.. ne hole is firmly established to be halogen chemistry…There is not a full accounting of the observed downward trend in global ozone . Plausible mechanisms include heterogeneous chemistry on sulfate aerosols [which convert reservoir chlorine to active chlorine – R.P.] and the transport of chemically perturbed polar air to middle latitudes. Although other mechanisms cannot be ruled out, those involving the catalytic destruction of ozone by chlorine and bromine appear to be largely responsible for the ozone loss and are the only ones for which direct evidence exists . (emphases mine – RP) The Executive Summary of the subsequent 1994 scientific assessment (available on the Web at http://www.al.noaa.gov/WWWHD/pubdocs/WMOUNEP94.htm l) states: Direct in-situ meaurements of radical species in the lower stratosphere, coupled with model calculations, have quantitatively shown that the in-situ photochemical loss of ozone due to (largely natural) reactive nitrogen (NOx) compounds is smaller than that predicted from gas-phase chemistry, while that due to (largely natural) HOx compounds and (largely anthropogenic) chlorine and bromine compounds is larger than that predicted by gas-phase chemistry. This confirms the key role of chemical reactions on sulfate aerosols in controlling the chemical balance of the lower stratosphere.
These and other recent scientific findings strengthen the conclusion of the previous assessment that the weight of scientific evidence suggests that the observed middle- and high-latitude ozone losses are largely due to anthropogenic chlorine and bromine compounds. [WMO 1994] For a contrasting view, see [Henriksen and Roldugin]. A legal analogy might be useful here – the connection between antarctic ozone depletion and CFC emissions has been proved beyond a reasonable doubt, while at middle latitudes there is only probable cause for such a connection. One must remember that there is a natural 10-20 year time lag between CFC emissions and ozone depletion. Ozone depletion today is (probably) due to CFC emissions in the 1970’s. Present controls on CFC emissions are designed to avoid possibly large amounts of ozone depletion 30 years from now, not to repair the depletion that has taken place up to now.
[Prather et al. 1996] —————————– Subject: 2.12) If the ozone is lost, won’t the UV light just penetrate deeper into the atmosphere and make more ozone? This does happen to some extent – it’s called self-healing – and has the effect of moving ozone from the upper to the lower stratosphere. Recall that ozone is created by UV with wavelengths less than 240 nm, but functions by absorbing UV with wavelengths greater than 240 nm. The peak of the ozone absorption band is at ~250 nm, and the cross-section falls off at shorter wavelengths. The O2 and O3 absorption bands do overlap, though, and UV radiation between 200 and 240 nm has a good chance of being absorbed by either O2 or O3. [Rowland and Molina 1975] (Below 200 nm the O2 absorption cross-section increases dramatically, and O3 absorption is insignificant in comparison.) Since there is some overlap, a decrease in ozone does lead to a small increase in absorption by O2.
This is a weak feedback, however, and it does not compensate for the ozone destroyed. Negative feedback need not imply stability, just as positive feedback need not imply instability. Numerical calculations of ozone depletion take the self-healing phenomenon into account, by letting the perturbed ozone layer come into equilibrium with the exciting radiation. —————————– Subject: 2.13) Do Space Shuttle launches damage the ozone layer? Very little. In the early 1970’s, when little was known about the role of chlorine radicals in ozone depletion, it was suggested that HCl from solid rocket motors might have a significant effect upon the ozone layer – if not globally, perhaps in the immediate vicinity of the launch. It was immediately shown that the effect was negligible, and this has been repeatedly demonstrated since. Each shuttle launch produces about 200 metric tons of chlorine as HCl, of which about one-third, or 68 tons, is injected into the stratosphere.
Its residence time there is about three years. A full year’s schedule of shuttle and solid rocket launches injects 725 tons of chlorine into the stratosphere. This is negligible compared to chlorine emissions in the form of CFC’s and related compounds (~1 million tons/yr in the 1980’s, of which ~0.3 Mt reach the stratosphere each year). It is also small in comparison to natural sources of stratospheric chlorine, which amount to about 75,000 tons per year. [Prather et al.
