CFC and Halon replacements in the environment

Substitute fluorocarbons may have direct environmental impact, for example as greenhouse gases, or indirect impacts through the products of their decomposition in the environment. The mechanisms of that atmospheric decomposition are reviewed here and shown to be well established now. The end products are halogen acids and trifluoroacetic acid, all of which pre-exist in the environment in quantities greater than are expected to arise from fluorocarbon use and emissions. Furthermore, the growth in use of fluorocarbon replacements has been shown to be far less than the fall in CFC and Halon production. Hydrochlorofluorocarbons (HCFCs) have replaced less than one third of CFCs and are, themselves, ozone depleting substances that will be phased out under the Montreal Protocol. The growth in hydrofluorocarbons (HFCs) amounts to about 10% of the fall in CFCs. It is likely that the impact of new fluorocarbons on climate change will be a very small fraction of the total impact, which comes mainly from the accumulation of carbon dioxide in the atmosphere.     

CFC phase-out: have we met the challenge?

In 1974 Nobel prize winners Rowland and Molina proposed that chlorofluorocarbons (CFCs) were stable enough to reach the stratosphere, where, under intense solar radiation they released Cl atoms that could destroy stratospheric ozone protecting the earth’s surface from UV rays. The CFC industry funded both scientific studies to test the Rowland and Molina hypothesis and programmes to identify potential replacements, from which the HFCs emerged as likely candidates. After 5 years it was concluded, on the best scientific evidence available, that stratospheric ozone was being depleted at ∼3% per decade, but sufficient time was available for an orderly phase-out. Although the USA and a few other countries stopped the use of CFCs in aerosols little further work was done until 1985 when the CFC debate was renewed following the discovery of stratospheric ozone depletion over the Antarctic during its spring. Manufacturers restarted their R&D programmes; governments negotiated the Montreal Protocol in 1987 agreeing the partial phase-out of the CFCs. As a result of subsequent amendments CFCs have now been phased-out in the developed world and HCFCs will follow over the next two decades. This paper reviews what has been achieved and what remains to be done. Has the world-wide effort been successful in protecting the ozone layer? Have “acceptable” alternatives been found for the CFCs/HCFCs in their various applications?     

《京都议定书》要减排哪些温室气体

《联合国气候变化框架公约--京都议定书》于2005年2月16日正式生效,本文介绍全球气候变暖的最新趋势,什么是温室气体,温室气体对于全球气候变暖的贡献大小所取决的主要因素,《京都议定书》要求减排的主要温室气体。     

WO3/ZrO2 Strong Acid as a Catalyst for the Decomposition of Chlorofluorocarbon (CFC-12)

IntroductionChlorofluorocarbons(CFCs) diffusing to the stratosphere isa major reason forozone de-pletion[1 ] .Also CFCshasbeen claimed to be notoriousforitsgreenhouseeffect[2 ] .So,recent-ly it has become very important to eliminate CFCs as far as protecting the ozone layer sur-rounding the earth is concerned.Among various kinds of approaches to do destruction toCFCs,the catalytic decomposition seems to be the most practical and energetically favorableone,especially for treating small amo…     

Skin Cancer Risks Avoided by the Montreal Protocol—Worldwide Modeling Integrating Coupled Climate‐Chemistry Models with a Risk Model for UV

The assessment model for ultraviolet radiation and risk “AMOUR” is applied to output from two chemistry‐climate models (CCMs). Results from the UK Chemistry and Aerosols CCM are used to quantify the worldwide skin cancer risk avoided by the Montreal Protocol and its amendments: by the year 2030, two million cases of skin cancer have been prevented yearly, which is 14% fewer skin cancer cases per year. In the “World Avoided,” excess skin cancer incidence will continue to grow dramatically after 2030. Results from the CCM E39C‐A are used to estimate skin cancer risk that had already been inevitably committed once ozone depletion was recognized: excess incidence will peak mid 21st century and then recover or even super‐recover at the end of the century. When compared with a “No Depletion” scenario, with ozone undepleted and cloud characteristics as in the 1960s throughout, excess incidence (extra yearly cases skin cancer per million people) of the “Full Compliance with Montreal Protocol” scenario is in the ranges: New Zealand: 100–150, Congo: ?10–0, Patagonia: 20–50, Western Europe: 30–40, China: 90–120, South‐West USA: 80–110, Mediterranean: 90–100 and North‐East Australia: 170–200. This is up to 4% of total local incidence in the Full Compliance scenario in the peak year.     

