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Aviation History
1991
1991 - 0028.PDF
a major area of uncertainty. Some nitrogen compounds might be converted into a benign form or equally they might lead to further ozone depletion. NASA is also devising more-precise mod elling tools, particularly those operating in three dimensions (3D). Once perfected, 3D models will simulate the effects of emis sions in flight corridors such as those in the eastern USA the UK and France. According to the assistant head of the theoretical studies branch in atmospheric sciences at Langley, Dr Bill Grose, "...this research is a high priority if we are to better predict the chemical effect on stratospheric ozone". International research on the subject is beginning to be pooled, and modelling groups from Europe, Japan, the USA and the Soviet Union will be meeting at Virginia Beach on 7 January, 1991, to compare initial results. More accurate measurement of emissions from supersonic aircraft operating in the stratosphere is the third area of NASA's research. It will involve validation trials, probably using the ER-2 to sample exhaust- plume emissions. Data collected by satellite will also assist the analysis. NOx RESEARCH NEEDED Earlier this year the then president of the European Civil Aviation Conference, Daniel Tenenbaum, made a plea for more research into the effects of NOx on the atmosphere. Tenenbaum voiced his concern that "...little work in this area has been done since the Concorde programme". Indeed, it was only very late in the debate over introducing SSTs in the early 1970s that the issue of ozone destruction was raised. Attention had been directed towards Concorde's engine noise and sonic boom. Once it became clear that only a small fleet of 14 SSTs would be built, however, re search interest in their environmental im pact waned. The prospect of SST development costs of up to $10 billion and the production of at least 300 aircraft has concentrated minds in the scientific community. NASA claims that spending more of its high-speed research programme budget on atmospheric studies would not be practical because there are more aeronautical and propulsion engineers than atmospheric chemists and meteorolo gists. Given that initial research shows that future supersonic travel would damage ozone levels and the chemical complexity of the atmosphere, others suggest that the priority is to understand chain reactions unleashed and to determine just how seri ous their consequences would be. Although the chemistries of the strato sphere and troposphere are quite different, emissions of nitrogen oxides from subsonic aircraft in the latter will raise the level of photo-chemically produced ozone in the troposphere. Unfortunately, this new ozone cannot replace that lost in the stratosphere. The distribution of ozone Stratosphere Troposphere Nox emissions from SSTs cause most damage to ozone Ozone Layer 15km Tropopause Most commercial aircraft operate up to 12km t Concentration of ozone at ground level up to 1 km Boundary layer Increased levels of ozone in the troposphere would actually be harmful to vegetation and animal life. • The emission of water by. aircraft in the form of vapour trails in the • upper tropo sphere and lower stratosphere will produce more cloud and hydroxyl radreal and con tribute to global warming, environmental experts argue. There is also the increased risk, they say, of forming stratospheric ice clouds which contribute to ozone holes at the poles. Addressing an international conference on the environment in June, Juan Cisneros, a research scientist from the Spanish Ant arctic weather station, forecast that the depletion of ozone would also cool the stratosphere because more ultra-violet en ergy would be allowed through. With the troposphere becoming warmer through the "greenhouse effect" the combined result would be greater convection, leading to clouds rising higher into the atmosphere, increasing water-vapour levels in the lower stratosphere. Johnson's research suggests that, even if the Nasa emission index goal is achieved, SSTs will reduce ozone levels at the same speed as indefinite usage of CFCs at the 1985 rate. Johnson says that ozone deple tion would not be so severe if the SSTs operated at lower altitudes, if there were fewer of them, or if they achieved greater fuel efficiency. Once the results of independent and NASA-funded research have been studied, the world will have to decide whether supersonic travel can be made safe. The decision must involve the United Nations Environmental Programme. As NASA's Grose emphasises: "The future of the world will be in their hands". • NASA's ER-2 research aircraft may fly behind Concorde or an SR-71 to examine emissions 26 FLIGHT INTERNATIONAL 2 - 8 January, 1991
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