Browse Publications Technical Papers 920325
1992-02-01

Speciation and Calculated Reactivity of Automotive Exhaust Emissions and Their Relation to Fuel Properties - Auto/Oil Air Quality Improvement Research Program 920325

Speciated exhaust emission data from Phase I of the Auto/Oil Air Quality Improvement Research Program are presented and analyzed. Eighteen fuels were tested which varied in four fuel parameters: aromatics, MTBE content, olefins, and T90. These fuels were tested in two fleets of vehicles. One consisted of twenty 1989 vehicles and the other consisted of fourteen 1983-1985 vehicles.
The 1990 version of Carter reactivity factors were used to calculate reactivities for each of these tests. Two types of reactivities were calculated. The first was Specific Reactivity and has units of grams ozone per gram NMOG (non-methane organic gas). The second was Ozone Forming Potential and has units of grams ozone per mile. Both types of reactivities were calculated using Carter's MIR (Maximum Incremental Reactivity) as well as MOR (Maximum Ozone Reactivity) factors.
Regression analysis showed that reducing T90 from 360°F to 280°F reduced all measures of exhaust reactivity by amounts that varied between 9% and 30%. Reducing olefins reduced Specific Reactivity in both fleets, while adding MTBE raised Specific Reactivity in both fleets. The impact of reducing aromatics was mixed.
The speciated data were broken down by molecular classes: methane, paraffins, aromatics, light olefins, heavy olefins, MTBE and aldehydes. The weight percents of paraffins, aromatics, heavy olefins, and MTBE in the exhaust were highly correlated with their corresponding fuel compositions. Exhaust methane concentrations were positively correlated with fuel paraffins and negatively correlated with fuel aromatics. Light olefins in the exhaust were positively correlated with fuel MTBE and negatively correlated with fuel aromatics. Aldehydes were positively correlated with fuel MTBE and, in the older fleet, negatively correlated with fuel paraffins as well.

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