Regional CO pollution and export in China simulated by the high-resolution nested-grid GEOS-Chem model

Abstract

Abstract. An updated version of the nested-grid GEOSChem model is developed allowing for higher horizontal (0.5 • ×0.667 • ) resolution as compared to global models. CO transport over a heavily polluted region, the Beijing-TianjinHebei (BTH) city cluster in China, and the pattern of outflow from East China in summertime are investigated. Comparison of the nested-grid with global models indicates that the fine-resolution nested-grid model is capable of resolving individual cities with high associated emission intensities. The nested-grid model indicates the presence of a high CO column density over the Sichuan Basin in summer, attributable to the low-level stationary vortex associated with the Basin's topographical features. The nested-grid model provides good agreement also with measurements from a suburban monitoring site in Beijing during summer 2005. Tagged CO simulation results suggest that regional emissions make significant contributions to elevated CO levels over Beijing on polluted days and that the southeastward moving cyclones bringing northwest winds to Beijing are the key meteorological mechanisms responsible for dispersion of pollution over Beijing in summer. Overall CO fluxes to the NW Pacific from Asia are found to decrease by a factor of 3-4 from spring to summer. Much of the seasonal change is driven by decreasing fluxes from India and Southeast Asia in summer, while fluxes from East China are only 30% lower in summer than in spring. Compared to spring, summertime outflow from Chinese source regions is strongest at higher latitudes (north of 35 • N). The deeper convection in summer transporting CO to higher altitudes where export is more efficient is largely responsible for enhanced export in summer.

Top-down estimates of biomass burning emissions of black carbon in the Western United States

“…The 0.5 • × 0.667 • resolution generally provides better results (compared with the observations) than the 2 • × 2.5 • resolution does. This is expected because the finer resolution allows for better resolved topography, meteorological fields, transport and emissions, and therefore provides better agreement with observations, as shown in previous modeling studies (e.g., Zhang et al, 2012;Chen et al, 2009;Wang et al, 2004). The surface BC simulations at 0.5 • × 0.667 • with the a priori emissions show better agreement with the observations compared with those at 2 • × 2.5 • , as evident in both a lower (by 44 % on average, Fig.…”

“…Wang et al (2004) reported the first nested-grid GEOS-Chem simulations of carbon monoxide over North America. Chen et al (2009) provided a detailed description of the one-way nesting in the model.…”

Persistent sensitivity of Asian aerosol to emissions of nitrogen oxides

“…The GEOS-Chem model is driven by assimilated meteorological data from the Goddard Earth Observation System (GEOS-5) of the NASA Global Modeling and Assimilation Office (GMAO) for the year 2006 with a temporal resolution of 6 h (3 h for surface variables and mixing depths). The nested version of GEOS-Chem for Asia (70 E-150 E, 11 S-55 N) uses the native resolution of GEOS-5 meteorological fields at 0.5 Â 0.67 [Chen et al, 2009]. The lowest model layer thickness is~130 m. A global simulation at 2 Â 2.5 spatial resolution is used to provide the boundary conditions every 3 h for the nested domain.…”

Regional data assimilation of multi-spectral MOPITT observations of CO over North America

“…Wang et al, 2004;Chen et al, 2009) and the MOPITT surface-level retrievals to better quantify North American emissions of CO. We focus on the period June 2004 to May 2005 for consistency with and Kopacz et al (2010). As mentioned above, regional inversion analyses are sensitive to the lateral boundary conditions, but use of global models to provide these boundary conditions is problematic if there are biases in transport and the chemistry in the models.…”

“…The nested capability was first implemented in GEOSChem by Wang et al (2004) for the GEOS-3 version of the meteorological fields. The model was then updated by Chen et al (2009) to support the GEOS-5 meteorological fields, with 0.5 • × 0.667 • resolution, which are used here. In the nested simulation the boundary conditions are based on fields archived from a global simulation (at 4 • × 5 • or 2 • × 2.5 • ) with a 3-hour temporal resolution, which are used to rewrite the tracer concentrations in a buffer zone around the nested domain before every transport step.…”