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DYNAMIC EVALUATION OF REGIONAL AIR QUALITY MODELS: ASSESSING CHANGES TO O 3 STEMMING FROM CHANGES IN EMISSIONS AND METEOROLOGY
Citation:
GILLILAND, A., C. Hogrefe, R. W. PINDER, J. M. GODOWITCH, K. FOLEY, AND S.T. RAO. DYNAMIC EVALUATION OF REGIONAL AIR QUALITY MODELS: ASSESSING CHANGES TO O 3 STEMMING FROM CHANGES IN EMISSIONS AND METEOROLOGY. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 42(20):5110-5123, (2007).
Impact/Purpose:
The objective of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not truly validated. Static and Dynamic Operational, Diagnostic, and ultimately Probablistic evaluation methods are needed to both establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Regional-scale air quality models are used to estimate the response of air pollutants to potential emission control strategies as part of the decision-making process. Traditionally, the model predicted pollutant concentrations are evaluated for the “base case” to assess a model’s ability to reproduce past observations. Dynamic evaluation approaches, which evaluate a model’s ability to accurately simulate air quality changes from given changes in emissions, are critically important to regulatory applications. Here, we investigate approaches to evaluate the Community Multiscale Air Quality (CMAQ) model’s predicted ozone (O3) response to large NOx emission reductions associated with the NOx State Implementation Plan (SIP) Call and on road mobile emissions. This case has the advantages that emission changes associated with the NOx SIP Call can be well characterized and substantial changes are observed in O3 levels. To consider the modeled response to emission changes in light of the strong meteorological influences on O3, two time periods after the NOx SIP Call are included with very different meteorological conditions. The sensitivity to chemical mechanisms is also considered by including simulations with the CB4, SAPRC, and CB05 chemical mechanisms. The evaluation results suggest that the air quality model predictions underestimate the O3 reductions observed after the NOx SIP Call was implemented. While the emission estimate uncertainties may also be a factor, the results suggest that the contribution of long-range transport of O3 and precursors is underpredicted, especially when using the CB4 chemical mechanism. Further investigation of the chemical mechanisms’ ability to characterize tropospheric chemistry aloft is recommended. Results based on the most recent CMAQ version 4.6 with CB05 and updated emission inventories show incremental improvements to the modeled O3 response to NOx emission reductions.