Evaluation of organic aerosol filter sampling artefacts and implications to gravimetric PM2.5 mass at a COALESCE network site - Bhopal, India.

Filter based PM 2.5 samples are typically used to measure its chemical constituents. Such measurements are made in dense sampling networks to assess regulatory compliance and for source apportionment. Thus, quantifying sampling artefacts is crucial. In this study, 24-h integrated PM 2.5 samples collected over Bhopal, India a COALESCE (CarbOnaceous AerosoL Emissions, Source apportionment and ClimatE impacts) site during 2019 and 2020, were used to estimate particulate organic carbon (OC) artefacts. Total OC and its thermal fractions (OC1, OC2, OC3, and OC4) measured on 349 bare quartz (Q) and QbQ filters each, were used to determine OC positive artefacts on quartz filters. 50 QbT (Quartz behind Teflon) filters in conjunction with the simultaneous QbQ samples (a subset of the total QbQ) were used to estimate OC volatilization from Teflon filters. On average, adsorbed gaseous OC contributed 17% and 11% to the measured total OC during 2019 and 2020, respectively. Further, the volatilization loss of organics from Teflon filter (used to quantify PM 2.5 mass) ranged between 7% and 9%, and 5% and 6% of the PM 2.5 mass during 2019 and 2020, respectively. The results of this study provide the first systematic long-term evaluation of thermal carbon fraction-wise sampling artefacts, estimates of organic volatilization losses from Teflon filters and their implications to PM 2.5 mass closure, over a regionally representative location in India. • Organic carbon sampling artefacts estimated using multiple filter configurations. • Adsorbed organics contributed 17% (2019) and 11% (2020) to the total particle OC. • Organics volatilization from Teflon filter ranged between 5% and 9% of PM 2.5 mass. • Thermal fraction-wise % OC and % TOC loss increased with ambient temperature. • The number of PM 2.5 NAAQS exceedances increased on accounting for volatilized OC. [ABSTRACT FROM AUTHOR]