Ambient-temperature caustic impinger traps were used in parallel sampling with cryogenic caustic traps to study the degree of conversion of dimethylamine (DMA) to A/-nitrosodimethylamine (DMN) when DMA and NO" were brought together by trapping. Under simulated use conditions where DMA at sub-ppm (0.05) and NO, (0.2 ppm) from light traffic were brought together by trapping, the cryogenic traps produced from one to two orders of magnitude more DMN than the ambient traps. For routinely measuring DMN in air, ambient trapping in caustic followed by combination gas chromatography-mass spectrometry readout has been shown to produce artifact-free results.Recent literature reports have expressed concern that N-nitrosodimethylamine (DMN) may be a widespread environmental contaminant which may have implications as a human carcinogen (1, 2). The necessity for DMN mea-