1990] [WMO 1991] [Ko et al.] See also the sci.space FAQ, Part 10, Controversial Questions, available by anonymous ftp from rtfm.mit.edu in the directory pub/usenet/news.answers/space/controversy, and on the world-wide web at: http://www.cis.ohio-state.edu/hypertext/faq/usenet /space/controversy/faq.html —————————– Subject: 2.14) Will commercial supersonic aircraft damage the ozone layer? Short answer: Probably not. This problem is very complicated, and a definitive answer will not be available for several years, but present model calculations indicate that a fleet of high-speed civil transports would deplete the ozone layer by * 2%. [WMO 1991, 1994] Long answer (this is a tough one): Supersonic aircraft fly in the stratosphere. Since vertical transport in the stratosphere is slow, the exhaust gases from a supersonic jet can stay there for two years or more. The most important exhaust gases are the nitrogen oxides, NO and NO2, collectively referred to as NOx.
NOx is produced from ordinary nitrogen and oxygen by electrical discharges (e.g. lightning) and by high-temperature combustion (e.g. in automobile and aircraft engines). The relationship between NOx and ozone is complicated. In the troposphere, NOx makes ozone, a phenomenon well known to residents of Los Angeles and other cities beset by photochemical smog. At high altitudes in the troposphere, similar chemical reactions produce ozone as a byproduct of the oxidation of methane; for this reason ordinary subsonic aircraft actually increase the thickness of the ozone layer by a very small amount. Things are very different in the stratosphere.
Here the principal source of NOx is nitrous oxide, N2O (laughing gas). Most of the N2O in the atmosphere comes from bacteriological decomposition of organic matter – reduction of nitrate ions or oxidation of ammonium ions. (It was once assumed that anthropogenic sources were negligible in comparison, but this is now known to be false. The total anthropogenic contribution is estimated at 8 Tg (teragrams)/yr, compared to a natural source of 18 Tg/yr. [Khalil and Rasmussen].) N2O, unlike NOx, is very unreactive – it has an atmospheric lifetime of more than 150 years – so it reaches the stratosphere, where most of it is converted to nitrogen and oxygen by UV photolysis.
However, a small fraction of the N2O that reaches the stratosphere reacts instead with oxygen atoms (to be precise, with the very rare electronically excited singlet-D oxygen atoms), and this is the major natural source of NOx in the stratosphere; about 1.2 million tons are produced each year in this way. This source strength would be matched by 500 of the SST’s designed by Boeing in the late 1960’s, each spending 5 hours per day in the stratosphere. (Boeing was intending to sell 800 of these aircraft.) The Concorde, a slower plane, produces less than half as much NOx and flies at a lower altitude; since the Concorde fleet is small, its contribution to stratospheric NOx is not significant. Before sending large fleets of high-speed aircraft into the stratosphere, however, one should certainly consider the possible effects of increasing the rate of production of an important stratospheric trace gas by as much as a factor of two. [CIC 1975] In 1969, Paul Crutzen discovered that NOx could be an efficient catalyst for the destruction of stratospheric ozone: [Crutzen 1970] NO + O3 -* NO2 + O2 NO2 + O -* NO + O2 ——————————- net: O3 + O -* 2 O2 (For this and other contributions to ozone research, Crutzen, together with Rowland and Molina, was awarded the 1995 Nobel Prize in Chemistry.
The official announcement from the Swedish Academy is available at http://www.nobel.se/announcement95-chemistry.html .) Two years later, Harold S. Johnston made the connection to SST emissions. Until then it had been thought that the radicals H, OH, and HO2 (referred to collectively as HOx) were the principal catalysts for ozone loss; thus, investigations of the impact of aircraft exhaust on stratospheric ozone had focussed on emissions of water vapor, a possible source for these radicals. (The importance of chlorine radicals, Cl, ClO, and ClO2, referred to as – you guessed it – ClOx, was not discovered until 1973.) It had been argued – correctly, as it turns out – that water vapor injection was unimportant for determining the ozone balance. The discovery of the NOx cycle threw the question open again. Beginning in 1972, the U.S.
National Academies of Science and Engineering and the Department of Transportation sponsored an intensive program of stratospheric research. [CIC 1975] It soon became clear that the relationship between NOx emissions and the ozone layer was very complicated. The stratospheric lifetime of NOx is comparable to the timescale for transport from North to South, so its concentration depends strongly upon latitude. Much of the NOx is injected near the tropopause, a region where quantitative modelling is very difficult, and the results of calculations depend sensitively upon how troposphere-stratosphere exchange is treated. Stratospheric NOx chemistry is extremely complicated, much worse than chlorine chemistry. Among other things, NO2 reacts rapidly with ClO, forming the inactive chlorine reservoir ClONO2 – so while on the one hand increasing NOx leads directly to ozone loss, on the other it suppresses the action of the more potent chlorine catalyst.
