Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
Department of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
Environ Int. 2021 Aug;153:106541. doi: 10.1016/j.envint.2021.106541. Epub 2021 Apr 9.
The Government of India (GOI) announced a nationwide lockdown starting 25th March 2020 to contain the spread of COVID-19, leading to an unprecedented decline in anthropogenic activities and, in turn, improvements in ambient air quality. This is the first study to focus on highly time-resolved chemical speciation and source apportionment of PM to assess the impact of the lockdown and subsequent relaxations on the sources of ambient PM in Delhi, India. The elemental, organic, and black carbon fractions of PM were measured at the IIT Delhi campus from February 2020 to May 2020. We report source apportionment results using positive matrix factorization (PMF) of organic and elemental fractions of PM during the different phases of the lockdown. The resolved sources such as vehicular emissions, domestic coal combustion, and semi-volatile oxygenated organic aerosol (SVOOA) were found to decrease by 96%, 95%, and 86%, respectively, during lockdown phase-1 as compared to pre-lockdown. An unforeseen rise in O concentrations with declining NO levels was observed, similar to other parts of the globe, leading to the low-volatility oxygenated organic aerosols (LVOOA) increasing to almost double the pre-lockdown concentrations during the last phase of the lockdown. The effect of the lockdown was found to be less pronounced on other resolved sources like secondary chloride, power plants, dust-related, hydrocarbon-like organic aerosols (HOA), and biomass burning related emissions, which were also swayed by the changing meteorological conditions during the four lockdown phases. The results presented in this study provide a basis for future emission control strategies, quantifying the extent to which constraining certain anthropogenic activities can ameliorate the ambient air. These results have direct relevance to not only Delhi but the entire Indo-Gangetic plain (IGP), citing similar geographical and meteorological conditions common to the region along with overlapping regional emission sources. SUMMARY OF MAIN FINDINGS: We identify sources like vehicular emissions, domestic coal combustion, and semi-volatile oxygenated organic aerosol (SVOOA) to be severely impacted by the lockdown, whereas ozone levels and, in turn, low-volatility oxygenated organic aerosols (LVOOA) rise by more than 95% compared to the pre-lockdown concentrations during the last phase of the lockdown. However, other sources resolved in this study, like secondary chloride, power plants, dust-related, hydrocarbon-like organic aerosols (HOA), and biomass burning related emissions, were mainly driven by the changes in the meteorological conditions rather than the lockdown.
印度政府于 2020 年 3 月 25 日宣布全国封锁，以遏制 COVID-19 的传播，这导致人为活动前所未有地减少，进而改善了环境空气质量。这是第一项专注于高度时间分辨的 PM 化学形态和源解析以评估封锁及其随后的放松对德里印度周围 PM 源影响的研究。从 2020 年 2 月到 2020 年 5 月，在德里 IIT 校园测量了 PM 的元素、有机和黑碳分数。我们报告了在封锁的不同阶段使用 PM 的有机和元素分数的正定矩阵因子分解（PMF）进行的源分配结果。与封锁前相比，在封锁阶段 1 期间，发现诸如车辆排放、国内煤炭燃烧和半挥发性含氧有机气溶胶（SVOOA）等已解析的来源分别减少了 96%、95%和 86%。与全球其他地区类似，观察到 O 浓度的意外上升，而 NO 水平下降，导致低挥发性含氧有机气溶胶（LVOOA）增加到接近封锁前浓度的两倍。在封锁的最后阶段，发现封锁对其他已解析来源的影响不那么明显，例如二次氯、发电站、与灰尘有关的、烃类有机气溶胶（HOA）和生物质燃烧相关的排放，这些来源也受到四个封锁阶段期间气象条件变化的影响。本研究结果为未来的排放控制策略提供了依据，量化了限制某些人为活动在改善环境方面的程度。这些结果不仅与德里有关，而且与整个印度-恒河平原（IGP）有关，因为该地区具有类似的地理和气象条件以及重叠的区域排放源。主要发现总结：我们发现，车辆排放、国内煤炭燃烧和半挥发性含氧有机气溶胶（SVOOA）等来源受到封锁的严重影响，而臭氧水平以及低挥发性含氧有机气溶胶（LVOOA）在封锁的最后阶段比封锁前的浓度上升了 95%以上。然而，在这项研究中解析的其他来源，如二次氯、发电站、与灰尘有关的、烃类有机气溶胶（HOA）和生物质燃烧相关的排放，主要是由气象条件的变化而不是封锁驱动的。
