Data on trace substances in air, obtained in mid-Pacific during two summers, are summarized. Particulate matter was analyzed for chloride, sulfate and nitrate; tests were performed for ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. The results give information concerning the composition of marine air which can assist in evaluating possible natural contributions to urban pollution on the West Coast of the United States during the summer months, in addition to the geochemical value of the work.