AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
The Effect of Model Spatial Resolution on Secondary Organic Aerosol Predictions
CHRIS WAINWRIGHT, Jeffrey Pierce, John Liggio, Kevin Strawbridge, Annie-Marie Macdonald, Richard Leaitch, Dalhousie University
Abstract Number: 92 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Between 20-90% of submicron aerosol mass throughout the continental boundary layer consists of secondary organic aerosol (SOA) mass. As such, the ability of chemical transport models to accurately reproduce the continental boundary layer greatly depends on their ability to predict SOA. Although there has been much recent effort to better describe SOA formation mechanisms in models, little attention has been paid to the effects of model spatial resolution on SOA predictions. The Whistler Aerosol and Cloud Study (WACS 2010), held between June 22nd and July 28th, 2010 and conducted at Whistler, BC, Canada provides a unique data set for testing simulated SOA predictions. The study consisted of intensive measurements of trace particles and gases in the atmosphere in a mountain valley. We test the ability of the global chemical transport model GEOS-chem (www.geos-chem.org) to predict the aerosol concentrations during this event and throughout the campaign. Simulations were performed using three different resolutions of the model: 4ºx5º, 2ºx2.5º and 0.5ºx0.667º. Predictions of organic aerosol concentrations at Whistler was greatly dependent on the resolution; the 4ºx5º version of the model significantly under predicts organic aerosol, while the 2ºx2.5º and 0.5ºx0.667º versions are much more closely correlated with measurements. In addition, we performed a comparison across North America between the 3 versions of the model. 0.5ºx0.667º simulations predicted 19% more SOA than 2ºx2.5º (time anddomain averaged) and 32% more than 4ºx5º. This increase in SOA with resolution is largely due to sub-grid variability of OA that leads to an increase in the partitioning of organic matter to the aerosol phase at higher resolutions. Aerosol lifetime and biogenic emissions have smaller, but non-negligible, changes with resolution. These results suggest that a portion of the traditional under-prediction of SOA by models may be due to coarse grid resolution.