Emissions of Fine Particles and Organic Compounds from Mopeds

Abstract

In 2004 worldwide sales of powered two-wheelers (PTWs) were about 34 million units and are predicted to rise to over 40 million by 2009. Only in the last 10 years has the environmental impact of mopeds (scooters included) and motorcycles been seriously considered. Particular concern has been raised over two-stroke (2-S) scooters which in several countries such as Italy are widely used in congested city centers.

In this study, the emissions of fine particles and some organic compounds (benzene, formaldehyde, 1,3-butadiene, and benzo(a)pyrene) the exhausts of nine mopeds (2-S and 4-S), responding to different European emission legislative standards (pre-Euro, Euro 1, and Euro 2), were evaluated during the type approval driving cycle. Particulate was characterized as total mass collected on filters and as the total number of particles and size distribution in the range 7 nm–10 μm measured by the ELPI (Electrical Low Pressure Impactor). Introduction of the 4-S working cycle and oxidation catalyst on small engine two-wheeler vehicles, resulting from Euro 1 and Euro 2 limits coming into force, has appreciably reduced emissions of total hydrocarbons (including benzene, 1,3-butadiene, formaldehyde, and benzo(a)pyrene) and particulate matter. When considering engine technology, 2-S emit about three times more quantified organic compounds compared to 4-S. Total particle number emissions, occurring mainly during the acceleration phase, which corresponds to a rich combustion mixture, range from 7 × 10¹²/km to 6 × 10¹³/km, with higher values for 2-S engines. Size distribution of solid particles peaks at about 0.1 μm.