Air pollution is produced by any sort of atmospheric contaminant whether caused by human or natural actions or located inside or outside of doors.  Air pollution can have large negative effects on human health.  Recently, it has been recognized as an international health problem.

There are a large variety of air pollutants.  One of the most long-standing is smoke.  Coal is, and has been for centuries, responsible for large quantities of smoke and is therefore itself an air pollutant.  Heavy reliance on fossil fuels has introduced sulfur and nitrogen oxides as major pollutants as well.  One of the largest producers of air pollution today is auto-emission -- and with it, nitrogen oxide, volatile organic compounds, and especially carbon monoxide.  Many newer pollutants are considered secondary pollutants; often these are a result of photochemical reactions -- for example, the photochemical smog that can be found in urban areas. Other major air pollutants include gaseous emissions from oil-burning furnaces, various emissions from incinerators, and a wide range of emissions from industrial processes.

Although it is widely agreed that air pollution control is very important, it is a nearly impossible task.  Not only are there intractable primary pollutants such as smoke, there are also secondary pollutants that are often even more difficult to eliminate.

All air pollution has a large effect on human health.  Bronchial diseases are caused by smoke and sulfur dioxide, making respiratory diseases a problem of widespread concern.  However, there are numerous other air pollution consequences: photochemical smog causes eye irritation, and carbon monoxide in strong concentrations can worsen heart conditions.  Air pollution has also been connected to asthma, and lead has been found to lower the IQs of urban youth.

Of growing concern is indoor air pollution, which can also have adverse effects on humans.  Nitrogen oxides from gas stoves can be harmful, and formaldehyde from insulation can cause not only short-term sickness, but cancer as well.  Radon leaks can introduce strong radioactive gas within homes, and cancer has been linked to fumes from glues and paints, as well as to mineral fibers such as asbestos.

The EPA on air pollution's health effects