The nationwide lockdown in India to curb the spread of Coronavirus disease 2019 (COVID-19) led to colossal reduction in anthropogenic emissions. Here, we investigated the impact of lockdown on surface ozone (O₃) and nitrogen dioxide (NO₂) over a tropical coastal station – Thumba, Thiruvananthapuram (8.5°N, 76.9°E). Daytime as well as night-time NO₂ showed reduction by 0.8 (40%) and 2.3 (35%) ppbv, respectively during the lockdown period of 25–30 March 2020 as compared with the same period of previous 3 years. Unlike many urban locations, daytime surface O₃ is found to be dramatically reduced by 15 ppbv (36%) with O₃ production rate being lower by a factor of 3 during the lockdown. Interestingly, a feature of O₃-hump during the onset of land breeze typically observed during 1997–1998 has reappeared with magnitude of 5–10 ppbv. A photochemical box model, capturing this feature, revealed that significant O₃ sustained till onset of land breeze over the land due to weaker titration with NO_x during lockdown. It is suggested that the transport of this O₃ rich air with onset of land breeze led to the observed hump. Our measurements unravel a remarkable impact of the COVID-19 lockdown on the chemistry and dynamics of O₃ over this tropical coastal environment.

印度为遏制 2019 年冠状病毒病 (COVID-19) 的传播而在全国范围内实施封锁，导致人为排放量大幅减少。在这里，我们调查了封锁对热带海岸站 Thumba，Thumba, Thiruvananthapuram (8.5°N, 76.9°E) 的表面臭氧 (O ₃ ) 和二氧化氮 (NO ₂ ) 的影响。与前三年同期相比，在 2020 年 3 月 25 日至 30 日的封锁期间，白天和夜间的 NO _{2 分别}减少了 0.8（40%）和 2.3（35%）ppbv。与许多城市地区不同，发现白天表面 O ₃与 O ₃显着减少了 15 ppbv (36%)在锁定期间，生产率降低了 3 倍。有趣的是，在 1997-1998 年期间通常观察到的陆风爆发期间，O _{3 -}驼峰的特征以 5-10 ppbv 的震级重新出现。捕获此特征的光化学盒模型显示，由于锁定期间用 NO _x较弱的滴定，显着的 O ₃一直持续到陆地上的陆风开始。这表明这种富含O _{3 的}空气随着陆风开始的传输导致了观察到的驼峰。我们的测量揭示了 COVID-19 封锁对这个热带沿海环境中 O ₃的化学和动力学的显着影响。