Variations of air pollutant response to COVID-19 lockdown in cities of the Tibetan Plateau

Coronavirus Disease 2019 (COVID-19) accidentally appeared in Tibet on August 7, 2022, and broke the 920 consecutive epidemic-free days. The cities in Tibet completely kept lockdown to restrict the public to homes. It provided a valuable opportunity for understanding how variations of urban air pollutants responded to the COVID-19 lockdown in the special highland cities of the third polar. Compared with the global COVID-19 restrictions in 2020, a slightly negative O₃ anomaly and greater PM_2.5 and NO₂ reductions were found. The study showed PM₁₀ (−65%) < NO₂ (−53%) < PM_2.5 (−52%) < O₃ (−15%) < CO (−11%) < SO₂ (10%) in the Tibetan Lockdown 2022. The total gaseous oxidant (O_x = NO₂ + O₃) decreased 18% in the Tibetan Lockdown 2022, but showed a limited change in the Lockdown 2020. Moreover, the diurnal profiles of NO₂ and PM₁₀ disappeared and the diurnal profiles of O_x, PM_2.5, and PM_2.5/CO became weakened. Via the random forest model-based weather normalization technique, we obtained the decoupled meteorological effects 1.3 ± 0.6 times higher than the net emission reduction due to the Tibetan Lockdown 2022. Meanwhile, we found that the deweathered PM_2.5 was mainly from residential combustion emissions due to the weak industrialization in Tibet. Here we roughly estimated that vehicle-related sources can contribute about 28% and 29% to PM_2.5 and NO₂ in urban cities of Tibet respectively. For eco-vulnerability protection and sustainable development in Tibet, more attention should be paid to reducing the more intensive local pollutant emissions from vehicles and residential combustion of urban cities.