Atmos. Chem. Phys. Discuss., 7, 13077-13119, 2007
www.atmos-chem-phys-discuss.net/7/13077/2007/
doi:10.5194/acpd-7-13077-2007
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Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
VOC reactivity in central California: comparing an air quality model to ground-based measurements
A. L. Steiner1, R. C. Cohen2,3, R. A. Harley4, S. Tonse5, A. H. Goldstein6, D. B. Millet7, and G. W. Schade8
1Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor MI, USA
2Department of Chemistry, University of California Berkeley, Berkeley, CA, USA
3Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, CA, USA
4Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA, USA
5Lawrence Berkeley National Laboratories, Berkeley, CA, USA
6Department of Environmental Science, Policy and Management, University of California Berkeley, Berkeley, CA, USA
7Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
8Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA

Abstract. Volatile organic compound (VOC) reactivity in central California is examined using a photochemical air quality model (the Community Multiscale Air Quality model; CMAQ) and ground-based measurements to evaluate the contribution of VOC to photochemical activity. We classify VOC into four categories: anthropogenic, biogenic, aldehyde, and other oxygenated VOC. Anthropogenic and biogenic VOC consist of primary emissions, while aldehydes and other oxygenated VOC include both primary anthropogenic emissions and secondary products from primary VOC oxidation. To evaluate the model treatment of VOC chemistry, we compare measured and modeled OH and VOC reactivities using the following metrics: 1) cumulative distribution functions of NOx concentration and VOC reactivity (ROH,VOC), 2) the relationship between ROH,VOC and NOx, 3) total OH reactivity (ROH,total) and speciated contributions, and 4) the relationship between speciated ROH,VOC and NOx. We find that the model predicts ROH,total to within 25–40% at three sites representing urban (Sacramento), suburban (Granite Bay) and rural (Blodgett Forest) chemistry. However in the urban area of Fresno, the model under predicts NOx and VOC emissions by a factor of 2–3. At all locations the model is consistent with observations of the relative contributions of total VOC. In urban areas, anthropogenic and biogenic ROH,VOC are predicted fairly well over a range of NOx conditions. In suburban and rural locations, anthropogenic and other oxygenated ROH,VOC relationships are reproduced, but measured biogenic and aldehyde ROH,VOC are often poorly characterized by measurements, making evaluation of the model with available data unreliable. In central California, 30–50% of the modeled urban VOC reactivity is due to aldehydes and other oxygenated species, and the total oxygenated ROH,VOC is nearly equivalent to anthropogenic VOC reactivity. In rural vegetated regions, biogenic and aldehyde reactivity dominates. This indicates that more attention needs to be paid to the accuracy of models and measurements of both primary emissions of oxygenated VOC and secondary production of oxygenates, especially formaldehyde and other aldehydes, and that a more comprehensive set of oxygenated VOC measurements is required to include all of the important contributions to atmospheric reactivity.

Citation: Steiner, A. L., Cohen, R. C., Harley, R. A., Tonse, S., Goldstein, A. H., Millet, D. B., and Schade, G. W.: VOC reactivity in central California: comparing an air quality model to ground-based measurements, Atmos. Chem. Phys. Discuss., 7, 13077-13119, doi:10.5194/acpd-7-13077-2007, 2007.
 
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