When the World Stopped: Insights into Aerosol masking effect and Black Carbon Source Shifts

Understanding the pathways through which aerosols are emitted, transformed, and removed in remote and climatically sensitive regions is essential for minimizing uncertainties in global climate modeling. This study capitalizes on the unique conditions created by the COVID-19 societal slowdown to explore anthropogenic aerosol behavior over South Asia. Observations during this period showed a marked decline in aerosol concentrations, resulting in a demasking effect comparable to nearly 75% of the radiative forcing induced by CO₂ in the region. Additionally, this reduction caused a ~7% increase in surface-reaching solar radiation and a ~0.4 K d⁻¹ decrease in atmospheric solar heating.

Black carbon (BC) aerosols were further analyzed using dual-isotope (Δ¹⁴C and δ¹³C) techniques at monitoring sites in the Maldives and Bangladesh. Findings revealed a significant decrease in fossil fuel-derived BC, dropping from 49% to 35%, while emissions from C₃ biomass burning rose from 31% to 55%. These changes reflect reduced fossil fuel usage alongside increased reliance on crop residue burning and biomass for domestic energy needs during the slowdown.

These findings highlight the complex interplay between human activities and natural processes in determining aerosol-climate interactions across South Asia. The rapid changes in emission patterns observed during societal disruptions underscore the potential for targeted policy interventions to mitigate climate impacts and reduce atmospheric pollution.