This paper summarizes the methods and results of an application of the variable-grid Urban Airshed Model (UAM-V) for the Baton Rouge ozone nonattainment area that was designed to obtain a quantitative assessment of the potential for compliance with the National Ambient Air Quality Standard (NAAQS) for (1-hour) ozone for a future year of 2005. The modeled attainment demonstration submitted as part of the 1995 SIP indicated that the changes in emissions that were expected to occur between 1990 and 1999 would result in attainment of the NAAQS by the 1999 attainment date. However the observation-based design value for this year was 126 ppb (just above the value of 124 required by the NAAQS). Under EPA’s 1998 policy document “ Extension of Attainment Dates for Downwind Areas,” Baton Rouge was given additional time to demonstrate attainment of the 1-hour ozone standard.

Additional regional-scale modeling was conducted in support of the 1-hour ozone SIP extension. The additional modeling considered three recent, multi-day ozone episode periods and used state-of-the-science regional-scale meteorological (MM5) and photochemical modeling tools and techniques to develop an attainment strategy for a future year of 2005.

The future-year modeling exercises consisted of (1) the establishment of a baseline simulation for 2005, (2) a number of emission-reduction sensitivity simulations to estimate the amount of emissions reductions needed for modeled attainment, (3) evaluation of several control-strategy options and components (both individually and in various combinations), and (4) a final attainment-strategy simulation. The results of each simulation were analyzed and compared using a variety of metrics and graphical analysis products related to 1-hour ozone. The ACCESSä Database for Visualizing and Evaluating Strategies for Ozone Reduction (ADVISOR) was a key component in the evaluation and selection of an attainment strategy.

The final attainment strategy simulation incorporates additional emissions reductions associated with a variety of “real-world”, source-category or facility-specific control measures. Compared to the baseline inventory, NOx emissions for Grid D (the Baton Rouge subdomain) are lower by approximately 20 percent, and VOC emissions are lower by approximately 3 percent. The magnitude of the reduction varies by source category.

The attainment strategy effectively and significantly reduces maximum ozone concentration and 1-hour ozone exceedance exposure for all three simulation periods. Exceedance exposure relative to the 1-hour ozone NAAQS is reduced by 99 percent for the primary episode days.

This attainment demonstration for Baton Rouge follows the most recent EPA guidance for 1-hour ozone attainment demonstration, and incorporates elements from newer EPA guidance to support a finding of modeling attainment for a future year of 2005. The Baton Rouge attainment demonstration is based primarily on a review of the modeling results relative to deterministic attainment. Elements that comprise the weight-of-evidence include:

* Consideration of uncertainties associated with model performance.

* Use of the modeling results in a relative sense (as a predictor of changes in ozone rather than absolute ozone concentrations)

* Assessment of simulation results relative to 8-hour ozone.

* Analysis of observed and simulated ozone trends.