COVID Lockdown Failed to Reduce Ambient PM2.5 in India Below Its National Standard

Abstract:

Nearly three-fourths of the Indian population is exposed to ambient PM_2.5 exposure exceeding its annual national ambient air quality standard (NAAQS) of 40 µg m^-3. Lockdown-related closures to address the COVID-19 pandemic provided an opportunity (i.e. a natural experiment) to consider how sectoral interventions might help clean up the air in India. Ground-based PM_2.5 measurements in India are confined to the urban centres, thereby ruling out any regional-scale assessments. Hence we used satellite-based PM_2.5 dataset at a 1-km resolution to examine the changes in PM_2.5 level over the entire country during the one-month of the pre-lockdown period and four phases of lockdown (during March 25-May 31, 2020) relative to the last five years (2015-2019). We also analyse wind and planetary boundary layer height data from ERA-5 and fire count data from VIIRS to understand the influence of meteorology and open biomass burning on the observed changes at a regional scale.

PM_2.5 concentration decreased from 87 µg m^-3 during the pre-lockdown period to 56 µg m^-3 during the lockdown compared to a decrease from 81 to 65 µg m^-3 during the same timeframe in the last five yeas. In the first phase of lockdown, PM_2.5 declined by 32% compared to 12% in the last five years; the additional 20% improvement can be attributed to the impact of reduced emissions during the lockdown. However, this initial improvement was not sustained in the second phase of lockdown due to a combined influence of meteorology and open biomass burning. Although the declined trend continues in the third phase, PM_2.5 increased to 55 µg m^-3 in the fourth phase when several relaxations were given conditionally. During the lockdown, emissions from industry, transport, construction and brick kilns were significantly reduced and the thermal power plants operated at a reduced capacity, while the household emissions continue unabated. Despite substantial emission reductions, we found that the regional ambient PM_2.5 concentrations were never below the Indian NAAQS consistently except in the high-altitude states. This analysis implies that unless the regional sources such as household emissions and seasonal sources such as open biomass burning are addressed, achieving NAAQS is practically difficult in India.