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Proceedings of "Modification of stratospheric properties by trace constituent changes: direct evidence from the Bali volcanic eruption. Nature, 227, 697-698. Stratospheric temperature change from the Mt. Agung volcanic eruption of 1963. J. Atmos. Sci., 27, 977-978. The effect of changing CO2 concentration on radiative The global circulation of atmospheric pollutants. STRATOSPHERE PROBLEMS Dr. NEWELL. We have been examining the stratosphere, the physics and dynamics, for the past 11 years under support from the U.S. Atomic Energy Commission, because they came to us with a fairly simple problem. They said why is it that nuclear tests in the Pacific stay in the atmosphere for 2 to 5 years, and why is it that the debris from these nuclear tests falls out mainly at middle altitudes? Why is it that it falls out and we have a maximum in the spring? We have been studying this for the past 11 years. This has given us a background on stratospheric physics and dynamics which we supplemented with teaching duties which I think gives us a background to comment on future problems in the stratosphere. Just briefly to summarize the problems, the first is that the SST will introduce water vapor in quantities which are comparable to the quantities which are introduced by nature, itself. I am talking about 20 to 30 percent of the natural contents of water vapor, the rate of introduction, and, therefore, similar numbers for the mean concentration. Water is not a pollutant in the troposphere. Why should it be a pollutant in the stratosphere? We burn fossil fuel and get carbon dioxide and water vapor. This is inevitable. If we are lucky we just get carbon dioxide and water vapor, otherwise carbon monoxide, CH, and various other hydrocarbons. But in the stratosphere the concentration is extremely low. It is maintained by a gentle, rising motion in the tropical region. The rates of maintenance is of the order of 7 to 10 million grams per second, and we are proposing now for the very first time to introduce water vapor into the stratosphere artificially at a rate of about 2 million grams per second. TROPOSPHERE AND STRATOSPHERE Senator CASE. Would you be good enough to define the troposphere and stratosphere? Dr. NEWELL. The troposphere is the lowest region of the atmosphere. I can refer you to the Scientific American article which you have. It is the region where the temperature decreases with altitude. A cross section of the atmosphere defining troposphere and stratosphere is on page 33 of the reprints which I have submitted. In the lowest 8 or 10 kilometers of the atmosphere the temperature decreases. Senator CASE. Can you define it roughly in terms of miles? Dr. NEWELL. Yes. In terms of miles we are talking about 35,000 to 40,000 feet at midle altitudes above the earth surface is the boundary. At low altitudes the boundary is about 50,000 feeet. Senator CASE. So, anything above that? Dr. NEWELL. Anything above that is the stratosphere up to approximately 50 kilometers, or 250,000 feet. Above that is the mesosphere. Then, we have other regions at the higher levels. But for the purposes of discussion today, I will confine my remarks to the stratosphere. The basic difference between the stratosphere and the troposphere is that in the troposphere we have precipitation, rain, and snow, and clouds. This rain, snow, and clouds is a very efficient scavenger of the troposphere and removes particular matter and some trace gasses with a mean residence time of about 30 days. So, if we put in extra S.O.2 from a chimney and it turns into small sulphate particles and these grow into larger particles, these are eventually washed out of the troposphere within 30 or 40 days. We do not have cleaning mechanisms in the stratosphere. We have been able to get away with polluting the troposphere for the past 50 years because of the cleansing mechanism, because we have only polluted the lowest 30,000 or 40,000 feet. In the stratosphere there is no direct cleansing mechanism. Material introduced into the stratosphere can exist for very many years. For example, the debris from the burnup of a satellite powerplant, plutonium-239, which was introduced in 1964, was still present in the stratosphere during 1969. The residence time for small particles and gasses at high levels when pollutants are introduced is very long indeed. There is no washout mechanism. For removal, one has to rely upon the fact that air from the stratosphere constantly enters the troposphere at middle altitudes and cycles through the troposphere and gets washed out, rinsed, and then goes back into the stratosphere. PARCELS OF AIR So, it is the constant cycle of air from the stratosphere which eventually removes debris from the stratosphere. Senator CASE. When you say air, you mean air? Oxygen and nitrogen molecules are passing back and forth. But if we attract the parcel at 50 kilometers, it might be 5 years before it comes into the troposphere. If we track it at 75,000 feet in low altitudes, typically a residence time would be about 2 years. We can get these tracking times directly from the fact that nuclear debris from weapons tests have been introduced at a series of altitudes over the past 10 or 15 years and, in addition, several very high-level rocket shots have introduced nuclear debris. Satellite powerplants have burned up and introduced nuclear debris directly. This is where we get the background numbers. The first point I wanted to make, then, was that water vapor is a pollutant in the stratosphere because it is introduced in quantities, or we propose to introduce it in quantities, which are comparable to the rate of introduction by nature. Nature manages to keep the stratosphere very dry with mean mixing ratios. The amount of water vapor per gram of air, taking a gram of air from the stratosphere and asking how much water vapor is in there, is two-millionths of a gram of water vapor that resides in every gram of air in the stratosphere. The reason that nature keeps it so dry is that it makes all the air in the tropics rise gently-actually it is sporadically but looked at from our point of view it has an average mean motion-rise gently through the cold temperatures in the tropics. I can refer you in the reprints to the fact that the temperature there is about a minus 80 degrees centigrade. |