Summary
Tropospheric ozone is a greenhouse gas, ranked third in anthropogenic radiative forcing after CO2 and CH4. Ozone in the troposphere makes up an important fraction of the atmospheric shield against ultraviolet radiation particularly when stratospheric ozone depletion events occur and tropospheric ozone drives tropospheric chemistry being the major precursor of the OH radical which is the sink for gases such as methane. In the boundary layer increases in background ozone have other impacts through urban and regional photochemical smog on human health, crop productivity and the sequestration of carbon into the biosphere. There are few long-‐term monitoring stations and few process studies of tropospheric ozone in the Southern Hemisphere. In an international collaboration, analyses are presented of two decades of observations from 7 background surface ozone stations spanning 34°S to 90°S and 4 long-‐ term ozonesonde stations spanning 38°S to 69°S. Special consideration is taken to consider only those parts of the ozone record that are free of local influences of ozone production and destruction. Halogen based ozone destruction and local ozone production are evident in lower tropospheric air at some Antarctic stations. The ozone distribution measurements reflect a NOx depleted environment where there is net ozone loss at most oceanic boundary layer and free troposphere locations. There is little destruction of ozone at the water and snow surfaces. The seasonal signature of stratospheric-‐tropospheric exchange is evident in the ozone record in upper troposphere in mid-‐latitudes but not polar regions. There has been a growth in ozone abundance in the lower troposphere over the last two decades, this growth is stronger over Antarctica compared with mid-‐latitudes, and regional differences are evident. As well, there is inter-‐annual variability that appears to be correlated over long distances. Possible drivers of both the growth and interannual variability will be discussed.
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