Environmental Pollution 195 (2014) 56e63
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
Urban snow indicates pollution originating from road traffic €ki*, Heikki Seta €la €, Anna-Lea Rantalainen, D. Johan Kotze Kirsi Kuoppama University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 May 2014 Received in revised form 13 August 2014 Accepted 16 August 2014 Available online 6 September 2014
Traffic is a major source of pollutants in cities. In this well-replicated study we analysed a broad array of contaminants in snowpacks along roads of different traffic intensities. The majority of pollutants showed a similar pattern with respect to traffic intensity: pH and conductivity as well as concentrations of PAHs, total suspended solids, phosphorus and most heavy metals were higher next to high intensity roads compared to low intensity roads. These pollutant levels also decreased considerably up to 5 m distance from the roads. Furthermore, apart from nitrogen, these variables increased in concentration from control sites in urban forest patches to road bank sites next to roads of low, intermediate and high traffic intensities. The deposition pattern of various traffic-derived pollutants e whether gaseous or particlebound e was the same. Such information can be useful for the purposes of managing pollutants in urban areas. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Urban Traffic Snow Nitrogen Phosphorus Metals PAH
1. Introduction Nutrients, metals and organic pollutants accumulate in cities (Kaye et al., 2006), primarily as a result of road traffic (Viklander, 1998; Bu cko et al., 2011; Berndtsson, 2014). In fact, pollution from traffic surpasses many other anthropogenic sources, such as power plants, industry and residential activities (Bucko et al., 2011). Various nutrients, metals and polycyclic aromatic hydrocarbons (PAH) have been reported to contaminate air, soil and both surface and ground waters close to roads in rural and urbanised areas (Van Bohemen and Janssen van de Laak, 2003; Helmreich et al., 2010). Furthermore, the degree of pollution varies with traffic intensity and traffic-derived pollutants spread to areas adjacent to traffic routes so that there is often a clear dilution of contaminants from the edge of the road to further away (Viskari et al., 1997; Bu cko et al., 2011). Under northern climatic conditions, snow has been shown to be an ideal medium to study pollutant loadings for several reasons: (i) snow samples are easy to collect and analyse, (ii) deposition time is definable from meteorological data, (iii) the concentrations of various impurities in the air are highest in winter, and (iv) the large surface area and slow fall velocity of snowflakes allow efficient accumulation of organic and inorganic pollutants from the
* Corresponding author. €ki). E-mail address: kirsi.kuoppamaki@helsinki.fi (K. Kuoppama http://dx.doi.org/10.1016/j.envpol.2014.08.019 0269-7491/© 2014 Elsevier Ltd. All rights reserved.
atmosphere (Hautala et al., 1995; Sharma and McBean, 2001; Glenn and Sansalone, 2002; Engelhard et al., 2007). In Sweden, Westerlund and Viklander (2006) found much higher loads of particles and associated metals during the snowmelt period compared to the rain period. Consequently, in regions where snow forms part of the precipitation, research on urban snow could be an important environmental research topic (Viklander, 1996, 1999), €a € and yet appears to be relatively scarcely studied (Sillanpa Koivusalo, 2013). Furthermore, to our knowledge, no single study has investigated the full array of traffic-derived nutrients and pollutants (such as heavy metals and PAHs) in snow, using a wellreplicated design of various traffic intensities and distances from roads. This study addresses these shortcomings in an attempt to provide a more general picture on the distribution of nutrients and other pollutants in urban roadside snow. As snow efficiently stores contaminants from the atmosphere to snowpacks alongside roads, considerable amounts of trafficderived pollutants can pose risks not only to the local environment but also to surface- and ground water reservoirs via stormwater sewer systems during spring snowmelt (Novotny et al., 2008; € and Koivusalo, 2013). This transfer is particularly evident Sillanp€ aa in highly urbanised areas with predominantly impervious surfaces connected to underground sewer pipelines that provide for fast and efficient drainage. Thus, contaminants enriched in road bank snow can pose an important, hitherto still poorly known risk to the quality of both surface and ground waters (Viklander, 1998; Valtanen et al., 2014).
