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Hydrocarbons and other organic materials emitted from S.I. engines cause ozone to form in the air. Since each species of organic materials has a different reactivity, exhaust components affect ozone formation in different ways. The effects of exhaust emission control devices and fuel properties on speciated emissions and ozone formation were examined by measuring speciated emissions with a gas chromatograph and a high-performance liquid chromatograph. In the case of gasoline fuels, catalyst systems with higher conversion rates such as close-coupled catalyst systems are effective in reducing alkenes and aromatics which show high reactivities to ozone formation. With deterioration of the catalyst, non-methane organic gas (NMOG) emission increases, but the specific reactivity of ozone formation tends to decrease because of the increase in alkane contents having low MIR values.

Gas chromatographic methods for analyzing hydrocarbon species in vehicle exhaust emissions were compared in terms of their collection efficiency, detection limit, repeatability and number of species detected using cylinder gas and tailpipe emission samples. The main methods compared were a Tenax cold trap injection (TCT) method (C5-C12 HCs) and a cold trap injection (CTI) method (C2-C4 HCs; C5-C12 HCs). Our own direct (DIR) method was used to confirm the collection efficiencies. Both methods yielded good results, but the CTI method showed low collection efficiency for some C2-C4 HCs. Measurement of individual species is needed with this method for accurate analysis of tailpipe emissions. Both the CTI method and the TCT method combined with the DIR method for determining C2-C4 HCs yielded nearly the same ozone specific reactivity values for the NMHC species analyzed.