Large quantities of volatile organic substances are emitted from mobile and stationary sources in the United States. When the US, east of 105 west longitude is divided into 80 by 80 km grids, most of these grid areas east of the Mississippi River and many west of the river, have organic emissions of at least 10,000 to 20,000 tons/y from area sources. In addition, point sources outside of large cities involving emissions from petroleum industrial processes and chemical manufacturing contribute substantially. Sources of natural emissions are distributed much differently than the sources of anthropogenic emissions. The emission rates are much higher throughout the year in the southern United States. Essentially all of the available measurements for biogenic hydrocarbons are related to isoprene and monoterpenes, particularly from forest species. There is no current evidence that the volatile natural organic compounds as emitted have adverse health or welfare effects. The interest and potential concern has been focused on formation of secondary atmospheric products from the natural organic compounds. All the pertinent results on product formation needs to be considered adequately. The capability of these natural organics to contribute to formation of ozone, aerosols and other products must be carefully assessed.