An observational study on the variation of black carbon aerosol and sourceidentification over a tropical station in south India

Özet

Continuous and high temporal resolution surface based measurements of Black Carbon (BC) concentrations havebeen carried out during 1stSeptember 2014 to 30thApril 2017 at Thiruvananthapuram (8.5°N, 76.9°E), a nearequatorial tropical coastal station, in South India. High diurnal and seasonal variations of BC aerosols in relationto changes in the regional meteorological conditions are examined. The BC exhibited well defined diurnal cyclewith a bimodal peak one in the morning (07.00–08.00 LST) and other in evening (21.00–23.00 LST). Relativehumidity of 60–90% and 70–90% favours the BC mass concentration in daytime and nighttime respectively. BCmass concentration is considerably less for the relative humidity category of 90–100%. BC greater than10μgm−3are mostly associated with low wind speed (less than 2 ms−1). Hence the local BC emissions are notwell mixed or transported to a larger distance in calm or low wind speed. In high wind speed local emissions arequickly and well mixed in the air. Coherence wavelet analysis between BC and rainfall shows periodicities in thesynoptic scale of less than 10 days and in the between 16–32 days. This shows the importance of intra seasonalrainfall scavenging on BC concentration over the tropical region. Synoptic systems over the monsoon regionshows high scavenging relation. The bivariate analysis pointed that the local emission from northeast sectorcontributes the black carbon aerosol to the observational site. HYSPLIT trajectory model reveals that the longrange transport of airmass is through northwest India and Bay of Bengal in winter season