AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Impact of Multi-generational Aging of Secondary Organic Aerosol Species In Regional PM Simulations
SHANTANU JATHAR, Christopher Cappa, Michael Kleeman, University of California, Davis
Abstract Number: 542 Working Group: Urban Aerosols
Abstract Multi-generational oxidation of volatile organic compound reaction products can significantly alter the mass, chemical composition and properties of secondary organic aerosol (SOA). However, the current state-of-the-science multi-generational oxidation schemes used in 3D regional or global models consider functionalization reactions but do not consider fragmentation reactions and have not been constrained to experimental data. In this work, we used the Statistical Oxidation Model (SOM) of Cappa and Wilson (2012) constrained by experimental “smog” chamber data to evaluate the regional implications of multi-generational chemistry. SOM was implemented into the regional UCD/CIT air quality model and applied to air quality episodes in California and the eastern US. Results show that SOA mass concentrations predicted by the UCD/CIT-SOM model were very similar to those predicted by a traditional “two-product” model when both models used parameters that were derived from the same chamber data. Despite the similarity in total SOA mass, the SOM model predicted modest changes in the SOA composition where contributions from anthropogenic (alkane, aromatic) and sesquiterpene SOA increased while those from isoprene and monoterpene SOA decreased relative to the two-product model calculations. The SOA predicted by SOM had a much lower volatility than that predicted by the two-product model and was in better qualitative agreement with volatility measurements of ambient OA. On account of its lower-volatility, the SOA mass produced by SOM did not appear to be as strongly influenced by the inclusion of oligomerization reactions whereas the two-product model relies heavily on oligomerization to form low volatility SOA products. Finally, an unconstrained contemporary scheme to model multi-generational oxidation within the framework of a two-product model formed at least three times more SOA than the SOM during regional simulations. This finding suggests that regional models need to care reconsider the use of these “hybrid” multi-generational schemes in the future.