Life on earth depends on theatmosphere. It provides oxygen

for respiration, transports gasesaround the globe and protects lifefrom harmful ultraviolet radiation.With a human population of over 6billion, the quality of this life-sustaining envelope is vital to ourcontinued survival. The CanadianSpace Agency’s Measurements OfPollution In The Troposphere(MOPITT) instrument is designed tomonitor from space the health ofthis thin layer of atmosphere, andgive an early warning of unexpectedchanges.

Cover: Biomass burning—from bothhuman activities and natural causes—isa major source of pollution in thetroposphere.

M e a s u r e m e n t s O f P o l l u t i o n I n T h e T r o p o s p h e r e

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The Canadian Space Agency’s Measurements

of Pollution in The Troposphere (MOPITT)

instrument will fly aboard NASA’s Terra sat-

ellite and monitor the troposphere from

space, providing scientists with a greater

understanding of the atmosphere’s most

chemically complex and dynamic region.

While large metropolitan areas have long battled airquality issues, it is now apparent that rural areas arealso threatened by damage to crops and forests causedby atmospheric pollutants. Increasing populations andindustrial activities continue to erode air quality. In ad-dition, climate change can influence air quality, and inturn, climate is affected by changing atmosphericcompositions.

In order to understand complex relationships amongEarth systems, a combination of measurements andmodels must be applied. In weather forecasting, theglobal models currently used assume a relatively con-stant composition for most atmospheric constituents.

Although the accuracy of weather forecasting has in-creased significantly over the last twenty years withenhanced data collection and modeling methods, thenew challenge is to further enhance global climate andmeteorological models by gaining extensive knowl-edge of atmospheric composition.

For more than 30 years, remote sensing from space hasbeen a highly successful tool used to monitor andstudy the stratosphere. However, scientists’ under-standing of the troposphere is considerably lessevolved. Challenges arise due to the greater variabilityof the troposphere. Highly dynamic factors such asstorms, biomass burning, and lightning are all signifi-cant issues that contribute to the region’s complexity.

MOPITT

The impact of storms on the atmosphere and ocean,the burning of forests and lightning strikes are allsignificant issues affecting measurements of thetroposphere

Increases in population, size of cities, and industrialactivity all threaten to further erode air quality

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MOPITT

MOPITTThe Canadian Measurements Of Pollution In The Tro-posphere (MOPITT) instrument will be the firstinstrument to simultaneously monitor two important at-mospheric chemical species, carbon monoxide (CO) andmethane (CH4). MOPITT will fly on board NASA’snewest spacecraft, EOS Terra (formerly EOS AM-1),and collect data over the entire globe for at least fiveyears. Combined with concerted modeling efforts,MOPITT will help create the first global and long-termpicture of the composition of the lower atmosphere.

Clouds obscure part of the planet atall times

Simulation of two minutes of data collection over the Great Lakesregion, showing the 320 km scanning area on both sides of the space-craft track

Two-day simulation of MOPITT data for mid tropospheric CO in October(ignoring clouds)

There are currentlyfew measurement sets

of tropospheric chemicalcomponents. Because of

the strong connection be-tween atmospheric composition

and global air quality, attention is be-ing focused on understanding tropospheric

chemical processes. Partial ground-based data sets ex-ist, but because of the atmospheric region’s greatvariability, incomplete data sets offer little help forcomprehensive modeling studies. Only with space-based measurements can a spatially and temporallyextensive data set of tropospheric constituents be col-lected and evaluated.

MOPITT will divide the globe into approximately1,000,000 individual cells, or “pixels,” and make ameasurement over each one every four days. Eachpixel is about 22 kilometers square, small enough sothat emissions from individual cities can be measured.

