Metal-ion concentrations in sea-surface microlayer and size-separated atmospheric aerosol samples in Hawaii

Abstract

A number of sea-surface microlayer and marine atmosphere samples have been taken from sites in Hawaii over a 2-year period from June 1969 to June 1971. The analysis of samples is reported for sodium, potassium, calcium, magnesium, strontium, copper, iron, and zinc, and some analyses of microlayer samples for marine nutrients are reported as total carbon, total phosphorus, and reactive nitrate. Data collected show chemical compositions and ion ratios of most samples to differ, often drastically, from normal sea-water data also collected for these chemical species. Microlayer samples represent a thin film approximately 150 μ thick removed from the surface of the open ocean. These samples generally have considerably higher total carbon, phosphorus, and nitrate concentrations than samples taken at the same site but at 0.6-meter depth. Microlayer samples are also found to be enriched to a small extent in some alkaline earth metals and to a much larger extent for the transition metals copper, iron, and zinc. The transition metals were also found to be proportionately more organically associated in the microlayer samples. Aerosol samples studied are enriched in most metals relative to sodium and to the metal to sodium ratio found in sea water. These enrichments range from values very close to zero up to unity or so for the alkali and alkaline earth metals, depending on element and particle size. Average enrichment values for the transition metals on smaller aerosols approach and exceed 3 and 4 orders of magnitude. Generally, enrichments are greatest on the smaller aerosols approaching Aitkin size; values are also pronounced for the giant aerosols, and lesser values occur for the intermediate-sized large aerosols. It is possible to consider the data in terms of mixing of globally spread, stratospheric continental dust of long residence time and pollution aerosols with normal marine aerosols. It is also important to consider separately or in combination with this concept fractionation and enrichment of selected chemical species before their ejection from the sea surface during agitation and bubbling. A qualitative mass spectrographic study of some of the samples indicates that organic coating materials on the aerosols are more concentrated on the smaller aerosols.