Variability of Carbonaceous Aerosols in Two Distinct Climatic Zones of the North-Western-Himalaya (India): An Expedition During Summer 2022

Abstract

The Northwestern Himalayas include two climatic zones: the temperate Kashmir Valley (KV) and the cold desert of Ladakh (LD), both hosting glaciers that sustain major Indo-Pak rivers. Carbonaceous aerosols (CA), key contributors to aerosol emissions, impact regional climate directly and indirectly. This study collected aerosol samples from four KV sites—Srinagar (SG), Qazigund (QZ), Pahalgam (PH), and Gulmarg (GM)—and two LD sites—Leh (LH) and Kargil (KG)—alongside real-time Black Carbon (BC) measurements during June-July 2022. Average BC concentrations were recorded as 6.36, 6.18, 6.10, 3.77, 1.10, and 0.94 µg/m’ over GM, QZ, SG, PH, LH, and KG, respectively, with peaks observed at SG and PH in the morning and evening, while GM had an evening peak. KG and LH, the Cold Desert LD sites, have very weak BC concentration variation from morning to evening.

BC source apportionment shows fossil fuel contributions of 81-94% in KV and 82-87% in LD, with biomass burning contributing 6-19% in KV and 13-18% in LD. KV’s bowl-shaped topography and higher anthropogenic activities increase fossil fuel BC, unlike LD’s open topography and windy conditions. An inverse relationship was observed between wind speed (WS) and BC concentration, while rainfall showed a weaker correlation. BC was negatively correlated with relative humidity (RH) in SG and GM, whereas PH and KG showed weak RH correlations, and LH showed a positive RH-BC relationship.

OC/EC ratios indicate biomass burning as the primary CA source, with OC/EC increasing with altitude. Back-trajectory analysis identified regional and local winds blowing in KV and Indo-Gangetic Plain (IGP) as the primary wind source over KG and LH, with elevated BC levels linked to local winds over KV and when wind paths moved from KV in LD.