Air Quality, Atmospheric Variables and Spread of COVID-19 in Delhi (India): An Analysis

Based on a time series analysis of the criteria pollutants, meteorological parameters, and COVID-19 positive cases, this paper explores the impact of epidemic prevention and control actions on air quality for five different periods of COVID-19 outbreak in Delhi, India. The study found that under the epidemic control measure during 11 May-19 June 2020, the average concentrations of atmospheric air pollutants PM2.5, PM10, NO2, and CO were reduced to 42.15 mu g m(-3), 128.68 mu g m(-3), 27.31 ppb, and 0.83 ppm respectively, and were 73.85%, 46.48%, 63.43%, and 50.18% lower than the pre-COVID-19 level of January 2020, respectively. The steep fall of PM2.5, NO2, and CO was due to a drastic reduction in vehicular emission, but PM10 did not fall below the National Ambient Air Quality Standard. Between January 2020 to 11 May-19 June 2020 period, the pollutants O-3 and SO2 increased significantly by 217.33% and 57.58 % respectively. The rise of SO2 in Delhi was due to long-distance transfer, power plant emissions, and biomass burning. The sharp increase of O-3 happened due to accumulation in the atmosphere. During the peak COVID-19 phase (9 April-10 May 2020) Delhi had unprecedented improved AQI classes of II and III only. However, the pivotal pollutants in terms of their cumulative contribution to the AQI classes were PM10 and O-3. Low RH and low-temperature situations exhibited positive correlations with the new COVID-19 infection cases in Delhi. Comparatively lower NO2 level in the air demonstrated a significant negative correlation with new COVID-19 cases while average SO2 concentration in the air, when increased to 24.05 ppb, showed a negative correlation with new COVID-19 cases in Delhi. This study indicated a possibility of O-3 exhibiting a positive correlation with new COVID-19 cases under the condition of comparatively low temperature and low humidity.