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Tracking Continental Scale Background Ozone with CMAQ
Citation:
Liu, P., C. Hogrefe, R. Mathur, U. Nopmongcol, S. Roselle, AND T. Spero. Tracking Continental Scale Background Ozone with CMAQ. 2017 Annual CMAS Conference, Chapel Hill, NC, October 23 - 25, 2017.
Impact/Purpose:
This presentation will be given in the session “Global/Regional Modeling Applications”at the 16th CMAS conference. It contains a comparison of different numerical techniques for representing the fate of large-scale ozone background concentrations in regional-scale air quality model applications. In particular, this represents the first time that chemically reactive ozone tracers were implemented in CMAQ. Results indicate that accounting for the loss of ozone due to photolysis during transport within the modeling domain is important for quantifying the contribution of boundary conditions to simulated ground level ozone. In addition, a comparison of inert tracers from two different model highlights the important impacts different physical process representations can have on such contribution estimates. Finally, the results emphasize the need for performing detailed process-level analyses when interpreting results from model intercomparison studies.
Description:
As the National Ambient Air Quality Standards (NAAQS) for ozone become more stringent, there has been growing attention on characterizing the contributions and the uncertainties in ozone from outside the US to the ozone concentrations within the US. Modeling techniques readily available in CMAQ to estimate such contributions or to estimate sensitivity of ozone to boundary conditions include inert tracers, the Integrated Source Apportionment Method (ISAM), and the Decoupled Direct Method in 3 Dimensions (DDM-3D). The computational burden associated with applying these methods ranges from minimal in the case of inert tracer to significant in the case of ISAM and DDM-3D. In this study, we present the implementation of a chemically reactive tracer for ozone from boundary conditions in CMAQ and compare it against prior simulations using chemically inert tracers. The simulations and analyses are performed for the year 2010 and leverage prior analysis performed in the third phase of the Air Quality Model Evaluation International Initiative (AQMEII3) which intercompared chemically inert tracers from different models. Implementation of the reactive tracer has only moderate impacts on CMAQ run time. Simulations are performed for both a base case scenario and a scenario without North American emissions to quantify how the differences between the inert and reactive tracer approaches depend on the chemical environment. Results are discussed in terms of temporal and spatial variations and directions for future work.
