Assessing Aerosol and Nitrogen Dioxide Concentration in Major Urban Cities over the Himalayan Region during the COVID-19 Lockdown Phases

Abstract

The SARS-COVID-19 pandemic has caused severe risk to human lives and huge economic loss due to periodic lockdown events across the world. However, the terrestrial environment got a rare window to heal itself during the lockdown periods. The present study was conducted across the Great Himalayan Region with special emphasis on the urban region for analyzing the concentration of air quality parameters (i.e., aerosol optical depth [AOD], nitrogen dioxide [NO2]) during the lockdown periods. The Moderate Resolution Imaging Spectroradiometer (MODIS)-based AOD product and Sentinel-5P-based near-real-time atmospheric NO2 data sets were employed for the assessment. The findings of the study indicate a significant reduction in the AOD and NO2 concentration over the Himalayan region during the lockdown phases as compared to the mean conditions. The maximum negative AOD anomaly was observed over Ladakh (57%) during phase 1, and a positive AOD anomaly was noted over West Bengal (11%) during phase 4. For NO2, Nepal has shown the highest negative anomaly during phase 3 (20%). Furthermore, within the 3-km buffer zone of 14 cities, the highest positive AOD anomaly has been recorded in Itanagar during phase 2 (~79%) and a negative anomaly in phase 4 over the Dishpur region (~59%). Whereas the highest negative anomaly was recorded in phase 1 in Shimla, in the Itanagar region, a positive NO2 anomaly was recorded in Darjeeling during phase 2. Thus, it is made up that COVID-19-induced shutdown events have significantly aided to improve the air quality condition, which is suggestive of formulating an effective policy for improving air quality measures.