Equilibrium Partial Pressures, Thermodynamic Properties of Aqueous and Solid Phases, and Cl₂ Production from Aqueous HCl and HNO₃ and Their Mixtures

Abstract

Equilibrium total pressures have been measured above aqueous HNO 3 (for 7.82, 15.73, and 35.99 mol kg -1 solutions from 294.6 to 224.7 K) and aqueous HCl (9.45 and 10.51 mol kg -1 , from 289.4 to 199.5 K) using a capacitance manometer. Equilibrium partial pressures of the acids have also been determined, by mass spectrometry, from 274.8 to 234.6 K for both HCl solutions, and from 265.0 to 240.1 K for 15.73 mol kg -1 HNO 3 . Results are generally consistent with model predictions, though with small (∼10%) systematic deviations for the total pressure measurements over aqueous HCl at about 220 K. Mixtures of HCl-HNO 3 -H 2 O composition yielded measured total pressures orders of magnitude greater than predicted for the gases H 2 O, HNO 3 , and HCl. Mass spectrometric determinations and equilibrium thermodynamic calculations suggest that Cl 2 and NOCl were produced by the reaction: 4H + (aq) + NO 3 -(aq) + 3Cl -(aq) h NOCl (aq) + Cl 2(aq) + 2H 2 O (l) , which is known to occur in aqua regia (a mixture of concentrated hydrochloric and nitric acids). Calculations for aqueous solutions of stratospheric aerosol composition suggest, purely on equilibrium grounds (and neglecting kinetics), that the reaction could be a source of active chlorine in the stratosphere. The correlation of Clegg and Brimblecombe (J. Phys. Chem. 1990, 94, 5369-5380; and 1994, 96, 6854) of the thermodynamic properties of aqueous HNO 3 activities has been revised, and vapor pressure products (for the reaction HNO 3 ‚nH 2 O (cr) h HNO 3(g) + nH 2 O (g) , where 1ene3) assessed from literature studies. The activity product for the reaction HNO 3 ‚2H 2 O (cr) h H + (aq) + NO 3 -(aq) + 2H 2 O (l) has also been determined. The model of Carslaw et al. (J. Phys. Chem. 1995, 99, 11557-11574) has been revised for the solubility of HBr in aqueous H 2 SO 4 to stratospheric temperatures.

Ice condensation on sulfuric acid tetrahydrate: Implications for polar stratospheric ice clouds

“…The dashed line in Fig. 5a represents S ice at the point SAT becomes thermodynamically unstable upon cooling, determined using the European Aerosol Inorganics Model (AIM) (Carslaw et al, 1995;Massucci et al, 1999). Comparison of this line to the experimental data demonstrates that, particularly at the higher temperatures, SAT dissolution followed by heterogeneous ice nucleation within the resulting liquid layer is indeed a possible mechanism.…”

New particle formation at a remote site in the eastern Mediterranean

“…The DMPS data corresponded to dried aerosol and were corrected for the hygroscopic growth of the particles in order to calculate the CS. Water uptake was calculated using the Extended ‐ Aerosol Inorganic Model II (E‐AIM) [ Carslaw et al , 1995; Clegg et al , 1998; Massucci et al , 1999]. The inorganic PM 1.3 monthly average concentrations for sulfate, ammonium, and nitrate based on filter measurements [ Koulouri et al , 2008], were used as inputs for E‐AIM in conjunction with RH and temperature measurements at ambient and dry conditions.…”

Homogeneous Freezing of Concentrated Aqueous Nitric Acid Solutions at Polar Stratospheric Temperatures

“…To estimate S NAX , we use the model of Carslaw et al 22 to calculate the activity of the species in the liquid and K S for NAT. To calculate K S for NAD we used eq A9 in Massucci et al 23 ∆G d (usually known as the activation diffusion energy) is the activation energy related to the diffusion of one molecule from the bulk liquid to the solid and is a function of the viscosity of the liquid. As the temperature decreases, ∆G* decreases, because S NAX increases and σ sl decreases as the liquid becomes more "solid-like".…”