Tropospheric ozone variability in Delhi during pre & post monsoon periods: Decoding influence of seasonal variation, diurnal variation, short-range and long-range transport

This study examines the contribution of various monitoring sites of Delhi categorized as Green Areas, Urban Areas, Industrial/Commercial Areas, Traffic Areas, and Residential Areas. The mean hourly surface O3 concentration during the pre-monsoon season (March - June 2018) varies from 26 +/- 30 to 85 +/- 69 mu g/m3 and in post-monsoon season (October 2018 - January 2019) varies from 13 +/- 18 to 49 +/- 58 mu g/m3. Maximum O3 concentration is found at sites categorized as Green Areas and minimum at Industrial/Commercial Areas for both the pre-and post-monsoon seasons. The contribution of O3 from short-and long-range transport, downward draft, biogenic emissions are found to be maximum at green Areas which act as a sink for the O3. HYSPLIT cluster analysis was done to see the influence of long-range transport on the O3 concentration across all sites. The air masses originating from 3500 m or above contributed more to O3 in green Areas only. Air masses originating from S-W during pre-monsoon and East during post-monsoon contributed to high concentration events in industrial/commercial Areas only. The stubble burning episode in N-W contributed to high concentration events in urban areas and residential areas. The contri-bution of O3 in Residential Areas can be attributed to long-range transport from the N-W di-rection with air-masses originating at height < 1500 m and the local influences.