The World Health Organization, which proclaimed the COVID-19 a pandemic in early March 2020, imposed a partial lockdown by the Government of India on 21 March 2020. The aim of this investigation was to measure the change in air pollutants, including particulate matter (PM_2.5 and PM₁₀) and gaseous pollutants (NO₂, CO and O₃) during COVID-19 lockdown (25th March to 14th April 2020) across four major polluted cities in North India. In all region, PM_2.5, PM₁₀, NO₂ and CO were significantly reduced while O₃ has been shown mixed variation with increased in Agra and decreased in all other stations during lockdown. PM_2.5 was reduced by ~20–50% and highly decreased in Noida. PM₁₀ was most significantly decreased by 49% in Delhi. NO₂ was reduced by ~10–70%, and high reduction was observed in Noida. Likewise, ~10–60% reduction was found in CO and most significantly decreased in Gurugram. However, an increased in O3 was observed in Agra by 98% while significantly reduced in other sites. Compared to the same timeframe in 2018–2019, PM_2.5 and PM₁₀ values for all sites were reduced by more than 40%.

世界卫生组织于 2020 年 3 月上旬宣布 COVID-19 为大流行病，并于 2020 年 3 月 21 日实施了印度政府的部分封锁。这项调查的目的是测量空气污染物的变化，包括颗粒物（印度北部四个主要污染城市在 COVID-19 封锁期间（2020 年 3 月 25 日至 4 月 14 日）PM _2.5和 PM ₁₀）和气态污染物（NO ₂、CO 和 O ₃）。在所有地区，PM _2.5、PM ₁₀、NO ₂和CO 均显着降低，而O ₃已显示出混合变化，在阿格拉增加，在锁定期间所有其他站点均减少。下午_2.5减少了约 20-50%，并且在诺伊达大幅减少。PM ₁₀在德里下降了 49%。NO ₂减少了约 10-70%，并且在诺伊达观察到了大量减少。同样，在 CO 中发现了约 10-60% 的减少，并且在 Gurugram 中减少了最显着。然而，在阿格拉观察到的 O3 增加了 98%，而在其他地点则显着减少。与 2018-2019 年同期相比，所有站点的PM _2.5和 PM ₁₀值降低了 40% 以上。