Reinvestigation of the Henry's law constant for hydrogen peroxide with temperature and acidity variation

Hydrogen peroxide is not only an important oxidant in itself; it also serves as both sink and temporary reservoir for other important oxidants including HOx (OH and HO2) radicals and O3 in the atmosphere. Its partitioning between gas and aqueous phases in the atmosphere, usually described by its Henry's law constant (KH), significantly influences its role in atmospheric processes. Large discrepancies between the KH values reported in previous work, however, have created uncertainty for atmospheric modelers. Based on our newly developed online instrumentation, we have re-determined the temperature and acidity dependence of KH for hydrogen peroxide at an air pressure of (0.960 ± 0.013) atm (1 atm = 1.01325 × 105 Pa). The results indicated that the temperature dependence of KH for hydrogen peroxide fits to the Van't Hoff equation form, expressed as lnKH = a/T – b, and a = –ΔH/R, where KH is in M/atm (M is mol/L), T is in degrees Kelvin, R is the ideal gas constant, and ΔH is the standard heat of solution. For acidity dependence, results demonstrated that the KH value of hydrogen peroxide appeared to have no obvious dependence on decreasing pH level (from pH 7 to pH 1). Combining the dependence of both temperature and acidity, the obtained a and b were 7024 ± 138 and 11.97 ± 0.48, respectively, ΔH was (58.40 ± 1.15) kJ/(K·mol), and the uncertainties represent σ. Our determined KH values for hydrogen peroxide will therefore be of great use in atmospheric models.