Formaldehyde
photochemically produced hydroxyl radicals. Formaldehyde absorbs ultraviolet (UV) radiation at
wavelengths of 360 nm and longer; therefore, it is capable of photolyzing in sunlight. A half-life of
6 hours has been measured for photolysis in simulated sunlight. There are two photolytic pathways,
one producing H2 and CO, and the other producing H and HCO radicals. When the rates of these
reactions are combined with estimates of actinic irradiance, the predicted half-life of formaldehyde
due to photolysis in the lower atmosphere is 1.6 hours at a solar zenith angle of 40 degrees. Based
on its rate of reaction with photochemically produced hydroxyl radicals, formaldehyde has a
predicted half-life of approximately 19 hours in clean air and about half that time in polluted air.
Water
When released to water, formaldehyde will biodegrade to low levels in a few days. In nutrient-
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