Systematic bias in evaluating chemical transport models with maximum daily 8-hour average (MDA8) surface ozone for air quality applications

  • Travis K
  • Jacob D
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Abstract

<p><strong>Abstract.</strong> Chemical transport models typically evaluate their simulation of surface ozone with observations of the maximum daily 8-hour average (MDA8) concentration, which is the standard air quality policy metric. This requires successful simulation of the surface ozone diurnal cycle including nighttime depletion, but models are generally biased high at night because of difficulty in resolving the stratified conditions near the surface. We quantify the problem with the GEOS-Chem model for the Southeast US during the NASA SEAC4RS aircraft campaign in August&amp;ndash;September 2013. The model is unbiased relative to the daytime mixed layer aircraft observations but has a +5&amp;thinsp;ppb bias relative to MDA8 surface ozone observations. The model also does not capture observed occurrences of <&amp;thinsp;20&amp;thinsp;ppb MDA8 surface ozone on rainy days. Restricting the evaluation to afternoon hours and dry days removes the bias. Better understanding of surface layer stratification and ozone depletion under nighttime and rainy conditions is needed. Resolving the timing of the day-night transition in atmospheric stability and its correlation with plant stomata closure is critical.</p>

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APA

Travis, K. R., & Jacob, D. J. (2019). Systematic bias in evaluating chemical transport models with maximum daily 8-hour average (MDA8) surface ozone for air quality applications. Geoscientific Model Development Discussions, 1–13. https://doi.org/10.5194/gmd-2019-78

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