NIWA Water & Atmosphere 11(3) 2003 ATMOSPHERIC RESEARCH The Antarctic atmosphere: barometer on a changing world Stephen Wood Ozone depletion and increasing greenhouse gases recover to pre-ozone-hole concentrations. gases both feature regularly in the news media Over the past few years the ozone hole has Dave Lowe these days and the connection between ozone varied considerably in size and severity (see Brian Connor and Antarctica is well known. We can also learn graph below and Water & Atmosphere 9(2): 12– much about greenhouse gas concentrations from 13 and 10(4): 4). To confirm the predicted ozone Karin Kreher studies in the Antarctic. NIWA’s atmospheric recovery, we need to demonstrate a consistent Sylvia Nichol research in Antarctica is aimed mainly at decrease in the extent and intensity of the ozone understanding these two important issues. hole over many years. Greg Bodeker Because the atmosphere has no national Greenhouse gases boundaries, the research involves scientists from Although it is widely accepted that increases in many countries. greenhouse gases in the atmosphere are causing Ozone the Earth’s surface to warm on a global scale, The ozone depletion that occurs over Antarctica we still do not fully understand where the gases Precision each spring – the Antarctic ozone hole – is come from and where they end up. Carbon instruments and a striking example of human influence on the dioxide (CO2), the most important greenhouse extensive atmosphere. In the space of a few weeks most gas, has increased by more than 30% since pre- of the ozone in the lower stratosphere over industrial times (see Water & Atmosphere 8(1): international and Antarctica disappears. This is due to a 14–16). We know that about half of the CO2 local collaboration remarkable combination of dynamics and emissions remain in the atmosphere, enhancing chemistry in the cold Antarctic atmosphere the Earth’s natural greenhouse effect, and that are the hallmarks that makes industrial chemicals far more the remainder probably gets incorporated into of NIWA’s effective in depleting ozone (see Water & land-based and ocean ecosystems. But how atmospheric Atmosphere 9(2): 12–13). much goes into each of these reservoirs? research in In the 1980s international action resulted in a The Southern Ocean is thought to be the world’s treaty – the Montreal Protocol – to limit and ban largest sink of carbon, but we still have to Antarctica. the chemicals responsible for the damage. determine how large. As a step towards Although the Montreal Protocol is now proving quantifying this, NIWA has made high- effective, it will be decades before some of these precision stable isotope measurements of The ozone hole: 17 September 2003 The Antarctic ozone hole: Highest 1980 – 2002 ozone Stephen Wood, The values plotted above are calculated from the amount of depleted ozone in the ozone hole area, Brian Connor, Karin averaged from 19 July to 1 December each year. Kreher and Greg Lowest In 2002 the size and lifetime of the ozone hole were ozone Bodeker are based at unusually low. In 2003 the ozone hole developed NIWA, Lauder; Dave early and has already been nearly as large in area as any recorded in the past (right), though its Lowe and Sylvia The blue area is the ozone hole, which covers almost duration (and therefore the total amount of ozone Nichol are at NIWA all of Antarctica. The white circle at the centre is an depletion) is not known at the time of printing. in Wellington. area with no data. 20 159486 WA Sept 20 10/21/03, 3:09 PM NIWA Water & Atmosphere 11(3) 2003 atmospheric CO and oxygen in the Antarctic 2 Bromine on Ice (Water & Atmosphere 4(2): 11–12, 5(2): 16–17). The Robyn Schofield Investigating the future of differences in stable isotope levels can be used in Antarctica. the Antarctic ozone hole to estimate how much CO is absorbed by the 2 brought a PhD student southern oceans. Early results show a significant from the University of effect of ocean circulation and upwelling events Auckland to Scott Base for the 2002 season. on atmospheric CO2 and O2 concentrations. This project is part of an ongoing international Robyn Schofield, a University of Otago research effort to work out the proportions of honours graduate and carbon from human activities absorbed by the FRST Bright Futures oceans and by the land. Scholarship recipient, Within another international programme, has pioneered a new NIWA is investigating changes in the isotope measurement technique in partnership with composition of greenhouse gases like methane NIWA scientists and and CO2 (see Water & Atmosphere 9(1): 22–23). successfully applied it to We know that the atmosphere is changing bromine monoxide, BrO. quickly. A key benchmark is the composition Knowing how much of the atmosphere before human activity bromine is in the stratosphere is critical to dramatically changed it. predicting the