Developing motor vehicle emission inventories and air quality regulation for ultrafine particles

Abstract

Most particle emissions generated by motor vehicle fleets are ultrafine size (diameters < 0.1 µm) and measured in terms of particle number. These sized particles are not routinely monitored nor are they regulated by ambient air quality standards. In urban areas around the world travel demand and dependence on private motor vehicle travel is increasing, and thereby potentially contributing higher concentrations of ultrafine particles to urban airsheds. Heavy duty vehicles (HDVs) continue to be a major freight mode. HDVs are particularly high emitters of ultrafine particles and can release over an order of magnitude more particles (in terms of particle number) than petrol-fuelled vehicles, with a significant number in the ultrafine size range. The health effects associated with exposure to particulate matter are well-documented. These are known to be serious, and a number of epidemiological studies have linked exposure to increases in hospital admissions, various respiratory and cardiovascular diseases and mortality. However, more epidemiological studies of the effects of ultrafine particles are needed, as well as development of motor vehicle emission inventories for ultrafine fine particles. These studies are vital to inform exposure assessment in terms of health, transport and land use planning. Current knowledge about levels of total particulate matter generated by urban motor vehicle fleets, including of ultrafine particle emissions, remain the subject of considerable uncertainty. This limited knowledge has severely impeded our ability to develop effective and relevant ambient air quality standards and strategies to manage and control ultrafine particle emissions. Such regulation is critical for two reasons. Firstly, ultrafine particles are the main source of vehicle fleet emissions. Secondly, because debate is presently focused on the notion that particle number is more directly related to health effects than particle mass. This chapter discusses some of the scientific and practical issues and challenges associated with developing ultrafine particle inventories for motor vehicle fleets and air quality regulation. It also introduces the world’s first published inventory of motor vehicle fleet emissions for particle number.