Articles | Volume 15, issue 10
Atmos. Chem. Phys., 15, 5929–5945, 2015

Special issue: SAPUSS: Solving aerosol problems by using synergistic strategies...

Atmos. Chem. Phys., 15, 5929–5945, 2015

Research article 28 May 2015

Research article | 28 May 2015

Traffic and nucleation events as main sources of ultrafine particles in high-insolation developed world cities

M. Brines1,2, M. Dall'Osto3,4, D. C. S. Beddows4, R. M. Harrison4,5, F. Gómez-Moreno6, L. Núñez6, B. Artíñano6, F. Costabile7, G. P. Gobbi7, F. Salimi8, L. Morawska8, C. Sioutas9, and X. Querol1 M. Brines et al.
  • 1Institute of Environmental Assessment and Water Research (IDÆA) Consejo Superior de Investigaciones Científicas (CSIC), C/ Jordi Girona 18–26, 08034 Barcelona, Spain
  • 2Department of Astronomy and Meteorology, Faculty of Physics, University of Barcelona, C/ Martí i Franquès 1, 08028 Barcelona, Spain
  • 3Institute of Marine Sciences (ICM) Consejo Superior de Investigaciones Científicas (CSIC), Pg. Marítim de la Barceloneta 37–49, 08003 Barcelona, Spain
  • 4National Centre for Atmospheric Science Division of Environmental Health & Risk Management School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
  • 5Department of Environmental Sciences/Center of Excellence in Environmental Studies, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
  • 6CIEMAT, Environment Department, Unidad Asociada CSIC-CIEMAT, Av. Complutense 40, 28040 Madrid, Spain
  • 7CNR – Institute for Atmospheric Sciences and Climate, via Fosso del Cavaliere, 100, Rome, Italy
  • 8International Laboratory of Air Quality and Health, Queensland University of Technology, G.P.O. Box 2434, Brisbane QLD 4001, Australia
  • 9University of Southern California, Sonny Astani Department of Civil and Environmental Engineering, 3620 S Vermont Ave., Los Angeles, CA, 90089, USA

Abstract. Road traffic emissions are often considered the main source of ultrafine particles (UFP, diameter smaller than 100 nm) in urban environments. However, recent studies worldwide have shown that – in high-insolation urban regions at least – new particle formation events can also contribute to UFP. In order to quantify such events we systematically studied three cities located in predominantly sunny environments: Barcelona (Spain), Madrid (Spain) and Brisbane (Australia). Three long-term data sets (1–2 years) of fine and ultrafine particle number size distributions (measured by SMPS, Scanning Mobility Particle Sizer) were analysed. Compared to total particle number concentrations, aerosol size distributions offer far more information on the type, origin and atmospheric evolution of the particles. By applying k-means clustering analysis, we categorized the collected aerosol size distributions into three main categories: "Traffic" (prevailing 44–63% of the time), "Nucleation" (14–19%) and "Background pollution and Specific cases" (7–22%). Measurements from Rome (Italy) and Los Angeles (USA) were also included to complement the study. The daily variation of the average UFP concentrations for a typical nucleation day at each site revealed a similar pattern for all cities, with three distinct particle bursts. A morning and an evening spike reflected traffic rush hours, whereas a third one at midday showed nucleation events. The photochemically nucleated particles' burst lasted 1–4 h, reaching sizes of 30–40 nm. On average, the occurrence of particle size spectra dominated by nucleation events was 16% of the time, showing the importance of this process as a source of UFP in urban environments exposed to high solar radiation. Nucleation events lasting for 2 h or more occurred on 55% of the days, this extending to > 4 h in 28% of the days, demonstrating that atmospheric conditions in urban environments are not favourable to the growth of photochemically nucleated particles. In summary, although traffic remains the main source of UFP in urban areas, in developed countries with high insolation urban nucleation events are also a main source of UFP. If traffic-related particle concentrations are reduced in the future, nucleation events will likely increase in urban areas, due to the reduced urban condensation sinks.

Final-revised paper