Submicrometer and supermicrometer particulate emission from spark ignition vehicles

Particulate emissions from 11 gasoline-powered and 2 liquefied petroleum (LPG)-powered passenger vehicles were characterized during the Accelerated Simulation Mode driving cycles on a chassis dynamometer. The test fleet consisted of 10 catalyst-equipped vehicles operated with unleaded gasoline (5 Ford Falcons and 5 Holden Commodores), 2 LPG-powered vehicles (both Ford Falcons), and 1 older type noncatalyst vehicle operated with leaded gasoline. Particulate characterization included determination of total particulate number concentration and size distribution using the scanning mobility particle sizer (SMPS) and the aerodynamic particle sizer (APS). The average particle number concentrations in the SMPS range for all modes was lower for Ford Falcons and somewhat higher for Commodores, with values of 1.5 x 10⁴ and 4.1 x 10⁴ cm^-3, respectively. This difference is significant and was observed for all modes. The number concentration levels were higher for the LPG-fueled cars (8.4 x 10⁴ cm^-3) and for the leaded gasoline-powered vehicle (7.9 x 10⁵ cm^-3). There was not a significant variation in particle count median diameter in the SMPS and the APS ranges, either for different operating conditions of the vehicles investigated or between different vehicle groups. The observed size distributions were bimodal with average values of CMD ranging from 39.1 to 60.2 nm in the SMPS range and from 0.9 to 1.4 μm in the APS range. The results obtained from this study can be used as a first-order estimation toward emission inventories for vehicle groups included in the investigations.