Source apportionment of particle number size distribution in urban background and traffic stations in four European cities

Ultrafine particles (UFP) are suspected of having significant impacts on health. However, there have only been a limited number of studies on sources of UFP compared to larger particles. In this work, we identified and quantified the sources and processes contributing to particle number size distributions (PNSD) using Positive Matrix Factorization (PMF) at six monitoring stations (four urban background and two street canyon) from four European cities: Barcelona, Helsinki, London, and Zurich. These cities are characterised by different meteorological conditions and emissions.  The common sources across all stations were Photonucleation, traffic emissions (3 sources, from fresh to aged emissions: Traffic nucleation, Fresh traffic – mode diameter between 13 and 37 nm, and Urban – mode diameter between 44 and 81 nm, mainly traffic but influenced by other sources in some cities), and Secondary particles. The Photonucleation factor was only directly identified by PMF for Barcelona, while an additional split of the Nucleation factor (into Photonucleation and Traffic nucleation) by using NO_x concentrations as a proxy for traffic emissions was performed for all other stations. The sum of all traffic sources resulted in a maximum relative contributions ranging from 71 to 94% (annual average) thereby being the main contributor at all stations. In London and Zurich, the relative contribution of the sources did not vary significantly between seasons. In contrast, the high levels of solar radiation in Barcelona led to an important contribution of Photonucleation particles (ranging from 14% during the winter period to 35% during summer). Biogenic emissions were a source identified only in Helsinki (both in the urban background and street canyon stations), that contributed importantly during summer (23% in urban background). Airport emissions contributed to Nucleation particles at urban background sites, as the highest concentrations of this source took place when the wind was blowing from the airport direction in all cities.

Image by Philipp Reiner from Pixabay

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Citation:  IoarRivas^aDavid C.S.Beddows^bFulvioAmato^cDavid C.Green^aLeenaJärvi^deChristophHueglin^fCristinaReche^cHilkkaTimonen^gGary W.Fuller^aJarkko V.Niemi^hNoemíPérez^cMinnaAurela^gPhilip K.HopkeⁱAndrésAlastuey^cMarkkuKulmala^dRoy M.Harrison^bjXavierQuerol^cFrank J.Kelly^a

^aMRC-PHE Centre for Environment and Health, Environmental Research Group, King’s College London, 150 Stamford Street, London SE1 9NH, UK

^bDivision of Environmental Health & Risk Management, School of Geography, Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

^cInstitute of Environmental Assessment and Water Research, IDAEA-CSIC, C/Jordi Girona 18–26, 08034 Barcelona, Spain

^dInstitute of Atmospheric and Earth System Sciences/Physics, Faculty of Science, University of Helsinki, P.O. Box 64, FI-00014, Finland

^eHelsinki Institute of Sustainability Science, Faculty of Science, University of Helsinki, FI-00014, Finland

^fLaboratory for Air Pollution and Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology (EMPA), Dübendorf, Switzerland

^gAtmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland

^hHelsinki Region Environmental Services Authority (HSY), Air Protection Unit, P.O. Box 100, FI-00066 Helsinki, Finland

ⁱCenter for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13699, USA

^jDepartment of Environmental Sciences/Centre of Excellence in Environmental Studies, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia