Gaseous dimethylamine, (CH3)2NH, reacts in air with gaseous nitrous acid, HONO, to yield N-nitroso dimethylamine, (CH.LNNO. Long path infrared spectroscopy is used to monitor these reactions at concentration levels of partsper-million. The measured reaction rate shows that a small degree of nitrosation of dimethylamine vapor might take place during the night in a heavily polluted urban atmosphere. Nitrosation reactions would essentially cease after sunrise because the nitrous acid would be destroyed by photolysis. The N-nitroso dimethylamine vapor is also destroyed by sunlight, the half-life under full sun being about 30 min. By midday any nighttime accumulation of nitrosamine would be rather fully destroyed. Any N-nitroso dimethylamine detected in the air in the afternoon could not be the result of the reaction of precursors. It could only be the result of direct emissions of the pollutant.
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