Continuous generation system for low-concentration gaseous nitrous acid

A flow type generation system based on the reaction of sodium nitrite solution with sulfuric acid has been developed for parts per billion levels of nitrous acid. The reagent solutions are continuously pumped into a reaction vessel and drawn off to waste. A carrier gas is passed through a mixture of the reagent solutions in the vessel and continuously purges nitrous acid vapor from the mixture. Nitrous acid output of the generator is characterized by using a Na{sub 2}CO{sub 3}-impregnated filter and a chemiluminescent NO{sub x} monitor. A stable generation of nitrous acid of known concentration can readily be achieved by adjusting the concentration of sodium nitrite solution.