Fig. 2. Soil NO_x emission influences on surface ozone levels and estimated anthropogenic ozone contribution.

Panels a and b show the spatial distribution of a observed and b simulated mean MDA8 ozone at urban sites over the NCP in July 2017. Mean values ± standard deviation and their spatial correlation coefficients (r) in the 55 NCP cities categorized as key cities for air pollution monitoring (marked with black circles) are shown in the inset. Panels c, d show ozone contributions from domestic anthropogenic emissions, estimated as the simulated ozone difference with domestic anthropogenic sources turned on/off, in the presence/absence of soil NO_x emissions (Methods). The mean values ± standard deviation over the NCP grids are shown in the inset.