OM/OC Ratio of Polar and Non-Polar Organic Matter during Wintertime from Indo-Gangetic Plain: Implications to Regional-Scale Radiative Forcing

Abstract

Ambient PM 2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) samples have been collected in two winter campaigns: I during 2nd December 2008-27th February 2009 and II during 3rd December 2010-11th February 2011 (n = 15). The PM 2.5 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 PM 2.5 , K + /PM 2.5 (0.010), EC/PM 2.5 (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/PM 2.5 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.

Source Impact Analysis Using Char-EC/Soot-EC Ratios in the Central Indo-Gangetic Plain (IGP) of India

“…The data set revealed that monthly averaged fPM concentration was maximum for November (317 µg m -3 ) whereas minimum for August (47 µg m -3 ). Our observation on higher concentrations of atmospheric particulates in the month of November is in good agreement with the previous studies (Ram et al, 2012;Ram and Sarin 2010;Pachauri et al, 2013;Singh et al, 2017;Rajput et al, 2018). Those studies have addressed the predominant impact through longrange transport of large-scale agricultural rice straw (100s of million tons) burning emissions occurring in the northwestern part of the IGP region (Sawlani et al, 2018).…”

“…However, most of the previous studies conducted over the Indian region have found the utility of OC/EC ratio (and sometimes molecular tracers) to characterize the BB and FFC emissions owing to higher contribution of OC from its predominant source of BB emission (Pachauri et al, 2013;Rajput, 2018;Ram and Sarin, 2010;Singh et al, 2018). Using various receptor modelling tools, source apportionment studies have revealed that BB and FFC contribute up to 60% of fine aerosols in urban areas of the upper IGP region (Jain et al, 2021a(Jain et al, , 2021bSingh et al, 2017).…”

Chemical characterization of aerosols in the South Asian outflow over the northern Indian Ocean: latitudinal gradients and ultrafine particle events

“…Though the contribution of OC to OM varies depending upon the ageing and extent of the oxidation, we have used an OM/OC ratio of 1.7 to convert the OC measurements to OM. 10,38,39 This conversion factor is applied only to the OC measurements adopted from the literature. It should be noted that the measured OC values over the Indian subcontinent are much higher than the sulfate loading (OC/ sulfate ratio ∼ 2), and hence the assumption of an OM/OC ratio of 1.7 does not inuence the ndings of this study.…”

Quantifying Air Pollutant Variations during COVID-19 Lockdown in a Capital City in Northwest China

“…Guo et al [12] observed that the proportion of sulfate in PM 2.5 ranged from 28.2% to 50.5% in Nanjing in 2015. The secondary air pollutants generated by the reaction of the primary pollutants also exert considerable effects on regional environmental quality and human health [13,14].…”