Ultrafine particles: unique physicochemical properties relevant to health and disease

Ultrafine particles (UFPs) are aerosols with an aerodynamic diameter of 0.1 mu m (100 nm) or less. There is a growing concern in the public health community about the contribution of UFPs to human health. Despite their modest mass and size, they dominate in terms of the number of particles in the ambient air. A particular concern about UFPs is their ability to reach the most distal lung regions (alveoli) and circumvent primary airway defenses. Moreover, UFPs have a high surface area and a capacity to adsorb a substantial amount of toxic organic compounds. Harmful systemic health effects of PM10 or PM2.5 are often attributable to the UFP fraction. In this review, we examine the physicochemical characteristics of UFPs to enable a better understanding of the effects of these particles on human health. The characteristics of UFPs from diesel combustion will be discussed in the greatest detail because road vehicles are the primary source of UFP emissions in urban pollution hotspots. Finally, we will elaborate on the role of UFPs on global climate change, since the adverse effects of UFPs on meteorological processes and the hydrological cycle may even be more harmful to human health than their direct toxic effects. Air quality: tiny particles with big effects Ultrafine particles (UFPs) from auto exhaust, factory emissions, and woodburning negatively affect human health and can alter weather patterns. UFPs, particles less than 100 nanometers, smaller than the smallest bacterium, are the most common airborne particles. Their size allows them to penetrate the deepest lung passageways, sometimes carrying toxic metals or organic compounds that trigger inflammation and disease. Hyouk-Soo Kwon at the University of Ulsan, Seoul, South Korea, and coworkers have reviewed the sources and effects of UFPs. Auto engines are a primary source; recent improvements in combustion technology have resulted in production of smaller particles, with worse effects on health. UFPs have also been found to affect cloud formation and behavior, altering rainfall patterns and potentially causing flooding or drought. Understanding the properties of UFPs will help find ways to mitigate their effects.