The Background Level of the Summer Tropospheric Aerosol Over Greenland and the North Atlantic Ocean

Abstract

An experiment to measure the concentration and size of Aitken nuclei, the concentration of cloud nuclei active at a supersaturation of 1%, the concentration of freezing nuclei activated at −20C, and the chemical nature of the tropospheric aerosol over Greenland and the seas surrounding it is described. The mean of the total Aitken nuclei concentration over the North Atlantic Ocean between Scotland, Iceland and Greenland was about 600 cm−2. The concentrations were generally less than 1000 cm−3 and the mean size was about 2 × 10−6 cm. Over the ice cap between Kulusuk and Sdr. Strømfjord the mean of the total nuclei concentration was around 300 cm−3, and the concentrations were generally less than 400 cm−3. The mean size was about 3 − 10−6 cm. Cloud nuclei concentrations were also very low, nearly 50% of the concentrations measured being less than 10 cm−3. Freezing nuclei concentrations were mostly less than 1 liter−1. The volumes of the samples taken for activation analysis (500 liters) were found to be too low to give reliable results. From air mass trajectories it was concluded that the air masses sampled were of polar or North American origin and had not, within their recent history, Passed over heavily populated areas.