Uptake of hypobromous acid (HOBr) by aqueous sulfuric acid solutions: low-temperature solubility and reaction L. T. Iraci1, R. R. Michelsen1,2, S. F. M. Ashbourn1,3, T. A. Rammer4, and D. M. Golden5 1Atmospheric Chemistry & Dynamics Branch, NASA Ames Res. Center, Mail Stop 245-5, Moffett Field, CA 94035, USA 2National Research Council Associate, USA 3now at: Earth Tech, Ltd., 91 Brick Lane, London EI 6QL, UK 4SRI International NSF Research Experiences for Undergraduates Program, Menlo Park, CA 94025, USA 5Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA
Abstract. Hypobromous acid (HOBr) is a key species linking inorganic bromine to the
chlorine and odd hydrogen chemical families. We have measured the solubility
of HOBr in 45-70wt% sulfuric acid solutions representative of upper
tropospheric and lower stratospheric aerosol composition. Over the
temperature range 201-252 K, HOBr is quite soluble in sulfuric acid, with an
effective Henry's law coefficient, H*=104-107mol L-1atm-1.
H* is inversely dependent on temperature, with ΔH=-45.0±5.4 kJ mol-1
and ΔS=-101±24 J mol-1K-1 for 55-70wt% H2SO4 solutions. Our study includes
temperatures which overlap both previous measurements of HOBr solubility.
For uptake into 55-70wt% H2SO4, the solubility is described by
log H*=(2349±280)/T-(5.27±1.24). At temperatures colder than
~213K, the solubility of HOBr in 45wt% H2SO4 is at
least a factor of five larger than in 70wt% H2SO4, with log
H*=(3665±270)/T-(10.63±1.23). The solubility of HOBr is
comparable to that of HBr, indicating that upper tropospheric and lower
stratospheric aerosols should contain equilibrium concentrations of HOBr
which equal or exceed those of HBr. Upon uptake of HOBr into aqueous
sulfuric acid in the presence of other brominated gases, particularly for 70wt%
H2SO4 solution, our measurements demonstrate chemical
reaction of HOBr followed by evolution of gaseous products including
Br2O and Br2.
Citation: Iraci, L. T., Michelsen, R. R., Ashbourn, S. F. M., Rammer, T. A., and Golden, D. M.: Uptake of hypobromous acid (HOBr) by aqueous sulfuric acid solutions: low-temperature solubility and reaction, Atmos. Chem. Phys., 5, 1577-1587, doi:10.5194/acp-5-1577-2005, 2005.