[Big Dave]

There are two types of smog.

One is "London smog" which is exactly what it souldns like: smoke+fog. there was a killer smog in London in 1952. Application of particulate emission controls (electrostatic precipitators for the most part) have eliminated the problem in London. It persists is cooler areas of the Third World.

The other is "LA smog" and it is what the pictures show. It is a photochemical reaction of VOCs (volatile organic coumounds) and oxides of nitrogen. This smog take quite a bit of sunlight to make the reaction go so you'd only rarely see it in the Great Lakes area. the surrogate for LA smog is ozone. The EPA standard for tropospheric ozone is 75 ppb. this pollutant shows up in concentrations three orders of magnitude less than other pollutants (usually they are in the parts per million) so tropospheric ozone is not the health hazard that Londo smog is. A variant of LA smog is denver smog which uses an entirely different reaction using carbon monoxide and is only seen on sunny winter days. The Great Smoky Mountains were never truly smoky. The "smoke" is actually LA type smog generated from the turpenes (a type of VOC) generated by the piney woods and dixie sunshine.

Maybe the best approach would be to dissolve the national EPA and let each state deal with their own conditons their own way.