EFFECTS OF FUEL TYPE, DRIVING CYCLE, AND EMISSION STATUS ON IN-USE VEHICLE EXHAUST REACTIVITY

The introduction of reformulated gasolines significantly reduced exhau st hydrocarbon (HC) mass emissions, but few data are available concern ing how these new fuels affect exhaust reactivity. Similarly, while it is well established that high-emitting vehicles contribute a signific ant portion of total mobile source HC mass emissions, it is also impor tant to evaluate the exhaust reactivity from these vehicles. The objec tive of this study was to evaluate the relative influence on in-use ve hicle exhaust reactivity of three critical factors: fuel, driving cycl e, and vehicle emission status. Nineteen in-use vehicles were tested w ith seven randomly assigned fuel types and two driving cycles: the Fed eral Test Procedure (FTP) and the Unified Cycle (UC). Total exhaust re activity was not statistically different between the FTP and UC cycles but was significantly affected by fuel type. On average, the exhaust reactivity for California Phase 2 fuel was the lowest (16 % below the highest fuel type) among the seven fuels tested for cold start emissio ns. The average exhaust reactivity for high-emitting vehicles was sign ificantly higher for hot stabilized (11%) and hot start (15%) emission s than for low-emitting vehicles. The exhaust reactivities for the FTP and UC cycles for light-end HCs and carbonyls were significantly diff erent for the hot stabilized mode. There was a significant fuel effect on the mean specific reactivity (SR) for the mid-range HCs, but not f or light-end HCs or carbonyls, while vehicle emission status affected the mean SR for all three HC compound classes.