Black carbon characterization and source apportionment over a semi-tourist site in the central Himalayan Region, India

Abstract

Black carbon (BC), released due to partial burning of fuel, has serious negative impacts on climate and human health. We conducted continuous BC measurements over 5 years (January 2019–December 2023) at Katarmal (29.38˚N, 79.37˚E, 1225 m amsl) in the Central Himalayan Region. We examined BC mass concentration, temporal fluctuations, meteorological alterations, source apportionment, and the impact of COVID-19 period. BC concentrations on daily basis ranged from 0.01 to 13.7 μg m⁻³, with an annual concentration of 1.6 ± 1.3 μg m⁻³. The highest BC levels were in April 2022 (5.9 ± 2.5 µg m⁻³), March 2022 (4.7 ± 1.8 μg m⁻³) and February 2023 (4.3 ± 1.4 μg m⁻³). Planetary boundary layer height (PBLH) was shallow in winter with higher BC concentrations, and higher in the monsoon (~ 1154 m), with lower BC levels (~ 0.11 μg m⁻³). Elevated BC in the pre-monsoon persisted despite of high PBLH (~ 1905 m). Meteorological parameters like wind speed exhibited a positive correlation (r = 0.71), while relative humidity, air temperature, and total rainfall were negatively correlated with BC as r = -0.82, -0.60, and -0.79, respectively. Over a period of five years, fossil fuel sources (BC_ff) accounted for 59.4% of the total BC, while biomass burning (BC_bb) contributed 40.6%, indicating a higher biomass-burning impact compared to other Indian Himalayan areas. During the COVID-19 lockdown period, a significant decrease (~ 16%) was observed in BC due to reduced anthropogenic activities, mainly vehicular emissions. This was supported by 10% increase in the absorption Ångström exponent. Despite reduced fossil fuel emissions during the lockdown, 67.8% of BC at the site still originated from fossil fuel combustion, which is likely due to long-range transported dust of BC from outside the region.