Abstract
The role of the wall of a smog chamber as a radical source has been investigated in several ways. From data in the literature evidence is obtained that HNO 3, present on the reactor wall, may react with NO in the gas phase according to the reaction HNO 3( wall) + 2 NO + H 2 O → 3 HNO 2 to give nitrous acid. Nitrous acid may subsequently photolyze to give hydroxyl radicals. Experimental evidence about the occurrence of this reaction was obtained by u.v.-irradiation of propane-NO x mixtures with and without NH 3. The presence of NH 3 resulted in a drastically reduced photochemical reactivity, suggesting that neutralization of nitric acid prevented the reaction of HNO 3 with NO. Inclusion of the reaction mentioned above into a computer-model gave a good agreement between experimental and calculated concentration profiles of NO, NO 2 and O 3 in experiments with CO-NO x and propane-NO x, mixtures. The results of our findings and those from others are discussed.
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