Phase-wise analysis of the COVID-19 lockdown impact on aerosol, radiation and trace gases and associated chemistry in a tropical rural environment

Phase-wise variations in different aerosol (BC, AOD, PM₁, PM_2.5 and PM₁₀), radiation (direct and diffused) and trace gases (NO, NO₂, CO, O₃, SO₂, CO₂ and CH₄) and their associated chemistry during the COVID-19 lockdown have been investigated over a tropical rural site Gadanki (13.5° N, 79.2° E), India. Unlike most of the other reported studies on COVID-19 lockdown, this study provides variations over a unique tropical rural environment located at a scientifically strategic location in the Southern Indian peninsula. Striking differences in the time series and diurnal variability have been observed in different phases of the lockdown. The levels of most species that are primarily emitted from anthropogenic activities reduced significantly during the lockdown which also impacted the levels and diurnal variability of secondary species like O₃. When compared with the same periods in 2019, short-lived trace gas species such as NO, NO₂, SO₂ which have direct anthropogenic emission influence have shown the reduction over 50%, whereas species like CO and O₃ which have direct as well as indirect impacts of anthropogenic emissions have shown reductions up to 10%. Long-lived species (CO₂ and CH₄) have shown negligible difference (<1%). BC and AOD have shown reductions over 20%. Particulate Matter (1, 2.5 and 10) reductions have been in the range of 40 to 50% when compared to the pre-lockdown period. The changes in shortwave downward radiation at the surface, diffuse component due to the scattering and diffuse fraction have been +2.2%, -4.1% and -2.4%, respectively, in comparison with 2019. In contrast with the studies over urban environments, air quality category over the rural environment remained same during the lockdown despite reduction in pollutants level. All the variations observed for different species and their associated chemistry provides an excellent demonstration of rural atmospheric chemistry and its intrinsic links with the precursor concentrations and dynamics.