Trends in Near Surface Ozone at Cape Grim and in the Southern Hemisphere Troposphere
Tropospheric ozone is: the third most important greenhouse gas after CO2 and CH4, the earth’s second line of defence against solar ultraviolet radiation, an essential precursor to the free radical chemistry of the troposphere, and one of the precursors to urban smog. Monitoring of tropospheric ozone is an important aspect of global atmospheric baseline observations.
Ozone has been measured in the surface air at Cape Grim Tasmania, 41°S, with ultraviolet adsorption methods since December 1981. The evolution of the Cape Grim measurement system, its performance and external calibration checks traceable to primary standards in 1986 and 2002 will be presented.
The ozone concentration measured in the surface air at Cape Grim has increased since the early 1980s by 10% in winter time, and less in other seasons. Similar increases in surface ozone have been observed at Cape Point South Africa, over the southern Atlantic Ocean and over Antarctica.
It appears that tropospheric ozone has been increasing since the pre-industrial period, and will continue to increase during the 21st century. The likely causes of the observed southern hemisphere surface ozone increases are discussed including: stratospheric ozone changes; changed stratosphere/troposphere exchange; changed tropospheric solar radiation; and increased NOx emissions from cities and biomass burning. The impact of ongoing tropospheric ozone changes will be discussed.