Fig. 4. Model prediction and optimization of SOA from NO₃· oxidation across Europe.

A The seasonally averaged and vertically integrated column density of secondary organic aerosol from NO₃· oxidation (NO₃-SOA) across Europe predicted by the EURAD-IM model, and (B) their relative increase of vertically integrated column density for optimized emissions and aerosol yields (ΔNO₃-SOA/ NO₃-SOA). Panel C showed a comparison of the concentrations of secondary organic aerosol from nighttime oxidation in the observations (NO-OOA) and the EURAD-IM (NO₃-SOA) before and after optimization at around 50-m height at the JULIAC site (marked by the red circle in A and B).