The health effects of the criteria air pollutants and the toxic air pollutants on humans have been determined by epidemiological and clinical evidence. These health problems occur either by causing new health conditions or exacerbating existing health conditions including: cardiovascular disease, cancer, impaired immune systems, birth defects, genetic mutations, asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, diabetes, eye diseases, etc. All body systems including the lungs, heart, brain, nerves, liver, kidneys, skin, etc., can be challenged on a short-term or long-term basis by the various air pollutants. Confounding factors include age, sex, previous exposures and concentrations of the exposures, cigarette smoke, secondhand smoke, lack of exercise, existing health conditions, predisposition to health problems, prescription drugs taken, nutrition, and environmental exposures including the type, concentration, and amount of time of exposure, associated with the individual during all times of the day and night.
An example of deleterious health effects is the relationship of ambient air pollution to heart disease and stroke. Carbon monoxide, nitrogen oxides, sulfur dioxide, ozone, lead, tobacco smoke, and particulate matter, especially fine particles, are associated with increased hospitalization and deaths due to cardiovascular disease. This occurs both in short-term air pollution episodes and longterm exposure to air pollutants, especially from inhaling the byproducts of automobile combustion. Another example is COPD, which is especially aggravated by particulates and ozone.