Formation of Secondary Organic AerosolEPA Grant Number: R833749
Title: Formation of Secondary Organic Aerosol
Investigators: Seinfeld, John , Flagan, Richard
Current Investigators: Seinfeld, John
Institution: California Institute of Technology
EPA Project Officer: Chung, Serena
Project Period: October 1, 2007 through September 30, 2010 (Extended to September 30, 2011)
Project Amount: $600,000
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air
Formation of secondary organic aerosol (SOA) occurs during the atmospheric oxidation of certain volatile organic compounds (VOCs). The last few years have witnessed an explosive growth of new understanding concerning the formation of secondary organic aerosol. The most important findings include the demonstration of the aerosol-forming potential of isoprene, elucidation of the role of NOx in SOA formation, and discovery of the ubiquitous existence of particle-phase reactions. The overall goal of the research proposed here is twofold: (1) to further develop the experimental database of the SOA-forming potential of the important classes of atmospheric VOCs, including dependence on atmospheric conditions, such as NOx level; and (2) to develop state-of-the-science models for SOA formation based on the latest scientific understanding derived from the laboratory studies.
Laboratory chamber experiments will be carried out to evaluate the SOA-forming potential of unstudied classes of VOCs, including ones previously thought not to be able to produce SOA because of volatility considerations. In addition, classes of VOCs already established to form SOA, such as aromatics and terpenes, will be restudied to establish fully the NOx dependence of SOA formation and to determine the role of particle-phase reactions, including the effect of particle-phase acidity. Chamber variables that will be considered for each parent VOC system are: (1) oxidant (OH vs O3, as relevant); (2) NOx level; (3) presence or absence of seed aerosol (in the latter case, aerosol forms via nucleation); (4) seed aerosol acidity; and (5) relative humidity. Current models of SOA formation in atmospheric chemical transport models, most notably CMAQ, do not incorporate the latest understanding in gas-phase mechanisms leading to formation of SOA species or in the effect of particle-phase reactions on SOA formation. The entire modeling basis needs to be rethought in light of recent findings and in light of the possibility that a wider range of VOCs are involved in SOA formation than previously thought.
(1) Gas-phase chemistry. With the clear and profound effect of the VOC/NOx ratio on SOA formation, we will augment gas-phase VOC oxidation mechanisms in atmospheric models to account for the effect of NOx level on the mechanism of SOA formation; (2) Revision/addition of parent VOCs. Isoprene will be added to the suite of SOA-forming VOCs. Aromatic species SOA formation will be completely revised. Sesquiterpenes will be added to the suite of VOCs. Large alkanes will also be added as a category. Small molecules, such as acetylene, will be added based on experimental results; (3) Structure of the SOA model will be reconsidered; and (4) Particle-phase reactions will be added.