Originally Posted by
GeorgeM
When there is a problem it's due to a temperature inversion - I'm not sure exactly how it works...
Now you know!
http://en.wikipedia.org/wiki/Temperature_inversion
http://www.bbc.co.uk/weather/feature...phabet27.shtml
An inversion occurs when the air at ground level is much cooler than the air at altitude (the inverse of the norm). The warmer air acts like a cap, preventing normal convection, and therefore trapping pollutants, smoke etc from dispersing. Seen also in LA due to the surrounding mountains funneling the air, and the huge amounts of heat generated from the city.