Fine Mode Carbonaceous Aerosols of PM 2.5 Over the High-Altitude Stations of the Indian Himalayas

Carbonaceous Aerosols (CAs) have played an active role in the Earth's atmospheric system, climate, human health, and radiative forcing. Due to their significant role in the atmosphere, it was imperative to characterize the carbonaceous components [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and total carbonaceous aerosols (TCA)] of PM 2.5 samples collected at three different urban locations (Mohal-Kullu, Almora, and Darjeeling) of the Himalayan region of India during August 2018–December 2019. The annual average mass concentrations of PM 2.5 were recorded as 40 ± 27, 27 ± 21, and 38 ± 13 µg m −3 for Mohal-Kullu, Almora, and Darjeeling, respectively, which is near the Indian National Ambient Air Quality Standards (NAAQS) (24 h: 60 µg m -3 ; annual: 40 µg m −3 ). The OC/EC ratio and significant correlation of OC with EC and WSOC with OC indicated a substantial effect of biomass burning and secondary organic aerosol formation over the study sites. OC was found to be secondary in nature over the study sites during the study period. The contribution of TCA in PM 2.5 showed CAs as a significant contributor to the mass concentration of particulate matter (PM) over the Himalayan regions. HYSPLIT model demonstrates that regionally transported air masses, mostly from Indo-Gangetic plain (IGP), the Thar desert, the semi-arid region, Nepal, and local areas, considerably influence PM concentrations and chemical composition over the pristine Himalayan altitudes. The study implies that to improve the air quality in booming urban areas, it is necessary to pay attention to both local emission sources and meteorological conditions.