Emissions for the Houston region were processed through EMS-HAP and annual average concentrations were calculated using the ISCST3 model. Emissions were processed with two methods: (1) all sources were modeled as 1 km grid cells, and (2) onroad mobile emissions were allocated to road segments. In method two, onroad mobile emissions not specifically allocated to road segments were modeled to 1 km grid cells. Other sources (major, area/other, and nonroad mobile) were modeled as in method one. After emission processing by EMS-HAP, sources were divided into rural and urban sources. ISCST3 was then run for each source type and concentrations added together at each receptor during postprocessing. ISCST3 was run for five pollutants: benzene, cadmium, chromium, formaldehyde, and lead. There were 711 receptors used in the model (700 census tract centroids and 11 monitors). For benzene and formaldehyde, ISCST3 was also run using the road segment emissions. Additionally, for benzene, ISCST3 was run in an area of high major/onroad emissions with receptors every 500m.