China and Taiwan: A Tale of Two COVID-19 Lockdown Measures and Air Quality Impacts

Abstract:

China placed a total lockdown measure to contain the novel coronavirus (2019-nCoV, referred to as COVID-19) that originated in Wuhan, Hubei province, in late January 2020. As the virus spread out of China across the world, many countries placed similar lockdown measures, either total or partial, to contain the spread of the virus. Taiwan did not implement any major lockdown measures. Instead, it contained the spread of the virus by aggressively screening and limiting international travelers. Due to these disparate measures between China and Taiwan, the impact on the environment was also drastically different. Most countries had an unexpected benefit of clean air during the lockdown due to reduced urban/industrial emissions. Most of Asia in the winter time experiences smog due to emissions from vehicles, industry, and long-range transport. The long-range transport is generally from biomass burning aerosols released from agricultural land clearing or wildfires and in some instances dust storms. In 2020, during March and February, air quality in Hubei province became relatively pristine; surface PM2.5 (particles smaller than 2.5 µm in median diameter) measurements made at Chengdu station showed that highest concentration was 102 µg/m³ compared to 1000 µg/m³ in 2019. In contrast, Taiwan did not experience any substantial reductions in particle concentrations and air quality. February and March are also the months where there is no significant transport of pollution from mainland China to Taiwan. Satellite observations of aerosol optical depth (AOD) from Suomi NPP Visible Infrared Imaging Radiometer Suite (VIIRS) show the same behavior, mainly reduced levels of AOD in 2020 compared to climatology in Hubei province in China and no significant difference between 2020 and climatology in Taiwan. The Nitrogen Dioxide (NO₂), key precursor for ozone and aerosols, observed from Sentinel 5P Tropospheric Ozone Monitoring Instrument (TROPOMI) and Suomi NPP Ozone Mapping and Profiler Suite (OMPS) also show similar patterns as observed by AOD. This presentation will compare and contrast the satellite observations of NO₂ and AOD in February and March 2020 between China and Taiwan to illustrate how two regions with different lockdown measures experienced the impact differently.