Photochemical Reactivity of Exhaust Hydrocarbons from Motor Vehicles

Abstract

The composition and pnotochemical reactivity of exhaust hydrocarbons from four kinds of vehicles equipped with various emission control systems are investigated by using five kinds of fuels varying in aromatic content and four kinds of test procedures.
An oxidation catalyst-equipped vehicle shows a small olefin and aromatic contentunder a warmed-up condition. As a result it is estimated that the specific reactivity of its exhaust hydrocarbons is significantly small under the warmed-up condition. The specific reactivities of two vehicles with other typesof the advanced emission control systems, however, are almost the same as that of a conventional engine-modified vehicle. On the contrary it is estimated that the overall reactivities of three advanced vehicles are almost close to one another.
We define the modified non-methane HC mass emission such as eq.(6). By assuminga curvilinear regression relation between the modified non-methane HC mass emission and the overall reactivity, eq.(9) is derived. This equation is possible to estimate the photochemical exhaust reactivity only by measuring the HC mass emission and the exhaust methane content. On the basis of eq.(9), it is estimated that the photochemical reactivity of the exhaust hydrocarbons significantly changes with the methane content, even if the vehicles show the same HC mass emissions.