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 O-3 anomaly and greater PM2.5 and NO2 reductions were found. The study showed PM10 (-65%) < NO2 (-53%) < PM2.5 (-52%) < O-3 (-15%) < CO (-11%) < SO2 (10%) in the Tibetan Lockdown 2022. The total gaseous oxidant (O-x = NO2 + O-3) 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, PM2.5, and PM2.5/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 PM2.5 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 PM2.5 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.