Diurnal and seasonal variations of black carbon and PM2.5 over New Delhi, India: Influence of meteorology

Black carbon (BC), which is one of the highly absorbing capacities of solar radiation, reduces albedo of atmospheric aerosol. BC along with fine particulate matters (PM2.5), which play crucial role in climate and health, was monitored online for an entire year of 2011 at an urban megacity of Delhi, situated in the northern part of India. Daily mass concentration of BC varies from 0.9 to 25.5 μg m− 3, with an annual mean of 6.7 ± 5.7 μg m− 3 displayed clear monsoon minima and winter maxima; however, PM2.5 concentration was ranging from 54.3 to 338.7 μg m− 3, with an annual mean of 122.3 ± 90.7 μg m− 3. BC typically peaked between 0800 and 1000 LST and again between 2100 and 2300 LST, corresponding to the morning and evening traffic combined with the ambient meteorological effect. During summer and monsoon, the BC concentrations were found less than 5 μg m− 3; however, the highest concentrations occurred during winter in segments from < 5 to > 10 μg m− 3. In over all study, the BC mass concentration was accounted for ~ 6% of the total PM2.5 mass, with a range from 1.0% to 14.3%. The relationship between meteorological parameters and BC mass concentrations was studied and a clear inverse relationship (r = − 0.53) between BC and wind speed was observed. Relation between visibility and BC mass concentrations was also significantly negative (− 0.81), having relatively higher correlation during post-monsoon (− 0.85) and winter (− 0.78) periods and lower during summer (− 0.45) and monsoon (− 0.54) periods. The mixed layer depths (MLDs) were found to be shallower during post monsoon (379 m) and winter (335 m) as compared during summer (1023 m) and monsoon (603 m). The study indicated that during post-monsoon season, the impact of biomass burning is higher as compared to combustion of fossil fuels. Results are well associated with the rapid growth of anthropogenic emissions and ambient meteorological conditions over the station.