Stratospheric sink for chlorofluoromethanes: chlorine atomc-atalysed destruction of ozone
TL;DR: Chlorofluoromethanes are being added to the environment in steadily increasing amounts as discussed by the authors and these compounds are chemically inert and may remain in the atmosphere for 40 to 150 years, and concentrations can be expected to reach 10 to 30 times present levels.
Abstract: Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for 40–150 years, and concentrations can be expected to reach 10 to 30 times present levels. Photodissociation of the Chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.
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TL;DR: An overview of the MERRA-2 system and various performance metrics is provided, including the assimilation of aerosol observations, several improvements to the representation of the stratosphere including ozone, and improved representations of cryospheric processes.
Abstract: The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), is the latest atmospheric reanalysis of the modern satellite era produced by NASA’s Global Modeling and Assimilation Office (GMAO). MERRA-2 assimilates observation types not available to its predecessor, MERRA, and includes updates to the Goddard Earth Observing System (GEOS) model and analysis scheme so as to provide a viable ongoing climate analysis beyond MERRA’s terminus. While addressing known limitations of MERRA, MERRA-2 is also intended to be a development milestone for a future integrated Earth system analysis (IESA) currently under development at GMAO. This paper provides an overview of the MERRA-2 system and various performance metrics. Among the advances in MERRA-2 relevant to IESA are the assimilation of aerosol observations, several improvements to the representation of the stratosphere including ozone, and improved representations of cryospheric processes. Other improvements in the quality of M...
4,524 citations
Cites background from "Stratospheric sink for chlorofluoro..."
...As discovered by Molina and Rowland (1974), anthropogenic emissions of chlorofluorocarbons provide the main contribution to the chlorine loading in the stratosphere, leading to destruction of the ozone layer....
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TL;DR: A brief history of the science of ozone depletion and a conceptual framework to explain the key processes involved, with a focus on chemistry is described in this article, and observations of ozone and of chlorine-related trace gases near 40 km provide evidence that gas phase chemistry has indeed currently depleted about 10% of the stratospheric ozone there as predicted, and the vertical and horizontal struc- tures of this depletion are fingerprints for that process.
Abstract: Stratospheric ozone depletion through cat- alytic chemistry involving man-made chlorofluorocar- bons is an area of focus in the study of geophysics and one of the global environmental issues of the twentieth century. This review presents a brief history of the sci- ence of ozone depletion and describes a conceptual framework to explain the key processes involved, with a focus on chemistry. Observations that may be considered as evidence (fingerprints) of ozone depletion due to chlorofluorocarbons are explored, and the related gas phase and surface chemistry is described. Observations of ozone and of chlorine-related trace gases near 40 km provide evidence that gas phase chemistry has indeed currently depleted about 10% of the stratospheric ozone there as predicted, and the vertical and horizontal struc- tures of this depletion are fingerprints for that process. More striking changes are observed each austral spring in Antarctica, where about half of the total ozone col- umn is depleted each September, forming the Antarctic ozone hole. Measurements of large amounts of ClO, a key ozone destruction catalyst, are among the finger- prints showing that human releases of chlorofluorocar- bons are the primary cause of this change. Enhanced ozone depletion in the Antarctic and Arctic regions is linked to heterogeneous chlorine chemistry that oc- curs on the surfaces of polar stratospheric clouds at cold temperatures. Observations also show that some of the same heterogeneous chemistry occurs on the surfaces of particles present at midlatitudes as well, and the abundances of these particles are enhanced following explosive volcanic eruptions. The partition- ing of chlorine between active forms that destroy ozone and inert reservoirs that sequester it is a central part of the framework for our understanding of the 40-km ozone decline, the Antarctic ozone hole, the recent Arctic ozone losses in particularly cold years, and the observation of record midlatitude ozone de- pletion after the major eruption of Mount Pinatubo in the early 1990s. As human use of chlorofluorocarbons continues to decrease, these changes throughout the ozone layer are expected to gradually reverse during the twenty-first century.
1,730 citations
Cites background from "Stratospheric sink for chlorofluoro..."
...Of particular importance was the identification of man-made chlorofluorocarbons as the major source of ozone-destroying stratospheric chlorine [Molina and Rowland, 1974]....
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...Section 2 of this paper briefly discusses the general theoretical understanding of the vulnerability of ozone to chemical change, particularly the depletions that were predicted to occur in the distant future based upon gas phase chlorine and bromine chemistry [Molina and Rowland, 1974]....
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TL;DR: It is completely unclear how important microbial diversity is for the control of trace gas flux at the ecosystem level, and different microbial communities may be part of the reason for differences in trace gas metabolism, e.g., effects of nitrogen fertilizers on CH4 uptake by soil; decrease of CH4 production with decreasing temperature.
1,622 citations
TL;DR: The physiological and biochemical parameters measured indicate the UV-B light has stronger stress effectors than drought on the growth of seedlings of both species.
Abstract: It emerged recently that there is an inter-relationship between drought and ultraviolet-B (UV-B) radiation in plant responses, in that both stresses provoke an oxidative burst. The purpose of this investigation was to compare the effects and interaction of drought and UV-B in wheat and pea. The absence of changes in relative leaf water content (RWC) after UV-B treatments indicate that changes in water content were not involved. RWC was the main factor resulting in reduced growth in response to drought. Increases in anthocyanin and phenols were detected after exposure to UV-B. The increases do not appear to be of sufficient magnitude to act as a UV-B screen. UV-B application caused greater membrane damage than drought stress, as assessed by lipid peroxidation as well as osmolyte leakage. An increase in the specific activities of antioxidant enzymes was measured after UV-B alone as well as after application to droughted plants. Proline increased primarily in drought-stressed pea or wheat. Proline may be the drought-induced factor which has a protective role in response to UV-B. The physiological and biochemical parameters measured indicate the UV-B light has stronger stress effectors than drought on the growth of seedlings of both species. The two environmental stresses acted synergistically to induce protective mechanisms in that pre-application of either stress reduced the damage caused by subsequent application of the other stress.
