An experimental protocol to determine photolysis rates of chemicals which photolyze relatively rapidly in the gas phase has been developed. This procedure provides a basis for evaluating the relative importance of one atmospheric reaction pathway (i.e., photolysis) for organic substances which may be emitted into the environment and which strongly absorb actinic radiation and photodecompose with high efficiencies. This technique is based upon monitoring the disappearance rates of the test compound and of a reference organic, both of whose OH radical reaction rate constants are accurately known, in irradiated NO-organic-air mixtures. This limits the procedure to these organics which photolyze relatively rapidly, such as nitrites, a-dicarbonyls and nitrosamines. However, while the technique cannot be used for simple aldehydes and ketones and other relatively weakly absorbing organics, for most species this may not be a serious limitation because their atmospheric lifetimes are determined mainly by reaction with OH radicals.

Caption title. "October 1983." Includes bibliographical references. "EPA-600/3-3-83-100." Microfiche.