Extended Data Fig. 4: Diurnal patterns of \(p{{\rm{NO}}}_{3}^{-}\) in different pollution scenarios.

Clean and polluted conditions are defined as PM2.5 < 50 μg m−3 and PM2.5 > 150 μg m−3, respectively. The concentration of \(p{{\rm{NO}}}_{3}^{-}\) is normalized to CO mixing ratio to eliminate the possible influence of air mass transport and fresh emission.