Surface ozone data are presented from up to 12 years of continuous measurements at Point Barrow, Alaska; Mauna Loa, Hawaii; American Samoa, South Pacific; and South Pole, Antarctica. Annual cycle characteristics of the data are described relative to atmospheric mixing and transport processes that give rise to the observed annual ozone distributions. Both positive and negative long-term trends are exhibited by the data. From examination of trends in the seasonal and monthly data, it is concluded that the cause of the trends is most likely a fluctuation over the years in the stratospheric-tropospheric exchange and tropospheric circulation processes that distribute ozone within the troposphere, coupled with tropspheric circulation distrubances such as those associated with the EL Nin-a/Southern Oscillation events of 1976 and 1982-1983. Because the positive ozone trend at Barrow occurs during summer months, photochemical ozone production in increasingly polluted Arctic air cannot be ruled out. Ozonesonde data are used to show that the surface ozone observations at Mau;na Loa observatory in the downslope wind regimes, and at South Pole, are repressentative of ozone measurments in the free troposphere, and that the ozone trends observed at Point Barrow and Samoa are likely representative of the lower free troposphere even though the measurments are made in air modified within the boundary layer.