25 January, 1999

Monday, January 25th, 1999, South Pole Station

Greetings from the Amundsen-Scott South Pole Station! The week has started again with glorious weather: clear and sunny sky's, temperature - 22C, wind at 7 knots, a nice Antarctic summer day.

Today we were awaiting visitors again: representatives of the National Science Foundation, among others the director of Polar Programs, Mr. Earl and the Deputy Director of NOAA, Mr.Garcia. On station, visitors like that are called DV's , 'distinguished visitors'.

They were due at ARO's around 2 p.m. and I hurried up in the morning to answer most of the emails. We were also busy rearranging the office for the Dave's presentation. I enjoyed talking to them and discussing my work as a TEA member and hearing about the project within the Polar Programs and NOAA. For instance, Mr. Garcia will be leaving for Alaska soon to initiate studies about the decline of salmon in some areas of Alaska. Mr. Earl discussed the increase in educational programs in the Arctic. In the evening, Dave and the DV's were supposed to leave for McMurdo. The plane was on time but was delayed several times because of bad weather in McMurdo. .I have gotten used to change of flight schedules, as you know. After all, this is Antarctica and weather can change suddenly. As it turned out, the whole group had to stay over night and did not leave until the next morning 10a.m; so there was more time to talk about ozone research.

Why does the ozone depletion appear in the stratosphere? What pollutants contribute to the depletion?

As I have learned, the chemistry of the ozone depletion is far more complicated than I ever anticipated. I will try to explain the major points. Chapman suggested around 1930 that ozone (O3) is formed from the reaction of sunlight with oxygen and that a stable layer will form when other molecules such as nitrogen and oxygen are present. He suggested that there is a natural balance between destruction (some of the destruction is due to UV light) and formation of ozone thus shielding the Earth from harmful UV. However, Chapman's theory predicted more ozone in the stratosphere then had been observed, suggesting that there must be additional destruction of ozone not accounted for in Chapman's theory. with some of the destruction due to UV light. the formula for the natural distraction and formation of ozone

Between 1960 and 1970, other possible chemical schemes for destruction of ozone were studied., scientists During that time, Crutzen, Molina, and Roland, who in 1995 received the Nobel prize for their studies, suggested that OH, NO, and Cl ( hydroxyl radical, nitric oxide and chlorine) are highly reactive ozone and could be responsible for the additional destruction of ozone.

Farman, who is credited with the discovery of the ozone hole, suggested that the ozone distraction must be photochemical because it appears always in October when the Antarctic rises. A few days ago, I discussed that the chlorine, as part of chlorofluorocarbons (CFC's), is responsible for the depletion of the ozone layer. It was Lovelock, who detected CFCs in the atmosphere with a gas chromatograph. Two of the most important types of CFC's are F-11 or CFCl and F-12 or CF2Cl 2. These CFC's were used in aerosol spray cans, in refrigeration and in foam production.

The question still remains: why does chlorine react with ozone and not with nitrogen (which was seen as highly reactive and should not allow chlorine to attack ozone) and why does this reaction take place mainly in the stratosphere?

The process is more complicated than I can explain here. I will therefore conclude only with the major concepts. During the Antarctic winter Polar Stratospheric Clouds (PSC's) form because of the extreme cold temperatures causing the condensation of parcticles in the very stable atmospheric wind system, called a vortex - like a huge tornado) over Antarctica in the winter stratosphere (see 1/24/ journal entry). Initially these parcticles are tiny sulfuric acid droplets upon which nitric acid condenses when the temperatures fall in winter These droplets become larger as ice forms around them and these large droplets can fall from the stratosphere and thus remove active nitrogen. In other words, the PSCs , first remove the active nitrogen and incorporate nitric acid into parcticles so chlorine remains free ( nitrogen dioxide will combine with chlorine monoxide to form chlorine nitrate which does not destroy ozone) . Second, chemical reactions (called "heterogeneous reactions") on the surface of PSC parcticles, allow the reaction of chlorine-containing molecules which normally do not destroy ozone ( like chlorine nitrate and hydrochloric acid) to form free chlorine atoms which can destroy ozone. But for the very few chlorine atoms available to destroy large amounts of ozone, sunlight is required to sustain the reaction (called a "catalytic" reaction). As soon as the sun gets up after the Antarctic winter, sunlight allows the destruction by chlorine to proceed rapidly. The more PSC's are formed, the more nitrogen is trapped and removed, the more chlorine is free to react with the ozone. In addition, the ozone depletion causes the stratosphere to cool even more and more PSCs are formed resulting in more ozone depletion This is an example of positive feedback ---except with a very negative effect! We have created a very efficient process to destroy the ozone --- with CFC-depending products we have used or are still using.

What has been done about saving the remaining ozone? Do we observe an overall depletion of the ozone over the whole Earth or only around the Antarctica?

We said 'good by' to Dave. He has been very supportive of the TEA program and my thanks and gratitude to him and his CMDL team! How did Dave become involved in the ozone program?

Dave Hofmann taught physics for 25 years at the University of Wyoming. He started his Antarctic with balloon flights in 1972. Each year from 1986 to 1989, he parcticipated in the National Ozone Expedition (NOZE) to study the ozone hole which began with WINFLY season (winter flights into the Antarctica in late August) and continued into November when the ozone hole closes up due to the winds bringing new ozone from the equatorial regions. In 1990 he became

the chief scientist of the Climate Monitoring and Diagnostic Laboratory (CMDL) in Boulder, Colorado. He became the director of CMDL in 1995. He has been working in the Antarctic for the past 27 years.

For the remaining part of the evening I was busy editing journal and answering email questions. I also needed to get to bed on time in order to make it to the computer-video session the next morning. I was looking forward connecting to UNIS (my school) and other schools. Bob Loewenstein, an astronomer from the CARA program had the system set up and offered me to use it. I was thrilled because of all the preparations schools had made to connect with me in special life video sessions.

Dave Hofmann in front of the LC 130, at South Pole Station

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