Investigation of size distribution and mass characteristics of ambient aerosols and their combustion sources during post-monsoon in northern India

This study explores the size distribution and mass characteristics of ambient atmosphere in the source region of biomass burning (Punjab). The enhanced level of particulate matter (PM) concentrations were interpreted through measurements of number and mass concentration. MODIS (Moderate Resolution Imaging Spectroradiometer) fire count data and HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory model) used to decipher the extent of burning activities and origin of air-masses, respectively. Significant diurnal variabilities were observed in the PM1 (PM with aerodynamic diameter <= 1 mu m) and PM2.5 (aerodynamic diameter <= 2.5 mu m) number and mass concentrations. Higher number (N-0.(3-2.5): 1.34 +/- 0.20 x 10(4) #/cm(3)) and mass concentration (PM2.5: 286 +/- 39 mu g/m(3), n = 5) during nighttime compared to daytime (N-2.5: 0.74 +/- 0.22 x 10(4) #/cm(3); PM2.5: 224 +/- 59 mu g/m(3), n = 3) indicates impact of meteorological conditions (low wind speed and shallower boundary layer height) and biomass (plausibly paddy) burning activity. Although possibility of multiple sources and their varying strength (poor correlation between organic carbon (OC) and elemental carbon (EC)) can't be neglected, however, biomass burning appeared to be the dominant source (good correlation (R-2 = 0.4) between water-soluble potassium (K+) and PM) of ambient PM. Further, near similar number and mass size distribution of ambient and bio-fuels derived aerosols along with similar K+/PM and OC/EC ratio compared to that for paddy-residue burning imply that bio-fuel burning in the household kitchen could be the dominant contributor to enhanced PM concentration at sampling location in upwind IGP during the study period.