Emissions near coastal areas are subject to complex physical, dynamic, and chemical atmospheric processes that are influenced by characteristics of the earth's surface and complexities exist in resolving land-water interface. The resulting mesoscale circulation and the associated land-sea breeze affect the fate of emitted pollutants and their secondary chemical derivatives, such as ozone and fine particulate matter. Modeling the thermodynamics of the mesoscale circulation associated with the land-sea breeze must accurately account for the land-sea surface temperature gradient. In addition, capturing this mesoscale circulation and the associated air quality patterns and their profiles requires fine horizontal grid resolution near coastal areas that have high-emission sources.

We present and discuss results of a modeling study using a variable-grid air quality modeling system that retains the aspects of the mesoscale circulation in terms of surface temperature gradients and fine grid resolution. We developed a variable-grid resolution (VGR) air quality model using the Multiscale Air Quality Simulation Platform (Mathur et al., 2005), referred to as the MAQSIP-VGR, to simulate a high-pollution episode (during August 2000) in the Houston-Galveston area. Horizontal grids in the VGR model vary from 36 km at the outermost edges of the modeling domain, to 4 km at the innermost portions of the domain. The grid system is devoid of discrete boundaries across different resolutions and consequently alleviates many shortcomings of the commonly used nesting approach, in particular the propagation of numerical noise at the boundary of the nested domain. The Mesoscale Model (MM5), which is the meteorological driver of MAQSIP-VGR, utilizes derived satellite sea surface temperature and surface data assimilation to capture the mesoscale circulation associated the land-sea breeze. We analyze key meteorological and air quality parameters during the pollution episode. Noticeable is the effect of using the derived sea surface temperatures on the horizontal and vertical extent of the pollution pattern, and the increase in hourly ozone concentrations associated with changes in atmospheric boundary layer characteristics resulting from the enhanced mesoscale circulation in the lower troposphere.

References:

Mathur, R., U. Shankar, A.F. Hanna, et al., The Multi-scale Air Quality Simulation Platform (MAQSIP): Initial applications, and performance for tropospheric ozone and particulate matter, J. Geophys. Res., 110:D13308, http://dx.doi.org/10.1029/2004JD004918, 2005.