Atmos. Chem. Phys. Discuss., 12, 15801-15836, 2012
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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.
Wintertime particulate pollution episodes in an urban valley of the Western US: a case study
L.-W. A. Chen1,2, J. G. Watson1,2, J. C. Chow1,2, M. C. Green1, D. Inouye3, and K. Dick3
1Division of Atmospheric Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA
2State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
3Washoe County District Health Department Air Quality Management Division, Reno, NV, USA

Abstract. This study investigates the causes of elevated PM2.5 concentrations and potential exceedences of the US National Ambient Air Quality Standards (NAAQS) in Truckee Meadows, Nevada, an urban valley of the Western US, during winter 2009/2010. Continuous PM2.5 mass and time-integrated chemical speciation data were acquired from a central valley monitoring site with meteorological measurements from nearby sites. All nine days with PM2.5>35 μg m−3 experienced 24-h average temperature inversion of 1.5–4.5 °C and snow cover of 8–18 cm. A stagnant atmospheric condition inhibited wind ventilation while highly reflective snow cover reduced daytime surface heating leading to persistent inversion. Elevated ammonium nitrate (NH4NO3) and water associated with it are most important to the PM2.5 exceedances during this unusually cold and snowy winter. An effective-variance chemical mass balance (EV-CMB) receptor model using locally-derived geological profiles and inorganic/organic markers identified secondary NH4NO3 (27–37%), residential wood combustion (RWC; 11–51%), and diesel engine exhausts (7–22%) as the major contributors to PM2.5. Paved road dust and de-icing materials were minor, but detectable contributors. RWC is a more important source than diesel for organic carbon (OC), but vice versa for elemental carbon (EC). A majority of secondary NH4NO3 is also associated with reactive nitrogen oxides (NOx) from RWC and diesel engines (including snow removal equipments). Findings from this study may apply to similar situations experienced by other urban valleys.

Citation: Chen, L.-W. A., Watson, J. G., Chow, J. C., Green, M. C., Inouye, D., and Dick, K.: Wintertime particulate pollution episodes in an urban valley of the Western US: a case study, Atmos. Chem. Phys. Discuss., 12, 15801-15836, doi:10.5194/acpd-12-15801-2012, 2012.
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