Detailed measurements from TES of the global tropospheric distributions of co-located O3, CO, water vapor, and nitrogen oxides are being used to investigate the impacts of biomass burning on air quality and climate. A vital aspect of calculating ozone (O3) and making better climate models is identification of the global concentration and distribution of carbon monoxide (CO). For example TES measurments reveal that the distribution of tropospheric ozone and carbon monoxide in the tropical Atlantic is closely related to biomass burning emissions. Read more: Tropical Atlantic Ozone Paradox Resolved.
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Carbon monoxide as a combustion tracer
Carbon monoxide (CO) is an excellent tracer for pollution sources and pollution pathways through the troposphere. Since the lifetime of most CO (situated in the lower troposphere, or boundary layer) is on the order of months, compared to the inter-hemispheric mixing time of 1–2 years, it is not thoroughly mixed throughout the troposphere. This means that the global distribution of CO closely resembles its source distribution, which is greatest near the surface. Conversely, in the free troposphere CO has a relatively long lifetime, which permits the study of long range transport in the upper troposphere and makes it a useful tracer of other pollutants.
Biomass burning and fossil fuel use (followed by oxidation of hydrocarbons and oxidation of methane) are the main sources of man-made CO emissions, and more than half of all CO emissions are considered to be man-made. The major global sink for tropospheric CO is reaction with the hydroxyl radical (OH). Carbon monoxide is the third most abundant carbon based trace gas in the atmosphere, after carbon dioxide and methane.
TES expands our understanding of carbon monoxide
Other instruments measure total column CO for the summer months in the mid-latitudes with good quality, but TES has the advantage of also detecting CO during the winter and in the lower troposphere. During major biomass burning events occurring in both equatorial and boreal regions, TES provides new information on gross emissions and vertical distribution of CO, which can be used to better understand changes to Earth's carbon cycle.
This dynamic movie (QuickTime, 4.48 MB) displays TES retrievals of co-located ozone and carbon monoxide (from 0 to 60N latitude), acquired during the Aura Validation Experiment (AVE) near Houston, TX, Oct-Nov, 2004.
Potential for CO to indirectly control the oxidative capacity of the troposphere
Vertically transported CO results in longer lifetimes of O3 precursors and enhanced O3 in convection regions in the middle and upper troposphere, thereby directly influencing the Earth’s radiation balance. Carbon monoxide reacts with hydroxyl (OH) radicals in the atmosphere, reducing their abundance. Since OH is the only significant tropospheric sink for many atmospheric trace gases emitted into the atmosphere, CO has the potential to indirectly control much of the oxidative capacity of the troposphere. Because OH radicals also help to increase the lifetimes of strong greenhouse gases such as methane, CO also indirectly increases the global warming potential of those gases. Tropospheric O3 is produced via photochemical oxidation of CO in the presence of NOx and water vapor. Then, in regions of water vapor, O3 then creates hydroxyl radicals (OH) via photolysis. TES also uses CO profiles to determine temperature/pressure profiles and boundary layer exit pathways.
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Biomass burning is the widespread practice, especially in the tropics, of using fire to clear forests and grassland for agriculture and to dispose of crop residue. Among its environmental impacts, biomass burning releases large amounts of carbon monoxide (CO) into the atmosphere, where it reacts with other chemicals to produce ozone. Other instruments observe and measure CO, but only TES measures both CO and ozone — at the same time and at various altitudes. This enables scientists to see the extent to which biomass burning contributes to ozone in the troposphere.