Space-time variations in aerosol and precursor gas characteristics from low to high altitude regions of Himalayas

Khan AA, Devara PCS, Pant NC, Srivastava AK and Varaprasad V

Published on: 2022-12-08

Abstract

A field observational campaign was carried out from the low-altitude region of arid/semiarid plains of Haryana to high-altitude remote mountains of the western part of the Himalaya to Ladakh with elevation spanning between 250 and >5000 meter above mean seal level from 1 to 10 August 2019. During this 10-day expedition program, aerosol optical depth (AOD), total column ozone (TCO), and precipitable water vapor (PWV) observations were carried out using a mobile Sun-photometer and Ozonometer. The height profiles of these parameters were obtained by making measurements at different altitudes while ascending to or descending from the highest elevation. The ground-based remote sensing measurements of AOD, TCO and PWV observations are compared with synchronous satellite data. AOD, PWV and TCO showed a steep decrease with an increase in altitude up to about 1 km and thereafter with a slow rate up to 5.5 km, which is attributed to the changes in local atmospheric boundary layer characteristics. Good correspondence between ground-based and satellite products (NASA’s MODIS and OMI) confirms the mutual validity and layer structures, contributing to the radiative forcing by aerosols and precursor gases present in the lower atmosphere over high-altitude stations such as Ladakh. The aerosol size distributions at most of the locations showed lower concentrations, indicating the abundance of aerosols originating from natural sources. A good relationship among altitudinal variation of relative humidity, wind speed and direction, loading of aerosol and precursor gases were observed. Lower AOD and TCO values with lower humidity were observed in higher-altitude regions. Greater PWV values were observed during the study period (south-west monsoon), indicating higher relative humidity, and vice versa.