MEASUREMENT OF ATMOSPHERIC NITRIC AND NITROUS ACIDS WITH A WET EFFLUENT DIFFUSION DENUDER AND LOW-PRESSURE ION CHROMATOGRAPHY POSTCOLUMN REACTION DETECTION

The interior wall of a borosillcate glass tube is modified to form a layer of porous soft glass that is highly wettable. Water is made to flow down the wall of this tube while sample air moves upward in countercurrent flow. The effluent liquid is debubbled, and the anionic constituents are preconcentrated on a 3 mm long anion-exchange column. Every 11 min the trapped species are eluted from this column to an 11 mm long main separation column where NO2- and NO3- are separated. The separated ions flow through a cadmium reductor to convert NO3- into NO2-, and Griess-Saltzman reagent is then added. Following a 3-min reaction time, the product dye is detected at 555 nm. For a 50-cm wet effluent diffusion denuder, essentially quantitative collection efficiency is observed for both HONO and HNO3 for sampling rates up to 2 L/min at 23 +/- 2-degrees-C. The system is relatively inexpensive and under typical operating conditions provides limits of detection (S/N = 3) of 80 and 230 parts per trillion by volume (pptrv) HONO and HNO3, respectively.