NASA Tropical Ozone Studies Yield Surprises

average amount of ozone produced from biomass, burning in South America, sub-equatorial Africa and Indonesia/Australia Elevated ozone levels over and downwind of biomass burning regions in the southern tropics, calculated by combining Aura satellite data with the GEOS-Chem atmospheric model. Image credit: NASA
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December 14, 2006

Two new NASA-funded studies of ozone in the tropics using NASA satellite data not previously available are giving scientists a fuller understanding of the processes driving ozone chemistry and its impacts on pollution and climate change.

Ozone pollution caused by burning of fossil fuels is a major health concern in Earth's Northern Hemisphere mid latitudes, including the United States. But for the more than two-thirds of Earth's population that lives in the tropics - the area bounded by the Tropic of Cancer on the north and Tropic of Capricorn on the south - ozone levels in Earth's lower atmosphere, called the troposphere, are also driven by other mechanisms, namely biomass burning (the burning of forests, grass lands, etc.).

In the first study, NASA and university researchers investigated the extent of biomass burning in the southern tropics and quantified its effects on ozone formation. Biomass burning is the driving form of pollution in these tropical areas. It adversely affects air quality and influences climate by producing carbon monoxide and nitrogen oxides, two pollutants that lead to the formation of ozone.

Until recently, scientists have had difficulty measuring how much biomass burning is occurring in this region, since much of it takes place in the world's developing countries. In addition, the complex interactions between chemistry, weather and natural sources of ozone make it difficult to understand how biomass burning and ozone formation are linked.

With the launch of new atmospheric monitoring satellites such as NASA's Aura in the past few years, scientists now have new ways to track different chemicals present in Earth's atmosphere. These data are giving researchers a more complete picture of the causes and effects of atmospheric pollution.

The scientists combined atmospheric models with actual measurements of ozone, carbon monoxide and nitrogen dioxide in Earth's lower atmosphere, collected from NASA and European Space Agency satellites during November 2004.

This combination technique led to a surprising result: the amount of biomass burning in sub-equatorial Africa and the Indonesia/Australia region was underestimated, by a factor of between two and three.

The new combination technique also enabled the researchers to link the observed biomass burning to ozone that was later formed over and downwind of these regions.

"Combining these new satellite data with atmospheric models will dramatically improve our understanding of the complex processes relating pollution sources to ozone throughout Earth's troposphere," said lead author Dr. Dylan Jones of the University of Toronto, Ontario, Canada.

"Biomass burning and ozone formation in this region are particularly sensitive to climate patterns such as El Nino," added co-author Dr. Kevin Bowman of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Using this approach, we will be able to monitor how changes in these patterns impact air quality and climate throughout the tropics."

In the second study, to be published soon in Geophysical Research Letters, NASA and university researchers investigated intraseasonal (30- to 90-day) variations of tropical total ozone -- the amount of ozone present in a column of Earth's atmosphere -- and whether they are connected to a climate pattern known as the Madden-Julian Oscillation.

The Madden-Julian Oscillation is a cyclical pattern of slow, eastward-moving waves of clouds, rainfall and large-scale atmospheric circulation anomalies that can strongly influence long-term weather patterns around the world. It's a 30-to-90-day cycle, and it spans nearly half of Earth's equator, primarily over the Indian Ocean and western Pacific.

Using NASA satellite data, the researchers found the total amount of ozone in the tropics varies significantly in association with the Madden-Julian Oscillation, with the strongest connection observed in the subtropics. These relatively short-term variations were found to be comparable to more well-known, longer time scale variations, such as El Nino or the solar cycle.

The subtropical high and low pressure systems generated by the Madden-Julian Oscillation in the upper troposphere were found to trigger upward and downward shifts of the tropopause (the top edge of the troposphere), which leads to variations in subtropical total ozone. In the high pressure systems that trail the oscillation's region of heavy rainfall, upward air motion draws up ozone-poor tropospheric air, decreasing the amount of subtropical total ozone. In the low pressure systems that lead the oscillation's region of heavy rainfall, downward air motion pushes down ozone-rich air from the stratosphere, increasing the amount of subtropical total ozone.

"This study demonstrates the potential for new global ozone measurements such as the Atmospheric Infrared Sounder to improve our understanding of ozone chemistry and its effects on climate change," said lead author Dr. Yuk Yung of the California Institute of Technology, Pasadena, Calif. "Further detailed data analyses of ozone from ozone measuring balloons, satellite instruments and models are needed to better understand the processes at work."

Study co-author Dr. Baijun Tian of JPL says this finding is significant because scientists already know that the beginning of Madden-Julian Oscillation cycles is potentially predictable two to four weeks in advance. "This implies that variations in total atmospheric ozone may also be predictable with similar lead times over much of the tropics," he said.

For the biomass burning study, Aura's Tropospheric Emission Spectrometer instrument contributed ozone and carbon monoxide measurements. Nitrogen dioxide readings were collected from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography instrument on the European Space Agency's Envisat spacecraft. Additional carbon monoxide readings were gathered by the Canadian Space Agency's Measurements of Pollution in the Troposphere instrument on NASA's Terra spacecraft.

For the Madden-Julian Oscillation study, data were obtained from NASA's Atmospheric Infrared Sounder on its Aqua spacecraft and its Total Ozone Mapping Spectrometer on the National Oceanic and Atmospheric Administration's Nimbus-7 spacecraft.

For more on Aura and the Tropospheric Emission Spectrometer: . For more on Aqua and the Atmospheric Infrared Sounder: . For more on Terra and Measurements of Pollution in the Troposphere: . For more on the Total Ozone Mapping Spectrometer: .

Media contact: Alan Buis/JPL


ozone anomaly on Earth map

Tropical total ozone anomalies (color shading) associated with equatorial Madden-Julian Oscillation. Image credit: NASA

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