Why Is There Smog in Big Cities?

Smog is primarily caused by the use and burning of fossil fuels such as oil and coal. It is especially prevalent in large cities because of population density. The more people there are in a given area the more fuel they use and the more smog they create. Weather patterns also play a role in that they can take smog from one place and disburse it to other areas. Smog and other forms of air pollution have been shown to cause serious adverse health effects, especially asthma.

Photochemical Smog

• Photochemical smog forms when unburned gasoline meets sunlight. Any machine that uses gasoline will emit some amount of unburned fuel. This fuel is irradiated by the sun and turns into such things as ozone, peroxyactyl nitrate, organic acids and aldehydes.

Industrial Smog

• The more well known type of smog is industrial smog, also called gray smog. Industrial smog is primarily made up of sulfur dioxide. Coal and heavy oil contain sulfur impurities. When these are burned it creates sulfur dioxide that mixes with moisture in the air and creates a gray fog or smog. Pollution controls have reduced this type of smog over the years. Health and environmental scientists are now primarily worried about smog of the photochemical type.

Large Cities

• Densely populated areas, as well as areas with a large amount of automobile traffic or industry, will have more smog than others. According to Revolution Health, the smoggiest cities in the United States are Los Angeles, Bakersfield, Visalia, Fresno and Sacramento, California; Houston and Dallas, Texas; New York, New York; Washington, D.C.; Baltimore, Maryland and Baton Rouge, Louisiana.

The Brown Cloud

• In Asia a rapid increase in population in certain areas combined with rapid industrialization and few filters have cause what is known as the "Asian Brown Cloud," a dense cloud of smog that is viewable from space. While the effects of the cloud are not fully known yet it is thought to have negative effects on the health of local populations. There is also concern that by blocking solar rays the cloud may reduce ocean evaporation and cause drought.

Health Effects

• According to the University of California at Berkeley, humans inhale 10 to 20 thousand liters of air per day. Naturally if that air is polluted with dangerous compounds it will have detrimental effects on health, especially the respiratory system. The effects are especially acute in children because their immune systems are not fully developed yet. According to the Canadian Medical Association, smog in that country accounts for 2,700 premature deaths, 11,000 hospitalizations and a health care cost of $1 billion annually.