Chemical characteristics of PM2.5 at a source region of biomass burning emissions: Evidence for secondary aerosol formation

A systematic study on the chemical characteristics of ambient PM2.5, collected during October-2011 to March-2012 from a source region (Patiala: similar to 30.2 degrees N, 763 degrees E; 250 m amsl) of biomass burning emissions in the Indo-Gangetic Plain (IGP), exhibit pronounced diurnal variability in mass concentrations of PM2.5, NO3 (-), NH4+, K+, OC, and EC with similar to 30-300% higher concentrations in the nighttime samples. The average WSOC/OC and SO42-/PM2.5 ratios for the daytime (similar to 0.65, and 0.18, respectively) and nighttime (0.45, and 0.12, respectively) samples provide evidence for secondary organic and SO42- aerosol formation during the daytime. Formation of secondary NO3- is also evident from higher NH4NO3 concentrations associated with lower temperature and higher relative humidity conditions. The scattering species (SO42- + NO3 (-) + OC) contribute similar to 50% to PM2.5 mass during October-March whereas absorbing species (EC) contribute only similar to 4% in October-February and subsequently increases to similar to 10% in March, indicating significance of these species in regional radiative forcing. (C) 2013 Elsevier Ltd. All rights reserved.