Contaminacion Atm

Global climate changes and air quality are closely coupled through many atmospheric meteorological, dynamic, chemical, and radiative processes. The two–way feedbacks between global climate change and urban/regional air quality requires the application of coupled climate and air quality models. The chemistry mechanism is a key component of these models because it must be applicable for a range ofatmospheric conditions and must include the reactions of importance for these conditions. Most operational atmospheric air quality models use condensed chemistry mechanisms because it is not feasible to include the entire set of atmospheric reactions and chemical species due to computational constraints. The condensation of the chemistry mechanism typically focuses on the representation in themechanism of reactive organic gases (ROGs), also referred to as volatile organic compounds (VOCs), by combining individual VOC species using either a “lumped molecule” or “lumped structure” approach. However, the reaction set is also reduced by excluding reactions that are not of interest based on the scales or regions for which the model is designed to be applied. For example, stratospheric models(e.g., Shibata et al., 2005) employ simplified parameterizations to represent tropospheric chemistry while tropospheric models use tropopause boundary conditions or boundary conditions from global chemical transport models (CTMs) and ignore stratospheric reactions that are not important in the troposphere. For models that are or will be applied over scales ranging from urban to global, it isnecessary to expand the reaction set to include all the important species and reactions of interest for a wide range of conditions. Models such as Stanford University’s Gas, Aerosol, TranspOrt, Radiation, General Circulation, Mesoscale, Ocean Model (GATOR–GCMOM) (Jacobson, 2001a; Jacobson, 2001b; Jacobson, 2004) and the Lawrence Livermore National Laboratory’s Integrated Massively Parallel AtmosphericChemical Transport model (IMPACT) (Rotman et al., 2004) are two examples of such models that incorporate the reaction set necessary to simulate the chemistry of the combined troposphere and stratosphere. The Weather Research and Forecasting/Chemistry (WRF/ Chem) (Grell et al., 2005) is a community model for the regional scale that is being adapted to simulate the range of scales from global throughurban (Zhang et al., 2009a; Zhang et al., 2009b). This Global–through–Urban version of WRF/Chem, referred to as GU–WRF/Chem, will provide a community tool with fully–coupled meteorology and air quality that can be used to study the interactions between climate and air quality at various scales and to support the development of emission control strategies with potential co–benefits for air qualitymanagement and climate mitigation. The latest release version of WRF/Chem (v3.2, as of April 2010) provides choices for several condensed gas–phase chemical mechanisms, including the second generation Regional Acid Deposition Model Mechanism (RADM2) (Stockwell et al., 1990), the Regional Atmospheric Chemistry Mechanism (RACM) (Stockwell et al., 1997), the Carbon Bond IV (CB–IV) mechanism (Gery etal., 1989) and the Carbon–Bond Mechanism version Z (CBM–Z) (Zaveri and Peters, 1999), a variant of CBM–IV. None of those mechanisms are suited for global or global–through–urban applications. The CB–IV mechanism, which uses the lumped structure approach, has been widely used in urban to regional air quality modeling systems for many years. The mechanism has been extensively updated in 2005(Yarwood et al., 2005). The updated mechanism, referred to as CB05, has now been implemented in recent versions of the Community Multiscale Air Quality model (CMAQ) (Sarwar et al., 2008) and the Comprehensive Air quality Model with extensions (CAMx), two of the most widely used urban to regional air quality modeling systems. CB05 has also been implemented into WRF/Chem (Huang et al., 2006; Pan et al.,...