Seasonal characteristics of black carbon aerosol mass concentrations and influence of meteorology, New Delhi (India)

This study investigates seasonal variability in black carbon (BC) aerosol mass concentrations at New Delhi, a monsoon-influenced urban agglomeration located at the edge of the Indo-Gangetic Plain and the Aravalli hills. Incessant measurement of BC has been carried out using Aethalometer AE-42 with the PM2.5 selective inlet. The BC concentrations show significant seasonal, diurnal and hourly variations. The hourly concentrations show a persistent peak distribution during the observation period with different magnitudes. There are two sharp peaks; first one in the morning between 8:00 and 11:00 h and the second one at night between 21:00 to 23:00 h. The morning high concentration peaks are more pronounced in all the observed months. The hourly and weekly analysis of BC concentrations indicates a significant contribution of vehicle emission, showing a definite pattern with the volume of traffic flow. Though, seasonal variation reveals that the local meteorological conditions directly influence it. Mean BC concentrations during summer; monsoon and post-monsoon seasons are 6.33, 4.95 and 17.4 μg mˉ3, respectively. The correlation coefficient of BC concentrations with temperature and relative humidity (RH) indicates that temperature and RH influence the boundary layer dynamics which in turn result into diurnal and seasonal variability in BC concentrations at the ground level.