And on top of all of this, the SST’s always spend part of their time in the troposphere, where NOx emissions cause ozone increases. Estimates of long-term ozone changes due to large-scale NOx emissions varied markedly from year to year, going from -10% in 1974, to +2% (i.e. a net ozone gain ) in 1979, to -8% in 1982. (In contrast, while the estimates of the effects of CFC emissions on ozone also varied a great deal in these early years, they always gave a net loss of ozone.) [Wayne] The discovery of the Antarctic ozone hole added a new piece to the puzzle. As described in Part III, the ozone hole is caused by heterogeneous chemistry on the surfaces of stratospheric cloud particles. While these clouds are only found in polar regions, similar chemical reactions take place on sulfate aerosols which are found throughout the lower stratosphere.
The most important of the aerosol reactions is the conversion of N2O5 to nitric acid: N2O5 + H2O -* 2 HNO3 (catalyzed by aerosol surfaces) N2O5 is in equilibrium with NOx, so removal of N2O5 by this reaction lowers the NOx concentration. The result is that in the lower stratosphere the NOx catalytic cycle contributes much less to overall ozone loss than the HOx and ClOx cycles. Ironically, the same processes that makes chlorine-catalyzed ozone depletion so much more important than was believed 10 years ago, also make NOx-catalyzed ozone loss less important. In the meantime, there has been a great deal of progress in developing jet engines that will produce much less NOx – up to a factor of 10 – than the old Boeing SST. The most recent model calculations indicate that a fleet of the new high-speed civil transports would deplete the ozone layer by 0.3-1.8%. Caution is still required, since the experiment has not been done – we have not yet tried adding large amounts of NOx to the stratosphere.
The forecasts, however, are good. [WMO 1991, Ch. 10] [WMO 1994] Very recently, a new complication has appeared: in situ measurements in the exhaust plume of a Concorde aircraft flying at supersonic speeds indicate that the ground-based estimates of NOx emissions are accurate, but that the exhaust also contains large amounts of sulfate-based particulates [Fahey et al. 1995]. Since reactions on sulfate aerosols are believed to play an important role in halogen-catalyzed ozone depletion, it may be advisable to concentrate on reducing the sulfur content of the fuels that are to be used in new generations of supersonic aircraft, rather than further reducing NOx emissions. …………………………… ………..
Aside : One sometimes hears that the US government killed the SST project in 1971 because of concerns raised by H. S. Johnston’s work on NOx. This is not true. The US House of Representatives had already voted to cut off Federal funding for the SST when Johnston began his calculations.
The House debate had centered around economics and the effects of noise, especially sonic booms, although there were some vague concerns about pollution and one physicist had testified about the possible effects of water vapor on ozone. About 6 weeks after both houses had voted to cancel the SST, its supporters succeeded in reviving the project in the House. In the meantime, Johnston had sent a preliminary report to several professional colleagues and submitted a paper to Science . A preprint of Johnston’s report leaked to a small California newspaper which published a highly sensationalized account. The story hit the press a few days before the Senate voted, 58-37, not to revive the SST. (The previous Senate vote had been 51-46 to cancel the project.
The reason for the larger majority in the second vote was probably the statement by Boeing’s chairman that at least $500 million more would be needed to revive the program.) …………………………… ………… —————————– Subject: 2.15) What is being done about ozone depletion? The 1987 Montreal Protocol (full text available on the world-wide web at http://www.unep.org/unep/secretar/ozone/treaties.h tm) specified that CFC emissions should be reduced by 50% by the year 2000 (they had been increasing by 3% per year.) This agreement was amended in London in 1990, to state that production of CFC’s, CCl4, and halons should cease entirely by the year 2000. Restrictions were also applied applied to other Cl sources such as methylchloroform. (The details of the protocols are complicated, involving different schedules for different compounds, delays for developing nations, etc.) The phase-out schedule was accelerated by four years by the 1992 Copenhagen agreements. A great deal of effort has been devoted to recovering and recycling CFC’s that are currently being used in closed-cycle systems.
For more information about legal and policy issues, see the books by [Bene*censored*] and [Litvin], and the following web sites: http://www.unep.org/unep/secretar/ozone/home.htm http://www.unep.ch/ozone/ (European mirror site for above) http://www.epa.gov/docs/ozone/index.html http://www.ciesin.org/TG/OZ/ozpolic.html Recent NOAA measurements [Elkins et al. 1993] [Montzka et al. 1996] show that the rate of increase of halocarbon concentrations in the atmosphere has decreased markedly since 1987. It appears that the Protocols are being observed. Under these conditions total stratospheric chlorine is predicted to peak at 3.8 ppbv in the year 1998, 0.2 ppbv above 1994 levels, and to slowly decline thereafter.
