What weather conditions characterize industrial smog?
An inversion. That is; warmer air above cold air. Then the air is not rising as it does usually. Over a humid region, fog is appearing and over an industrial area, smog. That happens often in a high pressure because: a) there is little wind to mix the air, and b) the sinking of the air warms it up adiabatically in the atmosphere while the earth surface reflects its heat toward the sky during the night. Fog and smog are most likely to happen in the coldest part of the day; just before or after sunrise.
