Fig. 1.

Spatial distribution of average nitrogen dioxide concentration and spreadability of COVID-19. This map of China shows the spatial distribution of the average nitrogen dioxide concentration in 63 Chinese cities from January 1, 2020 to February 8, 2020. The zoomed-in view of Hubei Province compares the spatial trend of the average nitrogen dioxide concentration (gradient blue map, bottom left) with that of the basic reproductive number R₀ (gradient brown map, bottom right). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)