MOPITT: follow carbon monoxide through the atmosphere

MOPITT, Measurements of Pollution in the Troposphere, was a Canadian-built instrument aboard NASA’s Terra spacecraft, launched in December 1999. Its science focused on carbon monoxide, a gas associated with incomplete combustion from sources including fires and human activities. Carbon monoxide is chemically different from carbon dioxide. An atmospheric map of one gas is not a measurement of the other.

The instrument began its operational record in March 2000 and was deactivated on April 9, 2025. That endpoint matters when describing the mission: an archived dataset can support new research after the hardware stops observing. Researchers can reprocess past measurements, compare events and improve interpretations without implying that new observations are still arriving from the instrument.

MOPITT used gas correlation spectroscopy. Incoming infrared radiation was compared along optical paths involving onboard carbon monoxide. The differences helped identify the gas’s atmospheric signature. Retrieval — open definition algorithms translated measured radiation into estimates of carbon monoxide profiles and total columns. This is a model-assisted inference from light, rather than physically collecting an air sample from every mapped location.

The Version 9 research paper describes sampling and validation of the retrieved products. Such work is necessary because the answer depends on calibration, atmospheric assumptions and which observations pass quality screening. A retrieval version identifies a particular processing method. When comparing two maps, record both observation dates and product versions so that an apparent environmental change is not confused with a processing change.

A total column — open definition describes gas through a vertical extent of the atmosphere. It is not automatically the concentration at a person’s breathing height. Winds can also transport carbon monoxide away from its source, so a high value over one location does not by itself prove that the emissions originated directly below it. Source interpretation needs weather, timing and other relevant evidence.

In a fictional comparison, a consistently processed regional column average increases from 80 to 100 units. The increase is 20 units, or 25 percent relative to the original value. Before attributing it to a new local source, check coverage, uncertainty and transport. The arithmetic describes the change in the stated product; it does not identify its cause. MOPITT’s long record is valuable precisely because careful comparisons can connect atmospheric patterns across many observations.