Date of Award

Fall 2007

Project Type

Dissertation

Program or Major

Earth and Environmental Science

Degree Name

Doctor of Philosophy

First Advisor

Robert J Griffin

Abstract

Secondary organic aerosol (SOA) is formed generally by the oxidation of gas-phase volatile organic compounds (VOCs) to form semi- or non-volatile products that then undergo gas to particle partitioning. In this work, the Caltech Atmospheric Chemistry Mechanism (CACM) and the Model to Predict the Multi-phase Partitioning of Organics (MPMPO) were updated with detailed chemistry associated with three monoterpene species---alpha-pinene, beta-pinene, and d-limonene. The updated CACM and MPMPO modules were calibrated by ozone formation and SOA yield data for alpha-pinene, beta-pinene, and d-limonene from chamber experiments. Then, the updated CACM and MPMPO were incorporated into the Community Multi-scale Air Quality Model v4.4 (CMAQ). CMAQ with the updated CACM and MPMPO was applied to the eastern United States (US) for August 3-4, 2004. It was found that SOA formation for this domain was dominated by monoterpenes. CMAQ with CACM and MPMPO predicted similar SOA formation when compared to CMAQ with the CB-IV gas-phase mechanism and the SORGAM SOA module. However, responses of SOA predictions at Thompson Farm, New Hampshire to domain NO, emissions changes and temperature variations are different for CACM/MPMPO and CB-IV/SORGAM.

In addition, an aqueous-phase chemistry mechanism (AgChem) was developed to study the potential of SOA formation via irreversible cloud processing of organic compounds. AgChem considers irreversible organic reactions that lead mainly to the formation of carboxylic acids, which are usually less volatile than the corresponding aldehydes. AgChem was incorporated into CMAQ with CACM/MPMPO and applied to the eastern US for August 3-4, 2004. The CMAQ simulation indicates that the maximum contribution of SOA formation from irreversible reactions of organics in clouds is 0.28 mug/m3 for 24-hour average concentrations and 0.60 mug/m3 for one-hour average concentrations at certain locations. On average, domain-wide surface SOA predictions over the episode are increased by 8.6% when irreversible, in-cloud processing of organics is considered. For our modeling domain and episode, the increase of SOA predictions is due to the cloud processing of oxidation products from monoterpenes, while contribution from irreversible cloud processing of isoprene oxidation products is negligible.

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