An Extensive Assessment of Ambient Air Quality in City Delhi: Air Quality Monitoring, Source Apportionment and Analysis

Abstract

The Analysis of air quality data for three consecutive years 2018, 2019 and 2020 showed that there was a significant reduction in the concentration of almost all pollutants in year 2020 except for ozone and benzene. In 2020 the decrease in concentration may be observed due to various restrictions imposed during lockdown called due to COVID - 19 pandemic. However, ozone showed an increasing trend, this may be due to more heat and sunlight as ozone primarily results from photochemical reactions involving nitrogen oxides and volatile organic compounds in the presence of sunlight and heat. Concentration of benzene has increased in 2020, this may be due to certain industries, especially those consuming or releasing benzene, might have started operating, resulting in the increase. Local influence of emissions on monitoring stations is also a possibility during lockdown period in 2020. A relative reduction of 35.38% in PM₁₀, 38.79% in PM_2.5, 23.90% in NO₂, 8.22% in SO₂ , 17.64% in CO, 22.36% in NO and 9.98% in NH₃ have been observed in 2020 when compared to 2019. Correlation and p-value analysis indicates that there is significant correlation between some of the pollutant pairs but the same pattern is not retained over time. The Principal component analysis (PCA) reflects that only first four principal components are significant, which identifies the pollution caused due to vehicles as primary and major source of air pollution in Delhi. Regional atmospheric transfer of pollutants from nearby areas from burning of agricultural waste, coal etc. were found to be the secondary major source of air pollution in Delhi. The objective of the present work is to analyze the distribution of eleven major pollutants namely particulate matters (PM₁₀ and PM_2.5), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), ozone (O₃), nitric oxide (NO), oxides of nitrogen (NOx), ammonia (NH₃), carbon monoxide (CO), benzene (C₆H₆), toluene along with meteorological parameters, air temperature (AT), wind speed (WS), wind direction (WD), barometric pressure (BP), solar radiation (SR) and relative humidity (RH) in the mega city Delhi for the three consecutive years 2018, 2019 and 2020.