Measurements of the partitioning of hydrogen peroxide in a stratiform cloud*

Abstract

Simultaneous measurements of hydrogen peroxide in cloud droplets and in the air in which the droplets were suspended are presented. In addition, a description of the new technique used to make the measurements is also presented. The ratio of the measured cloudwater concentration to the equilibrium cloudwater concentration predicted using Henry's law and the measured gas‐phase hydrogen peroxide was 0.64 (S.D = 0.32, n= 74). Analysis of both random and potential systematic errors indicate that while this ratio was statistically different from unity, the difference was not considered to be substantial. Henry's law appeared to have been valid for hydrogen peroxide in the ambient cloud we studied.

Hydrogen peroxide retention in rime ice

“…This generalization does not appear to be true in more polluted environments, such as those studied by Barth et al [1989]. The assumption of partition equilibrium is consistent with simultaneous measurements of gaseous and aqueous H202 in warm stratiform orographic clouds [Noone et al, 1991] and in tropical rain showers with precipitation rates of less than 1 mm h -1 [Jacob et al, 1990]. Because the time interval between sample collection and addition of the hydroperoxide reagent, referred to as the sample preparation time in Table 2, is larger than the lifetime of dissolved S(IV), a modified retention coefficient, F1, is used to account for the reaction between H202 and S(IV).…”

Calibration of a Counterflow Virtual Impactor at Aerodynamic Diameters from 1 to 15 μm

“…The utility of this device for cloud microphysical and chemical investigations is well established (e.g., Heintzenberg et al, 1989;Ogren et al, 1989;Twohy et al, 1989;Noone et al, 1991). Noone et al (1988a) presented the design and calibration of a land-based CVI *To whom correspondence should be addressed; address after June 1, 1993: Department of Atmospheric Sciences AK-40, University of Washington, Seattle, WA 98195. collection efficiency diameters) down to 7 ym, which is too small for calibration with previous methods (Noone et al, 1988a).…”

“…Several investigators (Tucker, 1989;Noone et al, 1991Noone et al, , 1992bOgren et al, 1992) have deployed miniaturized, landbased CVIs similar to the one discussed here. These have proven to be useful field instruments; however, they have yet to be carefully calibrated, especially with regard to the minimum cut size and the cut sharpness.…”

Airborne hydrogen peroxide measurements in supercooled clouds

“…Laboratory measurements of the Henry's law constant are limited to temperatures greater than 0øC Lind and Kok, 1994]. Studies conducted using a counterflow virtual impactor deployed at a mountaintop research facility [Noone et al, 1991] and using research aircraft [Bar& et al, 1989;Macdonald et al, 1995] indicate that departures from the predictions of Henry's law can exist. The largest of these appear to be the result of the reaction of dissolved H202 with S(IV) either prior or subsequent to cloud water sample collection.…”

“…Our approach is to compare the cloud interstitial values of H202 mixing ratio to the predictions of an equilibrium model. This technique sidesteps the possible problem of H202 destruction during droplet evaporation in a counterflow virtual impactor [Noone et al, 1991] or via reaction during or subsequent to cloud water collection. In addition, we examine H202 partitioning in the presence of ice hydrometeors and present profiles of gaseous H202 through a cloud-capped continental boundary layer.…”