Aerosol characteristics at a high-altitude location during ISRO-GBP Land Campaign-II

Abstract

We present detailed analysis of the extensively measured aerosol parameters at the Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak Nainital, during ISRO-GBP Land Campaign-II. This land campaign was focused on the winter month of December 2004, using eight fixed stations distinctly located over the Gangetic belt in the North Indian corridor, where thick fog conditions generally prevail during winter. Among these stations, Manora Peak was selected due to its high-altitude location, at an altitude of ~2 km, having a pristine location in the Shivalik Ranges of Central Himalayas and allowing a free tropospheric site. In this perspective, observations of aerosol optical depths (AODs), black carbon (BC) mass concentration, total columnar ozone (TCO), mass loading of total suspended particulates (TSP), and number concentration of near-surface aerosols have been carried out from Manora Peak. These experiments barring AODs, were made for the first time at this location. The monthly mean AOD at 500 nm was found to be 0.056 (±0.037). Temporal as well as the diurnal variation of BC mass concentration show almost similar variation as that of aerosol number (>0.3 µm) concentration, having relatively low values during night and early morning periods, and gradually increasing as the day advances reaching its maximum level around 1600 h local time. The monthly mean BC concentration was found to be 1.36 (±0.99) µg m^-3. Mass loading of TSP was in the range 20-40 µg m^-3, with a mean value of 27.1 (± 8.3) µg m^-3. During the period under study, average BC mass fraction at Nainital was found to be ~6.3±2%. The monthly mean TCO was found to be 268 ±22 DU. The diurnal variation of BC mass concentration shows a typical behaviour compared with other low-altitude stations, where simultaneous measurements were made by other investigators during the campaign. This behaviour in the diurnal trend of aerosols is due to the topography and the boundary-layer dynamics over the high-altitude station of ARIES at Nainital.