Black carbon aerosols: Relative source strengths of vehicular emissions and residential/open wood burning over an urban and a semi-urban environment

A comprehensive investigation of equivalent black carbon (eBC) mass concentration was conducted over an urban (Ahmedabad) and an adjoining semi-urban (Anand) environment using multi-wavelength aethalometer. The contributions of fossil fuel (eBC(ff)) and wood burning (eBC(wb)) emissions to total eBC were quantified using the aethalometer model. The spectral properties of eBC were obtained from the burning experiments conducted using different types of wood fuels. The absorption Angstrom exponent (alpha(wb)) values were found to vary in the 1.67 to 2.18 range for different wood fuels. The mean alpha(wb) for wood burning emerged to be 1.87, lower than the commonly used value of 2.0. The lower alpha(wb) contributes to a 14% decrease in the contribution of eBC(wb) to total eBC. The eBC(ff) (86%) dominates the total eBC throughout the year over Ahmedabad, whereas the contributions of eBC(ff) (55%) and eBC(wb) (45%) to total eBC are comparable over Anand. The study highlights the observed heterogeneity in eBC emission sources over an urban and an adjoining semi-urban environment with comparable total eBC mass concentrations. The application of region specific alpha(wb) and the resulting apportionment data will be useful in planning mitigation strategies, and for planning future air quality improvement policies.