« ПредыдущаяПродолжить »
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 uş 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. În 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.0.2 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.
If we ask ourselves what is the concentration of water vapor, if we take some air and cool it to minus 80 degrees centigrade, we find that the air is saturated with moisture at about 80 centigrade and the amount is about 2 micrograms per gram.
So, nature limits the amount of vapor going into the stratosphere by freezing out additional moisture in the areas of low temperatures.
For this reason, wherever we go we find numbers about this size, ranging about 1 to 4 micrograms per gram, but 2 or 3 is about the average value.
This way, nature puts a limit on the amount of moisture in the stratosphere. We are planning to circumvent that process by taking a plane and putting the water vapor in for the first time directly above this natural trap altitude of 60,000 or 70,000 feet.
This air, therefore, is not to be dried out, and the question is what will happen. Obviously, one can do simple things and show that the water vapor introduction will correspond to about 20 or 30 percent of the natural rate of introduction and, therefore, the long-term concentration will go up by the same amount.
My argument is that this will introduce additional clouds in the stratosphere in places where we no longer have any clouds. We already have clouds in the stratosphere in three general regions.
First of all, in the vicinity of 25 kilometers, 80,000 feet, roughly, 16 miles or so; there are clouds at high latitudes in the winter. These clouds are called mother-of-pearl clouds because they have an irridescence to them which resembles the mother-of-pearl. These clouds are present during January-February, in the winter, at high latitudes.
In the Northern Hemisphere, they are mainly seen over Norway because people are at those latitudes and the angles of viewing are right. There are clouds there.
SATURATION OF AIR
Then, if one looks at the temperature, then one finds again that the temperature is about minus 85 and one has produced saturation of this air which was introduced in the tropics when it passes to high latitudes.
It was introduced in the tropics and moves over to high latitudes. It is saturated again and clouds form. Whenever one has mean rising motion in the atmosphere and saturation is produced by the mean rising motion, then one gets clouds. This is the opposite effect of the bicycle pump. If you pump your bicycle pump, you make the air warm. Nature is taking the air up to a lower pressure. The air is rising and it is expanding. You know, if you have done these experiments in the laboratory, that as the air expands condensation occurs, once the temperature gets down to a certain value where saturation occurs. This is how nature produces clouds in the troposphere and the stratosphere.
EFFECT OF INTRODUCTION OF WATER VAPOR IN ATMOSPHERE
If we are looking for other regions where there are clouds, over the South Pole in the Antarctic, out to 70° south, there is a constant thin
layer which was reported by the Norwegian and Swedish Antarctic expeditions. It is at about 70,000 or 80,000 feet, existing from about June to the middle of October. It is seen in that general period. If we introduce more water vapor in the atmosphere, the regions where clouds form will increase. My point is, we don't know what effect this will have on the large-scale circulation of the atmosphere. When we don't know, we don't go ahead. That is my personal opinion in this
WATER VAPOR BREAKUP
There are other possible effects of the water vapor which other people have discussed. The argument I have given is my reprints
. Other people have pointed out that water vapor may influence ozone. The reason the influence of ozone is that people feel the water vapor will contribute hydrogen to the atmosphere when it breaks up, under the influence of sunlight at higher levels or under the influence of chemical reactions in the lower stratosphere.
Hydrogen is a catalyst for ozone. If you take ozone and mix hydrogen in it, the ozone concentration goes down. One ends up eventually with hydroxile, and eventually back with molecular oxygen. So the arguments outlined there are that hydrogen will come when water vapor is introduced and this will, in turn, influence the ozone distribution. It is difficult to decide how much this will influence the ozone distribution.
What needs to be done is a three-dimensional, thermodynamic model, such as is operated by the NOAA group at Princeton University. This needs to be studied in detail over longtime periods with different water vapor concentrations. The problem there is that it takes at present about a day of computer time to simulate a day of real time.
They have actually simulated two cases with hydrogen and without hydrogen, with water and without water, in the stratosphere, and they have produced a paper which I have referred to in my testimony here, which describes the differences between these two.
DECREASE OF OZONE
The details of the decrease of ozone due to water vapor is that has been studied. If we decrease ozone, then we will change the local heating rate. I have given a graph of local radiative heating rates. What makes the air have the temperature that it has in the stratosphere? It is the fact that it contains carbon dioxide, ozone and water vapor.
If you took all those out, the temperature distribution would be completely different. If you change the distribution the temperature difference would be completely different. So, what we have to do is to study the changes introduced by the additional hydrogen. I should make the point here that it is not just water vapor. If the combustion is inefficient and hydrocarbons are also introduced, they, too, can contribute to hydrogen.
METHANE IN THE STRATOSPHERE
There has been some discussion recently concerning methane introduction into the stratosphere, a natural constituent, and the change
over from methane to water vapor. I referred to that, too, in the literature. This was discussed in a seminar last year.
CHANGES IN ULTRAVIOLET RAYS
In addition, there will be changes in the ultraviolets reaching the surface. There was testimony on that before the House last week, the possible effects of changing that.
Certainly, if one changes ozone, one will certainly change the ultraviolets reaching the surface. The reason is that ozone provides the cutoff of the solar spectrum for all wavelengths short of about 3,000 angstroms.
If you look at the spectrum outside atmosphere, which we are able to do, you find there a distribution of energy with wavelengths, which I give in detail in a reference, again in the Scientific American in 1964, but part of this energy never gets down to the surface.
Much of the speculation on live information is that we were in the sea until there was enough oxygen liberated from the ocean to form
layer of protective ozone.
OZONE IN THE STRATOSPHERE
There is no questions if you look at the sun spectrum from the surface you see a cutoff from the spectrum. There is no energy at wavelengths short of 3,000 angstroms. The reason for this is the presence of ozone in the stratosphere.
If you remove the ozone or change it, then you can change the ultraviolet by, usually, a factor greater than 2. There is no question about that.
The question is where the debate comes in are on the other parts of the hypothesis.
There are other items which are related to the pollutants, the oxides of nitrogen, hydrocarbons and so on, and some of these have been discussed in the MIT summer study which has been published, and which is, again, referred to in my statement.
CONVERSION OF SUBSTANCES TO PARTICULATES
Two of the points which come out of this: First of all, if we introduce substances which convert to particulates, then we know we can produce temperature changes in the stratosphere of a fairly large size.
Los Angeles smog is a case where particulates originate from gases. One does not actually put in the particulates in Los Angeles. One ends up with a fine haze which is called smog. There is a very good question as to whether or not we can produce a smog in the stratosphere by similar processes if we put in similar constituents.
One of the points I would like to make is that we don't know enough about the composition of the stratosphere to say whether or not we will produce smog. We are turning up constantly items which were unknown a few years ago.
NITRIC ACID IN THE STRATOSPHERE
Last year, nitric acid was discovered in the stratosphere. We didn't know about that 3 years ago.