AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Simulating Secondary Organic Aerosol in a Regional Air Quality Model Using the Statistical Oxidation Model: Assessing the Influence of Vapor Wall Losses
CHRISTOPHER CAPPA, Shantanu Jathar, John Seinfeld, Anthony Wexler, Michael Kleeman, University of California, Davis
Abstract Number: 529 Working Group: Urban Aerosols
Abstract Losses of organic vapors to chamber walls during secondary organic aerosol (SOA) formation experiments can potentially bias the observed SOA formation. Here, the influence of such vapor wall losses on ambient SOA concentrations and properties have been assessed in the UCD/CIT regional air quality model using the statistical oxidation model (SOM), which was explicitly parameterized using chamber observations both with and without accounting for vapor wall losses. Two scenarios were considered: a “low” and a “high” wall-loss scenario. Simulations were run for the southern California/south coast air basin (SoCAB) and the eastern US. Only SOA from traditional VOCs was considered. Accounting for vapor wall losses led to substantial increases in the simulated SOA concentrations in both domains, by factors of ~2-5 for the low scenario and ~5-10 for the high scenario. The magnitude of the increase scaled inversely with the absolute SOA concentration. In SoCAB, the simulated SOA fraction of total OA increased from ~0.2 (basecase) to ~0.5 (low) and to ~0.7 (high), and the high wall-loss scenario provides best agreement with observations. In the eastern US, the SOA fraction was large even in the base model simulations and nearly all OA was SOA for the low and high wall-loss scenarios. The simulated O:C atomic ratio for SOA and for total OA increased when vapor wall losses were accounted for, and the O:C for total OA for the high wall-loss scenarios were in good agreement with observations. Accounting for vapor wall losses has only a minor influence on simulated SOA volatility. These results overall demonstrate that vapor wall losses in chambers have the potential to have a large influence on simulated SOA concentrations in the atmosphere, and further suggest that accounting for such effects in models can help explain a number of different observations and model/measurement discrepancies.