Uptake of hydrogen chloride in water ice and nitric acid ice films

Abstract

The uptake of HCl in water ice and nitric acid ice films has been investigated in a flow reactor interfaced with a differentially pumped quadrupole mass spectrometer. These studies were performed under experimental conditions that may mimic the polar stratosphere. The HCl uptake in ice films at 188 and 193 K was determined to be in the range of 8.7 X 1013 to 1.8 X 1015 molecules/cm2 (if the geometric area of the flow reactor, 290 cm2, was used in the calculation) when HCl partial pressures of 7 X 10-8 to 6 X 1 0 6 Torr were used. On the basis of a model which accounts for the total surface area of the films, the true surface density could be a factor of 25 lower than that calculated by the geometric area. A slightly higher uptake was observed at the lower temperature of 188 K. The uptake of HC1 in ice was significantly enhanced by using an HCl partial pressure greater than 1 X Torr. The observation was found to be consistent with the formation of the hexahydrate or the trihydrate of HC1 according to the phase diagram of the HCl/H20 system. The uptake of HCl in nitric acid ice at 188 K was determined to be in the range of 8.0 X 1013 to 5.3 X lOI4 molecules/cm2 at a HCl partial pressure of 4.5 X lo-' Torr. Measurement of both H N 0 3 and H2O vapor pressures was made to positively identify the formation of nitric acid trihydrate (NAT) surface according to the phase diagram of the HNOs/ H2O system. The HCl uptake in NAT is comparable to that in water ice in the present experiment, but significantly smaller than the previously reported values by Mauersberger and his co-workers. Implications of these results for the heterogeneous chemistry of the polar ozone depletion are briefly discussed.

FTIR spectroscopic studies of the simultaneous condensation of HCl and H2O at 190 K – Atmospheric applications

“…Our results show that this dopant will be incorporated and is likely to modify ice structure. The HCl : H 2 O mixing ratio in the winter polar stratosphere is about 1/2500 (Chu et al, 1993;Marti and Mauersberger, 1993), i.e. 12.5 times less than the smallest mixing ratio we have studied (1/200).…”

Quantitative Analysis of the Infrared Absorptivities of Nitric Acid Ices Aerosol Existing in Polar Stratospheric Clouds

“…The measured partial pressures of water and nitric acid were calibrated by using literature vapor-pressure data16 and data measured in our laboratory. 17 The errors of these measurements were estimated to be about 20%.…”

Uptake of nitric acid by sub‐micron‐sized ice particles

“…The goal of this work has been to address the first point, by measuring nitric acid uptakes on ice particles and comparing them to those measured on thin films. In particular, we seek to address whether the presence of grain boundaries [Wolff et al, 1989] and high levels of film porosity [Chu et al, 1993], both of which are potentially present in ice films depending on how they are formed, lead to enhanced uptake over that demonstrated by single-crystal ice particles. To within experimental uncertainties, we find that the uptakes measured on ice films formed by freezing liquid water and ice particles are the same.…”