OM/OC Ratio of Polar and Non-Polar Organic Matter during Wintertime from Indo-Gangetic Plain: Implications to Regional-Scale Radiative Forcing
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Ambient PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) samples have been collected in two winter campaigns: I during 2nd December 2008‒27th February 2009 (n = 24) and II during 3rd December 2010‒11th February 2011 (n = 15). The PM2.5 mass varied significantly from 35 to 220 and 80 to 244 μg m−3 during I and II campaigns, respectively. Based on similar inter-annual variability (statistical two-tailed t test) of PM2.5, K+/PM2.5 (0.010), EC/PM2.5 (0.04) and OC/EC (~ 6) ratio, it has been inferred that the strength of combustion sources, viz. biomass burning and fossil fuel combustion remained more or the less constant during I and II campaigns (OC: organic carbon; EC: elemental carbon). However, significant difference in OC/PM2.5 and WSOC/OC ratios between I and II campaigns indicated a significant change in organic aerosol composition attributable to fog processing vis-à-vis fog scavenging (WSOC: water-soluble organic carbon). The OM/OC (organic mass-to-organic carbon) ratio of polar and non-polar organics averaging at 2.0 and ~ 1.2 (and the overall OM/OC ratio at 1.7) look quite similar during both the campaigns. Principal component analysis (PCA) resolved total source contribution up to 81.4% of which ~ 64% was attributed to mixed contribution from biomass burning emission and secondary transformations, 25% of the resolved source fraction to fossil fuel combustion and 11% of the resolved source fraction to the mineral dust. These results have implications to better parameterization of organic aerosols in chemical transport model and accurate estimation of their influence on regional-scale radiative forcing.
KeywordsOrganic aerosols OM/OC ratio Fog processing IGP
I thank Prof. M. M. Sarin (Geosciences Division; Physical Research Laboratory, Ahmedabad, India) and ISRO-GBP office (Bengaluru, India) for supporting this study. I also thank, Prof. Darshan Singh and Dr. Deepti Sharma for support in aerosol collection and sampling logistics, and the Indian Meteorological Department (IMD; Punjabi University, Patiala in India) for providing the relevant meteorological parameters from the sampling site. Author thanks the reviewers for providing constructive comments and Prof. Junji Cao for editorial handling of this manuscript. PR is thankful to the Council of Scientific and Industrial Research (India) for providing CSIR-Senior Research Associate fellowship (CSIR-SRA Pool No # 8934-A/2017).
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Conflict of Interest
The author states that there is no conflict of interest.
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