The deleterious effects of hydrocarbons in the atmosphere result from their sunlight induced reactions with nitrogen oxides to produce photochemical smog. The techniques commonly applied to reduce the contribution of vehicles to smog normally take into account the overall quantity of hydrocarbons discharged to the atmosphere. This neglects the important fact that some hydrocarbons are inert and others react to varying degrees. Therefore, the reactivity of hydrocarbons, in addition to the quantity, is an important variable in any study of vehicular hydrocarbon emission.
This study was made to determine the effects of combustion and fuel variables on the relative amount and reactivity of vehicular exhaust and vented hydrocarbon losses. In order to minimize variables, several laboratory simulations with CFR engines were used to represent limits of actual vehicle exhaust. A laboratory test chamber, which provided a suitable environment for the pertinent reactions involving a sunlit atmosphere containing nitrogen oxides, was used to measure photochemical reactivities of pure hydrocarbons, fuel blending components, and exhaust gases.
Over the range of engine and fuel variables investigated, it has been shown that for gasoline engine vehicles there is no general relationship between quantity and reactivity of hydrocarbon emissions. Thus, the data obtained in this work support the thesis that both reactivity and quantity of hydrocarbon emissions must be measured in the assessment of the effect of emissions on photochemical smog.