MOPITT will make measurements of infrared radia-tion originating from the surface of the planet andisolate the energy being radiated from CO and CH4

molecules by using a technique called gas correlationspectroscopy. Because it measures infrared radiation,MOPITT will be able to collect data during the night

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Satellite

Atmosphere

TransmissionEmission

Surface Radiance(reflection + emission)

Earth

Sun

The Earth Observing SystemAs a major component of NASA’s Earth Science En-terprise, the Earth Observing System (EOS) is the firstof its kind designed to offer integrated measurementsof the Earth’s processes. While gathering a continuousstream of data over the next 18 years, EOS will enableresearch scientists to gain a better understanding ofhow our Earth works as an integrated system, and todetermine the effects of natural and human-inducedchanges on its environment.

MOPITT looks at emitted and reflected infrared radiation

Artist’s concept of NASA’s Terra spacecraft in orbit

as well as throughout the day. However, MOPITT can-not “see” through clouds, a limitation that will cause agap in data for cloud-covered areas. Sophisticatedmodels will be used to estimate values where there aredata gaps due to cloud cover.

MOPITT measurements will be analyzed and convertedinto maps of atmospheric composition for use by theMOPITT science team and other scientists. These mapswill be produced on weekly, monthly, and annual timescales so that effects due to weather, seasons, and long-term changes can be studied and interpreted.

The Terra spacecraft, the flagship in the EOS series, isscheduled for launch in 1999. Terra will fly in a sun-syn-chronous polar orbit, crossing the equator at 10:30 in themorning, when cloud cover over land is at a minimum. Itwill be followed by a series of satellites to be launchedby NASA and its interagency and international partnersthrough the year 2012. In addition to MOPITT, Terrawill carry four other instruments: ASTER, MISR, andMODIS, which will measure surface radiances, digitalelevations, and aerosols; and CERES, which will mea-sure cloud radiative forcing. The measurementsprovided from these instruments will be used to help in-terpret the data from the MOPITT experiment.

In addition to satellite measurements, other observa-tional programs from the ground, aircraft, andballoons will be implemented to ensure that data of thehighest quality are produced. These measurementswill be combined with modeling studies to provide ananalysis of possible changes that might be occurring inthe atmosphere and what activity, natural or human-in-duced, might be causing them.

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MOPITT

Carbon MonoxideIn The Atmosphere

Carbon monoxide is a colorless, odorless gas that ispresent in the lower atmosphere at a concentration ofabout one hundred parts per billion depending on thegeographic location. “Clean” areas may show concen-trations as low as 50 parts per billion, whereas pollutedareas may have much higher concentrations. At veryhigh levels, CO is poisonous.

Carbon monoxide is produced by a number of pro-cesses, almost all of which happen at or near theground. Some of these sources are natural and some,such as fossil fuel consumption and biomass burning,are connected with human activity. Total planetaryproduction of CO is estimated at between two and fivegigatons per year. The major loss, or “sink” of carbonmonoxide occurs through its reaction with the hy-droxyl (OH) radical.

The OH radical is one of the most important chemicalsin the troposphere and is intimately connected withatmosphere’s ability to control pollutants. Changes inOH concentration indicate changes in pollution levelsthat can have beneficial or detrimental effects. Since tro-pospheric OH can’t be measured from space, monitoringCO gives scientists a “window” into the chemical pro-cesses occurring in the atmosphere’s lowest layer.

The average life cycle of a CO molecule is on the orderof several months. Since it takes much longer than thatfor a chemical to completely mix throughout the loweratmosphere, the distribution of CO concentrationsshow the locations of respective sources and sinks.Thus, using advanced mathematical models it is pos-sible not only to locate the sources of CO, but also toestimate their distribution. In addition, by monitoringhow the patterns of CO concentration change withtime, we can build up an understanding of how the at-mosphere transports this and other chemicals from onearea of the planet to another.

Global measurements of CO have been made overshort periods of time by the shuttle-based Measure-ment of Air Pollution from Satellites (MAPS)instrument, which has flown a number of times duringthe past twenty years. MAPS has provided some in-triguing snapshots of the CO distribution in the middleof the troposphere as a function of time and, in so do-

ing, the effects of human activity have been observed.In the figure, the increased mixing ratios around theequator are undoubtedly due to biomass burning inSouth America, Equatorial Africa, and Indonesia.

