Formaldehyde

Formaldehyde is produced both from man-made and natural sources.
Burning fuels accounts for most man-made formaldehyde emissions.
The major direct emissions to ambient air are from automobile
exhaust, power plants, incinerators, refineries, wood burning and
cigarettes. Formaldehyde is used industrially to produce resins
used in particleboard products and as an intermediate in the
synthesis of other chemicals. Formaldehyde production also
occurs indirectly through the oxidation of hydrocarbons and other
formaldehyde precursors. These precursors include combustion
byproducts and solvent emissions. During the summer, indirect
sources of formaldehyde can be greater than direct sources.
Natural sources of formaldehyde such as forest fires, microbial
products of biological processes and plant volatiles also
significantly contribute to formaldehyde in ambient air.

Formaldehyde reacts rapidly in the air and generally breaks down
in just a few hours and is probably not transported long
distances. However, longer-lived formaldehyde precursors may
travel to downwind locations resulting in measurable formaldehyde
concentrations. People are primarily exposed to formaldehyde by
breathing contaminated air. In Minnesota, formaldehyde is found
in both rural and urban areas.

Acute (short-term) and chronic (long-term) inhalation exposure to
formaldehyde in humans can result in respiratory symptoms, and
eye, nose, and throat irritation. Limited human studies have
reported an association between formaldehyde exposure and lung
and nasopharyngeal cancer. Recent studies also indicate a link
between formaldehyde exposure and leukemia. EPA considers
formaldehyde a probable human carcinogen.