OH+ N02+ N2—HN03+'N2(1) has been recognized for several years. 1 In the stratosphere, this reaction simultaneously removes reactive HO* and NO* species of importance in ozone-destruction cycles. In the troposphere, this reaction is the most important gas-phase removal process for N02. Recent tropospheric modeling has shown that photochemically generated ozone is very sensitive to the rate constant used for this reaction, since it converts the photochemically active N02 to a less active form, HN03. 2, 3 In the urban atmosphere, reaction 1 is expected to be the dominant removal process for active NO* species. 4

Reaction 1 has been directly investigated at high pres-sures by using flash photolysis techniques5" 9 and at low pressures by using discharge-flow systems. 10" 15 High-pressure studies have provided information about the temperature and pressuredependence of this reaction in the falloff region between second-order and third-order behavior. The third-order behavior of the reaction is de-scribed most directly by the low pressure studies. Due to the importance of this reaction in the atmosphere, its temperature dependence should be studied in N2. This work reports the first direct measurement of the temperature dependence of the termolecular rate constant for the reaction in N2 between 225 and 389 K, as well as a