Effects of land use data on dry deposition in a regional photochemical model for eastern Texas

Land use data are among the inputs used to determine dry deposition velocit ies for photochemical grid models such as the Comprehensive Air Quality Mod el with extensions (CAMx) that is currently used for attainment demonstrati ons and air quality planning by the state of Texas. The sensitivity of dry deposition and O-3 mixing ratios to land use classification was investigate d by comparing predictions based on default U.S. Geological Survey (USGS) l and use data to predictions based on recently compiled land use data that w ere collected to improve biogenic emissions estimates. Dry deposition of O- 3 decreased throughout much of eastern Texas, especially in urban areas, wi th the new land use data. Predicted 1-hr averaged O-3 mixing ratios with th e new land use data were as much as 11 ppbv greater and 6 ppbv less than pr edictions based on USGS land use data during the late afternoon. In additio n, the area with peak O-3 mixing ratios in excess of 100 ppbv increased sig nificantly in urban areas when deposition velocities were calculated based on the new land use data. Finally, more detailed data on land use within ur ban areas resulted in peak changes in O-3 mixing ratios of similar to2 ppbv . These results indicate the importance of establishing accurate, internall y consistent land use data for photochemical modeling in urban areas in Tex as. They also indicate the need for field validation of deposition rates in areas experiencing changing land use patterns, such as during urban refore station programs or residential and commercial development.