Speciated hydrocarbon profiles and calculated reactivities of exhaust and evaporative emissions from 82 in-use light-duty Australian vehicles

Mass emissions of non-methane hydrocarbon (NMHC) from 26 pre-1986 and 56 post-1985 catalyst-equipped in-service vehicles were determined from measurements made on a chassis dynamometer using an urban drive cycle. Evaporative emissions were measured on a subset (4 pre-1986 and 8 post-1985) of these vehicles. Average ADR emissions (mg/km) of the individual HCs from the older pre-1986 vehicles were generally 4–7 times the emissions from newer catalyst-equipped vehicles. Evaporative emissions from the older vehicles are also much higher than those of newer vehicles. Exhaust from newer catalyst-equipped vehicles had lower proportions of substituted aromatics and alkenes and higher proportions of lower molecular weight alkanes. The effect of fuel type on the exhaust emissions was also investigated by refuelling 9 of the pre-1986 vehicles with both unleaded and leaded petrol. A 20–40% reduction in HC mass emissions was observed when unleaded petrol was used instead of leaded petrol. Reactivities of the emissions and the contributions from different classes of compounds are also reported. The specific reactivity of the exhaust emissions from newer vehicles was lower than that for older vehicles owing to the smaller proportions of highly reactive alkenes and substituted aromatic species. Moreover, as older vehicles have higher average mass emissions, when considered on a per-km basis, the pre-1986 vehicles have a greater ozone-forming potential than post-1985 vehicles. The specific reactivities of the NMHC (gO₃/gNMHC) of both the heat build and hot soak evaporative emissions were much lower than the exhaust emissions.