Inter-model comparison of the DRI-2001 and DRI-2015 for carbonaceous aerosol analysis in PM2.5: Method development and application in Chongqing

Abstract

Thermal-optical method is widely used to determine organic carbon (OC) and elemental carbon (EC) in PM_2.5 collected on filters. DRI-2001 and DRI-2015 analyzers have both been extensively employed with the IMPROVE_A protocol in the recent decades. However, differences in detectors and lasers between the two models can affect the measurement results. In this study, a novel using multiple linear regression was developed to equalize carbon fraction results between DRI-2001 and DRI-2015. After adjustment, high inter-model consistency was observed, with a mean bias within 5 % for total carbon (TC) and OC, and ∼10 % for EC. Larger inter-model differences (5.2 %–121.5 %) were found in OC1-OC4 and EC1-EC3. Fractions with high mass loading, particularly those linked to biomass burning (BB) and coal combustion (CC) (e.g., OC1, OC2 and OC4), exhibited better agreement after adjustment, with smaller mean bias within ∼15 % and higher R² values above 0.93 (p < 0.001). During winter in Wanzhou, the adjusted carbon fractions exhibited significantly improved inter-model agreement (p < 0.001). BB and CC were identified as the primary sources of carbonaceous aerosol, while secondary organic carbon (SOC) also contributed to elevated TC concentrations during pollution periods. Similar to DRI-2001 results, DRI-2015 measurements during winter indicated that CC and BB contributed 47.5 %, diesel exhaust 18.0 %, gasoline exhaust 21.6 %, and secondary formation 12.9 % to TC. These findings enhance our understanding of uncertainties and differences between models, leading to more accurate characterization of carbonaceous aerosol.