Quantifying the Impact of COVID-19 Lockdown on Air Quality in Two Indian Cities

Indian cities have well known air quality problems, with air pollution related diseases being the third biggest cause of death - up to 1.2 million cases a year. Of the 30 most polluted cities in the world in 2019, 21 were in India. The sources and chemistry underlying air quality in Indian cities is not well understood. Therefore, quantifying the impact of the COVID-19 lockdown on air quality (PM_2.5 , NO_x, and O₃) may aid in our understanding.

Like many countries, India underwent a nationwide lockdown to mitigate the spread of COVID-19 and thus provides an opportunity to study the effect of reduced human activity, and hence local emissions, on air pollution. In the current work, we aimed to quantify the reduction in NOx, O₃ and PM_2.5 due to the lockdown in two contrasting cities in India, Delhi and Hyderabad. Delhi is the second largest city in India with one of the highest pollution rates in the country, partly as it lies on the Indo-Gangetic plain. Similarly, Hyderabad is the fourth largest city but located in the south, and therefore outside the regional pollution that affects much of northern India.

We used publicly available monitoring network data from selected urban background sites in these two cities, and observed notable decreases in NOx, O₃ and PM_2.5 after the implementation of lockdown. In contrast, at Hyderabad only a decrease in NOx was observed after lockdown. The reasons for these differences and the implication on for local sources will be explored.

To quantify the impact of lockdown on air quality, the effect of meteorology must be accounted for by applying a boosted regression model to predict the absolute change in air quality and the results from this model will be presented.