We know, however, that this picture changes with theseasons, and there remain serious gaps in the coverageof CO measurements, both in space and time.MOPITT will enormously expand our knowledge of

Forest fires destroy resources and cause serious pollution

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Methane In The AtmosphereMethane is an important greenhouse gas that is involvedin atmospheric chemical processes. Its average concen-tration is around 1.7 parts per million and, unlike CO, theconcentration is very uniform both horizontally and ver-tically. The main observed variation to date has been a5% higher concentration in the Northern Hemisphere, ascompared to the Southern Hemisphere.

Most measurements of methane have been made bysampling the concentration at or near the Earth’s sur-face over long periods of time at specific sites. Usingthe assumption that there is no variation around acircle of latitude, global plots have been constructed.

Methane also has a wide variety of sources, many ofwhich are directly or indirectly affected by human ac-tivity. Moist land areas, such as the wetlands of thehigh northern latitudes and the rice paddies of the sub-tropical latitudes, are sources of methane. Cows,sheep, and other similar herbivores also produce sig-nificant amounts. The total annual production of

this important gas by providing high-resolution globalmaps twice a week.

Such maps, together with the individual measurementsthat comprise the maps, will enable scientists to testand refine their models of lower atmospheric chemis-try. The models will be used to display the transport ofthese chemicals, both horizontally and vertically, andverify our understanding of the chemical processes oc-curring in the lower atmosphere. They will also beused to test predictions of pollutant concentrations.This will allow the provision of reliable forecasts tothe general public, industry and government, eventu-ally leading to informed policy decisions related to ourinfluence on the global environment.

A schematic of tropospheric chemistry

Model distribution of CO over South America in September. Highvalues are from burning during forest clearing and the transportof CO over the Pacific by easterly winds at the Equator. The colorscale corresponds to a mixing ratio of CO in parts per billion.

Sheep and rice paddies are thoughtto be large sources of methane

H2O

H2O2

OH

RHCO

OH2

HN03

NO, O3HO2 , CH4

NO2 HO2

HNO3O3 , CO

O (1D)

hν + O3

RAIN

hν

hν

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MOPITT

MOPITT Data ProcessingMOPITT data processing will initially occur at the Na-tional Center for Atmospheric Research, Boulder,Colorado. Scientists will receive the raw instrumentdata on a daily basis and process the readings into dis-tributions of carbon monoxide and methane over thesurface of the planet.

After the first eighteen months, when the conversionprograms are well understood, processing will be per-formed at the Distributed Active Archive Center at theNASA Langley Research Center in Hampton, Virginia.

MOPITT InstrumentMOPITT is a multi-channel correlation radiometer andviews the Earth looking vertically downwards from thesatellite, scanning 320 km on each side of the spacecraftas it orbits the planet. This enables coverage of most ofthe planet every four days. Measurements are made in atotal of 64 channels at the rate of just over two measure-ments every second. These measurements are combinedto give profiles of carbon monoxide and columnamounts of methane at a rate of 8 points per second.

MOPITT is designed to operate continuously for a pe-riod of five years to permit the science team to observechanges in the concentrations of these chemicals overlong periods of time.

methane is thought to be about 500 megatons. Themain loss mechanism is through reaction with the hy-droxyl radical. Because of the strong biological linksin methane production, concentrations vary in a no-ticeable seasonal cycle.

Methane has a very long lifetime in the atmosphere—about 10 years—and therefore is able to become wellmixed in both hemispheres. In order to determine thesources and sinks, MOPITT must make very accuratemeasurements of the concentration of this gas.

Since methane is very efficient at absorbing infraredradiation emitted by the Earth’s surface—up to 60times more efficient than carbon dioxide—there isconcern over its increasing concentrations in the atmo-sphere. Thus, increases in methane concentration,although small in themselves, can have considerableconsequences. There is evidence that methane has in-creased fairly continuously for some time and hasdoubled in concentration since the beginning of the In-dustrial Revolution. The recent record is morevariable, with individual years showing both increasesand decreases. The reasons for these variations are notfully understood.

