ATMOSPHERIC CARBON MONOXIDE 141 



Data for this reaction are conflicting, but recent work suggests that the rate 

 constant is much smaller than earlier studies indicated. Using the rate constant 

 recently obtained by Simonaitis and Heicklen, 1 8 we can readily show that r(CO) 

 must be about 100 years at 20 km altitude and about 10 years at 60 km altitude 

 by reaction 5, much too small to be important. The reaction 



O('D) + CO ^products (6) 



seems to lead to quenching of the 0(' D) to the electronic ground state instead 

 of to chemical reaction. 1 



Just as Weinstock and Niki 1 invoked reactions 1, 2, and 3 for the formation 

 of CO in the troposphere, they invoked reactions 1, 2, and 4 for destruction in 

 the troposphere. The reaction of 0( 3 P) with aldehydes produces OH radicals in 

 smog, 20-22 and this reaction may be followed by reaction 4. Then the following 

 reactions occur: 



H + 2 + M^H0 2 +M (7) 



and 



HO a + NO -> OH + N0 2 (8) 



Other radicals may play a similar role: 



CO + RO -> C0 2 + R (9) 



R + 2 -> R0 2 (10) 



R0 2 + NO -> RO + N0 2 (11) 



where R is the organic fraction of the radical. 



However, Kummler, Bortner, and Jaffe 24 state that it is highly unlikely that 

 homogeneous gas-phase kinetics at ground level can be an appreciable sink for 

 CO, that possibly a heterogeneous chemistry is involved, but that it is more 

 probable that a biological sink is required to convert CO to C0 2 . Such a sink 

 could involve both land surfaces and oceans, and it is possible that at certain 

 times and places the oceans serve as a source of CO, whereas at other times they 

 serve as a sink. 



REFERENCES 



1. Public Health Service, Air Quality Criteria for Carbon Monoxide, National Air Pollution 

 Control Administration Publication No. AP-62, Washington, March 1970. 



