Monitoring of extreme air pollution on ring roads with PM2.5 soot particles considering their chemical composition (case study of Saint Petersburg)

Abstract

Based on the analysis of theoretical as well as experimental and computational studies on the nature of origin, morphology of the physical structure, chemical composition, and diffusion of PM2.5 diesel soot particles of dangerous sizes in a stratified atmosphere, the authors present data on the expected level of air pollution with suspended black carbon particles near the Saint Petersburg Ring Road in extreme weather (wind speed — less than 2 m/s, stable temperature inversions in the surface layer of the atmosphere) and transport (peak hour traffic) conditions. The experiments prove that due to the developed, physically active internal surface of primary soot particles, determined by the local values of the air/fuel ratio (λ up to 0.4) and flame temperature (up to 3500 K) in heterogeneous diffusion fuel combustion, pores in diesel exhaust black carbon deposits accumulate (adsorb) up to 0.015 ± 0.006 mg/kg of benzo[a]pyrene (С20Н12, a polycyclic aromatic hydrocarbon, which, according to the WHO criteria, is the most dangerous for the urban population); 17.5 ± 3.7 mg/kg of lead compounds; 0.5 ± 0.2 mg/kg of cadmium; 104 ± 48 mg/kg of nickel; 156 ± 28 mg/kg of chromium. The authors analyze the data on the digital monitoring of the traffic intensity of trucks with diesel engines, using their proprietary method, and draw the following conclusions: under the mentioned extreme conditions, near the Saint Petersburg Ring Road, we can expect the formation of local areas of air pollution (at the breathing level) with PM2.5 soot particles at the level of up to 2.5 MACms (maximum single allowable concentration); and with account for the measured С20Н12 content in the structure of diesel exhaust black carbon deposits and its MAC values in the air of urban areas in Russia (daily average MAC = 0.1 µg/100 m3) — at the level of up to 20 MACda (daily average). Given the tendency for the approximation of operating conditions, the technical state of vehicles, and the environmental performance of fuel in Saint Petersburg to the countries of the European Community, we can expect the representativeness of the research results in the largest cities of the world.