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GCOS Atmospheric Composition ECV* *over land, sea and ice Definition: Ozone is a nearly colorless gas, formula O3, molecular weight 48, that appears blue in the condensed phase or at high concentration, with a characteristic odor like that of weak chlorine. It is formed in the reaction between atomic oxygen and molecular oxygen: . It is a very strong absorber of ultraviolet radiation, and the presence of the ozone layer in the upper atmosphere provides an ozone shield that prevents dangerous radiation from reaching the earth's surface and allows the existence of life in its present forms. Ozone, produced by photochemical reactions, is found at all altitudes in the atmosphere. The total amount of ozone in the atmosphere would correspond to less than 1 part per million if uniformly distributed, or a column amount of about 3 mm if compressed to sea level pressure. In the troposphere, it is regarded as a pollutant, and its presence in high concentrations can lead to respiratory stress and crop damage. Ozone is an important component of photochemical smog and can also be formed locally by the action of electrical discharges on the air. Ozone in the free troposphere often results from downward transport from the stratosphere. In the stratosphere, ozone is formed following the absorption of radiation by molecular oxygen. Its mixing ratio there can reach several parts per million, and the temperature inversion characteristic of the stratosphere is due to the strong absorption of energy by ozone molecules in this region. In the stratosphere, ozone is destroyed predominantly by catalytic cycles involving free radicals, many of which are formed as products of human activity. Ozone has several radiation absorption bands that are atmospherically important: the very intense Hartley band, between 200 and 300 nm, which is responsible for much of the heating of the upper atmosphere; the Huggins bands, between 320 and 360 nm; the Chappuis bands, between 450 and 650 nm; and infrared bands, centered at 4.7, 9.6, and 14.1 µm. All the above bands have been used for the detection of ozone using various remote sensing techniques. Absorption by ozone in the infrared is responsible for its effectiveness as a greenhouse gas. See Dobson unit. Finlayson–Pitts, B. J., and J. N. Pitts, 1986: Atmospheric Chemistry, Wiley–Interscience, New York, 1098 pp. Seinfeld, J. H., and S. N. Pandis, 1998: Atmospheric Chemistry and Physics, Wiley–Interscience, New York, 1326 pp. Volz, A., and D. Kley, 1988: Evaluation of the Montsouris series of ozone measurements made in the nineteenth century. Nature, 332, 240–242. (AMS Glossary of Meteorology) Introduction: Routine measurements of column ozone from ground-based UV spectrometers are established under the guidance of the WMO GAW programme. Calibration of instruments is an ongoing requirement. Coarse ozone profile measurements are provided from these spectrometers through the Umkehr technique. In situ ozone profiles are measured to about 30 km using ozone sondes. The WMO GAW programme maintains a network of about 40 ozone-sonde stations and collaborates with other networks such as the NASA/Southern Hemisphere Additional Ozone Sondes (SHADOZ). Recent calibration and data protocols have significantly improved the accuracy of these data, but more needs to be done to ensure prompt data supply in uniform code formats, as the data are important for monitoring the quality of satellite data retrievals and products from data assimilation systems operated in near-real time. Ground-station networks such as the Network for the Detection of Atmospheric Composition Change (NDACC) also provide profiles using lidar and microwave techniques. Ground-based measurements still have very limited coverage in the Tropics and Southern Hemisphere. Both GAW column ozone and total ozone networks have been recognised as the GCOS Global Baseline Profile Ozone Network and the GCOS Global Baseline Total Ozone Network. Supporting Measurement of Precursors for Aerosols and Ozone: Global observation of the aerosol and ozone precursors NO2, SO2, HCHO and CO (in addition to CH4, covered earlier) has been shown to be feasible from space. In the last ten years major progress has been made in measuring these species in the troposphere and lower stratosphere using a range of instruments, and it will be possible to extend the data record forward to several decades with data that will come from existing and planned operational missions. Studies have shown that emission estimates using inverse modelling techniques and satellite