Scavenging efficiency of rainfall on black carbon aerosols over an urban environment

Abstract

Black carbon (BC) aerosols are the optically absorbing part of carbonaceous aerosols that have significantly different optical and radiative properties. The present study addresses the estimation of black carbon aerosol scavenging coefficient by using ground-based measurements over an urban environment of India, namely, Hyderabad. Extensive ground measurements of black carbon have been carried out during January to December 2004 over a tropical urban environment of Hyderabad. Seasonal variations of black carbon aerosol mass concentration showed high values during dry season and low values during monsoon season. The diurnal variations of BC suggest that the concentrations increased by a factor of ∼2 during morning and evening hours compared to afternoon hours. Drastic reduction in black carbon aerosol loading has been observed during rainy days. The statistical fit between black carbon aerosol mass concentration and rainfall suggests the reduction of ∼3.6 μg/m3 in atmospheric black carbon aerosol loading for every 1-mm increase in rainfall intensity over the study area. The scavenging coefficient of black carbon aerosols is found to be 1.64 × 10-5 s-1. © Crown Copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.