The journal, Atmospheric Chemistry and Physics, just published results of a recent experiment examining two stratosphere-to-troposphere (STT) events observed over California. NOAA/NESDIS researchers at the Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin-Madison, are collaborating with NASA scientists, university researchers and air quality and public health scientists to analyze airborne and in situ measurements of ozone and other trace gases that accompany STT events. STT events are of concern because the ozone may increase to dangerous levels, triggering public health warnings.
Ozone (O3, ppbv) and wind vectors (black, upper left) and Potential Vorticity (PVU) and wind vectors (black, upper right) maps at 4km altitude with ozone (O3, ppbv, lower left) and Potential Vorticity (PVU, lower right) cross sections at 120° W on 5 June 2012 at 1800 UTC from the RAQMS analyses. The NASA aircraft flight track is shown in black. Note the tropopause fold indicated by the tongue of relatively strong PV and high O3 extending from the lower stratosphere into the mid-troposphere. The flight track and observations were taken in a region where PV is < 2 PVU (bottom right), indicating STT occurrence (i.e. stratospheric air was sampled after crossing the tropopause). This SST event has been shown to contribute to the high surface ozone observed at Thunder Basin, WY on 6 June 2012. Credit: Brad Pierce (NOAA/NESDIS).
Background: On June 6, 2012, a day after one of the California flights, State of Wyoming surface monitors recorded high levels of tropospheric ozone around Thunder Basin, Wyoming. Increased levels of tropospheric ozone are usually caused by anthropogenic sources such as smog, but on occasion a naturally occurring, downward transport of stratospheric air can push tropospheric ozone to unsafe levels. On June 6, Thunder Basin region ozone concentrations spiked at nearly 100 parts per billion (ppb), well above the 75 ppb public health standard established by the Environmental Protection Agency (EPA).
The researchers used the Real-time Air Quality Modeling System (RAQMS), a global forecast model that assimilates ozone observations from multiple satellite instruments, along with in situ airborne measurements from NASA, to facilitate data interpretation and determine the source of the high ozone. The experiment improved understanding of the transport of ozone from Pacific weather systems to Wyoming.
Using the evidence gathered by this team, the State of Wyoming Department of Environmental Quality filed a report with the EPA, documenting Thunder Basin ozone levels as an “exceptional event,” and the result of a natural occurrence; not pollution.
Significance: The just-published California study is an important continuation of research on methods to identify and interpret STTs. The studies have implications for air quality, policy, and public health decision makers. This work supports NOAA’s mission of “understanding and predicting changes in climate and weather and sharing that knowledge and information with others.”