[WMO 1994] Extrapolation of current trends suggests that the maximum ozone losses will be [WMO 1994]: Northern Mid-latitudes in winter/Spring: 12-13% below late 1960’s levels, ~2.5% below current levels. Northern mid-latitudes in summer/fall: 6-7% below late 1960’s levels, ~1.5% below current levels. Southern mid-latitudes, year-round: ~ 11% below late 1960’s levels, ~2.5% below current levels. Very little depletion has been seen in the tropics and little is expected there. After the year 2000, the ozone layer will slowly recover over a period of 50 years or so.
The antarctic ozone hole is expected to last until about 2045. [WMO 1991,1994] Some scientists are investigating ways to replenish stratospheric ozone, either by removing CFC’s from the troposphere or by tying up the chlorine in inactive compounds. This is discussed in Part III. —————————– Subject: 3. REFERENCES FOR PART I A remark on references: they are neither representative nor comprehensive. There are hundreds of people working on these problems. Where possible I have limited myself to articles that are (1) available outside of University libraries (e.g. Science or Nature rather than archival journals such as J.
Geophys. Res. ) and (2) directly related to the frequently asked questions. I have not listed papers whose importance is primarily historical. (I make an exception for the Nobel-Prize winning work of Crutzen, Molina and Rowland.) Readers who want to see who did what should consult the review articles listed below, or, if they can get them, the WMO reports which are extensively documented. —————————– Subject: Introductory Reading [Garcia] R. R.
Garcia, Causes of Ozone Depletion, Physics World April 1994 pp 49-55. [Graedel and Crutzen] T. E. Graedel and P. J. Crutzen, Atmospheric Change: an Earth System Perspective , Freeman, NY 1993.
[Rowland 1989] F.S. Rowland, Chlorofluorocarbons and the depletion of stratospheric ozone, American Scientist 77 , 36, 1989. [Rowland and Molina 1994] F. S. Rowland and M.
J. Molina, Ozone depletion: 20 years after the alarm, Chemical and Engineering News , 15 Aug. 1994, pp. 8-13. [Zurer] P.
S. Zurer, Ozone Depletion’s Recurring Surprises Challenge Atmospheric Scientists, Chemical and Engineering News , 24 May 1993, pp. 9-18. —————————– Subject: Books and Review Articles [Bene*censored*] R. Bene*censored*, Ozone Diplomacy , Harvard, 1991. [Brasseur and Solomon] G. Brasseur and S. Solomon, Aeronomy of the Middle Atmosphere , 2nd.
Edition, D. Reidel, 1986 [Chamberlain and Hunten] J. W. Chamberlain and D. M. Hunten, Theory of Planetary Atmospheres , 2nd Edition, Academic Press, 1987 [Dobson 1968a] G.
M. B. Dobson, Exploring the Atmosphere , 2nd Edition, Oxford, 1968. [Dobson 1968b] G. M.
B. Dobson, Forty Years’ research on atmospheric ozone at Oxford, Applied Optics , 7 , 387, 1968. [CIC 1975] Climate Impact Committee, National Research Council, Environmental Impact of Stratospheric Flight , National Academy of Sciences, 1975. [Johnston 1992] H. S.
Johnston, Atmospheric Ozone, Annu. Rev. Phys. Chem. 43 , 1, 1992.
[Ko et al.] M. K. W. Ko, N.-D. Sze, and M.
J. Prather, Better Protection of the Ozone Layer, Nature 367 , 505, 1994. [Litvin] K. T. Litvin, Ozone Discourses , Columbia 1994. [McElroy and Salawich] M. McElroy and R.
Salawich, Changing Composition of the Global Stratosphere, Science 243, 763, 1989. [Rowland and Molina 1975] F. S. Rowland and M. J.
Molina, Chlorofluoromethanes in the Environment, Rev. Geophys. & Space Phys. 13 , 1, 1975. [Rowland 1991] F. S.
Rowland, Stratospheric Ozone Depletion, Ann. Rev. Phys. Chem. 42 , 731, 1991.
[Salby and Garcia] M. L. Salby and R. R. Garcia, Dynamical Perturbations to the Ozone Layer, Physics Today 43 , 38, March 1990. [Solomon] S. Solomon, Progress towards a quantitative understanding of Antarctic ozone depletion, Nature 347 , 347, 1990.
