Urban air quality in India during the COVID lockdown: Learnings from Bengaluru and New Delhi

Abstract:

In the wake of COVID 19 pandemic, India imposed a four phased nationwide lockdown with varying levels of stringency from 25^th March to 31^st May 2020. During this period, there was a near-total shutdown of transportation, industries and brick kilns which are major contributors to the air pollution load in Indian cities. Based on data derived from real-time air quality monitoring networks and satellite observations, this study discusses the reductions in the air pollution levels between 25^th March and 31^st May 2020 in two Indian cities (Delhi and Bengaluru) with widely varying pollutant levels and sources. The concentrations of key air pollutants like NO₂, PM₁₀ and PM_2.5 showed reductions of 50% in both cities during the lockdown period compared to their levels during the corresponding period in 2019. While PM_2.5 levels reduced by about 50% during the lockdown in both cities, the PM_2.5 concentrations even in the city with lower concentrations (Bengaluru) experienced PM_2.5 levels significantly higher than the 24-hour standard during normal conditions. This indicates the need to expedite investments in public transport to promote public health and inclusive growth.

Besides, tropospheric ozone (O₃) which is a secondary pollutant showed only marginal reduction in concentrations despite the significant reduction in the levels of its precursor gases like Volatile Organic Compounds (VOC), CO, NO, and NO₂. This anomaly is further explored by looking at the role of chemical and local-transport process in the regional balance of NO, NO₂ and O₃ and their corresponding photo-stationary states. The divergence of Leighton ratio from unity both in 2019 and 2020 in these cities suggest that the peroxy radicals produced from the oxidation of VOC also play a vital role in the production and destruction of tropospheric O₃.