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[1] Observations of nitrous acid (HONO) by laser-induced fluorescence (LIF) at the South Pole taken during the Antarctic Troposphere Chemistry Investigation (ANTCI), which took place over the time period of Nov. 15, 2003 to Jan. 4, 2004, are presented here. The median observed mixing ratio of HONO 10 m above the snow was 5.8 pptv (mean value 6.3 pptv) with a maximum of 18.2 pptv on Nov 30th, Dec 1st, 3rd, 15th, 17th, 21st, 22nd, 25th, 27th and 28th. The measurement uncertainty is ±35%. The LIF HONO observations are compared to concurrent HONO observations pe rformed by mist chambe r/ion chromatography (MC/IC). The HONO levels reported by MC/IC are about 7.2 ± 2.3 times higher than those reported by LIF.

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The temperature-programmed desorption of nitric oxide, NO, and nitrogen dioxide, NO 2 , during the 302 nm photolysis of KNO 3 -doped, spray-frozen ice layers was investigated using two-photon laser-induced NO x fluorescence detection in the range -35 e T/°C e 0. Upon applying steady illumination and a 0.67 °C min -1 heating ramp, frozen KNO 3 solutions begin to evolve NO 2 at increasing rates, while NO emissions plateau soon after until, at ∼ -8 °C, both species surge abruptly. Although the primary photoproduct NO 2 avoids geminate recombination by escaping from a permeable molecular cage throughout, NO 2 (g) levels are controlled by desorption from the outermost ice layers rather than by NO 3photolysis rates. The NO x accumulated in the deeper layers bursts when the solid undergoes a sintering transition following the onset of surface melting at -10 °C. Since elementary photochemical events occur in a communal fluid phase of molecular dimensions at temperatures far below the KNO 3 /H 2 O eutectic (T eutectic ) -2.88 °C), we infer that doped polycrystalline ice contains operationally distinguishable fluid phases of low dimensionality over various length scales and temperature ranges.