Effect of Particle Size and Moisture on Emission of Organic Carbon from Vehicular Exhaust

Abstract

For decades, the concentration of aerosols in the lower atmosphere has increased steadily primarily owing to anthropogenic sources such as industrial activity, vehicular emission, biomass burning, and also to secondary aerosol formation. As a consequence of urbanization, a phenomenal surge has been observed in the vehicular population in India, giving rise to elevated levels of traffic related pollutants like carbon monoxide, nitrogen oxides, hydrocarbons, and particulates in urban centers. These pollutants can have both acute and chronic effects on human health. The vehicular emissions are governed by various factors such as purity of the fuel, capacity and health of vehicle, type of fuel etc. Alongwith others, moisture is one of the major product of vehicular emission. The effect of moisture plays an important role not only in the physical characteristics of aerosols emitted from the vehicular exhaust, but also in the chemical characteristics. The tail pipe emission of automobiles mainly consists of soot (black carbon), some organic compounds, and moisture. The interactions between the organic compounds with or without the presence of moisture need to be effectively studied. In this study, the effect of size distribution and moisture on the emission of carbon in vehicular exhaust was studied. The size distribution of was carried out using variable configuration cascade impactor (VCCI). Additionally, a denuder of activated silica gel was designed to trap the moisture and to study the effect of moisture. The quantification of carbon was carried out using a TC-TN analyzer. The average emission of organic carbon aerosols from both diesel and petrol vehicles were maximum in the lowest particle size i.e. nucleation mode. Both diesel and petrol exhaust showed tri-modal distribution over the range of studied particle sizes. In both diesel and petrol vehicular exhaust, organic carbon was less in moisture free environment (with denuder) in the accumulation mode.