Assessment of PM2.5 chemical compositions in Delhi: primary vs secondary emissions and contribution to light extinction coefficient and visibility degradation
Haze fog conditions over northern India are associated with visibility degradation and severe attenuation of solar radiation by airborne particles with various chemical compositions. PM2.5 samples have been collected in Delhi, India from December 2011 to November 2012 and analyzed for carbonaceous and inorganic species. PM10 measurements were made simultaneously such that PM10 2.5 could be estimated by difference. This study analyzes the temporal variation of PM2.5 and carbonaceous particles (CP) focusing on identification of the primary and secondary aerosol emissions, estimations of light extinction coefficient (bext) and the contributions by the major PM2.5 chemical components. The annual mean concentrations of PM2.5, organic carbon (OC) elemental carbon (EC) and PM10 2.5 were found to be 153.6 59.8, 33.5 15.9, 6.9 3.9 and 91.1 99.9 mg m 3, respectively. Total CP, secondary organic aerosols and major anions (e.g. SO42 and NO3 maximize during the post monsoon and winter due to fossil fuel combustion and biomass burning. PM10 2.5 is more abundant during the pre monsoon and post monsoon. The OC/EC varies from 2.45 to 9.26 (mean of 5.18 1.47) indicating the influence of multiple combustion sources. The bext exhibits highest values (910 280 and 1221 371 Mm 1) in post monsoon and winter and lowest in monsoon (363 110 and 457 133 Mm 1) as estimated via the original and revised IMPROVE algorithms, respectively. Organic matter (OM =1.6 x OC) accounts for ~39 and ~48 of the bext, followed by (NH4)2SO4 ~21 and ~24 and EC ~13 and ~10 according to the original and revised algorithms, respectively. The bext estimates via the two IMPROVE versions are highly correlated (R2 0.95, root mean square error 38 and mean bias error 28 and are strongly related to visibility impairment (r 0.72) mostly associated with anthropogenic rather than natural PM contributions. Therefore, reduction of CP and precursor gas emissions represents an urgent opportunity for air quality improvement across Delhi.
Journal of Atmospheric Chemistry