€ki et al. / Environmental Pollution 195 (2014) 56e63 K. Kuoppama
By sampling snowpack alongside roads in the vicinity of a city centre, our focus was to distinguish local, traffic derived contamination from that originating from other potential sources. We also aimed at exploring whether the concentrations of various contaminants e emitted either in gaseous or dissolved form or bound to particles e follow the same accumulation pattern in snow regarding traffic load and how rapidly they change with distance from the roadside and with traffic intensity. To shed light on these questions we performed two studies during late winter in the city of Lahti, southern Finland, in 2011 and 2013. For the first study, during which snow samples were taken from the edge and at 5 m away from replicated sites next to roads of high and low traffic intensity, we hypothesized that snow from high traffic intensity roads would contain higher concentrations of heavy metals and PAHs as well as higher conductivity, pH and total suspended solids (TSS) than snow from low traffic intensity roads. These concentrations were also expected to decrease further away from the roads. We refined the second study and collected snow from replicated sites of low, intermediate and high traffic intensity roads as well as from nearby urban forest patches, which served as controls. Assuming that pollutants (heavy metals, PAHs and nutrients) and other variables (conductivity, pH and TSS) measured in this study are traffic-derived, we hypothesized that (i) snow in urban forests and next to low-intensity roads would have lower concentrations of these pollutants than snow next to higherintensity traffic, and (ii) concentrations of particle-bound air contaminants should be disproportionately higher in snow at the high traffic intensity sites and right next to roads as compared to those at sites with low or no traffic and further away from these roads. 2. Material and methods 2.1. Sampling We conducted two studies in the city of Lahti (60 590 N, 25 390 E), southern Finland. Lahti is a moderately-sized city with a population of 103 364, and a population density of 666 residents km2 (Lahti statistics, 2013). Temperature varies between 35 C and þ35 C within a year, and winter lasts for 135e145 days with snow cover from the end of November until mid-April. The average depth of snow at the end of March (the sampling time of this study) is 10e20 cm (Finnish Meteorological Institute, 2013). The first study, performed in MarcheApril 2011, investigated differences in contaminant loads with distance from the road edge within the city. Eight sites were selected, four near high traffic intensity roads (20,000e35,000 vehicles day1) and four near low traffic intensity roads (
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
Urban snow indicates pollution originating from road traffic €ki*, Heikki Seta €la €, Anna-Lea Rantalainen, D. Johan Kotze Kirsi Kuoppama University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 May 2014 Received in revised form 13 August 2014 Accepted 16 August 2014 Available online 6 September 2014
Traffic is a major source of pollutants in cities. In this well-replicated study we analysed a broad array of contaminants in snowpacks along roads of different traffic intensities. The majority of pollutants showed a similar pattern with respect to traffic intensity: pH and conductivity as well as concentrations of PAHs, total suspended solids, phosphorus and most heavy metals were higher next to high intensity roads compared to low intensity roads. These pollutant levels also decreased considerably up to 5 m distance from the roads. Furthermore, apart from nitrogen, these variables increased in concentration from control sites in urban forest patches to road bank sites next to roads of low, intermediate and high traffic intensities. The deposition pattern of various traffic-derived pollutants e whether gaseous or particlebound e was the same. Such information can be useful for the purposes of managing pollutants in urban areas. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Urban Traffic Snow Nitrogen Phosphorus Metals PAH
1. Introduction Nutrients, metals and organic pollutants accumulate in cities (Kaye et al., 2006), primarily as a result of road traffic (Viklander, 1998; Bu cko et al., 2011; Berndtsson, 2014). In fact, pollution from traffic surpasses many other anthropogenic sources, such as power plants, industry and residential activities (Bucko et al., 2011). Various nutrients, metals and polycyclic aromatic hydrocarbons (PAH) have been reported to contaminate air, soil and both surface and ground waters close to roads in rural and urbanised areas (Van Bohemen and Janssen van de Laak, 2003; Helmreich et al., 2010). Furthermore, the degree of pollution varies with traffic intensity and traffic-derived pollutants spread to areas adjacent to traffic routes so that there is often a clear dilution of contaminants from the edge of the road to further away (Viskari et al., 1997; Bu cko et al., 2011). Under northern climatic conditions, snow has been shown to be an ideal medium to study pollutant loadings for several reasons: (i) snow samples are easy to collect and analyse, (ii) deposition time is definable from meteorological data, (iii) the concentrations of various impurities in the air are highest in winter, and (iv) the large surface area and slow fall velocity of snowflakes allow efficient accumulation of organic and inorganic pollutants from the
* Corresponding author. €ki). E-mail address: kirsi.kuoppamaki@helsinki.fi (K. Kuoppama http://dx.doi.org/10.1016/j.envpol.2014.08.019 0269-7491/© 2014 Elsevier Ltd. All rights reserved.
