Monday, 24 December 2007

Mini ozone holes

You might wonder why I'm down here. Well, I'm just taking the air really. It's nice air here, very fresh, and rather bracing at times. It's got to be good for you.

Down here though, we are as far from big cities as it's possible to get, and so for a few years BAS has been studying what the atmosphere is like in non-polluted areas. Last time I was here we were setting up a clean air laboratory a kilometre away from the rest of the base where it wouldn't be affected by the generators and vehicles. 6 years on, I'm back to find that it's full of machines that go whirrrrr and buzz, and measure all sorts of exciting things like OH, BrO, HOx and Nox. And ozone.

Stop right there. I know what what you're thinking. Ozone holes, CFC's all that rubbish..... well, forget it. OK, yeah, Halley is the place where they discovered the hole in the ozone layer, but I know nothing about it. It's all 20 miles above our heads. It certainly goes over my head anyway.

Ozone down here at the surface is much more interesing anyway. And it does some odd things too. Shortly after the sun comes up after the dark Antarctic winter, the concentrations go haywire. One day we'll have otherwise normal value of about 20-30 ppb, the next all the ozone will suddenly vanish. A few days later, its suddenly there again.

For a while no-one knew what caused these mini-ozone holes, but we now suspect it's bromine given off from salty ice crystals - frost flowers - that grow on the surface of new sea ice. The bromine breaks down in sunlight into individual atoms that can destroy ozone - in pretty much exactly the same way that chlorine from CFC's breaks down the ozone in the ozone layer.

That's what I reckon anyway. To be honest, no-one is really quite sure, and that's why we've had this little project funded. How big are these depletion events? How far inland do they go? Well, hopefully we're about to find out. BAS has built a set of ten little autonomous instruments for me to deploy out in the snow. I build 'em and shove 'em in the snow; next year someone else comes along, digs 'em up, and we've got as much information as we like about the extent and timing of the events.

That at least is the theory. If we get a whole year's data from all 10 instruments I'll eat my woolly hat.


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