Atmos. Chem. Phys. Discuss., 14, 2043-2085, 2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Chemistry of new particle growth in mixed urban and biogenic emissions – insights from CARES
A. Setyan1,*, C. Song2, M. Merkel3, W. B. Knighton4, T. B. Onasch5, M. R. Canagaratna5, D. R. Worsnop5,6, A. Wiedensohler3, J. E. Shilling2, and Q. Zhang1
1Department of Environmental Toxicology, 1 Shields Ave., University of California, Davis, CA 95616, USA
2Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richmond, WA 99352, USA
3Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
4Montana State University, Bozeman, MT 59717, USA
5Aerodyne Research Inc., Billerica, MA 01821, USA
6Department of Physics, University of Helsinki, 00014 Helsinki, Finland
*now at: Département Sciences de l'Atmosphère et Génie de l'Environnement, Ecole Nationale Supérieure des Mines de Douai, 59508 Douai Cedex, France

Abstract. Regional new particle formation and growth events (NPE) were observed on most days over the Sacramento and western Sierra Foothills area of California in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Simultaneous particle measurements at both the T0 (Sacramento, urban site) and the T1 (Cool, rural site located ~40 km northeast of Sacramento) sites of CARES indicate that the NPE usually occurred in the morning with the appearance of an ultrafine mode centered at ~15 nm (in mobility diameter, Dm, measured by a scanning mobility particle sizer operating in the range 10–858 nm) followed by the growth of this mode to ~50 nm in the afternoon. These events were generally associated with southwesterly winds bringing urban plumes from Sacramento to the T1 site. The growth rate was on average higher at T0 (7.1 ± 2.7 nm h−1) than at T1 (6.2 ± 2.5 nm h−1), likely due to stronger anthropogenic influences at T0. Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), we investigated the evolution of the size-resolved chemical composition of new particles at T1. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. New particles appear to be fully neutralized during growth, consistent with high NH3 concentration in the region. Nitrogen-containing organic ions (i.e., CHN+, CH4N+, C2H3N+, and C2H4N+) that are indicative of the presence of alkyl-amine species in submicrometer particles enhanced significantly during the NPE days, suggesting that amines might have played a role in these events. Our results also indicate that the bulk composition of the ultrafine mode organics during NPE was very similar to that of anthropogenically-influenced secondary organic aerosol (SOA) observed in transported urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO, NOx, and toluene) were significantly higher whereas the photo-oxidation products of biogenic VOC and the biogenically-influenced SOA also increased moderately during the NPE days compared to the non-event days. These results indicate that the frequently occurring NPE over the Sacramento and Sierra Nevada regions were mainly driven by urban plumes from Sacramento and that the interaction of regional biogenic emissions with the urban plumes has enhanced the new particle growth. This finding has important implication for quantifying the climate impacts of NPE on global scale.

Citation: Setyan, A., Song, C., Merkel, M., Knighton, W. B., Onasch, T. B., Canagaratna, M. R., Worsnop, D. R., Wiedensohler, A., Shilling, J. E., and Zhang, Q.: Chemistry of new particle growth in mixed urban and biogenic emissions – insights from CARES, Atmos. Chem. Phys. Discuss., 14, 2043-2085, doi:10.5194/acpd-14-2043-2014, 2014.
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