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per gram of air.
Most of the moisture measurements made between the tropo
pause and 30 lom the limit of balloon sounding are in the range 1-4 micro
grans per gran (1). The stratosphere is kept dry by this natural freeze-out mechanism and the total moisture content above 16 km is about 2015
The flux of moisture into the stratosphere based upon current estimates
of the mean vertical velocity at the tropopause (2, 3) is between 7 and
the stratosphere from methane and hydrogen passing up from the troposphere
and oxygen already in the stratosphere (4). This possibility contributes
to the uncertainty in the flux figure.
For flux values of 7 and 10 million
grams per second the mean residence times (content derived, by flux) are
4.5 and 3.2 years respectively. Recent estimates of the mean residence
times of carbon 14 and tritium are 3.3 years and 3.5 years respectively
These residence times for gases are of course longer than those
for particles which are usually taken to be about 1 1/2 to 2 years in the
region below 25 km.
The water vapor observations fit together well, with perhaps the main
uncertainty being the methane contribution, and the natural flux is brac
500 planes will contribute about 2 million grams per second the main
difference being that this water vapor is added above the cold trap.
the long run then the stratospheric water vapor content will go up by 20
= mean flux times residence time). Locally in regions of
high travel density there will of course be regions of much higher concen
Patches of air with radioactivity concentrations well above the
global mean persist for many months after nuclear tests and radioactive
tungsten from the 1958 Pacific shots was seen to have higher concentrations
in the tropical stratosphere than in the high latitude stratosphere for
more than two years.
Water vapor enters the stratosphere at low latitudes in the rising
motion region of the lladley cell circulation (see figures in my Scientific
American article attached). There are no major middle lacitude sources;
if there were there would be a much higher mean concentration observed in
the stratosphere for the temperatures are much higher, at middle latitudes.
Much has been said in the press concerning thunderstorms as a source of
of the mean Hadley cell circulation at low latitudes but they cannot
Introduce more than the number quoted above of 7-10 million grams per
If they did the stratosphere would very soon show evidence of
increasing water vapor concentrations.
The hypothesis in these letters
to the press that one thunderstorm introduces as much as 2 million grams
per second and that thousands are penetrating to 70000ft. at any one time
implies rapid flooding of the stratosphere.
It is clearly an incorrect
hypothesis and it is significant to me that it has not been offered
seriously in the scientific literature; I cannot even trace its originator!
There are three consequences of this additional water vapor:
change the radiative cooling in the stratosphere; it will interact with
ozone to reduce the ozone concentration; and it may give rise to additional
The change in radiative cooling due to the presence of the vapor
alone is expected to be small (7). Basically this is because water vapor
plays a subsidiary role to ozone and carbon dioxide in the stratosphere.
The problems of computing the ozone concentration in an atmosphere
containing water vapor have been studied by a number of people in the
past few years. (8-13). Ozone (03) 1s formed when atomic oxygen (0) originating from molecular oxygen (O2) by the absorption of short wavelength radiation, combines with molecular oxygen (O2). The studies show an expected decrease of ozone; for example Harrison of the Boeing Company
predicts a decrease in ozone of about 4% from the additional SST water
vapor. Basically the decrease occurs because the hydrogen from the water
vapor acts as a catalyst to change ozone back to molecular oxygen.
reactions that take place at these high altitudes are not known with
it is quite possible that hydrogen introduced from the fuel
in forms other than water vapor would act in the same way to further
deplete the ozone.
Professor MacDonald has raised the possibility that
the decrease in ozone will permit more ultraviolet to reach the surface
and that this in turn will increase the incidence of skin cancer.
straightforward to estimate the magnitudes involved in the first part of
his hypothesis. For example at the latitude of Miami in summer ultraviolet at 30008 wavelength would increase by 11% if ozone decreased by 4%, assuming
the biological effects of ultraviolet light (e.g. 14, 15) and it is not
I discussed the possibility of cloud formation one year ago and there have been no scientific rebuttals in the literature since. It is also
discussed in the M.I.T. Study of Critical Environmental Problems (16).
Clouds form in air which is saturated with water vapor; the air can
hold less water vapor at low temperatures and in the stratosphere rising
motion and adiabatic expansion coupled with radiative processes produce
the low temperatures.
