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.

Automated summary

This study examines the contribution of various monitoring sites in Delhi to the O3 concentration. The highest O3 concentration is found in Green Areas, while the lowest is found in Industrial/Commercial Areas. Short-and long-range transport, downward draft, and biogenic emissions are the main factors contributing to O3 in Green Areas.