Aerosol black carbon at an urban site-Srinagar, Northwestern Himalaya, India: Seasonality, sources, meteorology and radiative forcing

Abstract

Black carbon (BC) mass concentration was measured first-time at a high altitude urban site-Srinagar (1600 m asl), in northwestern Himalaya, India using an Aethalometer during 2013 to study temporal variations (monthly, diurnal and seasonal), meteorological influences, source and its radiative forcing. Diurnal variations with two peaks (at 8–10 h and 20–23 h) and two dips (at 13–17 h and 0–3 h) were observed throughout the year with varying magnitude. November and April showed the highest (13.6 μg/m3) and the lowest (3.4 μg/m3) mean monthly BC concentration respectively. Seasonally, autumn displayed the highest (9.2 μg/m3) and spring the lowest (3.5 μg/m3) mean BC concentration. Annual average BC concentration was quite higher (6 μg/m3) than those reported for other high altitude stations. Wind speed, Minimum temperature and total precipitation showed a clear negative correlation with BC (r = −0.63, −0.51 and −0.55 respectively), while as, the evening relative humidity showed positive correlation (r = 0.56). During autumn, spring and winter seasons, the main source of BC at Srinagar is the biomass burning, while during summer season, equal contribution of BC is from fossil fuel and biomass burning. Back trajectory simulations revealed that, except summer, westerly air masses are the dominant winds, transporting BC from central Asia, west Asia, south Asia, Africa and some parts of Europe to Srinagar adding to its local sources. Clear-sky short wave radiative forcing of atmosphere due to BC was highest (58.2 W m-2) during autumn which leads to the increase in lower atmospheric heating rate by 1.6 K/d. The high concentration of BC observed over the high-altitude Himalayan Kashmir region has serious implications for the regional climate, hydrology and cryosphere which needs to be investigated.