HETEROGENEOUS REACTION OF NO3 WITH ICE AND SULFURIC-ACID-SOLUTIONS - UPPER LIMITS FOR THE UPTAKE COEFFICIENTS

Using a Knudsen cell reactor, we have studied the uptake kinetics of t he nitrate radical, NO3, on ice and on sulfuric acid solutions. The ex periments on ice were carried out over the temperature range 170 < T/K < 200. Experiments with liquid sulfuric acid were performed over the concentration range 60-95 wt % H2SO4. Nitrate radical is detected by l aser-induced fluorescence. Measures had to be taken to characterize th e fluorescence quenching by water vapor, for which we found a bimolecu lar rate constant of (6.9 +/- 0.5) x 10(-10) cm(3) molecule(-1) s(-1) Also, the rate of NO3 disappearance on the walls of the Teflon-coated reactor is determined and accounted for in the kinetic analysis. We fi nd that, within the detection limit of our apparatus, there is no inte raction between NO3 and these surfaces, allowing us to report the uppe r limit for the uptake coefficient of gamma < 10(-3).