AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Processes Controlling the Seasonal Cycle of Arctic Aerosol Number and Size
BETTY CROFT, Jeffrey R. Pierce, W. Richard Leaitch, Stephen D'Andrea, Randall V. Martin, Dalhousie University, Halifax, Canada
Abstract Number: 161 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Measurements at high Arctic sites show a strong seasonal cycle in aerosol number and size. The number of aerosols larger than 20 nm (N20) exhibits a maximum in late spring (dominant accumulation mode), and a second maximum in the summer (dominant Aitken mode). Seasonal mean aerosol effective diameter ranges from about 160 nm in summer to about 250 nm in winter. This study interprets these Arctic seasonal cycles with the GEOS-Chem-TOMAS model. We find improved agreement with in situ measurements (SMPS) of aerosol size at Alert, Nunavut, Canada and Zeppelin Mountain, Svalbard following model developments: 1) to increase the efficiency of wet scavenging in the Arctic summer and 2) to represent coagulation between interstitial aerosols and aerosols activated to form cloud droplets. We present Arctic regional-mean budgets for the processes controlling simulated aerosol number. Increased efficiency of wet removal during summer is shown to limit the number of larger aerosols (despite ongoing transport into the Arctic) and promotes new particle formation. We find an important role of interstitial coagulation in clouds, which limits the number of Aitken mode particles in non-summer seasons when cloud cover is persistent, and direct wet removal of these particles is inefficient. Implementation of this process in the model reduces the simulated Arctic-mean N20 by a factor of 2 in the non-summer months. We recommend that the key processes of aerosol wet removal, interstitial coagulation and new particle formation be carefully considered in size-resolved aerosol simulations of the Arctic.