Atmos. Chem. Phys., 20, 409–429, 2020 https://doi.org/10.5194/acp-20-409-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Long-range and local air pollution: what can we learn from chemical speciation of particulate matter at paired sites? Marco Pandolfi1, Dennis Mooibroek2, Philip Hopke3, Dominik van Pinxteren4, Xavier Querol1, Hartmut Herrmann4, Andrés Alastuey1, Olivier Favez5, Christoph Hüglin6, Esperanza Perdrix7, Véronique Riffault7, Stéphane Sauvage7, Eric van der Swaluw2, Oksana Tarasova8, and Augustin Colette5 1Department of Geosciences, Institute of Environmental Analysis and Water Research (IDAEA-CSIC), c/ Jordi-Girona 18-26, Barcelona, Spain 2Centre for Environmental Monitoring, National Institute of Public Health and the Environment (RIVM), A. van Leeuwenhoeklaan 9, P.O. Box 1, 3720 BA, Bilthoven, the Netherlands 3Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY, USA 4Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstr. 15, 04318 Leipzig, Germany 5National Institute for Industrial Environment and Risks (INERIS), DRC/CRA/ASUR, Verneuil-en-Halatte, 60550, France 6Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland 7IMT Lille Douai, Univ. Lille, SAGE – Département Sciences de l’Atmosphère et Génie de l’Environnement, 59000 Lille, France 8World Meteorological Organization, Research Department, Geneva, Switzerland Correspondence: Marco Pandolfi (marco.pandolfi@idaea.csic.es) Received: 24 May 2019 – Discussion started: 18 June 2019 Revised: 25 November 2019 – Accepted: 6 December 2019 – Published: 13 January 2020 Abstract. Here we report results of a detailed analysis of together explaining an additional 11 %–15 % of PM mass. the urban and non-urban contributions to particulate matter In all countries, the majority of PM measured at UB sites (PM) concentrations and source contributions in five Euro- was of a regionalCcontinental (RCC) nature (64 %–74 %). pean cities, namely Schiedam (the Netherlands, NL), Lens The RCC PM increments due to anthropogenic emissions (France, FR), Leipzig (Germany, DE), Zurich (Switzerland, in DE, NL, CH, ES and FR represented around 66 %, 62 %, CH) and Barcelona (Spain, ES). PM chemically speciated 52 %, 32 % and 23 %, respectively, of UB PM mass. Overall, data from 12 European paired monitoring sites (one traffic, the RCC PM increments due to natural and anthropogenic five urban, five regional and one continental background) sources showed opposite seasonal profiles with the former were analysed by positive matrix factorisation (PMF) and increasing in summer and the latter increasing in winter, Lenschow’s approach to assign measured PM and source even if exceptions were observed. In ES, the anthropogenic contributions to the different spatial levels. Five common RCC PM increment was higher in summer due to high con- sources were obtained at the 12 sites: sulfate-rich (SSA) and tributions from regional SSA and V–Ni sources, both being nitrate-rich (NSA) aerosols, road traffic (RT), mineral mat- mostly related to maritime shipping emissions at the Span- ter (MM), and aged sea salt (SS). These sources explained ish sites. Conversely, in the other countries, higher anthro- from 55 % to 88 % of PM mass at urban low-traffic-impact pogenic RCC PM increments in winter were mostly due to sites (UB) depending on the country. Three additional com- high contributions from NSA and BB regional sources dur- mon sources were identified at a subset of sites/countries, ing the cold season. On annual average, the sources show- namely biomass burning (BB) (FR, CH and DE), explaining ing higher RCC increments were SSA (77 %–91 % of SSA an additional 9 %–13 % of PM mass, and residual oil com- source contribution at the urban level), NSA (51 %–94 %), bustion (V–Ni) and primary industrial (IND) (NL and ES), MM (58 %–80 %), BB (42 %–78 %) and IND (91 % in NL). Published by Copernicus Publications on behalf of the European Geosciences Union. 410 M. Pandolfi et al.: Long-range and local air pollution Other sources showing high RCC increments were photo- more recent data were used for Spain (ES, 2010–2014), Ger- chemistry and coal combustion (97 %–99 %; identified only many (DE, 2013–2014) and France (FR, 2013–2014). in DE). The highest regional SSA increment was observed The approach proposed and described in this paper aimed in ES, especially in summer, and was related to ship emis- at identifying the urban and non-urban (RCC) contributions sions, enhanced photochemistry and peculiar meteorologi- (or a mix of both) to the particulate matter (PM) mass mea- cal patterns of the Western Mediterranean. The highest RCC sured at the urban level and at calculating the urban