data can help to reduce the uncertainties in emission data bases, and first studies are being performed combining precursor and aerosol data from space to obtain information on aerosol composition. Emerging integrated data products for the ozone and aerosol ECVs from comprehensive chemical data assimilation systems will be improved by assimilating observations of the precursors, as this will lead to better background model fields of ozone and aerosol. Combining observations of the precursors with those of tropospheric ozone and aerosols will be crucial for attributing change to natural and anthropogenic sources. High temporal and spatial resolution is needed to improve the emission estimates, especially for short-lived trace gases with a large diurnal cycle such as NO2 and SO2. International Data Centers and Archives for Atmospheric Composition:
Coordinating Body: WMO Commission for Atmospheric Science (CAS) Satellite Observations: Ozone is a relatively unstable molecule, and although it represents only a tiny fraction of the atmosphere, it is crucial for life on Earth. Depending on its location, ozone can protect or harm life on Earth. Most ozone resides in the stratosphere, where it acts as a shield to protect the surface from the Sun’s harmful ultraviolet radiation. In the troposphere, ozone is a harmful pollutant which causes damage to lung tissue and plants. Man-made chemicals and weather conditions over Antarctica combine to deplete stratospheric ozone concentrations during the southern hemisphere’s winter. The total amount of O3 in the troposphere is estimated to have increased by 36% since 1750, due primarily to anthropogenic emissions of several O3-forming gases. Satellite instruments have for many years provided data measuring interactions within the atmosphere that affect ozone, and more advanced sensors will soon be in orbit to collect more detailed measurements, increasing knowledge of how human activities are affecting the protective ozone layer. Total column measurements of ozone have been provided over long periods by NASA’s TOMS and NOAA’s SBUV instruments. Stratospheric ozone profiles have also been measured by instruments such as HALOE and MLS (UARS mission), GOME (ERS-2), and SAGE III (part of the International Space Station payload). Since launch in March 2002, GOMOS, MIPAS and SCIAMACHY on ESA’s Envisat mission have provided improved observations of the concentration of ozone and trace gases in the stratosphere. Operation of GOME-2 on EUMETSAT’s MetOp satellites guarantees the continuity of these observations for another decade. A wide range of instruments dedicated to, or capable of, ozone measurements are planned for the next decade. On the recently launched Aura mission, HIRDLS, OMI and MLS study and monitor atmospheric processes which govern stratospheric and mesopheric ozone, and continue the TOMS record of total ozone measurements. TES on Aura is used to create three-dimensional maps of ozone concentrations in the troposphere. AIRS on Aqua (and, in future, CrIS on NPP/NPOESS) also supplies an ozone product that has some application in the lower stratosphere and also can be used to identify regions of stratospheric/tropospheric mixing. IASI and GOME-2 on the MetOp series have provided information since early 2007 on both total column ozone and vertical profile. The Ozone Profiler on China’s FY-3 series has contributed further data since its launch in 2008. Though the infrared imagers on the GOES and Meteosat geostationary platforms have limited capabilities to provide vertical information on ozone, they provide total stratospheric ozone amount with a high temporal resolution. This information can be used to depict stratospheric dynamical processes, relevant for NWP applications. The IGOS theme on Atmospheric Chemistry Observations (IGACO) has developed a strategy for the integrated provision of chemistry observations (and associated meteorological parameters) required to realise the theme’s objectives, including the monitoring of atmospheric composition parameters related to climate change. The CEOS response to the GCOS IP acknowledged that profiles of ozone were to be addressed by the NPOESS OMPS, but that instrument has been removed from the payload manifest. Furthermore, the discontinuation of solar occultation measurements will profoundly impact one of the climate data record pillars of ozone assessments. CEOS agencies will participate in re-planning the OMPS limb instrument removed from the planned payload of NPOESS. (Satellite Missions) (Source: CEOS) News:
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