Henry's Law Constant Determinations for Hydrogen Peroxide, Methyl Hydroperoxide, Hydroxymethyl Hydroperoxide, Ethyl Hydroperoxide, and Peroxyacetic Acid

Abstract

The temperature-dependent solubilities of hydrogen peroxide (H 2 O 2 ), hydroxymethyl hydroperoxide (HOCH 2 O 2 H), methyl hydroperoxide (CH 3 O 2 H), peroxyacetic acid (CH 3 C(O)O 2 H), and ethyl hydroperoxide (C 2 H 5 O 2 H) were determined under conditions used in the aqueous collection and analysis of atmospheric hydroperoxides. Henry's law was obeyed over the source concentration range employed, nominally 10 -6 −10 -2 M. Measurements were made using either pH = 3 or pH = 6 source and collection solutions. The temperatures investigated ranged from 4 to 28 °C. A solution pH 3 was used for experiments with H 2 O 2, HOCH 2 O 2 H, and CH 3 C(O)O 2 H since these compounds decompose in less acidic solution. The solubility of HOC 2 H 4 O 2 H could not be accurately determined because of its rapid decomposition in solutions with pH > 3. The Henry's law solubility of H 2 O 2, HOCH 2 O 2 H, CH 3 O 2 H, and CH 3 C(O)O 2 H are in agreement with prior determinations. The solubility measurement of C 2 H 5 O 2 H is the first of its kind. Dimensional Henry's law constants (M/atm) can be expressed by ln( K h ) = A/T − B, where T is in degrees kelvin. K h at 25 °C and the A and B coefficients are The high solubility of HOCH 2 O 2 H implies it will be efficiently removed from the atmosphere by precipitation or surface deposition. Its decomposition and that of HOC 2 H 4 O 2 H and CH 3 C(O)O 2 H forming H 2 O 2 near neutral pH suggest these hydroperoxides may constitute a heterogeneous source of H 2 O 2 in atmospheric water if they are formed in the troposphere. The solubility of the listed organic hydroperoxides and the propensity of three of them to decompose at neutral pH further underscores the potential for interference's and artifacts in the aqueous collection and nonspecific analysis of H 2 O 2 in the atmosphere.