Optical and chemical properties of aerosol from on-road experiments of heavy-duty vehicles in India: Key inputs for climate assessment

Previous emission inventories have reported fast growing on-road transport sector as one of the major contributors to emissions of aerosol and its carbonaceous fraction in India. The diesel-powered heavy-duty vehicles (HDVs Trucks and tractor/trailers) dominate emissions of light absorbing black carbon at national level. These emission inventories relied on emission factors generated from dynamometer studies which are known to be unrepresentative of real-world driving cycle. Therefore, data generated from dynamometers studies can be considered illusionary. This study will present the emission factors and climate relevant properties of aerosol emitted from on-road operation diesel powered trucks and tractors. The aerosol emissions were measured during on-road operation of heavy-duty vehicles using Versatile Source Sampling System (VS3). The VS3 was designed to iso-kinetically to withdraw a fraction of emission directly from tailpipe and abruptly mix with particle free dilution air for complete aerosol quenching. Before on-road experiments the VS3 was evaluated for homogenous mixing inside dilution tunnel, particle loss and formation. The emission factors of PM_2.5 and BC were estimated as 1.2 – 2.4 and 0.5 – 1.3 gkg^-1 respectively. The mass absorption cross section for heavy duty trucks were observed as 0.9 – 6.5 m²/gPM_2.5. Emission factors of heavy-duty trucks in different emission norms along with the emission factor of organic carbon (OC) will be presented in the paper. The study will also discuss the chemical and optical properties of emissions from HDVs in detail including mass scattering coefficients (MSC), Absorption Angstrom exponent (AAE) and single scattering albedo (SSA). The finding from this study has implications in climate assessment through climate models and framing the policies for on-road vehicles for improving local air quality.