A study of marine aerosols over the Pacific Ocean

Aerosol samples were collected on a Pacific cruise from 47°N to 55°S. Particle morphology, concentrations, and size distributions were analyzed with an electron microscope; elemental compositions of individual particles were determined with an X-ray energy spectrometer; and chemical compositions of bulk samples were measured with an ion chromatograph. Temporal and spatial variations of aerosol physico-chemical characteristics were studied in relation to ocean currents and atmospheric parameters. The results show that number and mass concentrations of primary particles depend mainly on surface wind speeds. However the ratios between the major ions, e.g., Na⁺, Cl^-, and Mg⁺⁺, are similar to the ratios in seawater regardless of location or meteorological conditions. The concentrations of secondary aerosols, e.g., non-seasalt sulfate, nitrate, and ammonium particles, show maxima at upwelling regions, such as along the California coast, at the Equator, and near the Chatham Rise where ascending motion brings nutrient-riched deep water into the surface layer. The number concentrations of small sulfate particles and large nitrate-coated particles showed diurnal variations with maxima in the early afternoon and minima at night, indicating that the particles are the products of photo-chemical reactions. Their precursor gases, e.g., CH₃SCH₃, NO, and NH₃ are known to be released from seawater in upwelling regions where biological activities thrive.