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Springtime high surface ozone events over the western United States: Quantifying the role of stratospheric intrusions

January 21st, 2013

Key Findings

  • Stratospheric intrusions can episodically increase surface ozone by 20-40 ppb
  • Stratospheric impacts may confound efforts to attain ozone air quality standards
  • Global high-res model, satellite and in situ observations yield process insights

Meiyun Lin, Arlene M. Fiore, Owen R. Cooper, Larry W. Horowitz, Andrew O. Langford, Hiram Levy II, Bryan J. Johnson, Vaishali Naik, Samuel J. Oltmans, Christoph J. Senff. Journal: Journal of Geophysical Research. DOI:10.1029/2012JD018151


Stratosphere-to-troposphere transport of ozone is a common occurrence at mid- and high latitudes, but its influence on tropospheric ozone levels remains a long-standing question, despite decades of research. GFDL scientists and colleagues analyzed balloon soundings, lidar, surface and satellite measurements using GFDL’s new global high-resolution chemistry-climate model, to look at the extent to which naturally occurring stratospheric ozone intrusions reach the surface and affect air quality.

The team found that stratospheric ozone intrusions can episodically increase ground-level ozone by 20-40 ppb in parts of the western United States and directly lead to episodes of high-ozone in excess of EPA’s health-based limit (75 ppb). Evidence is found for 13 such events from April to June 2010, in notable contrast to prior work concluding that stratospheric influence in surface air is rare.

These estimates are up to 2-3 times greater than previously reported. The findings imply that naturally occurring stratospheric intrusions may pose a challenge for springtime ozone over the U.S. Mountain West to stay below federal limits with domestic emission controls.

A deep stratospheric ozone intrusion over the U.S. West Coast simulated in GFDL's global high-resolution chemistry-climate model (AM3).
A deep stratospheric ozone intrusion over the U.S. West Coast simulated in GFDL’s global high-resolution chemistry-climate model (AM3).