Influence of Vehicular Traffic on Concentration and Mass Size Distribution of Two Fractions of Carbon in an Urban Area Atmospheric Aerosol

Ambient particulate matter (PM) is a component of the natural environment and a certain number of particles that varies with time, having many different properties which also change over time, is constantly present in the air. It can be assumed that the scope of environmental effects of PM is the broadest among all air pollutants: it affects the human health, climate, ecological conditions and visibility. Organic carbon (OC) and elemental carbon (EC) are the two most important components of suspended dust. The continuously increasing road traffic intensity is highly correlated with increasing concentrations of both of these components in the air of urbanized areas all over the world. In spite of this, the amount of data on OC and EC concentrations in Poland is still insufficient, especially in the case of areas located close to busy roads. The aim of this study was to determine the influence of vehicular traffic on ambient concentrations of PM-related OC and EC, and their mass size distribution in a typical urban area of the Upper Silesia. PM samples were collected simultaneously at two sites located in the Katowice city. One of the selected measurement points was situated in the city centre and characterized so-called urban background. The second measurement point, located near the A4 motorway, was in the area directly exposed to the influence of traffic emission. Dust was sampled during two measurement periods (2-10 August and 15-22 September 2011) using thirteen-stage impactors - DEKATI Ltd. (DLPI, Dekati Low Pressure Impactor). Analysis for the content of OC and EC in the collected dust samples was carried out by means of a thermo-optical method with the use of a Sunset Laboratory OC/EC carbon analyzer. During the entire measurement program strict adherence to the rigorous requirements for quality control of the obtained results was ensured. Concentrations of PM1-, PM2.5- and PM10-related OC and EC in Katowice, near the A4 motorway, were close to values obtained in other parts of the world in different measurement periods, at traffic sites of similar characteristics. Also values of the concentration ratio of OC bound to PM10 and PM2.5 (or PM1) were similar to quantities determined in different locations. In Katowice, due to municipal emission and poor quality of vehicles, travelling the roads, also the coarse fraction of dust was enriched in EC. This situation is unusual in comparison to other regions. The effect of emission from engines of the cars travelling the motorway manifested itself mainly by elevated EC concentrations compared to the urban background site. For TSP the EC concentration was higher, five times in the beginning of August and two times in the second half of September. The largest differences between EC concentrations in the location near the motorway and in the urban background area were observed for the PM0.06-0.108, PM0.108-0.17 and PM0.17-0.26 fractions. In both measurement periods, at the traffic site in Katowice, the maxima of mass size distribution of EC were in the diameter range characteristic for soot emitted from Diesel engines (0.108-0.26 mu m). The fact that the influence of exhaust emission from vehicles travelling the motorway on EC concentrations was more pronounced in the second half of September than in the first half of August, was caused by larger EC emission from various sources in Katowice during the period following summer holidays. Concentrations of organic carbon bound to TSP in both measurement periods in Katowice was only 10% higher in the urban traffic site than in the urban background site. The largest differences between OC concentrations near the motorway and in the urban background are observed in the ranges 0.06-0.17 and 1.0-2.5 mu m. Maxima of the mass size distribution of PM-related OC, both at the urban traffic site and at the background site, were similar in both measurement periods. It was inferred that the small differences between OC concentrations in the traffic and the background site are caused by the process of secondary aerosol formation, less intensive near the motorway than in the urban site.