Characteristics of Surface Ozone Levels at Climatologically and Topographically Distinct Metropolitan Cities in India

Abstract

Surface ozone (O3) data at Pune (1998-2014) and Delhi (1998-2013) are studied to examine their temporal characteristics. Study also examines role of meteorology and atmospheric boundary layer height (ABLH) in modulating surface O3 at these sites. Using diurnal variability of surface O3, rate of change of surface O3, [d(O3)/dt] is estimated to infer the nature of surface O3 formation/destruction mechanisms. Analysis of data reveals that at both locations, surface O3 concentrations during daytime are significantly high as compared to those during nighttime. Seasonally, at Pune averaged daytime surface O3 concentrations are high during pre-monsoon and low in monsoon while those during winter and post-monsoon are found to be significantly higher than those in monsoon but half as compared to those in pre-monsoon. At Delhi, averaged daytime surface O3 concentration is minimum in winter and maximum in pre-monsoon with monsoon and post-monsoon values being about 0.79-0.82 times with respect to pre-monsoon O3 concentrations. High natural/anthropogenic pollutant concentration, abundance of ozone precursor gases, high temperature and high rate of photo-oxidation of precursor gases due to solar flux are the causal factors for increased surface O3 concentrations in pre-monsoon season. Reduced solar flux decreases photo-dissociation of ozone precursor gases resulting in low O3 concentration during winter season. Occurrence of low surface O3 during early morning hours in monsoon, post-monsoon and winter seasons is because of low ABLH and low stratosphere-troposphere exchange (STE). [d(O3)/dt] values during morning/evening at Pune and Delhi are indicative of asymmetric and symmetric nature of ozone formation/destruction mechanisms.