[Wallace and Hobbs] J. M. Wallace and P. V. Hobbs, Atmospheric Science: an Introductory Survey , Academic Press, 1977.
[Wayne] R. P. Wayne, Chemistry of Atmospheres , 2nd. Ed., Oxford, 1991. [WMO 1988] World Meteorological Organization, Report of the International Ozone Trends Panel , Global Ozone Research and Monitoring Project – Report #18.
[WMO 1989] World Meteorological Organization, Scientific Assessment of Stratospheric Ozone: 1991 Global Ozone Research and Monitoring Project – Report #20. [WMO 1991] World Meteorological Organization, Scientific Assessment of Ozone Depletion: 1991 Global Ozone Research and Monitoring Project – Report #25. [WMO 1994] World Meteorological Organization, Scientific Assessment of Ozone Depletion: 1994 Global Ozone Research and Monitoring Project – Report #37. The Executive Summary of this report is available on the World-Wide Web at http://www.al.noaa.gov/WWWHD/pubdocs/WMOUNEP94.htm l —————————– Subject: More Specialized References [Bojkov et al. 1995] R.
D. Bojkov, V. E. Fioletov, D. S. Balis, C.
S. Zerefos, T. V. Kadygrova, and A. M. Shalamjansky, Further ozone decline during the northern hemisphere winter-spring of 1994-95 and the new record low ozone over Siberia, Geophys.
Res. Lett. 22 , 2729, 1995. [Brasseur and Granier] G. Brasseur and C. Granier, Mt. Pinatubo aerosols, chlorofluorocarbons, and ozone depletion, Science 257 , 1239, 1992.
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Met. Soc. 90 , 320, 1970. [Elkins et al. 1993] J. W. Elkins, T.
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D. Hall, S. O. Cummings, D. A.
Fisher, and A. G. Raffo, Decrease in Growth Rates of Atmospheric Chlorofluorocarbons 11 and 12, Nature 364 , 780, 1993. [Fahey et al. 1995] D.
W. Fahey, E. R. Keim, K. A. Boering, C.
A. Brock, J. C. Wilson, H. H. Jonsson, S.
Anthony, T. F. Hanisco, P. O. Wennberg, R. C.
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S. Gao, S. G. Donnelly, R. C. Wamsley, L.
A. Del Negro, S. Solomon, B. C. Daube, S.
C. Wofsy, C. R. Webster, R. D. May, K.
K. Kelly, M. Loewenstein, J. R. Podolske, and K.
R. Chan, Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere, Science 270 , 70, 1995. [Gleason et al.] J. Gleason, P. Bhatia, J. Herman, R.
McPeters, P. Newman, R. Stolarski, L. Flynn, G. Labow, D. Larko, C.
Seftor, C. Wellemeyer, W. Komhyr, A. Miller, and W. Planet, Record Low Global Ozone in 1992, Science 260 , 523, 1993. [Henriksen and Roldugin] K.
Henriksen and V. Roldugin, Total ozone variations in Middle Asia and dynamics meteorological processes in the atmosphere, Geophys. Res. Lett. 22 , 3219, 1995.
[Henriksen et al. 1992] K. Henriksen, T. Svenoe, and S. H. H.
Larsen, On the stability of the ozone layer at Tromso, J. Atmos. Terr. Phys. 55 , 1113, 1992.
[Herman et al.] J. R. Herman, R. McPeters, and D. Larko, Ozone depletion at northern and southern latitudes derived from January 1979 to December 1991 TOMS data, J. Geophys. Res.
98 , 12783, 1993. [Hofmann and Solomon] D. J. Hofmann and S. Solomon, Ozone destruction through heterogeneous chemistry following the eruption of El Chichon, J.
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J. Oltmans, W. D. Komhyr, J. M. Harris, J.
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J. Johnson, A. Torres, and W. A. Matthews, Ozone Loss in the lower stratosphere over the United States in 1992-1993: Evidence for heterogeneous chemistry on the Pinatubo aerosol, Geophys.
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J. Hofmann, S. J. Oltmans, J. M. Harris, J.
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Deshler, and B. J. Johnson, Recovery of stratospheric ozone over the United States in the winter of 1993-94, Geophys. Res. Lett. 21 , 1779, 1994. [Hofmann et al.
1996] D. J. Hofmann, S. J. Oltmans, G.
