Atmospheric and precipitation chemistry over the North Atlantic Ocean: Shipboard results, April–May 1984

Abstract

During a North Atlantic cruise from Dakar, Senegal, to Woods Hole, Massachusetts (April 14–May 11, 1984), crossing the area of 14°–48°N; 17°–70°W, we collected atmospheric aerosols (C, N, S species), gases (SO⁴, HNO₃, dimethyl sulfide (DMS), synthetic organic chemicals), and precipitation (major inorganic/organic ions, trace metals). Air masses that had not contacted land for over 5 days had a composition close to that from the remote marine atmosphere. Oxidation of biogenic DMS to SO₄⁼ aerosol accounted for most nss-SO₄⁼ in these air masses. Air masses that had transected densely populated North America (in the westerlies) or the Mediterranean/North Africa ( in the easterlies) within 2–5 days of being sampled over the North Atlantic were enriched in acid precursor compounds and synthetic hydrocarbons relative to air that had spent longer over the North Atlantic. Strong acids and trace metals were also elevated in precipitation. Air masses that had transected regions of strong emissions within the preceding 2 days had concentrations of atmospheric pollutants approaching those typically found in continental air masses. More frequent storm tracks between the Icelandic low and the Bermuda high favored transport of North American emissions northeasterly, toward Europe. Trajectory analyses suggested that air masses sampled off the northwest African coast had passed over the Mediterranean. Composition of the aerosol and precipitation of these air masses was also indicative of continental emissions, including biomass and petroleum burning. Transport and deposition of continental emissions to the North Atlantic were significantly influencing surface atmospheric and oceanic chemistry of this region.