Articles | Volume 9, issue 6
Geosci. Model Dev., 9, 2143–2151, 2016
https://doi.org/10.5194/gmd-9-2143-2016
Geosci. Model Dev., 9, 2143–2151, 2016
https://doi.org/10.5194/gmd-9-2143-2016

Model description paper 10 Jun 2016

Model description paper | 10 Jun 2016

Development of aroCACM/MPMPO 1.0: a model to simulate secondary organic aerosol from aromatic precursors in regional models

Matthew L. Dawson1, Jialu Xu2,3, Robert J. Griffin2, and Donald Dabdub1 Matthew L. Dawson et al.
  • 1Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697, USA
  • 2Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA
  • 3ACS Engineering, 16225 Park Ten Place Suite 110, Houston, TX, 77084, USA

Abstract. The atmospheric oxidation of aromatic compounds is an important source of secondary organic aerosol (SOA) in urban areas. The oxidation of aromatics depends strongly on the levels of nitrogen oxides (NOx). However, details of the mechanisms by which oxidation occurs have only recently been elucidated. Xu et al. (2015) developed an updated version of the gas-phase Caltech Atmospheric Chemistry Mechanism (CACM) designed to simulate toluene and m-xylene oxidation in chamber experiments over a range of NOx conditions. The output from such a mechanism can be used in thermodynamic predictions of gas–particle partitioning leading to SOA. The current work reports the development of a model for SOA formation that combines the gas-phase mechanism of Xu et al. (2015) with an updated lumped SOA-partitioning scheme (Model to Predict the Multi-phase Partitioning of Organics, MPMPO) that allows partitioning to multiple aerosol phases and that is designed for use in larger-scale three-dimensional models. The resulting model is termed aroCACM/MPMPO 1.0. The model is integrated into the University of California, Irvine – California Institute of Technology (UCI-CIT) Airshed Model, which simulates the South Coast Air Basin (SoCAB) of California. Simulations using 2012 emissions indicate that “low-NOx” pathways to SOA formation from aromatic oxidation play an important role, even in regions that typically exhibit high-NOx concentrations.

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Short summary
The atmospheric oxidation of aromatic compounds is an important source of aerosol-forming species, and thus contributes to pollution in urban areas. However, details of the mechanisms by which oxidation occurs are only recently being elucidated. Here we report the incorporation of a newly developed mechanism for aromatic oxidation into the UCI-CIT regional air quality model. Results suggest an unexpected role for chemical pathways typically associated with cleaner environments.