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Frequently Asked Questions


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Q.  a) Which gases make up the whole of the Earths atmosphere?
b) What their respective percentage levels are?
c) Do these percentage levels vary with altitude?
d) Are any seasonal variations in these levels?
e) How much carbon dioxide is annually deposited into the atmosphere?
f) What percentage of (e) above is produced naturally?
g) How much carbon dioxide is absorbed/released by the worlds oceans?
h) Is (g) above is affected by the temperature of the oceans?
j) How much sulphur is present in the atmosphere?  

A.  Nitrogen (N2) makes up 78% of the atmosphere (fraction of molecules),
which is 75.5% by mass. It is well mixed throughout the atmosphere
and there is no seasonal variation.
Oxygen (O2) makes up 21% by fraction, or 23% by mass and it is also
well mixed throughout the atmosphere and the seasonal variation os
miniscule.
Argon (A) is 0.9% by fraction, or 1.3% by mass and is well mixed
throughout the atmosphere and there is no seasonal variation.
Water vapor (H2O) is highly variable, and amounts to no greater than
4% by fraction. The vertical distribution of water vapor is highly
weighted toward the lowest altitudes. Once you rise above the 300mb
level of the atmosphere (about 30,000 ft) it has all but disappeared.

Once you get past these, the fractions are exceedingly small. we
measure CO2 in parts per million by volume (ppmv). One ppmv means one
molecule of the species per million of air. Google "Keeling Curve"
and you will see how CO2 has changed over the last 50 or so years. We
have now reached a CO2 concentration of about 380 ppmv, and the
seasonal variation is about 4 or 5 ppmv. This is on top of a long-
term increase in CO2 with a trend of about 1.8 ppmv/year. There is a
definite difference in concentration between the troposphere (pretty
well mixed) and the stratosphere ("old" air, CO2 concentration lags
that of the troposphere by several years and the lag is greater at the
higher latitudes).

Your questions (e), (f), (g) and (h) are all topics of ongoing
research. We do know that only half of the CO2 produced ends up in
the atmosphere, and the search is on for the sinks. We believe that
cold ocean is a sink, while warm ocean can release CO2 (but
phytoplankton can consume it, so it is a matter of competing reaction
rates that are time-variable).

You don't hear much about acid rain any more. Sulphur is for the most
part removed from coal before it is burned to generate power. If a
large volcanic eruption (like Pinetubo), then we will see SO2 releases
that will result in H2SO3. That, by the way, works opposite to CO2
because it result in higher reflectivity of the Earth to solar
radiation.

So, welcome to the study of a complex and dynamic planet.

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