A “plot” of global methane with time, taken from a number offixed ground sites

A COM DEV technician prepares the MOPITT instrument for flight

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MOPITT Data ProductsMOPITT produces two major data products, one foreach of the gases that it monitors:

Carbon monoxide (CO)Profiles in cloud-free conditions at a spatial resolution ofabout 22 km x 22 km horizontally and an approximateequivalent vertical resolution of 3-5 km. During day-light, reliable information is obtained down to thesurface. After dark, the information near the surface be-comes less reliable. The measurement accuracy aftervalidation is estimated to be about 10% rms–10 parts perbillion in a profile of about 100 parts per billion.

Methane (CH4)Total vertical column amounts in cloud-free condi-tions at a spatial resolution of about 22 km x 22 km.There is no vertical information, only the integratedamount is measured. The methane channels are onlyactive during daylight, thus no information is returnedat night. The measurement accuracy is estimated to beabout 1% after validation.

MOPITT Facts

Spacecraft: EOS Terra (AM-1)

Orbit: 705 km; 10:30 amdescending node,sun-synchronous,near polar, circular

Size: 1.1m x 0.9m x 0.5m

Mass: 190 kg

Power: 250W

Data Rate: 30 kbps

Spatial Resolution: 22 km x 22 km (nadir)

Detector Temperature: <100K

Design Life: 5 years

Spectral Bands:

4.562-4.673 µm2140-2192 cm-1 CO profiles

2.323-2.345 µm4265-4305 cm-1 CO column

2.222-2.293 µm4361-4500 cm-1 CH4 column

MOPITT is supplied to the EOS program by the Canadian Space Agency. The MOPITT instrument was built by COM DEV Interna-tional of Cambridge, Ontario, and will be operated by the University of Toronto, both under contract to the Canadian Space Agency.The Principal Investigator is Prof. James R. Drummond of the Department of Physics, University of Toronto. For further informationcontact Prof. Drummond at (416)-978-4723; jim@atmosp.physics.utoronto.ca

Information on MOPITT is available at:

http://www.atmosp.physics.utoronto.ca/MOPITT/home.html

http://www.eos.ucar.edu/mopitt/home.html

http://www.science.sp-agency.ca/J1-MOPITT(Eng).htm

http://www.science.sp-agency.ca/J1-MOPITT(Fr).htm

Information on the Terra mission is available at:

http://eos-am.gsfc.nasa.gov/

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MOPITT

International CollaborationThe Mission Statement of the Canadian Space Agencyis to lead the development and application of spaceknowledge for the benefit of Canadians and humanity.The provision of MOPITT to the EOS program dem-onstrates Canada’s commitment to participate ininternational missions focused on understanding howchanges in our atmosphere affect global climatechange. Since atmospheric pollution is a worldwideproblem, international teams of scientists on all conti-nents will work closely with MOPITT data.

The FutureThe ultimate objective of research in this area is to de-velop our understanding to a level where ourpredictions are reliable. This will allow us to managethe environment more effectively and improve thequality of life for the entire biosphere—including hu-manity.

MOPITT Science Team

The international MOPITT science team has been working for more than a decade to develop both the MOPITT instrumentand the algorithms needed to turn MOPITT measurements into maps and profiles of CO and CH4.

Principal Investigator:James R. Drummond, University of Toronto, Toronto, ON

Co-Investigators:G.P. Brasseur, National Center for Atmospheric Research, Boulder, COG.R. Davis, University of Saskatchewan, Saskatoon, SKJ.C. Gille, National Center for Atmospheric Research, Boulder, COG. Mand, University of Toronto, Toronto, ONJ.C. McConnell, York University, Toronto, ONG.D. Peskett, Oxford University, UKH.G. Reichle, Jr., North Carolina State University, Raleigh, NCN. Roulet, McGill University, Montreal, QCJ. Wang, National Center for Atmospheric Research, Boulder, CO

M e a s u r e m e n t s O f P o l l u t i o n I n T h e T r o p o s p h e r e