L. Koenig, B. A. Bodhaine, J. M. Harris, J.
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23 , 1533, 1996. [Kerr et al.] J. B. Kerr, D. I. Wardle, and P.
W. Towsick, Record low ozone values over Canada in early 1993, Geophys. Res. Lett. 20 , 1979, 1993. [Khalil and Rasmussen] M. A.
K. Khalil and R. Rasmussen, The Global Sources of Nitrous Oxide, J. Geophys. Res. 97 , 14651, 1992.
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R. Trepte, Atmospheric effects of the Mt Pinatubo eruption, Nature 373 , 399, 1995. [McPeters et al. 1996] R. D.
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15 , 171, 1992. —————————– Subject: Internet Resources This list is preliminary and by no means comprehensive; it includes a few sites that I have found particularly useful and which provide good starting points for further exploration. Probably the most extensive collection of online resources is that provided by the Consortium for International Earth Science Information Network: http://sedac.ciesin.org/ozone/ It includes links to many other documents, including on-line versions of some of the original research papers. At the present time portions of the site are very much under construction. Lenticular Press publishes a multimedia CD-ROM (for Apple Macintosh) containing ozone data and images, as well as a hypertext document similar to this FAQ. For sample images and information about ordering the CD, see http://www.lenticular.com/ Note that these samples are copyrighted and may not be further distributed. The NOAA Aeronomy Lab: http://www.al.noaa.gov/ , has the text of the Executive Summary of the 1994 WMO Scientific Assessment, http://www.al.noaa.gov/WWWHD/pubdocs/WMOUNEP94.htm l The United Nations Environmental Program (UNEP) Ozone Secretariat: Main page http://www.unep.org/unep/secretar/ozone/home.htm (Nairobi, Kenya). Mirror site http://www.unep.ch/ozone/ (Geneva, Switzerland). The US Environmental Protection Agency has an ozone page that includes links to both science and policy resources: http://www.epa.gov/docs/ozone/index.html Some of the more interesting scientific web pages include: The Centre for Antarctic Information and Research (ICAIR) in New Zealand: http://icair.iac.org.nz/ozone/index.html Environment Canada: http://www.doe.ca/ozone/index.htm The TOMS home page: http://jwocky.gsfc.nasa.gov/ The EASOE home page: http://www.atm.ch.cam.ac.uk/images/easoe/ The UARS Project Definition page: http://daac.gsfc.nasa.gov/CAMPAIGN DOCS/UARS project.html The HALOE home page: http://haloedata.larc.nasa.gov/home.html The British Antarctic Survey: http://www.nbs.ac.uk/public/icd/jds/ozone/ The ETH Zuerich Institute for Atmospheric Science http://www.umnw.ethz.ch/LAPETH/lapeth.html The Institute for Meteorology at the Free University of Berlin: http://strat-www.met.fu-berlin.de/ The Climate Prediction Center’s TOVS Total Ozone Analysis page: http://nic.fb4.noaa.gov:80/products/stratosphere/t ovsto/ The USDA UV-B Radiation Monitoring Program Climate Network, http://uvb.nrel.colostate.edu/UVB/uvb climate network.html [ By Archive-name | By Author | By Category | By Newsgroup ] [ Home | Latest Updates | Archive Stats | Search | Usenet References | Help ] Send corrections/additions to the FAQ Maintainer: [email protected] Last Update September 28 2000 @ 04:24 AM Ozone Depletion FAQ Part IV: UV Radiation and its Effects From: [email protected] (Robert Parson) Newsgroups: sci.environment,sci.answers,news.answers Subject: Ozone Depletion FAQ Part IV: UV Radiation and its Effects Followup-To: poster Date: 24 Dec 1997 20:51:43 GMT Organization: University of Colorado, Boulder Expires: Sun, 1 Jan 1998 00:00:00 GMT Message-ID: *[email protected]* Reply-To: [email protected] Summary: This is the fourth of four files dealing with stratospheric ozone depletion.
It describes the properties of solar UV radiation and some of its biological effects. Keywords: ozone layer depletion UVB UVA skin cancer phytoplankton Archive-name: ozone-depletion/uv Last-modified: 16 Dec 1997 Version: 5.9 —————————– Subject: How to get this FAQ These files are posted to the newsgroups sci.environment, sci.answers, and news.answers. They are also archived at a variety of sites. These archives work by automatically downloading the faqs from the newsgroups and reformatting them in site-specific ways. They usually update to the latest version within a few days of its being posted, althou.