Airborne measurements of hydrogen peroxide and its partitioning between the aqueous and gas phases were conducted during studies of wintertime orographic clouds at temperatures ranging between -9¿ and -24 ¿C. A subset of the derived values of the H2O2 Henry's law coefficient, based on measurement of gas-phase H2O2 and the physical properties of the cloud, were found to agree with laboratory measurements extrapolated to the cloud temperature. Disparities between the derived and temperature-extrapolated values were also observed, but this was attributed to overestimates of the in-cloud H2O2 mixing ratio that result from solute H2O2 volatilization on the reverse-flow air sample inlet during cloud droplet impaction and freezing. This hypothesis is supported by the fact that the derived Henry's law coefficients which exhibit agreement with the temperature-extrapolated values were conducted using a narrower inlet which intercepts less cloud water. Also discussed are vertical profiles of gaseous H2O2 within and above a cloud-capped boundary layer and in-cloud measurements which reveal that H2O2 scavenging by ice hydrometeors is minimal in comparison to uptake by an equivalent mass of liquid cloud droplets. ¿ American Geophysical Union 1995