Measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented. The data given are the most extensive and accurate measurements of the submicron marine aerosol size distribution to date and are supplemented by extensive meteorological observations. Eight detailed case studies of the evolution of the size distribution that occurred under different meteorological conditions are presented and discussed. The data indicate that repeated cycling of MBL air through nonprecipitating clouds at the top of the MBL is a major factor in shaping the size distribution and that new particle formation by heteromolecular, homogeneous nucleation is the most likely mechanism for sustaining the particle concentration below 0.04‐μm radius. Calculations of the scattering and extinction coefficients and optical depth of the MBL as a function of wavelength directly from the measured size distribution and MBL vertical structure are compared to measured values of the scattering coefficient and optical depth. These measured and calculated optical properties correlate well throughout the cruise and the results give a relatively consistent picture of the relationship between the aerosol size distribution and electromagnetic properties in the MBL.

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The principal factor determining the sharpness of the electrometric end-point with polarized electrodes of pure platinum is the difference in the degree of reversibility of the electrode reaction before and after the end-point. Other factors such as concentration and rate of stirring are of minor importance. The end-point phenomena are more distinct, the more nearly the electrode reactions conform to the requirement of complete reversibility on one side of the end-point and complete irreversibility on the other, but are sharp enough for practical use in analysis in some cases which fall far short of meeting this requirement.2. Although the polarization sometimes produces a slight displacement of the end-point break of a single electrode, the errors so introduced are generally too small to be of significance in a volumetric analysis.3. The end-point break in titrations of the ordinary type, based on the single potential of a platinum electrode, may often be improved and the behavior of the electrode made much more dependable and satisfactory by polarizing it with respect to an auxiliary electrode.

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