Polar and non-polar organic aerosols from large-scale agricultural-waste burning emissions in Northern India: Implications to organic mass-to-organic carbon ratio

This study focuses on characteristics of organic aerosols (polar and non-polar) and total organic mass-toorganic carbon ratio (OM/OC) from post-harvest agricultural-waste (paddy- and wheat-residue) burning emissions in Northern India. Aerosol samples from an upwind location (Patiala: 30.2 degrees N, 76.3 degrees E) in the Indo-Gangetic Plain were analyzed for non-polar and polar fractions of organic carbon (OC1 and OC2) and their respective mass (OM1 and OM2). On average, polar organic aerosols (OM2) contribute nearly 85% of the total organic mass (OM) from the paddy- and wheat-residue burning emissions. The water-soluble-OC (WSOC) to OC2 ratio, within the analytical uncertainty, is close to 1 from both paddy- and wheat-residue burning emissions. However, temporal variability and relatively low WSOC/OC2 ratio (Av: 0.67 +/- 0.06) is attributed to high moisture content and poor combustion efficiency during paddy-residue burning, indicating significant contribution (similar to 30%) of aromatic carbon to OC2. The OM/OC ratio for non-polar (OM1/0C1 similar to 1.2) and polar organic aerosols (OM2/OC2 similar to 2.2), hitherto unknown for open agricultural-waste burning emissions, is documented in this study. The total OM/OC ratio is nearly identical, 1.9 +/- 0.2 and 1.8 +/- 0.2, from paddy- and wheat-residue burning emissions. (c) 2013 Elsevier Ltd. All rights reserved.