Seasonal and daily cycles of surface ozone in the extratropical latitudes

Abstract

Major characteristics are considered of the time dependence of the surface-ozone mixing ratio obtained at a number of stations of the world network, which transmit observational data to the World Data Centre for Greenhouse Gases and to the databank of the European Monitoring and Evaluation Program for long-range transport of air pollution. The 1990–2004 data, obtained mainly in the Northern Hemisphere, are analyzed. The seasonal cycle of surface ozone is clearly defined at all 114 observation sites under consideration, and its daily cycle is also pronounced at all stations except for the polar ones. Six basic types of seasonal and daily variations in surface ozone are revealed with the use of cluster analysis. In addition to quantitative characteristics, these types are distinguished by the forms of seasonal and daily cycles (in particular, by the presence of one or two seasonal maxima and by the time of maximum occurrence). Six groups of stations are classified according to these differences: remote (unpolluted), lowland slightly polluted, lowland polluted, upland slightly polluted, mountain, and polar/remote coastal stations. For the group of remote stations in the Northern Hemisphere, the seasonal maximum of surface ozone occurs in April in the daytime and at night. For the group of polluted stations (including most of the European rural stations), whose observational data are characterized by two seasonal maxima (in spring and in summer) or one broad spring-summer maximum, the spring maximum is observed in the daytime and at night, and the summer maximum is observed only in the daytime. It is concluded that spring maximum is caused mainly by dynamic processes—air-mass transport—and the amplitude of the summer maximum is determined by photochemical generation of ozone.