The 2nd Aerosol Characterization Experiment (ACE-2): meteorological and chemical context

A review is given of the climatological and actual meteorological conditions in the sub-tropical northeast Atlantic, during June−July 1997, when the 2nd Aerosol Characterization Experiment (ACE-2) took place. Surface pressure maps, trajectory calculations and in-situ measurements show how the outflow of European pollution into the marine boundary layer of this area is determined by the location of the Azores high pressure cell. Observations during ACE-2 and 3 preceding summers show that pollution outbreaks both from the Iberian peninsula and from northern or central Europe can occur during such situations. During ACE-2, an unusually low number of strong North African dust outbreaks were recorded at the free tropospheric station of Izaña (Tenerife, 2360 m asl), although dust was recorded aloft the station.