Abstract. We offer further comments regarding the controversial claim of Zhang et al.[1994] that a standard vibrating orifice aerosol generator modifies the hydrogen bonding ratio of laboratory water droplets. New data reported here fail to support their observation of a surface charge induced Raman spectral change as reported by Aker et al.[1996a1.
IntroductionRecently, P.M. Aker's group at the University of Pittsburgh reported [Zhang et al., 1994[Zhang et al., , 1995] that a commonly used laboratory aerosol generator produced water droplets with a modified hydrogen bonding ratio (HBR) and concluded that this invalidated previous gas uptake measurements [
Flaws in the Aker et al. and Zhang et al. Experimental ProceduresThe most serious problem with Zhang et al.'s experimental procedure is the presence of Raman gain saturation which could lead to erroneously low estimates of HBR. Saturation occurs as the most intense MDSRS modes at spectral line center (i.e., those with the highest gain) grow to a level requiring significant conversion of the circulating green pump light to the red SRS modes, resulting in pump depletion. As the pump level is lowered, the overall SRS gain decreases. MDRs at the