Water soluble inorganic species of PM10 and PM2.5 at an urban site of Delhi, India: Seasonal variability and sources

Abstract

Comprehensive data of 2years (2013–2014) of water soluble inorganic species (WSIS) in the particulate matter (PM10: mean: 233.0±124.6μgm−3 and PM2.5: mean: 108.0±86.5μgm−3) have been used to study seasonal effect on the variation of total WSIS concentration, composition variability of inorganic aerosols and extent to which secondary formation of sulfate and nitrate aerosol occurred from their precursor gases. Mean concentrations of total WSIS in PM10 and PM2.5 were 82.12±72.15μgm−3 and 54.03±49.22μgm−3, respectively during the study period. Concentrations of total WSIS (PM10: 140.11±90.67μgm−3; PM2.5: 74.41±47.55μgm−3) during winter season was recorded higher than summer, monsoon and spring seasons. Significant correlation (p<0.01) between NH4+ and Cl−, SO42−, NO3− in PM10 and PM2.5, respectively indicates NH4+ as the major cation species for the neutralization of acidic components in the winter season. On the contrary, in summer season Ca2+, Mg2+, Na+ and K+ were the alkaline species responsible for the neutralization of acidic components in the PM10 samples. Principal Component Analysis (PCA) showed that secondary aerosol, biomass burning and soil driven dust were the possible sources that explained ~70% of the total variance. Cluster analysis and Concentration Weighted Trajectory (CWT) analysis for different season depicts the advection of air masses over the continental landmasses of Afghanistan (summer season), northwestern region of Pakistan (summer and winter season), marine region (monsoon season) and adjoining states of Delhi. These air masses from different regions could be the cause of an increase in PM10 and PM2.5 aerosol over the study site.