Airborne dust collections over the North Atlantic

Abstract

Day-to-day airborne dust collections using the mesh technique on the bows of ships have been made across the temperate North Atlantic. In January 1969 the dust concentration (down to grain size of about 2-μ equivalent spherical diameter) was roughly constant at 0.003 μg/m3 air between Ireland and Newfoundland. In August 1969 the concentration was greater and varied between 0.003 at Ireland and 0.01–0.03 μg/m3 near Newfoundland. In the Bay of Maine the concentrations rise steeply, and off Cape Cod, if the exposure intersects a stream of black city pollution, it can rise to 4 μg/m3. All the dusts are gray to dark gray due to pollution by carbon and fly ash spherules. In the ≥3-μ size fraction, the spherules alone can be 60% of the sample when near the land; usually there are about 5% spherules in mid-ocean. The largest spherule seen (Bay of Maine) was 18 μ in diameter; in open ocean the spherules do not exceed 6 μ. Talc, especially abundant in the January collections, is noticeably present in the crystalline fraction of all samples. An estimation of air spreading across the ocean is attempted with the spherules used as tracers; a pollution stream increases its width fivefold in moving from Newfoundland to Ireland. Close to the West African coast, near Dakar, the concentration of red-brown dusts is 10 μg/m3 with grains ≥23 μ (hydraulic equivalent spherical diameter) contributing 0.1% of the total weight. At Barbados the corresponding size decreases to ≥11 μ with a marked fall in the percentage of quartz.