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Edith Gégo, P. Steven Porter, Alice Gilliland, and S. Trivikrama Rao

impact of any regulatory program ( Cox and Chu 1993 ; Flaum et al. 1996 ; Kuebler et al. 2001 ). Accordingly, the concentration changes we report here were obtained after moderating the influence of meteorological conditions on ambient ozone concentrations. Following Brankov et al. (1998) , we use back-trajectory analysis in an attempt to specifically assess the changes that occurred throughout the eastern United States following the reduction in emissions from sources in the ORV, the source

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Francis S. Binkowski, Saravanan Arunachalam, Zachariah Adelman, and Joseph P. Pinto


A prototype online photolysis module has been developed for the Community Multiscale Air Quality (CMAQ) modeling system. The module calculates actinic fluxes and photolysis rates (j values) at every vertical level in each of seven wavelength intervals from 291 to 850 nm, as well as the total surface irradiance and aerosol optical depth within each interval. The module incorporates updated opacity at each time step, based on changes in local ozone, nitrogen dioxide, and particle concentrations. The module is computationally efficient and requires less than 5% more central processing unit time than using the existing CMAQ “lookup” table method for calculating j values. The main focus of the work presented here is to describe the new online module as well as to highlight the differences between the effective cross sections from the lookup-table method currently being used and the updated effective cross sections from the new online approach. Comparisons of the vertical profiles for the photolysis rates for nitrogen dioxide (NO2) and ozone (O3) from the new online module with those using the effective cross sections from a standard CMAQ simulation show increases in the rates of both NO2 and O3 photolysis.

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