A methodology to estimate source-specific aerosol radiative forcing

This paper presents a novel approach to estimate source-specific radiative forcing by combining source apportionment results for particulate matter mass with satellite (moderate resolution imaging spectroradiometer (MODIS)) derived aerosol optical depth (AOD). Positive matrix factorization (PMF) was applied to particulate matter (PM) mass and its chemical constituents measured during a winter intensive study (December 2004) at Hisar, Haryana, India. The model resolved four factors including carbonate rich dust, combustion rich aerosol, secondary sulfate/nitrate, and an unidentified factor likely to be emission from polymer industries. Carbonate rich dust was the highest contributor to the measured PM mass closely followed by combustion rich aerosol with their average contributions accounting for 34.0% and 33.6%, respectively. Model apportioned species concentrations corresponding to each factor were then used to estimate factor specific optical and radiative properties, and radiative transfer calculations were performed for the shortwave regime. During the study period, although carbonate rich dust and combustion rich aerosol mass contributions were comparable, carbonate rich dust contributed to only 22% of top of the atmosphere forcing while combustion rich aerosol contributed nearly 56%. Overall, the results suggested that the aerosol radiative forcing was primarily governed by the aerosol optical and radiative properties, while the mass concentrations played a secondary role.