The effect of galactic cosmic rays on the chemical composition of the atmosphere,greenhouse effect and ozone layer of the Earth

Estimations of the effects of galactic cosmic rays (GCR) on chemical composition of the troposphere and stratosphere in view of known mechanisms of formation of NO and OH under impact of GCR have been made. It has been shown that GCR may significantly change a chemical composition of the upper troposphere and the stratosphere. However, GCR do not influence on an abundance of H-containing greenhouse gases (such as methane and ozone-harmless freons) but can noticeably reduce the concentration of atmospheric ozone. Those estimations have shown a necessity to take into account the influence of GCR on the composition of the atmosphere at the analysis of ozone related processes and, in particular, at forcasting recovery of the ozone layer.     

A New Mechanism for the Formation of the Ozone Hole in the Earth Atmosphere

It is generally accepted that the Earth ozone layer is depleted by chlorine atoms produced via solar photolysis of chlorofluorocarbons (CFCs) in the upper stratosphere^[1]. This photodissociation model predicts an ozone depletion maximum at an altitude between 30 and 40 km and negligible ozone depletion below 20 km^[1]. However, the Antarctic/Arctic ozone hole appearing in each spring is observed to be located at an altitude of about 15 km^[2]. The formation of the ozone hole has been attributed to heterogeneous reactions on the surface of polar stratosphere clouds (PSCs) consisting mainly of condensed water ice:HCl+ClONO₂→Cl₂+HNO₃^[3,4]. Recently, it has been observed that dissociation of CFCs by capture of low-energy electrons is enhanced by several orders of magnitude when CFCs are adsorbed on the surfaces of ice films of polar molecules such as H₂O and NH₃^[5,6]. This enhancement is due to transfer of electrons in precursors of solvated states in polar molecular ice to CFCs that then dissociate^[7]. This effect should be most efficient in the lower stratosphere of about 15 km, where low-energy electrons can be produced by cosmic-ray ionization and localized in precursors of solvated electrons in PSCs^[8]. Strong and straightforward evidence of this new mechanism for ozone depletion has also been found in data obtained from field measurements (satellites, balloons, etc.)^[8]. In this talk, we will present the data from both field and laboratory measurements and discuss the new mechanism for the formation of the ozone hole.     

功能化金属有机框架材料催化二氧化碳转化研究进展

作为主要温室气体,二氧化碳(CO_2)导致了全球变暖与海洋酸化,同时CO_2也是重要的C1资源。在温和条件下,利用催化剂将CO_2高效、高选择性地转化为具有高附加值的化学品,对缓解CO_2给气候变化带来的负面影响和减少对化石能源的依赖具有重要意义。作为一类新兴的多孔晶态材料,金属-有机框架(metal-organic frameworks,MOFs)同时具备多相催化剂的可分离回收再利用以及均相催化剂的高选择性和高活性等性质,是优良的多相催化剂。本文主要聚焦功能化MOFs催化剂的结构特性及其在催化转化CO_2方面的应用,着重介绍该领域近期的研究进展,并对今后该领域的研究趋势及应用前景进行了展望。     

大气臭氧层破坏和CFCs替代物

CFCs 是与国民经济发展有关的重要化学材料。因为CFCs 破坏大气臭氧层,要限制它的使用并努力寻找它的替代物。研究和发展CFCs 替代物是有机氟化学的一个重要课题。     

Reagents for Selective Fluoromethylation: A Challenge in Organofluorine Chemistry

The introduction of a monofluoromethyl moiety has undoubtedly become a very important area of research in recent years. Owing to the beneficial properties of organofluorine compounds, such as their metabolic stability, the incorporation of the CH₂F group as a bioisosteric substitute for various functional groups is an attractive strategy for the discovery of new pharmaceuticals. Furthermore, the monofluoromethyl unit is also widely used in agrochemistry, in pharmaceutical chemistry, and in fine chemicals. The problems associated with climate change and the growing need for environmentally friendly industrial processes mean that alternatives to the frequently used CFC and HFBC fluoromethylating agents (CH₂FCl and CH₂FBr) are urgently needed and also required by the Montreal Protocol. This has recently prompted many researchers to develop alternative fluoromethylation agents. This Minireview summarizes both the classical and new generation of fluoromethylating agents. Reagents that act via electrophilic, nucleophilic, and radical pathways are discussed, in addition to their precursors.