Improved air quality and associated mortalities in India under COVID-19 lockdown

Abstract

India enforced stringent lockdown measures on March 24, 2020 to mitigate the spread of the Severe Acute Respiratory Syndrome Coronovirus-2 (SARS-CoV-2). Here, we examined the impact of lockdown on the air quality index (AQI) [including ambient particulate matter (PM₁₀ and PM_2.5), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), and ammonia (NH₃)] and tropospheric NO₂ and O₃ densities through Sentinel-5 satellite data approximately 1 d post-lockdown and one month pre-lockdown and post-lockdown. Our findings revealed a marked reduction in the ambient AQI (estimated mean reduction of 17.75% and 20.70%, respectively), tropospheric NO₂ density, and land surface temperature (LST) during post-lockdown compared with the pre-lockdown period or corresponding months in 2019, except for a few sites with substantial coal mining and active power plants. We observed a modest increase in the O₃ density post-lockdown, thereby indicating improved tropospheric air quality. As a favorable outcome of the COVID-19 lockdown, road accident-related mortalities declined by 72-folds. Cities with poor air quality correlate with higher COVID-19 cases and deaths (r = 0.504 and r = 0.590 for NO₂; r = 0.744 and r = 0.435 for AQI). Conversely, low mortality was reported in cities with better air quality. These results show a correlation between the COVID-19 vulnerable regions and AQI hotspots, thereby suggesting that air pollution may exacerbate clinical manifestations of the disease. However, a prolonged lockdown may nullify the beneficial environmental outcomes by adversely affecting socioeconomic and health aspects.

Keywords: COVID-19; Ground AQI; India; Pandemic lockdown; Tropospheric pollutants.

Graphical abstract

Fig. 1

Study area. Spatial locations of Air Quality Index (AQI) ground monitoring stations in the different states of India.

Fig. 2

Datasets and methodology used for the study. Schematic depicting detailed data assimilation for ambient and tropospheric pollutants, PM-, HAP- and RA-attributed mortalities, and COVID-19 infections/mortalities.

Fig. 3

Improvement in air quality index (AQI) concentrations following the COVID-19 lockdown in India. Spatial variations in AQI a. one month pre-lockdown, b. 2 d before the Janata/People’s Curfew, c. 1 d post-lockdown, and d. one month post-lockdown. e. Histogram showing the percent change in mean AQI concentrations for March (1 d post-lockdown) and April (one month post-lockdown) relative to those in February (one month pre-lockdown). A similar analysis for the corresponding period in 2019 was also performed to compare the direct impact of the lockdown on air quality.

Fig. 4

Restoration of NO₂, O₃, and land surface temperature (LST) post-COVID-19 lockdown. Spatial distribution and deviations in tropospheric a–c. NO₂ and e–g. O₃ concentrations over India derived from Sentinel-5 satellite data for the indicated period. Histograms showing improvement in tropospheric d. NO₂ density and h. O₃ density (5 d mean) one month post-lockdown compared with one month pre-lockdown or immediately post-lockdown. For comparison, the tropospheric densities of NO₂ and O₃ are included for the same period in 2019. i–l. Spatial distribution of LST (°C) immediately after lockdown and one month post-lockdown compared with that in the corresponding period in 2019.

Fig. 5

Decline in AP-attributed mortalities during COVID-19 lockdown and correlation of AP with COVID-19 cases/mortalities. Statewide estimation of monthly mortalities attributed to a. COVID-19, b. particulate matter, c. household air pollution, and d. road accidents. Regions (labelled 1, 2, and 3) with the highest COVID-19 mortalities (as of May 5, 2020) are highlighted in panel a. e. Spatial distribution of NO₂ (tropospheric) and AQI in the COVID-19 vulnerable regions (highlighted in panel a). Histograms showing a comparison of f. COVID-19 cases, g. COVID-19 mortalities, h. ambient NO₂, and i. AQI in metropolitan cities with severe or low air quality (separated by a dotted red line). Regression analysis of COVID-19 cases and mortalities with j. and k. NO₂ (μg/m³) and l. and m. AQI, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)