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Summertime weekly cycles of observed and modeled NOx and O3 concentrations as a function of land use type and ozone production sensitivity over the Continental United States

Author(s): Y. Choi | H. Kim | D. Tong | P. Lee

Journal: Atmospheric Chemistry and Physics Discussions
ISSN 1680-7367

Volume: 12;
Issue: 1;
Start page: 1585;
Date: 2012;
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Simulation results from the Community Multiscale Air Quality (CMAQ) model version 4.7.1 over the Conterminous United States (CONUS) for August 2009 are analyzed to evaluate how satellite-derived O3 sensitivity regimes capture weekly cycles of the U.S. EPA's Air Quality System (AQS) observed ground-level concentrations of ozone (O3). AQS stations are classified according to a geographically-based land use designation or an O3-NOx-VOC chemical sensitivity regime. Land use designations are derived from the Advanced Very High Resolution Radiometer (AVHRR) global land cover characteristic data representing three features: urban regions, forest regions, and other regions. The O3 chemical regimes (NOx-saturated, mixed, and NOx-sensitive) are inferred from low to high values of photochemical indicators based on the ratio of the HCHO to NO2 column density from the Global Ozone Monitoring Experiment 2 (GOME-2) and CMAQ. Both AQS-observed weekly cycles of NOx at measurement sites over AVHRR geographical regions and GOME-2 sensitivity regimes show high NOx on weekdays and low NOx on weekends. However, the AQS-observed O3 weekly cycle at sites over the GOME-2 NOx-saturated regime is noticeably different from that over the AVHRR urban region. Whereas the high weekend O3 anomaly is clearly shown at sites over the GOME-2 NOx-saturated regime in both AQS and CMAQ, the weekend effect is not captured at other sites over the AVHRR urban region. In addition, the weekend effect from AQS is more clearly discernible at sites above the GOME-2 NOx-saturated regime than at other sites above the CMAQ NOx-saturated regime. This study suggests that chemical classifications of GOME-2 chemical regime stations produces better results for weekly O3 cycles than either the CMAQ chemical or AVHRR geographical classifications.
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