To curb the 2nd wave of COVID-19 disease in April–May 2021, a night curfew followed by full lockdown was imposed over the National Capital Territory, Delhi. We have analyzed the observed variation in pollutants and meteorology, and role of local and transboundary emission sources during night-curfew and lockdown, as compared to pre-lockdown period and identical periods of 2020 lockdown as well as of 2018 and 2019. In 2021, concentration of pollutants (except O₃, SO₂, and toluene) declined by 4–16% during night-curfew as compared to the pre-lockdown period but these changes are not statistically significant. During lockdown in 2021, various pollutants decreased by 1–28% as compared to the night-curfew (except O₃ and PM₂.₅), but increased by 31–129% compared to the identical period of 2020 lockdown except O₃. Advection of pollutants from the region of moderate lockdown restrictions and an abrupt increase in crop-residue burning activity (120–587%) over Haryana and Punjab increased the air pollution levels over NCT during the lockdown period of 2021 as compared to 2020 in addition to a significant contribution of long-range transport. The increase in PM₂.₅ during the lockdown period of 2021 compared to 2020 might led to 5–29 additional premature mortalities.

为了遏制 2021 年 4 月至 5 月第二波 COVID-19 疫情，国家首都辖区德里实施夜间宵禁，随后全面封锁。与封锁前和 2020 年封锁期间以及 2018 年和 2019 年的同一时期相比，我们分析了夜间宵禁和封锁期间观察到的污染物和气象变化，以及本地和跨境排放源的作用。2021 年，与封锁前相比，宵禁期间污染物浓度（除 O₃、SO2 和甲苯外）下降了 4-16%，但这些变化在统计上并不显着。 2021年封城期间，各项污染物较宵禁期间下降1%~28%（除O₃和PM2.₅外），但较2020年同期封城期间除O₃外增加31%~129%。与 2020 年相比，来自适度封锁限制地区的污染物平流以及哈里亚纳邦和旁遮普邦农作物残渣燃烧活动的突然增加（120-587%），导致 2021 年封锁期间NCT 的空气污染水平较 2020 年有所增加。远程运输的重大贡献。与 2020 年相比，2021 年封锁期间 PM2.5 的增加可能会导致 5-29 人过早死亡。