308 nm Photolysis of Nitric Acid in the Gas Phase, on Aluminum Surfaces, and on Ice Films

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We have studied the photolysis of nitric acid (HNO(3)) in the gas phase at 253 and 295 K, on aluminum surfaces at 253 and 295 K, and on ice films at 253 K, by using 308 nm excimer laser photolysis combined with cavity ring-down spectroscopy. We monitored both the ground-state NO(2) and the electronically excited NO(2), NO(2)*, produced from the HNO(3) photolysis. NO(2)* + OH is a predominant photolysis pathway (if not the only photolysis pathway) from the gas-phase photolysis of HNO(3) at 308 nm. The NO(2)* quantum yields from the HNO(3) photolysis on aluminum surfaces are 0.80 +/- 0.15 at 295 K and 0.92 +/- 0.26 at 253 K, where errors quoted represent 2sigma measurement uncertainty. The corresponding NO(2)* quantum yield from the HNO(3) photolysis on ice films is 0.60 +/- 0.34 at 253 K. The 308 nm absorption cross sections of HNO(3) on Al surfaces and on ice films have been directly measured. Absorption cross sections of HNO(3) on Al surface at 308 nm are (4.19 +/- 0.17) x 10(-18) and (4.23 +/- 0.45) x 10(-18) cm(2)/molecule at 253 and at 295 K, whereas the corresponding absorption cross section of HNO(3) on ice films is (1.21 +/- 0.31) x 10(-18) cm(2)/molecule at 253 K (errors quoted represent 2sigma measurement uncertainty). Atmospheric implications of the results are discussed.