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Preprints
https://doi.org/10.5194/acp-2019-990
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-990
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Dec 2019

Submitted as: research article | 03 Dec 2019

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This preprint is currently under review for the journal ACP.

Characterizing sources of high surface ozone events in the southwestern U.S. with intensive field measurements and two global models

Li Zhang1,2, Meiyun Lin1,2, Andrew O. Langford3, Larry W. Horowitz2, Christoph J. Senff3,4, Elizabeth Klovenski5, Yuxuan Wang5, Raul J. Alvarez II3, Irina Petropavlovskikh3,4, Patrick Cullis3,4, Chance W. Sterling3,4,6, Jeff Peischl3,4, Thomas B. Ryerson3, Steven S. Brown3,7, Zachary C. J. Decker3,4,7, Guillaume Kirgis3,4, and Stephen Conley8 Li Zhang et al.
  • 1Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
  • 2NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 3NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 5Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
  • 6C&D Technologies Inc., Philadelphia, PA, USA
  • 7Department of Chemistry, University of Colorado, Boulder, CO, USA
  • 8Scientific Aviation Inc., Boulder, CO, USA

Abstract. The detection and attribution of high background ozone (O3) events in the southwestern U.S. is challenging but relevant to the effective implementation of the lowered National Ambient Air Quality Standard (NAAQS; 70 ppbv). Here we leverage intensive field measurements from the Fires, Asian, and Stratospheric TransportLas Vegas Ozone Study (FAST-LVOS) in MayJune 2017, alongside high-resolution simulations with two global models (GFDL-AM4 and GEOS-Chem), to pinpoint the sources of O3 during high-O3 events. We show stratospheric influence on four out of the ten events with daily maximum 8-hour average (MDA8) surface O3 above 65 ppbv in the greater Las Vegas region. While O3 produced from regional anthropogenic emissions dominates pollution in the Las Vegas Valley, stratospheric intrusions can mix with regional pollution to push surface O3 above 70 ppbv. GFDL-AM4 captures the key characteristics of deep stratospheric intrusions consistent with ozonesondes, lidar profiles, and co-located measurements of O3, CO, and water vapor at Angel Peak, whereas GEOS-Chem has difficulty simulating the observed features and underestimates observed O3 by ~ 20 ppbv at the surface. The two models also differ substantially during a wildfire event, with GEOS-Chem estimating ~ 15 ppbv greater O3, in better agreement with lidar observations. At the surface, the two models bracket the observed MDA8 O3 values during the wildfire event. Both models capture the large-scale transport of Asian pollution, but neither resolves some fine-scale pollution plumes, as evidenced from aerosol backscatter, aircraft, and satellite measurements. U.S. background O3 estimates from the two models differ by 5 ppbv on average and up to 15 ppbv episodically. Our multi-model approach tied closely to observational analysis yields process insights, suggesting that elevated background O3 may pose challenges to achieving a potentially lower NAAQS level (e.g., 65 ppbv) in the southwestern U.S.

Li Zhang et al.

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Li Zhang et al.

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Short summary
Measuring and quantifying the sources of elevated springtime ozone in the southwestern U.S. is challenging but relevant to the implications for control policy. Here we use intensive field measurements and two global models to study ozone sources in the region. We find that ozone from the stratosphere, wildfires, and Asia are important sources of high-ozone events in the region. Our analysis also helps understand the uncertainties in ozone simulations with individual models.
Measuring and quantifying the sources of elevated springtime ozone in the southwestern U.S. is...
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