but it is more probable that a biological sink is required to convert CO to C o n , such as the fungi suggested by Inman (1971). Literature Cited Bawn, C., Trans. Faraday SOC.,31,461 (1936). Bortner, M., Kummler, R., Jaffe, L. “CO Sink Anomaly,” (in press) 1971. SCI.TECHNOL..5. Dimitriades. B.. Whisman. M.. ENVIRON. 219 (1971j. ’ Fisher E., McCarty, M., J. Chem. Phys., 45,781 (1966). Inman, R.. Chem. Ena. News. May 10.1971. Krause, A:, Bull. Acaa. Pol. Sci. Ser. Sci. Chem., 9, 5 (1961). Kummler, R., Bortner, M., Ann. N.Y. Acad. Sci., 171, 273 (1970). Kummler, R., Bortner, M., Baurer, T., ENVIRON. SCI.TECHNOL.,3,248 (1969). Leighton, P.. “Air Pollution Photochemistry.” Academic Fress, New’York, N.Y., 1961. Madley, D., Strickland-Constable, R., Trans. Faraday SOC., 49, 1312 (1953). ,
I
I
_
Schofield, P., Planet. Space. Sci., 15, 643 (1967). Smith, R., Mooi, J., J . Phys. Chem., 59, 814 (1955). Strickland-Constable, R., Trans. Faraday SOC.34, 137 (1938). Zipf, E., Can. J. Chem., 47,1863 (1969).
R. H. Kummler‘ Wayne State University Detroit, Mich. 48202 M. H. Bortner
,
I
SIR: We agree with Messrs. Kummler, Bortner, and Jaffee that heterogeneous reactions may have a role in the oxidation of CO in our experimental system, but we disagree with the contention that heterogeneous catalysis provides a “much more plausible explanation” of our results. It is true, as Kummler et al. observe, that certain metal oxides are capable of effecting relatively rapid oxidation of CO at room temperature. However, no such effect was observed in the Pyrex glass reactor of our study, as can be deduced from our data on CO oxidation in the dark. Evidently, solar irradiation is prerequisite for initiating the oxidation process. A reaction-vessel effect, while conceivable, certainly is not evidenced by the comparison of the Fisher-McCarty data and our data. The Fisher-McCarty data did suggest a much slower oxidation of CO by oxygen under irradiation, but this difference could have been caused by difference in the type of radiation used. Fisher and McCarty used radiation in the visible and infrared region, well outside the near ultraviolet region used by us. In fact, in the few tests by Fisher and McCarty where the radiation spectrum extended into the near ultraviolet, they did observe faster oxidation of COand consequently shorter CO lifetime-which they attributed to the presence of nitrogen oxide impurity. The requirement that the unknown oxidizing species be present at constant concentration during each and every one of our tests in order to explain the observed kinetics is in-
Space Sciences Laboratory General Electric Co. Philadelphia, Pa. 19101
L. S. Jaffe George Washington University Washington, D . C . 20006 1
To whom correspondence should be addressed.
deed a difficult one to accept, as Kummler et al. reasonably observe. However, it is doubtful that this difficulty can be removed by assuming that heterogeneous, rather than homogeneous, chemistry is operative. This is because for heterogeneous oxidation of CO to follow the observed first-order kinetics, the oxidant species must have no effect on the reaction rate. This, in turn, requires that the unknown oxidant species be at a sufficiently high partial pressure to displace CO from, and saturate the catalytic sites in, the reactor’s surface. Such a required condition, however, is unlikely to exist because available evidence precludes any of the abundantly present species as being the oxidant. Thus, molecular oxygen at the ground or activated states must be precluded on the basis of the Fisher-McCarty and our studies, and, if the estimates of Kummler et al. concerning the hydroxyl radical role are correct, then hydroxyl is precluded also. In conclusion, the oxidant species must be present at extremely low partial pressures where first-order kinetics would not be likely unless the oxidant is present at constant concentration. B. Dimitriades’ M. Whisman Bartlesville Energy Research Center Bureau of Mines Bartlesville, Okla. 74003 To whom correspondence should be addressed.
Volume 5, Number 11, November 1971 1141
