Chemical and isotopic characteristics of PM2.5 over New Delhi from September 2014 to May 2015: Evidences for synergy between air-pollution and meteorological changes

Abstract

The capital city of India, New Delhi, is experiencing serious PM_2.5 pollution in the form of recurrent hazy skies and smoky fog (SMOG) episodes in recent years. Besides source-emission strengths, frequency and time-spans of these air-pollution episodes are uncertain due to variable urban meteorological influences, preventing the formation of a cohesive policy to tackle air-quality degradation. About 70% mass of PM_2.5 particle is composed of Carbon (C), Nitrogen (N), and Sulphur (S) and, hence, their mass concentrations along with their stable isotopic imprints (viz. δ¹³C_PM2.5, δ¹⁵N_PM2.5 and δ³⁴S_PM2.5) provide powerful tools to gain insights into complex aerosol chemistry. This study presents the aforementioned data generated for PM_2.5 collected from New Delhi covering full post-monsoon, winter, and summer months of 2014-15. Temporal variability in the generated dataset was analyzed with variabilities in atmospheric concentrations of key gaseous species (NH₃, NO_x, and SO₂) and meteorological indices. The highest PM_2.5 concentrations were observed in winter months with enhanced aerosol N and S concentrations. Active biomass (crop-residue) burning in the northwest Indo-Gangetic Plains (IGP) appears to be the major source of aerosol TC for post-monsoon and winter months in addition to emission sources from the combustion of bio- and fossil- fuels. Aerosol TN contents appear to be largely impacted by ambient ammonia emissions, especially during winter. Aerosol TS contents could be manifested by emissions from coal combustion, road dust, and biogenic sulphur. Total C + N + S contents of PM_2.5 showed significant negative correlations with surface solar radiation and air-visibility. Both δ¹⁵N_PM2.5 and δ³⁴S_PM2.5 values show remarkable correlations with air-quality and meteorological parameters during winter months demonstrating considerable secondary cycling. Cluster analysis and concentrated weighted wind trajectories over New Delhi for the study-period showed ~64% and ~58% of air mass trajectories from the northwest (Punjab-Haryana) region during post-monsoon and winter months respectively.

Keywords: Air-visibility; Ammonia emissions; Biomass burning; PM(2.5) aerosols; Stable isotopes of Carbon-Nitrogen-Sulphur.