Monitoring ozone levels

Dr Greg Bodeker was a research scientist for the National Institute of Water and Atmospheric Research (NIWA), based at Lauder in Central Otago. Lauder is the primary southern hemisphere mid-latitude site in the Network for the Detection of Atmospheric Composition Change (NDACC), and Greg collaborated with other scientists around the world in this network to monitor the amount of ozone in the atmosphere, mainly where ozone has greatest concentration in the ‘ozone layer’ between 15 and 30 kilometres above the Earth’s surface. This is important work because ozone absorbs most of the UV radiation from the Sun and so protects the Earth from too much UV.

One way the Lauder scientists measure ozone concentrations is through weekly launches of an ozonesonde attached to a hydrogen-filled weather balloon. As it rises, the ozonesonde takes regular samples of air, mixes the samples with chemicals to determine the ozone concentration, and radios the measurement back to Lauder along with measurements of altitude, temperature, humidity and air pressure. This way, a vertical profile of ozone concentration is obtained.

The researchers at Lauder also use a ground-based instrument – the Dobson spectrophotometer – to measure the total amount of ozone above Lauder. The spectrophotometer measures and compares the UV light intensity at wavelengths that are strongly absorbed and weakly absorbed by ozone. The column ozone content of the atmosphere is calculated from the ratios of these intensities.

Greg’s research centred on trying to find a better understanding of the links between ozone depletion and climate change and to improve computer models of those links so that more accurate predictions can be made, so he and other colleagues around the world can advise politicians in the implementation of international policies. Linked with this, Greg and his colleagues have found a definite increase in atmospheric ozone levels since the 1989 Montreal Protocol, where countries started to phase out emissions of ozone-depleting substances such as chlorofluorocarbons (CFCs) used in spray cans.

Studies by Greg and his colleagues have shown a two-way link between ozone and climate change. Using a very complex ‘coupled chemistry-climate model’ developed by the United Kingdom Metrological Office and running on NIWA’s supercomputer, Kupe, they have shown that increases in greenhouse gases in the atmosphere will actually speed the recovery of the ozone layer, at least over New Zealand. On the other hand, the Antarctic ozone hole has played a key role in the surface climate in Antarctica. It has caused the interior of the Antarctic continent to warm more slowly than it would otherwise.

Greg and Hamish Struthers at Lauder also collaborated with 21 other scientists world-wide to extend their coupled chemistry-climate computer model to simulate the effect of the Sun’s 11-year cycle on ozone and temperature in the Earth’s atmosphere. Their results agree with actual satellite observations but are in contrast with most previously published simulations.