1-8 effects of hydrocarbons,oxides of nitrogen,photochemical oxidants
1-8-A hydrocarbons
Although a national air quality standard was originally established in 1971 for non-methane hydrocarbons,it was withdrawn after extensive review in 1983.hydrocarbons,in combination wit the oxides of nitrogen in the presence of sunlight,from petrochemical oxidants including ozone that do have adverse effects on human health and on plants.
For that reason,however,it was felt that an ozone standard was more appropriate than a hydrocarbon standard.
studies of the effects of ambient air concentrations of many of the gaseous hydrocarbons have not demonstrated direct adverse effects upon human health[43].Studies of the carcinogenicity of certain classes of hydrocarbons do indicate that some cancers appear to be caused by exposure to aromatic hydrocarbons found in Soots and tars. Identifiable airborne carcinogens include polynuclear aromatic hydrocarbons
gaseous hydrocarbons as broad class also do not appear to cause any appreciable corrosive damage to inaterials. Of all the hydrocarbons, only ethylene has adverse effects on plants at known ambient concentrations. The principal effect of ethylene is to inhibit plant growth [48]. Concentrations of ethylene from 0.001 to 0.5ppm have caused damage to sensitive plants including flower droppings and failure of the leaves to open properly. Injury to orchids and to cotton has been demonstrated.
While hydrocarbons as a general class of pollutants are not currently listed as criterir pollutants, a large number of specific hydrocarbon compounds are listed among the list of 189 hazardous air pollutants which are I the process of being regulated under the title iii air toxics provisions of the clean air act amendments of 1990. Hazardous air pollutants are discussed in more detail in chapter 2.