Scientists at the Commerce Department’s National Oceanic and Atmospheric Administration (NOAA) and their federal and academic colleagues have developed a new way to diagnose the origins of one of the major greenhouse gases in the atmosphere. The research, published in the April 9 issue of the journal Science, focuses on ozone in the uppermost part of the troposphere.

The troposphere is a region of the atmosphere that extends from the surface of the Earth to about 12 kilometers (about 7.5 miles). Ozone in the upper troposphere absorbs infrared (heat) radiation and thereby affects climate. After carbon dioxide and methane, it is the most potent of the greenhouse gases that are influenced by human activities.

Unlike most other greenhouse gases, significant sources of upper tropospheric ozone originate from above in the stratosphere—in addition to the troposphere. The stratosphere is an atmospheric region that extends from about 12 to 50 kilometers (about 30 miles) above the surface and that contains 90 percent of the atmosphere’s ozone. Authors of the paper developed a new method to diagnose how much of the ozone in the upper troposphere is from air that has been transported down from the stratosphere.

Scientists want to learn how much upper tropospheric “greenhouse” ozone comes from above and below, to better understand the role of ozone and atmospheric transport processes in climate. Until now, no experimental approach could reliably quantify stratospheric ozone in tropospheric air parcels.

Lead author Timothy Marcy, with NOAA’s Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, used a new technique that measures hydrogen chloride more accurately than previous instruments.

“The pieces fell in place when it became possible to measure hydrogen chloride and ozone in the same air samples. Together, they give us the key to diagnosing the stratospheric component of the ozone we measure in the upper troposphere.”

The authors showed that their technique could detect even small amounts of stratospheric ozone mixed into tropospheric air parcels.

The authors made their measurements in the upper troposphere and lower stratosphere during flights of a high-altitude research aircraft in the July 2002 NASA Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) field mission. They also used a computer model to simulate how the ozone and hydrogen chloride in the stratosphere travel downward into the upper troposphere.

The authors found that they could use measurements of atmospheric hydrochloric acid as a “marker” for the ozone that comes from the stratosphere, because the only significant source of hydrogen chlorine in the upper troposphere is the stratosphere. In research flights during CRYSTAL-FACE, the scientists measured both gases and used their relationship in the stratosphere to sort out the “stratospheric” part of the ozone that they saw in the upper troposphere.

“There is a lot of uncertainty about how much of the tropospheric ‘greenhouse’ ozone comes from the stratosphere, and this new technique gives us a much firmer grip on it. Ultimately it should enable climate models to give a more accurate picture of the factors that heat and cool the planet,” said David Fahey, of the NOAA Aeronomy Laboratory, one of the paper’s coauthors.

Scientists from the NOAA Aeronomy Laboratory in Boulder, Colo., and CIRES teamed up with colleagues from the Jet Propulsion Laboratory, the National Center for Atmospheric Research, the NASA Ames Research Center, Lawrence Livermore National Laboratory, and Harvard University in the study.

The Commerce Department's National Oceanic and Atmospheric Administration (NOAA) Office of Oceanic and Atmospheric Research is dedicated to enhancing economic security and the nation’s welfare through research to better understand atmospheric and climate variability and to manage wisely our nation's coastal and marine resources.

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