Sensitivity of Urban Photochemical Models to Upper Wind Measurements

The 1992 Atlanta Field Intensive of the Southern Oxidants Research Program on Ozone Non-Attainment (SORP -ONA) provided a unique data set of urban meteorological measurements. The data were used to investigate the sensitivity of photochemical model results to the spatial and temporal resolution of upper-air meteorological measurements. Root Mean Square Differences (RMSD) and average absolute deviations for winds and model calculated rm NO_ {y} and rm O_3 values were computed for a variety of measurement strategies which differed in the spatial and temporal resolution of the upper-air data. A Lagrangian particle dispersion model (LPDM) was used to study the movement of the plumes from the Atlanta urban core and an elevated power plant located northwest of Atlanta. Scenarios with different sets of wind measurements were performed. The results show that placement of upper-air measurements at or near the center of emissions density should be highest priority of field measurements campaigns. A prognostic model, the Regional Atmospheric Modeling System (RAMS), was used to generate the three dimensional winds to run the UAM. Results from the UAM runs also support the conclusion that upper-air measurements at or near the center of emissions density should be highest priority of field measurements campaigns. A number of Large Eddy Simulations (LES) were performed for urban forested and unforested areas with different soil moisture to examine the extent of the thermals that represent the height of the mixed layer. Results from the LES runs show that simulations with dry soil produce higher sensible heat flux and stronger thermals with a deeper mixed layer than simulations with moister soil. LES runs also showed that sensible heat fluxes, vertical motion, and mixing is weaker over forested areas compared to over urban areas. Three methods were used to calculate the height of the convective mixed layer. Differences of up to 200 m were found between the three methods.