTER-URBAN
AIR
QUALITY
This index, designed to give an indication of air quality in the regions around urban at Canadirtn .airports. Hourly readings m which precentrcs, is based on booty cipit&ori or fog were not& luded. The quantity chosen asan indicator was the average visibility for each hour. The visibilities were summed.and divided by the number of hours with precipitation. The year 1971 was USed em@loyingthe avenge vie&iEty fsr all 365 &ys. There are many f~etora,~~~ the relati~nahip of visibility-and air polhtion, such as wind direction and v&city, types of ~~~~~~ and distancea frum cities to airports (Larsen, 1969; Miller er ai., 1972; Munn, 1973).Due to lack of knowledge of these factors pmdble to &dceaccount of them in the cakulations. s for visi&iWes have been or are likely to be set, the average visibility of 14.6 miles, the mean for the years 1953-1971at two far northern stations, Yel-
A set of proposed air quality indices for
Can3d3
361
lowknife and Whitehorse, was taken as a baseline measure. It was assumed that since these stations were ‘so small and distant from major urban areas they would be little affected by air pollution. Because the average visibility was a function of the overall density of air pollutants in the vicinity. the index of visibility had to be approximately numerically comparable to the index lsP derived from the specific pollutant data. It was found after computation that this could be accomplished by dividing the ratio of far northern visibilities to visibility at other airports by a factor of two. The index of inter-urban air quality then became:
where f,,, is the index of inter-urban (or regional) air quality, C$, is the average visibility for the two far northern stations, and V’, is the average visibility for other airports. An airport fidving the same average visibility as the far northern stations had Irvg = 0.5. Results of the computation are shown in Fig. 5. Because of the large amount of data available. the information was contoured. Regions of highest value are in extreme southern Ontario, with indices in that region at least 20
Fig. 5. Index of inter-urbsnair quality, I,,. Extreme southern Ontario has the highest values of this index. Values decrease towards the north. The southern parts of British Columbia, Alberta and Saskatchewan have relatively low values of the index. as does western Alberta. Sampiing stations within a given shade lie within that range of values of the index. This arrangement does not imply that all areas in a particular shade have the same range of values
per cent higher than in most other areas. The entire industrialized region from there to mid-Quebec tends to have higher indices than western Canada, although part of this ma> be due to natural conditions (Hare, 19731. The region of high indices also extends into the Maritimes, with the southern Maritimes tending to have higher indices than the north. In western Canada, there is a ridge of extremely low indices with values less than 0.5 running along the southern extremes of British Columbia, Alberta and Saskatchewan. The indes rises farther north. but it stiI1 remains low and comparable to the average for the far northern stations. Southwest British Columbia has an index comparable to that of au average eastern station, but considerably Iess than southern Ontario. X national index of regional air quality was computed b, population weighting. and results are shown in Table I. 3. iNOES
OF
fNDt;‘STRIAL
EMISSIONS
The third and finat component of the Air Quality Tndex was the index of industrial emissions Ii,. designed to give a measure of air quality outside urban areas. Use was made of the Xatiotwitiu Incmtor!~ of’ Air Pollutam Emissions. published by Environment Canada. This listed the estimated weight of emissions for major point and area sources, defined as those emitting more than 5000 tons of a particuIar pollutant per Fear. The estimates are based on the level of production of various commodities. the type of emission controls installed, and other factors. Although emission estimates were made for more than two pollutants, only sulphur dioxide and suspended particulate matter were considered for the AQf. They were chosen because they were in the first group of pollutants mentioned in Section I-tise_for which extensive physica measurements have been made. The emission data could be grouped into two sections. The first j~~~~ tba~e locations where physical measuremenfs of air qality have been made; t&se*-wer@&me& “urban”. A11other locations were termed “industrial”. A small prop&& of the emiakms in those areas were non-industrial in origin. The index of industrial emit&ons was defined as
where 15, is the sum of the industrial emissions. for a given pollutstnt for a county. and P, is the population of that county. Ei is the sum of the industrial emissions for a given pollutant for all of Canada, and P,,, is the population of Ci@tia. In this way. we can take account of the r&&e ~~~~ibu~ns ofeach: of the countis, both compared to each other rd” ofa Canadian average was chosen because and to the Canadian a~~~~~ no others were available. Counties ate used as crude surrogates for airsheds because the boundaries of the latter are often not well-defined. For the sulphur dioxide index, 31 industrial sources in 9 provinces Lvere noted. The total emissions for all Canada were 6222000 tons. of which 5363000 tons were emitted from industrial sites. The county indices are shown in Fig. 6. Because the data are relatively scattered, it is difEcult to draw national conclusions. However, British Columbia has the Iargest number of areas with relatively high values of the index. Manitoba. Ontario and Quebec are the only other provinces with areas with values of the index in the highest category. To compute a national index for industrial emissions of sulphur dioxide. the
h set of proposed air quality indices for Canada
.363
Fig. 6. Index of industrial emissions of sulphur dioxide, I,,,,_.
