AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Effect of Secondary Organic Aerosol Amount and Condensational Behavior on Global Aerosol Size Distributions
STEPHEN D'ANDREA, Dominick Spracklen, Ilona Riipinen, Jeffrey Pierce, Dalhousie University
Abstract Number: 726 Working Group: Aerosols, Clouds, and Climate
Abstract Recent research has shown that secondary organic aerosols (SOA) are major contributors to ultrafine particle growth to climatically relevant sizes, increasing global cloud condensation nuclei concentrations within the continental boundary layer (BL). While many global models contain only biogenic sources of SOA (emissions generally 10-30 Tg yr$^(-1)), recent studies have shown an additional source of SOA around 100 Tg yr$^(-1) is required to match measurements. Additionally, many models treat SOA solely as semivolatile which leads to condensation of SOA onto the aerosol mass distribution; recent closure studies with field measurements show that a significant fraction of SOA condenses to the aerosol surface area suggesting a very low volatility. We explore the significance of these two findings using GEOS-Chem-TOMAS global aerosol microphysics model. The additional SOA was added to the model globally by distributing the 100 Tg yr$^(-1) correlated with the global fraction of carbon monoxide within each grid box. The condensation of SOA was varied to condense via the aerosol mass distribution and the aerosol surface area. The percent change in particles of size D$_p > 80 nm (CN80) within the BL between the base simulation (10-30 Tg yr$^(-1)) and the additional SOA (100 Tg yr$^(-1)) both using the surface area condensation scheme yielded a global change of 28%, in regions with large CO emissions the increase in CN80 exceeds 100%. The percent change in CN80 within the BL between the surface area and mass distribution condensation schemes both without the additional SOA yielded a global change of 3% but exceeds 25% in biogenically active regions. Thus, the additional SOA as well as treating SOA as very low volatile cause a significant global increase in the number of climatically relevant sized particles and we must continue to refine our SOA treatments in aerosol microphysics models.