What is the difference between smog and fog. A very simple question, but one with some interesting complications..
Smog is defined in the Merriam-Webster Online Dictionary as ": a fog made heavier and darker by smoke and chemical fumes; also : a photochemical haze caused by the action of solar ultraviolet radiation on atmosphere polluted with hydrocarbons and oxides of nitrogen especially from automobile exhaust". It is man-made pollution of poisons mixed with fog.
So, what is fog? Fog is basically a cloud on the ground. It is best described by this exert from the BBC Weather Centre "Our atmosphere is made up of many gases, one of which is water vapour. It can hold a certain amount of water as invisible water vapour at any given temperature. If air is cooled it can hold less water and becomes super saturated. At saturation point, some of the water has to condense to form water droplets, which forms cloud." Fog occurs as a function of temperature, humidity and atmospheric pressure. If the water particles are large, they become mist or rain.
So the basic difference is that fog is natural and smog is created by pollution produced by cars and factories. Is this difference important? Should people worry about if they have fog or smog? Is the "poisons" in smog enough to cause problems? Definitely!
Fog helps plants by providing moisture and contains no toxic compounds. The damp air can actually make breathing easier for most people. Fog can be dangerous, but only to people traveling to fast or to airplanes. It doesn't cause illness or physical discomfort. Worrying about fog for most people isn't needed.
Smog can be deadly. It is created from toxic fumes and deadly emissions. The levels of heavy metals can damage the lungs and open the body to infections. Even without infections it can make breathing more difficult and increases the potential for cancers. Smog frequently contains high levels of carbon monoxide which by mixing with the air reduces oxygen levels and that can cause asphyxia and death in elderly people. It also kills birds. Check out this report on the Science of Smog.
Almost everywhere in the world gets fog, it is natural and cannot be controlled, but only places with excessive numbers of cars and industry get smog. The smog can be controlled with emission standards on automobiles and factories. It needs to be done to protect the people and the environment.