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Ongoing EPA efforts to evaluate modeled NOy budgets
Citation:
Simon, H., B. Henderson, D. Luecken, K. Foley, B. Timin, A. Eyth, AND K. Baker. Ongoing EPA efforts to evaluate modeled NOy budgets. Atmospheric Chemical Mechanisms Conference 2018, Davis, CA, December 05 - 07, 2018.
Impact/Purpose:
In recent years, some researchers have proposed that EPA's mobile source emissions are too high by about 30-70%, based on comparisons of ambient concentrations to modeled or inventory values. In this presentation, we show that this type of comparison is not straightforward. Other factors, including measurement uncertainties, potential errors in time/space pairing, meteorological uncertainties and chemistry condensations may impact these comparisons. Ongoing, collaborative work at EPA and with other Federal Agencies is continuing to further identify the role and magnitude of these different uncertainties.
Description:
This presentation examines the potential factors which might influence the overprediction of NOy by air quality models. Determining if there is a problem with an individual piece of this system is not straightforward, and we need to look holistically at all the processes that may impact the comparisons of model predictions and measurements. We have conducted a range of studies to isolate impact of different pieces of the system on model bias and have found evidence that emissions, modeled meteorology, and measurement uncertainty all play important roles in explaining our model biases. Different representations of the chemistry of NOx to NOz conversion also plays a role, and we find that different versions of the Carbon Bond mechanisms, used in CMAQ, are relatively unbiased and insensitive for NOx, but are biased and sensitive for NOz components. Continuing work is being done to improve this treatment of NOz chemistry.
