A remote sensing based study of tropospheric ozone concentration amid COVID-19 lockdown over India using Sentinel-5P satellite data

Abstract

Amid the COVID-19 crisis, governments all over the world, and not excluding India, took to lockdown measures to deaccelerate the spread of the COVID-19 virus. This led to reduction of atmospheric pollution by declining the harmful Nitrogen and Sulphur Oxide (NO_X and SO_X) concentrations. However, one hand while the stratospheric Ozone (O₃) showed repair, the lower atmospheric O₃ concentrations demonstrated a remarkable increase during lockdown phase over India. This study aims to estimate the O₃ concentration during the Covid-19 lockdown over Pune city in India using freely available Sentinel-5P satellite datasets. The study makes use of the Ordinary Least Squares (OLS) and Random Forest (RF) regressions and compares the findings of the two algorithms based on estimation results. This study utilizes lower atmospheric O₃ concentration data from Sentinel-5P satellite of the European Space Agency (ESA) over the Indian mainland for a month of lockdown scenario (March 22^nd, 2020, to April 25^th, 2020) and shows the remarkable increase in concentration of O₃ gas as a pollutant. Despite the complete lockdown over India during this given time frame, there has been enough emission of O₃ precursors from other sources such as stubble burning. The estimates of tropospheric O₃ concentration for May 2020 for Pune city, using OLS and RF Regressions, have been validated with May 2020 data. The results have provided a RMSE of 1.05 and 1.23 with R²-statistics of 0.90 and 0.857 in training and testing phases for OLS and RMSE of 0.98 and MAE of 1.07 with R²-statistics of 0.968 and 0.895 in training and testing phases of the RF. The outcome of this study has proven that O₃ gas concentrations in the atmosphere depends upon various other causative factors apart from the precursor gases. The study also shows that the remotely sensed Sentinel-5P datasets, supplemented with ground-based sensor data can help in time and cost saving estimation of O₃ concentrations in the troposphere with considerable accuracy.

Keywords:

• Air pollution
• stubble burning
• atmospheric ozone
• remote sensing
• Sentinel-5P

Data availability statement

The relevant research data to this study would be made available by the corresponding author upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the European Space Agency for providing the Sentinel-5P datasets, Central Pollution Control Board (CPCB) India, and the Department of Civil Engineering, Indian Institute of Technology (IIT) Ropar.