title: Comparison of regional and global land cover products and the implications for biogenic emission modeling.
abstract: Accurate estimates of biogenic emissions are required for air quality models that support the development of air quality management plans and attainment demonstrations. Land cover characterization is an essential driving input for most biogenic emissions models. This work contrasted the global Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product against a regional land cover product developed for the Texas Commissions on Environmental Quality (TCEQ) over four climate regions in eastern Texas, where biogenic emissions comprise a large fraction of the total inventory of volatile organic compounds (VOCs) and land cover is highly diverse. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) was utilized to investigate the influences of land cover characterization on modeled isoprene and monoterpene emissions through changes in the standard emission potential and emission activity factor, both separately and simultaneously. In Central Texas, forest coverage was significantly lower in the MODIS land cover product relative to the TCEQ data, which resulted in substantially lower estimates of isoprene and monoterpene emissions by as much as 90%. Differences in predicted isoprene and monoterpene emissions associated with variability in land cover characterization were primarily caused by differences in the standard emission potential, which is dependent on plant functional type. Photochemical modeling was conducted to investigate the effects of differences in estimated biogenic emissions associated with land cover characterization on predicted ozone concentrations using the Comprehensive Air Quality Model with Extensions (CAMx). Mean differences in maximum daily average 8-hour (MDA8) ozone concentrations were 2 to 6 ppb with maximum differences exceeding 20 ppb. Continued focus should be on reducing uncertainties in the representation of land cover through field validation.
  
  
  CONCLUSIONS
  Uncertainties in the estimation of biogenic emissions associated with the characterization of land cover in global and regional data products were examined in eastern Texas. Misclassification between trees and low-growing vegetation in central Texas resulted in substantial differences in isoprene and monoterpene emission estimates and predicted ground-level ozone concentrations. Results from this study indicate the importance of land cover validation at regional scales.
authors.affiliation: a Center for Energy and Environmental Resources , University of Texas at Austin , Austin , TX , USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Huang
authors.affiliation: a Center for Energy and Environmental Resources , University of Texas at Austin , Austin , TX , USA.
authors.forename: Elena
authors.initials: E
authors.lastname: McDonald-Buller
authors.affiliation: a Center for Energy and Environmental Resources , University of Texas at Austin , Austin , TX , USA.
authors.forename: Gary
authors.initials: G
authors.lastname: McGaughey
authors.affiliation: a Center for Energy and Environmental Resources , University of Texas at Austin , Austin , TX , USA.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kimura
authors.affiliation: a Center for Energy and Environmental Resources , University of Texas at Austin , Austin , TX , USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Allen
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis*; D004777:Environment; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D013781:Texas
chemical_list: D000393:Air Pollutants