29 January, 1999

Friday, January 29th, 1999, South Pole Station

Greetings to all from the South Pole. We had a clear sky again with temperatures at about -26C, it is slowly getting colder.

After a long night of emailing and editing questions and journals, I continued in the morning. Great questions once again and I hope you get them in time for your class activities.

Yesterday I stated the question: why does the ozone hole " fill up again", as one of you asked me. I consulted Dave Hoffmann and here is his answer:

" OZONE FORMATION:

Ozone is produced by oxygen (O2) and sunlight in the UVC wavelength range (wavelength < 240 nm, very high energy UV which is required to break the O2 bond): (you can sometimes smell ozone around a copy machine as it produces UV light and there is always oxygen in the room). O2 + UV -> O + O (O = atomic oxygen) In the atmosphere, this reaction only works at higher altitudes where there is adequate high energy UV penetration (>10 km), thus there is a lower bound on the ozone layer. The atomic oxygen so formed can combine with O2 to form ozone which is formed in an excited state (not stable and will dissociate unless it is de-excited) O2 + O -> O3* (excited ozone). If there are enough molecules of nitrogen and oxygen around, the excited ozone can be stabilized through molecular collisions:

O3* + (N2, O2) -> O3

In the atmosphere, there is adequate N2 and O2 for this de-excitation only below about 40 km so there is also an upper bound on the ozone layer. Result: Ozone layer forms between about 10 and 40 km.

OZONE DESTRUCTION:

Ozone is destroyed by two processes in the Chapman theory:

O3 + O -> 2 O2

O3 + UV (mainly UVB) -> O + O2 (this is the reaction that shields the Earth from harmful UVB) Calculations of the ozone profile with these ozone formation and destruction reactions (Chapman's theory) gave an ozone layer which had too much ozone. "

About the actual 'filling' of the ozone, I asked D. Hofmann which of the two facts are more important:: 1. the disappearance of the PSC during the Antarctic spring or 2. that the hole is closed because more ozone is being transported from the equator where the main formation of ozone takes place.

His answer was the following:

" Both are important. The disappearance of the PCS and the formation of new ozone are important. When the stratosphere warms in spring, the PSCs evaporate releasing the nitric acid (HNO3) in the cloud parcticles which is photolyzed forming reactive nitrogen (NO, NO2) which combines with reactive chlorine and stops the depletion by chlorine, e.g., ClO + NO2 -> ClONO2 (chlorine nitrate which does not destroy ozone). But also, the warming causes the polar vortex to dissipate, breaking down the walls that have kept the winter chemical "container" from being disturbed, allowing new ozone which has been formed in the tropics to enter the Antarctic stratosphere and "fill up" the ozone hole that had formed in spring (remember, ozone is formed wherever there is adequate oxygen - O2- and sunlight, and you get a lot of sunlight in the tropics). In addition, the general circulation of the atmosphere is up at the equator, into the stratosphere, and then out to the poles). So each year new ozone comes in the late-spring, early summer (October-January) and fills the Antarctic summer stratosphere with ozone. You can look at our ozone profiles and see this. The stratosphere fills from the top down - there is still an ozone deficit in the lower stratosphere well into January. As a result, summer total ozone (the integrated amount of ozone from the surface to space, as measured by the Dobson) is now lower than it used to be because of this "ozone hole hangover" in the lower stratosphere (10-14 km). "

Thank you, Dr. Dave Hofmann for all the explaining.

During the day the Station Science Coordinator and leader for emergencies such as fires and medical emergencies, Mike Masterman asked me, if I would be able to help out as an interpreter during a medical evacuation (Medev) Saturdy night. A person who had a stroke on a research boat was going to be brought to the South Pole by a German flight crew. Of course, I was happy to help. I answered email after Our ARO 'slushies" went for a ski before bed time and thought about the man who needed desperate help. So many people were trying to get him there where he needed to be: a hospital.