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Originally Posted by jjjnettie
Robert, I watched a doco on that topic on SBS.
Didn't they also say that, after recording the highest UV and temp. readings during that time, that the smog was keeping the greenhouse effect at bay?
The smog eats the ozone, but the smog also stops us from feeling most of the effects from ozone depletion.
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I understand that photochemical smog is the product of the action of sunlight on motor vehicle exhausts to produce (principally) nitrous oxide. The effects of industrial output are also part of this problem, which is almost totally confined to large cities. From a distance, this is observed as a brown haze over a cityscape, as you look towards Brisbane from, say, the Blackbutt ranges. The effect is more noticable when there is a temperature inversion and no wind, and the smog just hangs around and builds up. The main impact is on human health. I am not sure that it keeps anything at bay, but I have heard that it does increase the reflection of solar radiation into space, so that greenhouse heating effect is less (at least for cities). As it only happens in big cities, the impact on the overall greenhouse effect would be miniscule. This does not make a lot of sense to me, as an ugly brown smudge would, I would think, absorb more solar radiation and increase the temperature of cities so that they are hotter than they otherwise would be. Whatever.
I do recall (correctly I hope) that some part of the chemical reaction process in the creation of photochemical smog does involve the conversion of ozone into nitrous oxide. As this happens in the lowest level of our atmosphere, it is totally different to ozone depletion, which occurs very high in our atmosphere. The reasons for the depletion of the ozone layer, which is very high in our atmosphere and protects us from UV radiation, is well understood. It is due to freons and various other nasty chemicals produced by our industrial civilisation which find their way high into the atmosphere where they eat ozone. I think someone got a Nobel for explaining the chemistry of this.
