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Concept
Greenhouse gas monitoring
Résumé
Greenhouse gas monitoring is the direct measurement of greenhouse gas emissions and levels. There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments. Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.
Manometry is a key measurement tool for atmospheric carbon dioxide by first measuring the volume, temperature, and pressure of a particular amount of dry air. The air sample is dried by passing it through multiple dry ice traps and then collecting it in a five-liter vessel. The temperature is taken via a thermometer and pressure is calculated using manometry. Then, liquid nitrogen is added, causing the carbon dioxide to condense and become measurable by volume. The ideal gas law is accurate to 0.3% in these pressure conditions.
Infrared analyzers were used at Mauna Loa Observatory and at Scripps Institution of Oceanography between 1958 and 2006. IR analyzers operate by pumping an unknown sample of dry air through a 40 cm long cell. A reference cell contains dry carbon dioxide-free air. A glowing nichrome filament radiates broadband IR radiation which splits into two beams and passes through the gas cells. Carbon dioxide absorbs some of the radiation, allowing more radiation that passes through the reference cell to reach the detector than radiation passing through the sample cell. Data is collected on a strip chart recorder. The concentration of carbon dioxide in the sample is quantified by calibrating with a standard gas of known carbon dioxide content.
Titrimetry is another method of measuring atmospheric carbon dioxide that was first used by a Scandinavian group at 15 different ground stations. They began passing a 100.0 mL air sample through a solution of barium hydroxide containing cresolphthalein indicator.
Source officielle
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