Volatile natural emission

Methane and the Nonmethane Hydrocarbons. It is traditional to distinguish CH4 from all other atmospheric hydrocarbons. Methane is by far the most abundant atmospheric hydrocarbon and has very large natural emissions. Its abundance in auto exhaust but low atmospheric reactivity has led air pollution scientists to enact controls on nonmethane hydrocarbons NMHC (also called VOC for volatile organic compounds, which include oxygenated hydrocarbons). 

Guenther A., Geron C., Pierce T., Lamb B., Harley P., and Fall R. (2000) Natural emissions of nonethane volatile organic compounds, carbon monoxide, and oxides of nitrogen from North America. Atmos. Environ. 34, 2205-2230. 

For solvent operations, benzene use had to be estimated by a series of tenuous assumptions about the amount of benzene in "other uses," the percent of that used for solvents, and the loss of benzene from those operations. As an upper limit, it might be assumed that all of the purchased benzene is eventually lost to the atmosphere. However, some measured concentrations suggest that perhaps only 10% is lost at the plant. The remainder might be incinerated after becoming unusable or sent elsewhere for disposal. A general rule for volatile solvents is that they eventually reach the environment unless they are destroyed deliberately or degrade naturally. The distribution of solvent emissions geographically is much more difficult to determine. 

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