title: Ultrafine particles in cities.
abstract: Ultrafine particles (UFPs; diameter less than 100 nm) are ubiquitous in urban air, and an acknowledged risk to human health. Globally, the major source for urban outdoor UFP concentrations is motor traffic. Ongoing trends towards urbanisation and expansion of road traffic are anticipated to further increase population exposure to UFPs. Numerous experimental studies have characterised UFPs in individual cities, but an integrated evaluation of emissions and population exposure is still lacking. Our analysis suggests that the average exposure to outdoor UFPs in Asian cities is about four-times larger than that in European cities but impacts on human health are largely unknown. This article reviews some fundamental drivers of UFP emissions and dispersion, and highlights unresolved challenges, as well as recommendations to ensure sustainable urban development whilst minimising any possible adverse health impacts.
authors: Department of Civil and Environmental Engineering, Faculty of Engineering and Physical Sciences (FEPS), University of Surrey, Guildford GU2 7XH, United Kingdom; Environmental Flow (EnFlo) Research Centre, FEPS, University of Surrey, Guildford GU2 7XH, United Kingdom. Electronic address: P.Kumar@surrey.ac.uk.
authors: Prashant
authors: P
authors: Kumar
authors: International Laboratory for Air Quality and Health, Queensland University of Technology, 2 George Street, Brisbane, Qld 4001, Australia.
authors: Lidia
authors: L
authors: Morawska
authors: Leibniz Institute for Tropospheric Research, Permoserstraße 15, 04318 Leipzig, Germany.
authors: Wolfram
authors: W
authors: Birmili
authors: Department of Physics, University of Helsinki, 00014 Helsinki, Finland; International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria.
authors: Pauli
authors: P
authors: Paasonen
authors: State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
authors: Min
authors: M
authors: Hu
authors: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
authors: Markku
authors: M
authors: Kulmala
authors: Division of Environmental Health & Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom; Department of Environmental Sciences / Center of Excellence in Environmental Studies, King Abdulaziz University, Jeddah, 21589, Saudi Arabia.
authors: Roy M
authors: RM
authors: Harrison
authors: Department of Architecture, Massachusetts Institute of Technology, Boston, MA 02139, USA.
authors: Leslie
authors: L
authors: Norford
authors: Urban Studies and Planning, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors: Rex
authors: R
authors: Britter
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001208:Asia; D002947:Cities; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005060:Europe; D006801:Humans; D001335:Vehicle Emissions / Q000032:analysis* / Q000331:legislation & jurisprudence
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions
keywords: City environment; Health impacts; Particle exposure; Particle number concentration; Ultrafine particles