The global pandemic COVID-19 necessitated various responses throughout the world, including social distancing, use of mask, and complete lockdown. While these measures helped prevent the community spread of the virus, the resulting environmental benefits of lockdown remained mostly unnoticed. While many studies documented improvements in air quality index, very few have explored the reduction in black carbon (BC) aerosols and polycyclic aromatic hydrocarbons (PAHs) concentrations due to lockdown. In this study, we evaluated the changes in concentrations of BC, PAHs, and PM_2.5 before and during the lockdown period. Our results show that lockdown resulted in a significant reduction in concentrations of these pollutants. The average mass concentration of BC, PAHs, and PM_2.5 before the lockdown was 11.71 ± 3.33 μgm⁻³, 108.71 ± 27.77 ngm⁻³, and 147.65 ± 41.77 μgm⁻³, respectively. During the lockdown period, the concentration of BC, PAHs, and PM_2.5 was 2.46 ± 0.95 μgm⁻³, 23.19 ± 11.21 ngm⁻³, and 50.31 ± 11.95 μgm⁻³, respectively. The diagnostic ratio analysis for source apportionment showed changes in the emission sources before and during the lockdown. The primary sources of PAHs emissions before the lockdown were biomass, coal combustion, and vehicular traffic, while during the lockdown, PAHs emissions were primarily from the combustion of biomass and coal. Similarly, before the lockdown, the BC mass concentrations came from fossil-fuel and wood-burning, while during the lockdown period, most of the BC mass concentration came from wood-burning. Human health risk assessment demonstrated a significant reduction in risk due to inhalation of PAHs and BC-contaminated air.

全球大流行 COVID-19 需要在世界各地采取各种应对措施，包括保持社交距离、使用口罩和完全封锁。虽然这些措施有助于防止病毒在社区传播，但封锁所带来的环境效益大多未被注意到。虽然许多研究记录了空气质量指数的改善，但很少有人探索由于封锁而降低黑碳 (BC) 气溶胶和多环芳烃 (PAH) 浓度。在本研究中，我们评估了锁定期间和锁定期间BC、PAH 和 PM _{2.5浓度的变化。}我们的结果表明，封锁导致这些污染物的浓度显着降低。BC、PAHs 和 PM _{2.5的平均质量浓度}锁定前分别为 11.71 ± 3.33 μgm ^-3、108.71 ± 27.77 ngm ^-3和 147.65 ± 41.77 μgm ^-3。在封锁期间，BC、PAHs 和 PM _2.5的浓度分别为 2.46 ± 0.95 μgm ^-3、23.19 ± 11.21 ngm ^-3和 50.31 ± 11.95 μgm ^-3， 分别。源分配诊断比分析显示，在封锁之前和封锁期间排放源的变化。封城前多环芳烃排放的主要来源是生物质、燃煤和车辆交通，而封城期间，多环芳烃排放主要来自生物质和煤炭的燃烧。同样，在封锁之前，BC 质量浓度来自化石燃料和木材燃烧，而在封锁期间，大部分 BC 质量浓度来自木材燃烧。人类健康风险评估表明，由于吸入 PAHs 和 BC 污染的空气，风险显着降低。