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June 2001

MOPITT hits pay dirt, miles above ground

John Gille.

The most complete view to date of air pollution as it churns through the atmosphere, crossing continents and oceans, has been produced by MOPITT (Measurements of Pollution in the Troposphere). Aboard NASA's spacecraft Terra, the innovative instrument is allowing policy makers and scientists to identify the major sources of air pollution and closely track where the pollution goes all year round and anywhere on Earth.

Launched in December 1999, the MOPITT instrument was developed by scientists at the University of Toronto; an NCAR team led by John Gille (ACD) developed the software to retrieve and analyze the data. The first MOPITT data were released late last month at the American Geophysical Union spring meeting in Boston.

"With these new observations you clearly see that air pollution is much more than a local problem. It's a global issue," says John, MOPITT's lead U.S. investigator.

MOPITT is making the first long-term global observations of carbon monoxide (CO) as Terra circles Earth from pole to pole 16 times every day. The most dramatic features in the first set of MOPITT global observations from March to December 2000 are the immense clouds of CO from forest and grassland fires in Africa and South America. The plumes quickly travel across the Southern Hemisphere as far as Australia during the dry season.

Carbon monoxide at the 700-millibar level, roughly 2 miles (3.2 km) above ground, is shown here in MOPITT data averaged for October 2000. The maxima across South America and Africa are mainly due to biomass burning. (Illustration courtesy Jean- François Lamarque.)

John was surprised to discover a strong source of CO in Southeast Asia during April and May 2000. The plumes from this region move over the Pacific Ocean and reach North America, frequently at fairly high concentrations. While fires are the major contributor, he suspects that at times industrial sources may also contribute to these events.

Carbon monoxide is a byproduct of the incomplete burning of fossil fuels in cars, industry, and home heating and the burning of natural organic matter such as wood. MOPITT captured the emissions from forest fires across the western United States last summer as well as from the burning of fossil fuels for home heating and transportation, a major source of air pollution in the Northern Hemisphere winter.

Jean-François Lamarque. (Photo by Carlye Calvin.)

ACD's Jean-François Lamarque and Boris Khattatov have been working on data-assimilation techniques to blend the MOPITT measurements with MOZART (Model for Ozone and Related Chemical Tracers) in order to map a fully global picture of CO. "If a lot of observational data are available [as with MOPITT], then most of the information contained in these maps comes from the data, not the model. The model is simply a smart interpolator," says Jean- François.

Assimilating the CO data in MOZART makes it possible to constrain the model's distribution of other chemical species, such as ozone and the hydroxyl radical, that are related to CO through chemical reactions but cannot be directly detected from space. Also, the location and strength of CO sources can be inferred and the data applied to other pollutants, such as nitrogen oxides, produced by the same combustion processes.

Pinpointing the sources of airborne chemical species is an important role for MOPITT. Although it cannot distinguish between individual industrial sources in the same city, it can map different points of origin that cover a few hundred square miles. This is accurate enough to differentiate air pollution from a major metropolitan area, for example, from a major fire in a national forest. About half of the global emissions of CO are caused by human activities.

Hazardous in itself—at ground level, it's regulated by the EPA—carbon monoxide also produces ozone. MOPITT tracks CO in the atmosphere from 2 to 3 mi (3.2–6.4 km) above the surface, where it interacts with other gases. The resulting ozone can move up to altitudes where it can be blown rapidly for great distances, or it can move down to Earth's surface.

Terra is part of the Earth Observing System, a suite of spaceborne instruments and interdisciplinary research dedicated to improving understanding of global change. EOS is managed by NASA Goddard Space Flight Center.

On the Web:

MOPITT images and animations:

New NASA/CSA Monitor Provides Global Air Pollution View from Space
Visible Earth
MOPITT home page


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Last revised: Thu Jun 21 11:00:53 MDT 2001