Covid-19 lockdown effects on regional meteorology and air quality in delhi (ncr)

Abstract

This study investigates the influence of the COVID-19 lockdown on meteorology and air quality in Delhi (NCR) by analysing reanalysis datasets (from ERA5 and MERRA2-CNN) in three time periods - the baseline (2016–2019), lockdown (2020), and recovery (2021). It focuses on the pre-monsoon (April to June) and monsoon months (July to August). The research examines variations in key atmospheric factors such as temperature, relative humidity, wind speed, boundary layer height, total cloud cover, and total precipitation, alongside air quality indicators such as PM2.5 and the Air Quality Index (AQI). These parameters are analysed at two vertical levels - 1000 hPa (surface level) and 875 hPa (free troposphere). The results show a substantial drop in total precipitation from a baseline of ~5000 mm to just 500 mm, with only partial recovery (~1300 mm) in 2021 for the same amount of cloud cover (80%-100%). The pre-monsoon showers disappeared completely in 2020 and 2021 due to the shift in precipitation levels. April 2020 also saw a 3°C temperature drop (from 32.5°C to 29.5°C), while May 2020 exhibited a slight increase due to enhanced solar radiation from reduced pollutant concentrations. PM₂.₅ levels dropped by 30 μg/m³, improving the Air Quality Index (AQI) from “Poor” (200-300) to “Moderate” (100-200) or “Satisfactory” (50-100), particularly in April–May 2020. These observations explain the influence of anthropogenic activities on atmospheric systems in urban settings and highlight the transient nature of the environmental gains achieved during the lockdown.