An analysis of particulate pollution using urban aerosol pollution island intensity over Delhi, India

The accent of the present study is determination of Urban Aerosol Pollution Island (UAPI) intensity and spatial variability in particulate matter concentration (PM 10 and PM 2.5 ) over Delhi. For analysis, the hourly concentration dataset of PM 2.5 and PM 10 from January 2019 to December 2020 was obtained from ten air quality monitoring stations of Delhi. Additionally, UAPI Index has been calculated to assess the intensity of particulate pollution. The daily, monthly, and annual variations in the trends of PM 10 , PM 2.5 , and UAPI index along with related meteorological parameters have been analyzed. Particulate pollution peaked majorly during two seasons, i.e., summer and winter. The highest concentration of PM 10 was observed to be 426.77 µg/m 3 while that of PM 2.5 was observed to be 301.91 µg/m 3 in January 2019 for traffic-affected regions. During winters, higher PM 2.5 concentration was observed which can be ascribed to increased local emissions and enhanced secondary particle formations. While the increase in PM 10 concentrations led to an increment in pollution episodes during summers over most of the sites in Delhi. The UAPI index was found to be declining in 2020 over traffic affected regions (77.92 and 27.22 for 2019 and 2020, respectively) as well as in the background regions (64.91 and 19.80 for 2019 and 2020, respectively) of Delhi. Low traffic intensity and reduced pollutant emission could have been responsible for the reduction of UAPI intensity in the year 2020. The result indicates that lockdown implemented to control the COVID-19 outbreak led to an unexpected decrease in the PM 10 pollution over Delhi.