Ambient Air
Higher
Concentrations of formaldehyde in ambient air may be of concern in several areas in the U.S. (see Considerations for Decision Making). Background levels of formaldehyde exceeded the U.S. EPA Air Concentration at Specified Risk Level of 1 in one million in over 90% of census tracts analyzed from 1996 emissions data. Major sources of formaldehyde in ambient air include emissions from power plants, manufacturing facilities, and incinerators; and mobile sources such as cars, trucks, and construction equipment.
Indoor Air
Higher
Formaldehyde contamination of indoor air can result from off-gassing of certain building materials (e.g., some forms of particle board and other pressed wood products; new carpeting), and from mainstream and second-hand cigarette smoke. For those reasons, indoor levels of formaldehyde can be substantial, even in non-smoking homes. Formaldehyde is also used in medical settings, and in preservatives of biological samples often in school settings.