Aerosol composition, transport, and radiative impact derived from ground-based and satellite remote sensing in the...

The study aims to quantify the individual contributions of light-absorbing aerosols, i.e., BC, OC, and dust, to the aerosol absorption over the Central Himalaya, a poorly studied and sensitive region, ranging from low to high altitude, using the in-situ observations. The seasonal mean SSA, AAOD, and AOD values were found in the range of 0.76 ± 0.017 to 0.99 ± 0.005, 0.001 ± 0.0004 to 0.067 ± 0.034, and 0.083 ± 0.003 to 0.751 ± 0.328 at all sites. Several stations showed lower SSA values during the pre-monsoon, inferring the dominance of the light-absorbing aerosols originating from natural and anthropogenic sources. We utilized external and internal mixing approaches to estimate aerosol component fractions. The results from the external mixing approach showed the presence of >50 % of BC and < 10 % of the dust in most of the high and mid-altitude sites. However, the presence of dust was greater at the low-altitude sites. Nevertheless, the presence of dust was estimated in almost all the sites, considering the internal mixing case. The results from both approaches agreed well with the CALIPSO aerosol subtype. Though a few discrepancies were found, the MG approximation occasionally overestimated the dust fraction. The aerosol radiative forcing at the surface and in the atmosphere showed an increasing trend toward the lower altitude, except for a few anomalies at Kathmandu and Lumbini. The vertical aerosol extinction profiles were also analyzed, and vertical heating rates were calculated, which revealed a significant loading of aerosols above the 3 km altitude and a substantial presence of carbonaceous aerosols and heating over the 5 km altitude, crucial for the survival of glaciers. The study will improve the regional representation of aerosol compositions in climate simulations, the quantification of impact on the glaciers, and aerosol-induced changes in the hydrological cycle in the region.