Reduced anthropogenic activities during the COVID-19 pandemic caused significant reductions in ambient fine particulate matter (PM(2.5)), SO(2) and NO(x) concentrations across India. However, tropospheric O(3) concentrations spiked over many urban regions. Moreover, reductions in SO(2) and NO(x) (atmospheric cooling agents) emissions unmask heating exerted by warming forcers. Basing governmental guidelines, we model daily emissions reductions in CO(2) and short-lived climate forcers (SLCFs) during different lockdown periods using bottom-up regional emission inventory. The transport sector, with maximum level of closure, followed by power plants and industry reduced nearly −50% to −75% emissions of CO(2), primary PM(2.5), SO(2) and NO(x), while warming SLCFs (black carbon, CH(4), CO and non-methane VOCs) showed insignificant reduction from continuing activity in residential and agricultural sectors. Consequently, the analysis indicates that reduction in the emission ratio of NO(x) to NMVOC coincided spatially with observed increases in O(3), consistent with reduced uptake of O(3) from night-time NO(x) reactions. Also, similar reductions, occurring for longer timescales (say, a year), can potentially increase the annual warming rate over India from the positive regional temperature response, estimated using climate metric. Further, by linking ongoing policies to sectoral reductions during lockdown, this study shows that the relative pacing of implementation among policies is crucial to avoid counter-productive results. A key policy recommendation is introduction and improving efficacy of programs targeting reduction of NMVOC and warming SLCF emissions (shifts away from biomass cooking technologies, household electrification and curbing open burning of crop residues), must precede the strengthening of policies targeting NO(x) and SO(2) dominated sectors.
COVID-19 lockdown closures of emissions sources in India: Lessons for air quality and climate policy