Yearlong first measurements of black carbon in the western Indian Himalaya: Influences of meteorology and fire emissions

Abstract

Measurements of equivalent black carbon (EBC) aerosols are presented for the first time from a high-altitude station Ranichauri (30°18′ N, 78°24′ E; 2200 m amsl) in the lesser Himalaya during January-December 2016. The influences of meteorology, fire emissions and transport, on [EBC] variations have been investigated here. The daily mean values of [EBC] are observed to vary from 0.04 ± 0.03 μgm−3 to 7.83 ± 2.66 μgm−3 with peak during April. A significant enhancement in [EBC] is observed towards the end of April, reaching the levels as high as 23.95 μgm−3 and attributed to fire emissions. Diurnal variations are suppressed with typically lower [EBC] levels during the summer monsoon (0.42 ± 0.25 μg m−3 in July) due to the transport of marine air mass and scavenging. On a seasonal basis, the average [EBC] levels are found to be higher during winter (2.72 ± 1.86 μgm−3) and pre-monsoon (2.56 ± 1.80 μg m−3), and lowest during the summer monsoon (0.89 ± 01.03 μg m−3).Our measurements in conjunction with the analysis of model meteorology (Era Interim reanalysis) show profound effects of boundary layer dynamics on EBC concentrations. Wintertime [EBC] maximum is suggested to be due to confinement of regional anthropogenic emissions in shallow boundary layer. In addition, transport from the North-West, and Western regions, characterized by wood-burning and fossil fuel combustion, also affected [EBC] the variations here, except during the summer monsoon.