county averages were weighted according to county populations. The index had a value
of 0.87. The same method was used to compute the index of industrial emissions of suspended particulate matter. For this index, 28 industrial sources in 9 provinces were noted. The total emission was 758000 tons, of which 566000 tons were emitted from industrial sites. Because the graphical presentation is available elsewhere (Inhaber, in press), it is not shown here. All provinces except Manitoba, New 3runswick and Prince Edward Island have at least one area with a relatively high value of the index. Quebec and Ontario have the largest number of areas with relatively high values. To compute a national index for industrial emissions of suspended particulate matter, the county averages were weighted according to county populations. The index had a value of 0.75. The root-mean square equation used to calculate the overall index of industrial emissions is
When sufficient physical measurements of air quality are available for other specific pollutants, this equation can be modified appropriately. Using the values for the two components noted above, Ii, = 0.81.
364
H. 1. COiMBINED
ISHABER
AIR
QUALITY
INDEX
The three components of the combined air quality index. dealing with specific pollutants, regional air quality. and industrial emissions, can be combined by the root-meansquare technique. Weights of 5, 3 and 2 were respectively assigned to the three components. These weights were suggested to reflect the approximate contributions of each index to the overall Canadian air quality index. The overall air quality index then is: ,
= ‘\ (5(I&
i
y’
+ :!u,‘.)‘i
(6)
where the denominator is, as usual. the sum of the weights. Using equation (6), we have I,i, = 0.99. Because of the relatively small amount of data available for many areas. it was not possible to compile an overall air quality index for specific cities and provinces. Acknowledgements-Mike Kwizak and Ted Munn supplied wise suggestions and informed counsel. I protited by conversations with Dr. S. 0. Winthrop and B. C. Newbury. Without the help of Kristina Przednowek. this work would have been impossible. Rob MacKay and Susan Vadeboncoeur also supplied clerical and typing assistance. Ken Hare and Peter Meyboom gave me much encouragement. REFERENCES Babcock L. R. (1970) Combined pollution index for measurement of total air pollution. J. .-tir Pollrtr. Courrol Ass. 20 (IO). 653-659. Babcock L. R. and Nagda N. L. (1972) Indices of air quality. Indicarors of Enrironr~rrnal Qualify (Edited by Thomas W. A.) pp. 183-198. Plenum, New York. Bisselle C. A., Lubore S. H. and Pikul R. R. ( 1972) !b’ntioml encirowtlentul iruficrs: Air yrrulity ad odoor r~‘ow~tion. MITRE Corp.. Washington. Hare F. K. (1973) Private Communication. Inhaber H. Science. (In press). Larsen R. I. (1969) A new mathematical model of air pollutant concentration averaging time and frequency. J. Air Pollur. Control Ass. 19 (I ). 24-30. Leblanc F. and Rao D. N. (1972) Indices of atmospheric purity and fluoride pollution pattern in Arvida, Quebec. Can. J. Rot. 50 (5). 99 l-998. McNeely M. D., Nechay M. W. and Sunderman F. u’. (1972) Measurements of nickel in serum and urine as indicators of environmental exposure to nickel. Clirt. Chem. 18 (9). 992-995. Miller M. E., Canfield N. L., Ritter T. A. and Weaver C. R. (1972) Visibility changes in Ohio. Kentucky and Tennessee from 1962 to 1969. Monthly Weather Rec. 100 (I ). 67-7 I. Munn R. E. (19721Secular increases in summer haziness in the Atlantic Provinces. Arrtxwhere 11 (41 156-161. Porch W. M.~(1971)Visibility of Mount Rainier as an index of background pollution. Titan;. Am. Geophp. L’nion 52; 430. Shenfield L. (1970s) Ontario’s air pollution index. War. Pollrtt. Control 10s (I I), 55-58. Shenfield L. (197Ob) Ontario’s air pollution index and alert system. J. Air Pollut. Connol Ass. 20 (9). 612. Shettfteld L. (1971) Ontario’s air quality monitoring network and air pollution index. Presented at American Industrial Hygiene Conference, Toronto, 2128 May 1971. Thomas W. A., Babcock L. R. and Shults W. D. (1971) Oak Ridge air quality index. Report NO. ORNL-NSF-EP8. Oak Ridge National Laboratory, Oak Ridge, Term. Thomas W. A. (Editor) (1972) Indicators ofEncironmer& Quality. Ptenum. New York. This is probably the best collection of articles relating to environmental indices.
