Characterizing black carbon aerosols in relation to atmospheric boundary layer height during wet removal processes over a semi urban location

Black Carbon (BC) mass concentration has been analysed during rainy and non-rainy days of Northeast (NE) Monsoon months of the years 2015 and 2017 over a semi-urban environment near Chennai (12.81 N, 80.03 E), located on the east coast of India. BC, measured using an Aethalometer (AE-31) has been related to the atmospheric Boundary Layer Height (BLH) obtained from the ERA Interim Reanalysis data during rainy and non-rainy days on monthly mean basis to understand the wet removal of BC over the study location. The study reveals that BLH has a profound effect on the BC concentration on rainy days and non rainy days. It is found that the BC concentration in the night time is lower on rainy days compared to non rainy days owing to wash out on rainy days and the BLH remaining nearly the same on rainy and non rainy days. On the other hand, in the daytime it is found that the BC concentration remains nearly the same on rainy and non rainy days whereas the BLH is lower on rainy days compared to non rainy days. This reveals that in daytime lower boundary layer heights compensate for the wet removal effect on BC concentration on rainy days. A quantitative relation is found between the product of BC and BLH during rainy and non-rainy days which indicates the extent of redistribution of BC during non-rainy days when compared to the rainy days. In the process of analysing BC during the wet removal processes, the basic features of BC such as its mean diurnal variations, transport pathways, local sources and its relation with relative humidity were also reported.