Evaluation of secondary organic aerosol formation in winter |
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| Institution: | 1. Department of Civil/Environmental Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, USA;2. Sonoma Technology, Inc., 5510 Skylane Boulevard, Suite 101, Santa Rosa, CA 95403, USA;3. Departments of Chemical Engineering, Engineering and Public Policy, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, USA;1. University of California, Riverside, Department of Chemical and Environmental Engineering, Riverside, CA, USA;2. College of Engineering – Center for Environmental Research and Technology (CE-CERT), Riverside, USA;1. Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA;2. SRA International, Washington, DC 20005, USA;3. NASA Langley Research Center, Hampton, VA 23681, USA;4. Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005, USA;5. Department of Civil and Environmental Engineering, Portland State University, OR 97021, USA |
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| Abstract: | Three different methods are used to predict secondary organic aerosol (SOA) concentrations in the San Joaquin Valley of California during the winter of 1995–1996 Integrated Monitoring Study, (IMS95)]. The first of these methods estimates SOA by using elemental carbon as a tracer of primary organic carbon. The second method relies on a Lagrangian trajectory model that simulates the formation, transport, and deposition of secondary organic aerosol. The model includes a recently developed gas–particle partitioning mechanism. Results from both methods are in good agreement with the chemical speciation of organic aerosol during IMS95 and suggest that most of the OC measured during IMS95 is of primary origin. Under suitable conditions (clear skies, low winds, low mixing heights) as much as 15–20 μg C m−3 of SOA can be produced, mainly due to oxidation of aromatics. The low mixing heights observed during the winter in the area allow accumulation of SOA precursors and the acceleration of SOA formation. Clouds and fog slow down the production of secondary compounds, reducing their concentrations by a factor of two or three from the above maximum levels. In addition, it appears that there is significant diurnal variation of SOA concentration. A strong dependence of SOA concentrations on temperature is observed, along with the existence of an optimal temperature for SOA formation. |
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