Factors Controlling Spring and Summer Time Aerosol Size Distributions in the Arctic: A Global Model Study.

A global size-segregated aerosol model is used together with aerosol size distribution measurements to study the observed spring to summer transition of aerosol properties in the Arctic. Previous studies have suggested that the shift from accumulation to Aitken mode dominated distribution is driven by decreasing particle surface area or increasing solar radiation flux that favour nucleation in the atmosphere. We find that binary nucleation mechanism, which forms new particles in free troposphere and is typically considered the main source of marine Aitken mode particles, cannot explain the high summer concentrations of ultrafine particles in the boundary layer. However, when a simple boundary layer nucleation mechanism is included into the model, a transition similar to observations is simulated for the spring months. Our simulations suggest that summer time DMS emissions play a role in the spring to summer transition of the aerosol distribution. The model runs also show that the formation of new particles is highly sensitive to the treatment of aerosol wet scavenging and other aerosol-cloud interaction mechanisms in the model. Keywords Arctic aerosol, new particle formation, global modelling [ABSTRACT FROM AUTHOR]