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Comparison of 18 years of modeled and observed day-of-week ozone patterns
Citation:
Simon, H., Keith Appel, K. Foley, B. Henderson, C. Hogrefe, S. Koplitz, Norman Possiel, G. Tonnesen, L. Valin, B. Wells, AND A. Whitehill. Comparison of 18 years of modeled and observed day-of-week ozone patterns. International Technical Meeting on Air Pollution Modeling and its Application, Chapel Hill, NC, May 22 - 26, 2023.
Impact/Purpose:
EPA’s Air QUAlity TimE Series Project (EQUATES; www.epa.gov/cmaq/EQUATES) uses the state-of-the-science emissions, meteorological, and air quality methods and models to provide a unified set of modeling data for 2002-2017 to support regulatory and policy analyses as well as health and ecological studies. Modeled datasets cover the Conterminous US at a 12km resolution and the northern hemisphere at a 108km resolution using the Community Multiscale Air Quality modeling system version 5.3.2 (CMAQv5.3.2; https://www.epa.gov/CMAQ). New hemispheric and North American emissions inventories were developed using, to the extent possible, consistent input data and methods across all years, including emissions from mobile, fire, and oil and gas sources. The new emissions datasets and CMAQ output have been made publicly available to support a wide variety of human health and ecological applications. For example, modeled deposition will be used by the National Atmospheric Deposition Program (NADP) Total Deposition Science Committee (TDEP) to estimate total sulfur and nitrogen deposition for use in critical loads and other ecological assessments. Model estimated trends will be used for dynamic and diagnostic evaluation of the CMAQ system to inform model development and build confidence in the use of the model for quantifying the impact of meteorological and emissions changes on air quality.
Description:
Past studies have leveraged distinct observed weekly patterns in emissions of two ozone precrsurs, volatile organic compounds (VOCs) and nitrogen oxides (NOX = NO + NO2), to better understand ozone chemistry. These studies evaluated day-of-week (DOW) patterns in ozone concentrations to characterize whether ozone formation in certain locations occurs in VOC-limited or NOX-limited chemical regimes. In this work, we leverage 18 years (2002-2019) of CMAQ data from EPA’s Air QUAlity TimE Series Project (EQUATES) in combination with measured data to evaluate the CMAQ’s ability to capture changes in ozone formation chemistry in nonattainment areas across the US. Statistically significant ozone DOW patterns are quantified using the Welsch t-test. Multi-year trends in DOW patterns were determined using Theil-Sen regression with the MannKendall test for significance. Overall, the model captures DOW ozone trends in many areas, with the model reproducing observed trends especially well in Milwaukee, Cincinnati, Louisville, Houston, San Antonio, Denver, Salt Lake City, Provo, Los Angeles, San Diego and San Francisco. The analysis shows that in the Eastern US, the CMAQ model appears to predict conditions that are more VOC-limited than suggested by the observations. In these locations, the model often shows a more substantial trend towards NOX-limited conditions than shown in the observations. In the Western US, the model predicts a slower transition to NOX-limited conditions than the observations in several nonattainment areas.