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TAMPA BAY MODEL EVALUATION AND ASSESSMENT
The objective of this work is to apply state-of-the-art atmospheric models, estimating the atmospheric contributions to multimedia issues and evaluating the models' strengths and weaknesses. A sub-objective of this work is to test the new sea salt version of CMAQ against field data and make necessary improvements so that it is an evaluated tool for coastal ocean and coastal estuary studies. A sub-objective of this work also is to develop an understanding of the relative contribution of the different emissions sources to the atmospheric nitrogen deposition to Tampa Bay and quantify an estimate of the benefit of the utility NOx reductions that have recently occurred. This will inform State and local managers as to the main estimated sources of nitrogen deposition to Tampa Bay. A sub-objective also is to also clarify the importance of sea salt to estimates of nitrogen deposition to coastal systems.
A long term goal of multimedia environmental management is to achieve sustainable ecological resources. Progress towards this goal rests on a foundation of science-based methods and data integrated into predictive multimedia, multi-stressor open architecture modeling systems. The strategic pathway aim is to progress from addressing one stressor at a time to a comprehensive multimedia assessment capability for current and projected ecosystem health. The multimedia tasks in AMD address a number of issues that arise in multimedia modeling with an emphasis on interactions among the atmosphere and multiple other environmental media. While the watershed is a fundamental unit of ecosystem analysis, due primarily to its containment of the hydrologic cycle and related stresses, the relevant atmospheric scale of modeling and analysis for linking to watersheds is regional/continental in scope, encompassing multiple States and/or watersheds. The interaction between the atmosphere and the underlying surface is increasingly being recognized as an important factor in multimedia issues. Targeted development, evaluation and application of state-of-the-art, multi-pollutant atmospheric models of nitrogen and mercury to multimedia issues help determine how to further improve the one-atmosphere models and support ongoing ecological assessments. Software tools are needed to support linkage of models across media and specialized multimedia data analysis applications. This multimedia work helps to bring the results of air pollution control, that primarily stem from addressing human health effects, into the management purview for addressing multimedia or ecosystem problems. The multimedia tasks support Goal 4 (Healthy Communities and Ecosystems) and its Long-Term Goals ECO-3, Restoration - develop scientifically defensible methods to protect ecosystem conditions, and HG-3, Transport and fate - understand the transport and fate of mercury from release to the receptor.
Targeted development and evaluation of state-of-the-art atmospheric models of nitrogen deposition is important and necessary to make the atmospheric modeling results as scientifically defensible as feasible, given the current state of knowledge, and as applicable as possible to multimedia management issues. The targeted development is accomplished in coordination with the AMD CMAQ development tasks. Application of these new models to select regions with particular management issues helps identify and define multimedia modeling needs to keep the atmospheric model application in tune with them, helps determine how to further improve the models to better support ecological assessments and/or TMDL assessments, and helps define specialized needs for multimedia tool development in Task 20477.
Atmospheric deposition is extremely important to Tampa Bay's nitrogen loading. Direct deposition to Tampa Bay is central and is estimated to be second only to storm water runoff, but a portion of storm water runoff is due to atmospheric deposition (wet and dry). Tampa is an excellent example of a coastal bay where the existence of sea salt is a determining factor in the rate of local nitrogen dry deposition. Tampa Bay is unusual in that a majority of the oxidized nitrogen deposition to Tampa Bay is estimated to come from local sources (approximately 60%). Two of the largest utility emitters of NOx emissions in the country are located at the edge of Tampa Bay. They have, through a consent decree, agreed to reduce their NOx emissions by up to 95%. A science version of CMAQ, CMAQ-AIM incorporates sea salt. The Florida Department of Environmental Protection (FDEP) organized, with EPA/ORD help, the Bay Regional Air Chemistry Experiment (BRACE) field study that took place in Tampa during May 2002. One key objective of BRACE is to provide field data to evaluate CMAQ-AIM. The three major thrusts of the Tampa Bay Model Evaluation and Application task are: (1) to evaluate CMAQ-AIM against the BRACE May 2002 data and make any model refinements that may be required, (2) to assess the relative contributions from the different emissions sectors, particularly mobile sources and utilities, to the annual oxidized nitrogen deposition to Tampa Bay, and (3) to assess the change in annual deposition to Tampa Bay that could be attributed to the NOx emissions reductions by the two power plants on its shores. The Tampa Bay assessment will be conducted in concert with FDEP and the Tampa Bay Estuary Program.