Clouds occur naturally in the 22-27 km height range
at high latitudes in winter.
These mother-of-pearl clouds are often
reported as patches over Norway but as continuous sheets over the Antarctic
where temperatures are lower.
The region of cloud formation would be
expected to grow in extent as the water vapor concentration Increases.
The feedback of the clouds on the temperature distribution cannot properly
be assessed without a comprehensive dynamical model and this is not yet
The region of increased cloudiness will correspond fairly
closely with the region of lowest temperatures at 25 kom. In January this
region is over Norway, Greenland and Iceland and sometimes moves over
(see two examples in Figure 1). Temperatures are normally too
high for additional clouds to form in the summer season near 25 km.
Clouds form near 80 km in summer at high latitudes; again they occur
In regions of low temperatures and rising motions.
clouds are often obsrved over Norway and Sweden. Again increased water
vapor would be expected to result in increased clouds.
I note here that changes in other gaseous constituents such as the oxides
of nitrogen and hydrogen as mentioned earlier, can alter ozone amounts. Few
computations have been performed (11).
All the estimates of the influence on the real atmosphere require a full
dynamical model simulation before they can be properly assessed; this applies
to the photochemical computations which need to have the effects of atmospheric
motions included (after all they are dominant in the lower stratosphere) as well
as the discussion of clouds.
In addition a careful study of all other
possible reactions is needed.
Measurements are required of all the gaseous
and particulate components of the stratosphere and for a full understanding
these should be on a global basis.
3. AEROSOL FORMATION
The SST fleet will introduce small particles directly into the stra
tosphere and as there are no processes acting to wash them out their resi
dence time is long, typically 2 years.
This hold-up of particulate debris
was quite evident in the nuclear test observations and contrasts sharply
to the case of the troposphere where most of the muclear debris was removed
within 30 days (much by rainfall). The amounts of aerosols that might be
lavolved are discussed in the M.I.T. Summer-Study book (16) and I will
Qot repeat the discussion here.
Not discussed at length there is the
possibility of smog formation from the gases introduced by the sst. Large
quantities of oxides of nitrogen are expected, together with traces of
hydrocarbons and these seem to be the necessary ingredients of smog.
short-wave flux favorable to smog formation is stronger in the stratosphere
than at the surface and there is of course ozone in abundance,
topic of particle formation in the stratosphere is at a very rudimentary
stage and needs much more work. In fact the joint Interaction between
to be done.
Parenthetically suppose that you had been told in 1920 that the emissions
from autos in California would build up to the point where in 50 years
time school-children would be kept indoors and told not to excercise
would have been the response? We now have the smog and are taking plece
meal actions aimed at ensuring that it does not get too much worse but
there is little serious hope of major improvement. If the SST fleet does
produce stratospheric smog in 1990 what hopes would there be for a rever
sal then? By then so many jobs will be involved that the arguments will
be the same as those used to justify the condition of Los Angeles now.
We do know that when particles appear in the stratosphere they absorb
sunlight and lead to higher temperatures. After the Mt. Agung, Bali
eruption in 1963 temperatures in the lower stratosphere increased by 5-8°C
over equatorial regions (18). We do not know whether the volcano Intro
duced particles directly or whether it introduced gases (sulphur dioxide
and water vapor) which contributed to particle growth.
4. PARTICLE-WATER VAPOR INTERACTION
The small particles introduced by the volcano absorbed sunlight and
this caused a rise in temperature of the lower tropical stratosphere. In
turn this higher temperature permits more water vapor to enter the
scratosphere (as the cold trap is heated) and there has been some evidence from noctilucent cloud occurrence that volcanoes are associated with the clouds. My point here is that if the SST's introduce substances from
which particles can form then nature can augment the additional water
vapor introduced by the planes by its own water vapor from the troposphere
passing upwards through the cold trap.
5. GLOBAL POLLUTION AND ENERGY RESOURCES
500 SST's flying 7 hours/day and using 28000 lbs of fuel per hour per
engine will require about 340 million barrels of fuel per year. This
should be compared with the present jet fuel production rate
present jet uses.
If we assume that 100 barrels of crude oil give 44 barrels of jet fuel
the total crude oil necessary will be about 775 million barrels per year
or in round figures 2 million barrels per day. As can be seen in the