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

We have Studied the photolysis of nitric acid (HNO3) 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 NO2 and the electronically excited NO2, NO2*, produced from the HNO3 photolysis. NO2* + OH is a predominant photolysis pathway (if not the only photolysis pathway) from the gas-phase photolysis of HNO3 at 308 nm. The NO2* quantum yields from the HNO3 photolysis on aluminum Surfaces are 0.80 +/- 0.15 at 295 K and 0.92 +/- 0.26 at 253 K, where errors quoted represent 2 sigma measurement uncertainty. The corresponding NO2* quantum yield from the HNO3 photolysis on ice films is 0.60 +/- 0.34 at 253 K. The 308 nm absorption cross sections of HNO3 on Al surfaces and on ice films have been directly measured. Absorption cross sections of HNO3 oil 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 HNO3 on ice films is (1.21 +/- 0.31) x 10(-18) cm(2)/molecule at 253 K (errors quoted represent 2 sigma measurement uncertainty). Atmospheric implications of the results are discussed.