Development of a photo-fragmentation/laser-induced fluorescence measurement of atmospheric nitrous acid

Atmospheric nitrous acid (HONO) is an integral part of HOx (OH and HO2) and NOx (NO and NO2) cycles. In the arctic atmosphere measurements of HONO are an important part of understanding the dynamics of snow-air chemistry and atmospheric photochemistry. The low levels of HONO present in such regions necessitate the development of instrumentation with low detection limits. An improved method of detecting HONO is introduced in this paper, using photo-fragmentation and laser-induced fluorescence. HONO is photo-fragmented into OH and NO at 355 nm. OH is then probed using a wavelength of 282 nm and the fluorescence of OH is observed at 309 nm. The instrument is calibrated using HONO produced from the reaction of sulfuric acid and sodium nitrite. The detection limit of this method is 15 pptv for 1-min integration time with 35% uncertainty.