Evaluation of aerosol number concentrations in NorESM with improved nucleation parameterization

The Norwegian Earth System Model (NorESM) is evaluated against atmospheric observations of aerosol number concentrations. The model is extended to include an explicit mechanism for new particle formation and secondary organic aerosol (SOA) formation from biogenic precursors. Three nucleation mechanisms are included in NorESM: binary sulfuric acid, activation type, and organic nucleation. Ten model experiments are conducted to study the sensitivity of the simulated aerosol number concentrations to nucleation, SOA formation, black carbon size distribution and model meteorology. Simulated vertical profiles are evaluated against 12 flight campaigns. Comparison of monthly averaged aerosol number concentrations against 60 measurement sites reveals that the model with explicit nucleation and SOA scheme performs well in terms of correlation coefficient, R2 = 0.41 and a bias of −6 %. NorESM generally overestimates the amplitude of the seasonal cycle, possibly due to underestimated sinks or exaggerated sensitivity to biogenic precursors.