Formation of nitrous acid and nitric oxide in the heterogeneous dark reaction of nitrogen dioxide and water vapor in a smog chamber

✍ Scribed by Fumio Sakamaki; Shiro Hatakeyama; Hajime Akimoto

• Publisher: John Wiley and Sons
• Year: 1983
• Tongue: English
• Weight: 823 KB
• Volume: 15
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550151006

✦ Synopsis

The dark reaction of NO, and HzO vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO2 and H2O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO2 and HzO, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO2 and H2180 gave H180N0 exclusively. Taking into consideration the heterogeneous reaction of NO2 and HzO, the upper limit of the rate constant of the third-order reaction NO + NO2 + HzO -2HONO was deduced to be (3.0 f 1.4) X ppm-2.min-1, which is one order of magnitude smaller than the previously reported value.

Nitrous acid formed by the heterogeneous dark reaction of NO2 and H20 should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.