Public health is concerned with the physical, mental and environmental health of communities and populations at risk for disease and injury. Generally, the determination of health effects associated with indoor and outdoor exposures is difficult since documented cause-and-effect relationships are rare and the exposure and dosage data is sparse. Information about actual human exposure to different types of pollution has several important uses, including informing risk assessments, helping predict the potential consequences of exposures, and developing exposure criteria for regulations and other public policy guidance.