Particulate Emissions from On-Road Vehicles

Abstract

The short term standard defined by the European Union (Directive 2008/50/EC) (European Parliament, Council of the European Union 2008) for particulate matter smaller than 10 μm (PM10) is violated in many European cities, therefore the current air quality status of PM10 is under investigation in many countries, in particular to understand the source terms of the particulate matter and to propose a catalogue of measures to avoid further exceeding of the limiting value. For a targeted reduction of PM10 levels, detailed knowledge of sources and their respective contribution to the PM levels is required. Emissions from motor vehicles are among the major contributors to fine particle concentrations in the urban atmosphere they make substantial direct and indirect contributions to ambient PM levels. Direct particulate emission sources from vehicles include their exhaust, the mechanical wear of tires and brakes, and the ejection of particles from the pavement and unpaved road shoulders as well as resuspension processes. Indirect contributions include the emission of reactive gases, both organic and inorganic, which form secondary particulate matter via atmospheric transformations. For assessment of the contribution of traffic derived emissions to total pollution levels in an urban atmosphere, detailed information about the emission characteristics of motor vehicles operated under real-world conditions is needed. Emission factors can be used for this purpose; they may be expressed as the amount of species emitted per vehicle km driven or per volume of fuel consumed. So far, considerable information of the gaseous exhaust pipe emission factors and some of particulate matter is available from the 1990s. More recent studies reported emission factors for PM mass, organic carbon (OC), elemental carbon (EC) and some metals, which improved present knowledge about composition and size distribution of particulate motor vehicle emissions, and more important which allowed the creation of emission profiles-a prerequisite for source apportionment studies with statistic methods such as chemical mass balance models. However, since fuel composition, engines and vehicle technologies evolve data on the combined mass emission rate and chemical composition of primary particle emissions from motor vehicles need to be updated periodically. This contribution comprehensively reviews the literature reported for particulate emissions of motor vehicles operated under real-world conditions. This article will mainly focus on the results published for size segregated emissions factors of particle mass, elemental and organic carbon, crustal components and selected trace metals, since information is important for health effects studies and source reconciliation modeling efforts.