Researchers selected East Asia to study how air pollution changed during the COVID-19 outbreak. Prior to the outbreak, in February 2019:

• average AOD levels were recorded at 1.26 for the Beijing-Tianjin-Hebei area, 1.63 for Wuhan, 0.68 for Seoul, and 0.48 for Tokyo
• NO2 levels were recorded at 9.3E+15 molecules/cm2 for the Beijing-Tianjin-Hebei area, 1.5E+16 molecules/cm2 for Wuhan, 1.6E+16 molecules/cm2 for the Soul Metropolitan Area, and 9.8E+15 molecules/cm2 for the Tokyo Metropolitan Area
• Formaldehyde levels were recorded at 7.4E+15 molecules/cm2 for the Beijing-Tianjin-Hebei area, 7.3E+15 molecules/cm2 for Wuhan, 5.8E+15 molecules/cm2 for Soul, and 3.9E+15 molecules/cm2 for Tokyo
• SO2 levels were recorded at 1.3E+16 molecules/cm2 for the Beijing-Tianjin-Hebei area, 3.9E+15 molecules/cm2 for Wuhan, 8.2E+15 molecules/cm2 for Soul, and 2.7E+15 molecules/cm2 for Tokyo
• CO levels were recorded at 3.23E+18 molecules/cm2 for the Beijing-Tianjin-Hebei area, 3.51E+18 molecules/cm2 for Wuhan, 2.95E+18 molecules/cm2 for the Soul Metropolitan Area, and 2.51E+18 molecules/cm2 for the Tokyo Metropolitan Area
• O3 levels were recorded at 48.5 µg/m3 for East China, 47.3 µg/m3 for the Beijing-Tianjin-Hebei area, and 37.1 µg/m3 for Wuhan