future When snow falls it traps air; over time, as the severity of the ozone snow turns to ice, the trapped air remains as tiny hole. Chlorine-containing bubbles within the ice. The deeper the bubble gases (which derive from breakdown of CFCs) are in the ice, the older is the air within it. The ice controlled under international agreements and rapid decreases are sheets in Antarctica thus provide a remarkable expected. However, bromine-containing gases also play a major role in ozone loss, and will decline more slowly. The more bromine in the stratosphere, the longer the ozone hole will persist. For some years NIWA has been measuring total volumes in the atmosphere of BrO, nitrogen dioxide (NO2), and chlorine dioxide (OClO), all of which are involved in ozone depletion. We have now Air bubbles developed a “direct-sun” spectrometer to separate tropospheric from trapped in stratospheric information. The new technique combines two different Antarctic ice can viewing methods with a computer model developed by Robyn. In the provide first method, looking directly at the sun results in a long light path information through the troposphere; in the second, looking at scattered light about past atmospheric from the zenith produces a similar enhancement in the stratosphere. conditions. After successfully applying the new technique to BrO measurements (Photo: David at Lauder (45 oS), Robyn went on campaign in the Antarctic. She Etheridge) operated a direct-sun instrument from early September to late October every clear morning and evening. Robyn then used these observations museum of the chemical state of the atmosphere to measure stratospheric and tropospheric BrO. extending over millennia. For example, the A high variability was observed for the stratosphere, partly because naturally occurring radioactive isotope carbon- of the unusual stratospheric warming in spring 2002. Robyn measured a background concentration of 0.3 parts per trillion (ppt) BrO in the 14 in methane trapped in these bubbles can tell troposphere. On 24 and 25 October 2002 there was a “bromine us whether the gas came from fossil fuels or from explosion”, equivalent to 7 ppt BrO in the lower 2 km of the atmosphere. natural sources like swamps. Initial results show First measured in the mid 1990s, these events are thought to result that 60 years ago up to 15% of atmospheric from an accumulation of bromine- and chlorine-containing sea salt on methane was derived from fossil sources. the winter ice pack, leading to a rapid release of bromine and consequent severe ozone depletion close to the ground. Higher percentages imply a larger industrial component in sources of atmospheric methane. Gas measurements and modelling greenhouse gases and other gases in the To measure atmospheric trace gases, especially troposphere, such as the products of fires in those in the stratosphere, we rely on the fact that the tropics. different gases absorb light in different parts of Most of our measurements use sunlight, though the spectrum. We use specialised ground-based it is possible to use moonlight for some equipment to measure quantities of ozone and measurements in the dark winter months. A several other gases active in ozone depletion perennial task is to refine our measurement and chemistry, such as HCl, ClO and BrO. These analysis techniques to improve the information instruments can also be used to determine retrieved (see panel above). 21 159486 WA Sept 21 10/21/03, 3:10 PM NIWA Water & Atmosphere 11(3) 2003 Teachers: this We also measure gas concentrations effect of spring-time ozone depletion on article can be used directly from air samples collected both places at mid-latitudes. The work has for NCEA in Antarctica and during transport flights shown that more than half of the observed Achievement Standards in between Christchurch and McMurdo. summer time reduction in ozone over New Geography (1.1, 2.1, To interpret the measurements of Zealand since pre-ozone-hole times is 3.1, 1.7, 2.7, 3.7, 1.6, 2.6, 3.6), C&S (1.2), stratospheric gases, we have developed a due to the dilution effect when annual Physics (1.2, 2.2, model that tracks how stratospheric chemistry ozone holes dissipate, leading to significant 2.7). See other changes under given conditions. We plan to increases in UV over New Zealand in the curriculum connections at use the model to separate the effects of gas past two decades (see also Water & Atmosphere www.niwa.co.nz/ movement from chemical changes in a series 7(4): 7–8). pubs/wa/resources of measurements of trace gases made at NIWA will continue to recognise the regular intervals over time at a single site. A importance of the Antarctic atmosphere separate modelling project has looked at the in the global system with a strong measurement programme, backed up with modelling and analytical research and increased collaboration with overseas researchers.