1,538 citations
TL;DR: The Earth Observing System Microwave Limb Sounder measures several atmospheric chemical species to improve the authors' understanding of stratospheric ozone chemistry, the interaction of composition and climate, and pollution in the upper troposphere.
Abstract: The Earth Observing System Microwave Limb Sounder measures several atmospheric chemical species (OH, HO/sub 2/, H/sub 2/O, O/sub 3/, HCl, ClO, HOCl, BrO, HNO/sub 3/, N/sub 2/O, CO, HCN, CH/sub 3/CN, volcanic SO/sub 2/), cloud ice, temperature, and geopotential height to improve our understanding of stratospheric ozone chemistry, the interaction of composition and climate, and pollution in the upper troposphere. All measurements are made simultaneously and continuously, during both day and night. The instrument uses heterodyne radiometers that observe thermal emission from the atmospheric limb in broad spectral regions centered near 118, 190, 240, and 640 GHz, and 2.5 THz. It was launched July 15, 2004 on the National Aeronautics and Space Administration's Aura satellite and started full-up science operations on August 13, 2004. An atmospheric limb scan and radiometric calibration for all bands are performed routinely every 25 s. Vertical profiles are retrieved every 165 km along the suborbital track, covering 82/spl deg/S to 82/spl deg/N latitudes on each orbit. Instrument performance to date has been excellent; data have been made publicly available; and initial science results have been obtained.
1,191 citations
References
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TL;DR: The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.
Abstract: Although a great deal of attention has been given to the role of water vapor from supersonic transport (SST) exhaust in the stratosphere, oxides of nitrogen from SST exhaust pose a much greater threat to the ozone shield than does an increase in water. The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.
812 citations
TL;DR: In this article, it was shown that an artificial increase of the mixing ratio of the oxides of nitrogen in the stratosphere by about 1×10−8 may lead to observable changes in the atmospheric ozone level.
Abstract: The distribution of the compounds NO, NO2, NO3, N2O5, and HNO3 has been calculated for different choices of relevant parameters, the values of which are uncertain. An appreciable part of the NO and NO2 is converted to NO3, N2O5, HNO3 and possibly HNO2 is the ozone layer. Reactions of odd oxygen with NO and NO2 may be the dominating reassociation processes for odd-oxygen particles in the region below 45 km which is very important for the global ozone budget. Several processes may lead to the presence of significant amounts of nitrogen oxides, nitrous acid, and nitric acid in the stratosphere. Reported variations during the solar cycle of ozone concentrations above 30 km (Dutsch, 1969) can be explained by corresponding variations in the stratospheric odd nitrogen oxide content. An artificial increase of the mixing ratio of the oxides of nitrogen in the stratosphere by about 1×10−8 may lead to observable changes in the atmospheric ozone level. Chains of reactions involving the constituents OH, H2O2, and HO2 also lead to the catalytic destruction of odd oxygen. The presence of nitric acid with a mixing ratio of about 3×10−9 in the ozone layer (Murcray et al., 1968; Rhine et al., 1969) indicates much larger OH and HO2 concentrations than can be explained solely by the reaction O(1D) + H2O → 2 OH. The reaction N2O5 + H2O → 2HNO3 followed by O + HNO3 → OH + NO3 may also be an important source of OH if the rate constants given by Jaffe and Ford (1967) are adopted. It is difficult to explain the measured nitric acid concentrations between 20 and 30 km with the reaction HO2 + NO + M → HNO3 + M. Laboratory data (Asquith and Tyler, 1969) indicate that the reaction H2O2 + NO2 → HNO3 + OH (Nicolet, 1970α) is unimportant in the atmosphere.
551 citations
TL;DR: McCarthy as discussed by the authors estimated that the integrated production of CCl2F2 and CCl3F, the two principal compounds of the class, was about one megaton of each in mid 1971; they are unusually stable chemically and only slightly soluble in water and might therefore persist and accumulate in the atmosphere.
Abstract: DURING the past few decades the production of the chlorofluorocarbons, the propellant solvents for aerosol dispensers, has grown exponentially. R. L. McCarthy (unpublished) estimates that the integrated production of CCl2F2 and of CCl3F, the two principal compounds of the class, was about one megaton of each in mid 1971; they are unusually stable chemically and only slightly soluble in water and might therefore persist and accumulate in the atmosphere. Preliminary tests in 1970 showed that CCl3F was present in the air over Ireland at concentrations exceeding 10−11 by volume1.
539 citations
TL;DR: In the sheep and pig, the recognition signal has been transmitted even before the embryonic tissue becomes intimately attached to the uterine epithelium and is therefore clearly distinct from implantation.
Abstract: A LONG-STANDING problem in reproductive biology is that of the maternal recognition of pregnancy, the mechanism by which the developing conceptus signals its presence to the mother. An essential requirement for the establishment and maintenance of pregnancy is that the normal ovarian cycle should be arrested and the activity of the corpus luteum prolonged. In the sheep and pig, the recognition signal has been transmitted even before the embryonic tissue becomes intimately attached to the uterine epithelium and is therefore clearly distinct from implantation. In species such as the pig the blastocyst, while it remains free in the uterine lumen, may produce some substance that is capable of diffusing into uterine “milk” and across the lumen, exerting a local effect on the uterine tissues.
280 citations