June 2, 1969

Dr. Louis S. Jaffe

Physical Science Administrator

Department of Health, Education, and Welfare
National Air Pollution Control Administration
411 West Chapel Hill Street

Durham, North Carolina 27701

Dear Dr. Jaffe:

Thank you for your recent letter of May 20, 1969, inquiring
about a calculated estimate of the mean residence time based on
your figure of CO production and our data on C!" content of atmos-
pheric Co.

Actually, given the concentration of CO and its rate of pro-
duction we can calculate its mean life without recourse to the c!*
specific activity. If we assume the CO concentration to be 0.1 pom
this means there is 0.1 mg CO/cm? of the earth surface. Your
estimate of the rate of production of CO, 2 x 10° tons/year, works
out to ae mg CO/year-cm* earth surface = 0.04 mg/cm? year.

x
Dividing this into the inventory of 0.1 mg/cm? we get Y = 2.5 years.

From the value of the specific activity obtained by us, and
again assuming a CO concentration of 0.1 opm, we can use the
formulae given in our papers to obtain an independent value of
This turns out to be much smaller, Y * 4 x 107* years. However,
this value is certainly low hecause the CO concentration of the
air from which the CO was collected 18s much higher than 0.1 pom.
It is in the range 0.3 - 1 pom and might be even higher. * would
accordingly be 0.1 - 0.4 years, or possibly higher. TI have no
explanation for the remaining discrepancy - there could be a
number of reasons for this.

I hope that this may be of some use to you.

Sincerely yours,

Richard Wolfgang

RW:b