Tuesday, 16 January 2007: 11:45 AM
A numerical study to understand impact of meteorological fields on Houston's high O3 problem using CMAQ/MM5
212A (Henry B. Gonzalez Convention Center)
The Houston-Galveston-Brazoria (HGB) area is known as the most severe ozone (O3) non-attainment region in the United States. Houston's high O3 concentration is primarily the product of the precursor volatile organic compound (VOC) emissions from biogenics and petrochemical industrial emission sources (e.g. the Ship Channel), and nitrogen oxides (NOx) emissions from mobile sources and power plants. Furthermore, specific meteorological conditions typical of the HGB, such as the land/sea breeze, have the ability to greatly enhance O3. In air quality modeling, the correct representation of the local wind transport and planetary boundary layer (PBL) information is especially important to understand the transport and diffusion of pollutants within the boundary layer. These processes are strongly dependent on the land surface characteristics. Improvement of the input of the initial land use representation is extremely important to characterize the local wind transport and mixing characteristics within the boundary layer. The goal of the present research is to understand the effects of meteorological fields such as mixing layer depth and wind transport on Houston's ambient O3 and its precursor concentrations. The meteorological modeling was performed using Fifth-generation Mesoscale Model (MM5), and air quality modeling was performed using Models-3/Community Multiscale Air Quality (CMAQ) modeling system. The simulation results demonstrate that, through improvements of the numerical model inputs such as the land use and land cover (LULC) data, the meteorological fields are well captured for simulating the HGB high O3 events. With favorable wind conditions at night and early morning, the O3 precursors will be transported from the Ship Channel emission sources towards the area with low mixing, trapping the pollutants in a confined shallow layer. There, a rapid development of O3 can occur as the sunlight intensifies in the morning and as the weak northerly synoptic flow is balanced by the developing sea breeze during midday resulting in a stagnant wind condition.