Relationships of surface ozone with its precursors, particulate matter and meteorology over Delhi

Abstract

The paper presents the temporal variations of surface ozone (O3) and its precursors (oxides of nitrogen (NOX), carbon monoxide (CO), methane (CH4) and non-methane hydrocarbons (NMHCs)) along with particulate matter (PM10 and PM2.5) and their relationship with meteorology during January 2012 to December 2014 at an urban site of Delhi, India. The mean mixing ratio of surface O3, NOX, CO, CH4 and NMHCs were 29.5 ± 7.3 ppb, 34.7 ± 11.2 ppb, 1.82 ± 0.52 ppm, 3.07 ± 0.37 ppm and 0.53 ± 0.17 ppm, respectively. This study also comprises an analysis of the relation between UV irradiance and surface O3. A relationship between the total oxidant concentrations (OX) and NOX has been used to identify the regional background O3 values and the local levels of primary pollution. An attempt has been made to identify the existence of NOX or NMHC sensitive regime by charting out relationships between O3, NOX and NMHCs. The respective high pollution periods of surface O3 and PM differ on a seasonal timescale. Linear regression analysis has been used to quantify the negative influence of the chemical constituents of PM (elemental carbon, NO3 −, SO4 2−) on O3 values. Statistical validation using bivariate correlation analysis, multiple linear regression (MLR) analysis and principal component analysis (PCA) strongly describes the intricate relationships among the aforesaid variables and meteorology. Potential Source Contribution Function (PSCF) and Concentration Weighted Trajectory (CWT) analysis indicated upper Indo-Gangetic Plain (IGP) as a significant source region of O3 precursor gases contributing for O3 values at the study site.