Extended Data Fig. 9: Observations of nighttime NOx (NO and NO2) and O3 levels in major cities around the globe. | Nature Geoscience

Extended Data Fig. 9: Observations of nighttime NOx (NO and NO2) and O3 levels in major cities around the globe.

From: Increasing contribution of nighttime nitrogen chemistry to wintertime haze formation in Beijing observed during COVID-19 lockdowns

Extended Data Fig. 9

The world map illustrates the global NOx emission in 2020. The corresponding location of the city is shown by an alphabet (a–m) on the map. The reported NO (cyan bar), NO2 (blue bar), and O3 (red bar) data are the average values between 10 p.m. and 4 a.m. (local time) during the winter. Relatively polluted (denoted by ‘P’) and clean (denoted by ‘C’) conditions are separated based on PM2.5 levels, or CO concentrations if PM2.5 concentration is not available. In cities with high pollution levels (that is, cities in China and India), ‘P’ and ‘C’ conditions are separated based on PM2.5 < 50 µg m−3 and PM2.5 > 150 µg m−3, respectively. In European and US cities, where PM2.5 barely exceeded 150 µg m−3, 25 and 75 quantiles of PM2.5 (or CO, when the PM2.5 is not available) are used to define the relatively polluted and clean conditions. Details of the measurement sites, durations, and data sources are provided in Table S2 in the Supplementary Information.

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