Abstract
A climatological study has been carried out of the occurrence and properties of a large number of dry and sunny spells in recent summers (1976–83). The frequency of the spells, which are very favorable for atmospheric photochemical activity, were found to be significantly higher in the investigated period than in previous years. A detailed examination of 25 episodes has been carried out. During the episodes, 72 h back trajectories have been computed, and information provided on temperature, humidity, cloud cover and inversion height. The trajectories, determined at different altitudes for five receptor locations [Soltau, Freiburg (FRG), De Bilt (Netherlands), Soissons, Nancy (France)] in Europe, show a predominance for advection from eastern to western Europe. For the two more northerly European locations [Soltau (FRG) and de Bilt (the NL)], the air trajectories also pass over less densely populated or maritime regions. Ozone concentrations recorded at a station in the Netherlands, are examined in relation to the direction of the arriving air mass.
