Simulating PM concentration during a winter episode in a subtropical valley: Sensitivity simulations and evaluation methods P.L. Livingstone a, * , K. Magliano a , K. Gu ¨ rer a , P.D. Allen a , K.M. Zhang c,1 , Q. Ying a, 2 , B.S. Jackson a , A. Kaduwela a, b , M. Kleeman d , L.F. Woodhouse a , K. Turkiewicz a , L.W. Horowitz e , K. Scott a , D. Johnson a , C. Taylor a , G. O’Brien a , J. DaMassa a , B.E. Croes a , F. Binkowski f , D. Byun g a Air Resources Board, California Environmental Protection Agency, Sacramento, CA 95812, USA b Department of Land, Air, and Water Resources, University of California, Davis, CA 95616, USA c Department of Mechanical and Aeronautical Engineering, University of California, Davis, CA 95616, USA d Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, USA e NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08540, USA f Department of Environmental Science and Engineering, University of North Carolina, Chapel Hill, NC 27599, USA g Earth and Atmospheric Sciences Department, University of Houston, Houston, TX 77204, USA article info Article history: Received 22 October 2008 Received in revised form 16 July 2009 Accepted 17 July 2009 Keywords: Aerosol Photochemical–microphysical transport model Gradient evaluation abstract We investigated a two-week episode with high PM concentrations in California Central Valley during the Christmas–New Year of 2000–2001 using a modeling system that consists of a computationally efficient, 3-D photochemical–microphysical transport model, a mesoscale meteorological model, emission models, and an evaluation package. One hundred simulations were conducted with fine resolutions and obser- vational constraints, to reproduce spatial and temporal features of observed PM concentrations and to understand the formation mechanism of the episode. Simulated PM concentrations consist of secondary inorganic components, mainly ammonium nitrate, and total carbon in areas with elevated concentrations in the accumulation mode, and consist of mainly dust and sea salt in the coarse mode. Simulated oxidants and nitrate were significantly elevated over the valley, and the latter showed much less amplitude than the former. Simulated PM concentrations were evaluated with observations systemati- cally with spatially and temporally paired method, a more restrictive multivariate method (NMFROC), and a more flexible ‘‘gradient evaluation’’ method. The paired evaluation shows that high correlation coefficient (R ¼ w0.8) and low fractional error (FE ¼ w0.1) could be achieved at stations with elevated 24-h concentration of PM in the accumulation mode in some simulations. The NMFROC method was used to extract useful information from seemingly failed simulations. A ‘‘gradient evaluation’’ method is introduced here to extract additional information from simulations. We found that emission reductions of NO x and AVOC showed similar effects on percentage basis in different areas, and both are more effective than reducing NH 3 for abating elevated concentrations of accumulation mode PM in California Central Valley during the winter episode. Published by Elsevier Ltd. 1. Introduction Numerical models are useful in many fields to help interpret observations and cast cautious predictions. In weather forecasting, they have improved the quality of life significantly. In climate science research, they have been used to explore the atmospheric response to anthropogenic perturbations. In environmental management, they have been used to study the origin of and anthropogenic contributions to air pollutant concentrations. Air Quality in California Central Valley has subjected to a number of intensive studies which involved observational data acquisition and analysis as well as predictive modeling (Waldman et al., 1982; Yamartino et al., 1989; Chow et al., 1992; Chang et al., 1997; Motallebi et al., 2003; Chu et al., 2004; Held et al., 2004; Herner et al., 2005; Kleeman et al., 2005; Wang et al., 2006; Watson and Roth, 2006; Zhang et al., 2006; Jakober et al., 2008; Kleeman et al., 2008a,b,c; Ying et al., 2008). For example, Chang et al. (1997) * Corresponding author. Tel.: þ1 916 327 8543; fax: þ1 916 323 1045. E-mail address: plivings@arb.ca.gov (P.L. Livingstone). 1 Present address: Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA. 2 Present address: Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA. Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Published by Elsevier Ltd. doi:10.1016/j.atmosenv.2009.07.033 Atmospheric Environment 43 (2009) 5971–5977