Long-term (2012-2021) Variation in Carbonaceous Aerosols of PM_2.5 at an urban site of Megacity Delhi situated over Indo-Gangetic Plain of India

Carbonaceous species [organic carbon (OC), elemental carbon (EC), elemental matter (EM), primary organic carbon (POC), secondary organic carbon (SOC), total carbon (TC), and total carbonaceous matter (TCM)] of PM_2.5 were estimated to study the seasonal variability and annual variability of carbonaceous aerosols (CAs) in megacity Delhi, India from January 2012 to April 2021. The annual average concentrations (± standard deviation) of PM_2.5, OC, EC, TC, EM, TCM, POC, and SOC were estimated as 127±77, 15.7±11.6, 7.4±5.1, 23.1±16.5, 8.2±5.6, 33.3±23.9, 9.3±6.3 and 6.5±5.3 µg m^-3, respectively during the entire study period (10-year). During the entire sampling period of PM_2.5, the average CAs accounted for 26% of the PM_2.5 concentration. Significant seasonal variations in concentrations of PM_2.5, OC, EC, POC, SOC, and TCM were recorded with maxima in post-monsoon and minima in monsoon seasons. A linear relationship between OC and EC concentrations, and OC/EC, as well as EC/TC ratios, suggested that vehicular emissions (VE), fossil fuel combustion (FFC), and biomass burning (BB) could be major sources of CAs of PM_2.5 at megacity Delhi, India.