Seasonal Trends and source Apportionment of Carbonaceous Aerosols in PM10 at Central Delhi, India

Abstract

The present study shows seasonal trends and potential sources of carbonaceous contents in PM₁₀, i.e., organic carbon (OC), elemental carbon (EC), total carbonaceous aerosols (TCA), and secondary organic carbon (SOC) at central Delhi during January-December 2019. The annual mass abundance of PM₁₀ exhibited large seasonal variability and varied from 42.0 to 397.2 µg/m³ (Average 182.4 ± 17.2 µg/m³). The highest mass abundance of PM₁₀ was observed during winter (260.5 ± 24.7 µg/m³), followed by summer (200.4 ± 28.4 µg/m³), post-monsoon (190.0 ± 36.5 µg/m³), and monsoon (78.1 ± 13.7 µg/m³). Annual average mass concentrations of OC and EC were observed as 24.1 ± 2.7 and 7.9 ± 0.9 µg/m³, respectively, and their seasonal averages followed a similar trend as winter > post-monsoon > summer > monsoon. OC/EC ratio varied from 2.0 to 8.7 (Average 3.5), suggesting a wide range of contributions throughout the year arising from vehicular exhausts, wood-fuel burning, biomass burning, coal combustion, waste burning, and secondary organic aerosols. The annual average contribution of TCA to PM₁₀ was ~ 26%, whereas the seasonal contribution was found to be the highest during winter (31%) and post-monsoon (30%) followed by, summer (28%), and monsoon (17%) respectively. The estimated concentrations of SOC were the highest during winter (12.9 ± 3.7 µg/m³), followed by post-monsoon (9.2 ± 4.6 µg/m³), summer (7.0 ± 1.7 µg/m³), and monsoon (2.3 ± 0.8 µg/m³) seasons. The highest contribution during winter and post-monsoon suggests the active role of boundary layer dynamics resulting in secondary particle formation. The study of carbon sub-fractions, along with PCA, revealed that EC1 and OC3 were the dominating fractions suggesting gasoline vehicular exhaust as the significant emission source.