Tethered balloon-born and ground-based measurements of black carbon and particulate profiles within the lower troposphere during the foggy period in Delhi, India.

The ground and vertical profiles of particulate matter (PM) were mapped as part of a pilot study using a Tethered balloon within the lower troposphere (1000m) during the foggy episodes in the winter season of 2015-16 in New Delhi, India. Measurements of black carbon (BC) aerosol and PM <2.5 and 10μm (PM & PM respectively) concentrations and their associated particulate optical properties along with meteorological parameters were made. The mean concentrations of PM, PM, BC and BC were observed to be 146.8±42.1, 245.4±65.4, 30.3±12.2, and 24.1±10.3μgm, respectively. The mean value of PM was ~12 times higher than the annual US-EPA air quality standard. The fraction of BC in PM that contributed to absorption in the shorter visible wavelengths (BC) was ~21%. Compared to clear days, the ground level mass concentrations of PM and BC particles were substantially increased (59% and 24%, respectively) during the foggy episode. The aerosol light extinction coefficient (σ) value was much higher (mean: 610Mm) during the lower visibility (foggy) condition. Higher concentrations of PM (89μgm) and longer visible wavelength absorbing BC (25.7μgm) particles were observed up to 200m. The BC and PM aerosol concentrations near boundary layer (1km) were significantly higher (~1.9 and 12μgm), respectively. The BC (i.e BC) aerosol direct radiative forcing (DRF) values were estimated at the top of the atmosphere (TOA), surface (SFC), and atmosphere (ATM) and its resultant forcing were - 75.5Wm at SFC indicating the cooling effect at the surface. A positive value (20.9Wm) of BC aerosol DRF at TOA indicated the warming effect at the top of the atmosphere over the study region. The net DRF value due to BC aerosol was positive (96.4Wm) indicating a net warming effect in the atmosphere. The contribution of fossil and biomass fuels to the observed BC aerosol DRF values was ~78% and ~22%, respectively. The higher mean atmospheric heating rate (2.71Kday) by BC aerosol in the winter season would probably strengthen the temperature inversion leading to poor dispersion and affecting the formation of clouds. Serious detrimental impacts on regional climate due to the high concentrations of BC and PM (especially PM) aerosol are likely based on this study and suggest the need for immediate, stringent measures to improve the regional air quality in the northern India.