Size Distribution as a Forensic Tool to Source Apportion Ambient PM

Abstract

The particulate matter (PM) emitted from multiple sources contribute to air pollution near highways, affecting, mainly the commuters on road, dwellers and shopkeepers nearby. In this study, the size distribution of the PM near a highway, obtained using real time laser aerosol spectrometer, was used to apportion the contributions from vehicular traffic and road dust. Data on vehicle count and type were obtained for the selected highway stretch. The size distribution of emission from petrol and diesel vehicles and the size distribution of re-suspended dust were obtained through independent studies. Size based distribution of PM in the study area contributed by vehicles, were modelled using AERMOD using the vehicle emissions and vehicle count data. Aggregation of the modelled concentrations of PM of various size ranges with the contribution from re-suspended dust gave size based concentration distributions closely matching with that of PM in ambient air. The size based PM analyses showed that in the study area, 47.36%, 15.74%, and 15.46% of PM2.5, were contributed by diesel vehicles, petrol vehicles and suspended dust, respectively. The corresponding contributions to PM10 were, 14.42%, 10.59% and 68.35%. The emission studies on vehicles showed diesel vehicles contributing significantly higher concentration of PM to ambient air than petrol vehicles, with condition of vehicle influencing the amount of PM emitted. The use of particle size distribution pattern for preliminary source apportionment, demonstrated in this study, has promising environmental forensic applications as it provides a cheap and fast corroborative evidence for responsibility allocation.