Increasing attention is being given to atmospheric formaldehyde as actual and potential levels may increase. Atmospheric formaldehyde results from both natural processes and anthropogenic emissions. Natural processes include in situ formation through the photooxidation of volatile organic compounds (VOCs); releases from forest and grass fires; and biogenic emissions from bacteria and vegetation. Anthropogenic sources of atmospheric formaldehyde are numerous and include fuel combustion, garbage incineration, solvent use, electricity generation, among many others. The results of the fumigation study show that formaldehyde in fog water, at ambient concentrations currently reported in the SCAB (concentrations that, according to the literature, also likely occur in other regions of the United States), may inhibit the growth and reproductive potential of some plant species.