A series of Urban Airshed Model (UAM) simulations were performed using inputs derived from Regional Oxidant Model (ROM) data files. The gridded ROM results employed in the UAM simulations included concentrations for specifying initial and boundary conditions, wind fields, other meteorological and surface geophysical parameters, and biogenic emissions. Two approaches were applied to nest the 3-D UAM grid (a four and a five level scheme) inside the regional model grid framework. The model sensitivity study was conducted with the variation in a single gridded input parameter or method in order to assess the impact on ozone concentrations for different high ozone days during 1980 over a domain covering the greater New York metropolitan area. Differences in the domain peak ozone and maximum ozone concentration at individual grid cells from the sensitivity runs are compared to base case simulations for each day. Maximum ozone levels were examined for different wind fields, with/without surface land use for the dry deposition method, with/without biogenic emissions, and the number of UAM vertical levels and nesting approach for initial and boundary concentrations. The magnitudes of peak ozone concentration changes from several sensitivity simulations were found to be comparable to those obtained from previous model runs with emissions control strategy reductions for the greater New York City urban domain.