atmosphere (Hautala et al., 1995; Sharma and McBean, 2001; Glenn and Sansalone, 2002; Engelhard et al., 2007). In Sweden, Westerlund and Viklander (2006) found much higher loads of particles and associated metals during the snowmelt period compared to the rain period. Consequently, in regions where snow forms part of the precipitation, research on urban snow could be an important environmental research topic (Viklander, 1996, 1999), €a € and yet appears to be relatively scarcely studied (Sillanpa Koivusalo, 2013). Furthermore, to our knowledge, no single study has investigated the full array of traffic-derived nutrients and pollutants (such as heavy metals and PAHs) in snow, using a wellreplicated design of various traffic intensities and distances from roads. This study addresses these shortcomings in an attempt to provide a more general picture on the distribution of nutrients and other pollutants in urban roadside snow. As snow efficiently stores contaminants from the atmosphere to snowpacks alongside roads, considerable amounts of trafficderived pollutants can pose risks not only to the local environment but also to surface- and ground water reservoirs via stormwater sewer systems during spring snowmelt (Novotny et al., 2008; € and Koivusalo, 2013). This transfer is particularly evident Sillanp€ aa in highly urbanised areas with predominantly impervious surfaces connected to underground sewer pipelines that provide for fast and efficient drainage. Thus, contaminants enriched in road bank snow can pose an important, hitherto still poorly known risk to the quality of both surface and ground waters (Viklander, 1998; Valtanen et al., 2014).
€ki et al. / Environmental Pollution 195 (2014) 56e63 K. Kuoppama
By sampling snowpack alongside roads in the vicinity of a city centre, our focus was to distinguish local, traffic derived contamination from that originating from other potential sources. We also aimed at exploring whether the concentrations of various contaminants e emitted either in gaseous or dissolved form or bound to particles e follow the same accumulation pattern in snow regarding traffic load and how rapidly they change with distance from the roadside and with traffic intensity. To shed light on these questions we performed two studies during late winter in the city of Lahti, southern Finland, in 2011 and 2013. For the first study, during which snow samples were taken from the edge and at 5 m away from replicated sites next to roads of high and low traffic intensity, we hypothesized that snow from high traffic intensity roads would contain higher concentrations of heavy metals and PAHs as well as higher conductivity, pH and total suspended solids (TSS) than snow from low traffic intensity roads. These concentrations were also expected to decrease further away from the roads. We refined the second study and collected snow from replicated sites of low, intermediate and high traffic intensity roads as well as from nearby urban forest patches, which served as controls. Assuming that pollutants (heavy metals, PAHs and nutrients) and other variables (conductivity, pH and TSS) measured in this study are traffic-derived, we hypothesized that (i) snow in urban forests and next to low-intensity roads would have lower concentrations of these pollutants than snow next to higherintensity traffic, and (ii) concentrations of particle-bound air contaminants should be disproportionately higher in snow at the high traffic intensity sites and right next to roads as compared to those at sites with low or no traffic and further away from these roads. 2. Material and methods 2.1. Sampling We conducted two studies in the city of Lahti (60 590 N, 25 390 E), southern Finland. Lahti is a moderately-sized city with a population of 103 364, and a population density of 666 residents km2 (Lahti statistics, 2013). Temperature varies between 35 C and þ35 C within a year, and winter lasts for 135e145 days with snow cover from the end of November until mid-April. The average depth of snow at the end of March (the sampling time of this study) is 10e20 cm (Finnish Meteorological Institute, 2013). The first study, performed in MarcheApril 2011, investigated differences in contaminant loads with distance from the road edge within the city. Eight sites were selected, four near high traffic intensity roads (20,000e35,000 vehicles day1) and four near low traffic intensity roads (
