Measurements of the scavenging efficiency of aerosol particles in fog are presented. The scavenging efficiency as a function of size for accumulation‐mode particles is presented, along with efficiencies for the total number, accumulation‐mode number, and accumulation‐mode volume. Particles below ca. 0.3 µm diameter were not efficiently scavenged in the fogs. The scavenging efficiency for accumulation‐mode particles showed two steps, indicating that the hygroscopic/hydrophobic nature of the aerosol appeared to have been a controlling factor in determining scavenging efficiencies. Observed changes in the aerosol size distributions are discussed in reference to the processes (i.e., in‐cloud scavenging, aqueous‐phase reactions) potentially influencing them.
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.
The difference in chemistry between interstitial aerosol particles and particles that were scavenged into fog droplets is examined using multivariate statistical techniques. 15 trace elements (P, S, Cl, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Pb, EC) were used in the analysis. There was a significant difference in composition between the two types of particles. S, Fe, Mn, and Cu were among the elements best describing the scavenged aerosol, while the interstitial aerosol was best described by elemental carbon (EC).
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