incre- and urban NSA increments were observed in NL and asso- ments that correspond to the concentration difference be- ciated with high availability of precursors such as NOx and tween the city and the regional locations (Lenschow’s ap- NH3. Conversely, on average, the sources showing higher lo- proach; Lenschow et al., 2001). This method, detailed in cal increments were RT (62 %–90 % at all sites) and V–Ni Sect. 2.2 and developed by Lenschow et al. (2001), is based (65 %–80 % in ES and NL). The relationship between SSA on measurements of atmospheric pollutants at sites of dif- and V–Ni indicated that the contribution of ship emissions ferent typologies (i.e. rural and urban background) and has to the local sulfate concentrations in NL has strongly de- been widely used to discriminate the local and non-local in- creased since 2007 thanks to the shift from high-sulfur- to crements (e.g. Pope et al., 2018; Petetin et al., 2014; Gianini low-sulfur-content fuel used by ships. An improvement of et al., 2012, among others). air quality in the five cities included here could be achieved The uniqueness of the present work is that we were able by further reducing local (urban) emissions of PM, NOx and to allocate urban and non-urban pollution to major primary NH3 (from both traffic and non-traffic sources) but also SO2 sources by activity sector or to main secondary aerosol frac- and PM (from maritime ships and ports) and giving high rel- tions thanks to the application of positive matrix factorisa- evance to non-urban contributions by further reducing emis- tion (PMF) (described in Sect. 2.1) that quantitatively groups sions of SO2 (maritime shipping) and NH3 (agriculture) and species emitted from the same source. The PMF is a widely those from industry, regional BB sources and coal combus- used receptor model to perform PM source apportionment tion. studies, identifying main sources of pollution and estimating their contributions to PM concentrations in ambient air (e.g. Hopke, 2016; Liao et al., 2015; Amato et al., 2009; Kim and Hopke, 2007; Kim et al., 2003, among others). This infor- 1 Introduction mation is useful for devising opportune abatement/mitigation strategies to tackle air pollution. In the last scientific assessment report from the Conven- Chemistry transport models (CTMs) are regularly used tion on Long-Range Transboundary Air Pollution (CLRTAP) to design air pollution mitigation strategies and a recurring “Toward Cleaner Air”, it is stated that because non-urban question regards the identification of the main activity sec- sources (i.e. regionalCcontinental sources) are often major tors and geographical areas that produce the pollutants. The contributors to urban pollution, many cities will be unable performances of CTMs in this identification must therefore to meet WHO guideline levels for air pollutants through lo- be compared to measurements. A first step consists in com- cal action alone. Consequently, it is very important to esti- paring the chemical composition of PM between models and mate how much the local and regionalCcontinental (RCC) observations. Such comparison has been performed before sources (both natural and anthropogenic) contribute to urban for specific areas or overall for Europe (Bessagnet et al., pollution in order to design global strategies to reduce the 2016), but the synthesis presented in the present paper will levels of pollutants in European cities. be particularly relevant to identify the main characteristics There are various modelling approaches to disentangle the of the diversity of sites in terms of both chemical composi- local/remote contribution to urban air pollution. But it is also tion and urban–regional gradients. In a second step, a com- relevant to investigate how in situ measurements can be used parison with the models that provide a direct quantification for that purpose. The Task Force on Measurements and Mod- of activity sectors is also relevant. Whereas CTMs focus es- eling (TFMM-CLRTAP) therefore initiated an assessment of sentially on chemical composition, some models (e.g. the the added value of paired urban and regional–remote sites in TNO LOTOS-EURO; Kranenburg et al., 2013) include tag- Europe. Experimental data from paired sites were used to al- ging or source apportionment information (also referred to locate urban pollution to the different spatial scale sources. as source-oriented models). However, we can also include The paired sites selected for this study provided chemi- integrated assessment models such as GAINS (Amann et cally speciated PM10 or PM2:5 data simultaneously measured al., 2011; Kiesewetter et al., 2015) or SHERPA (Pisoni et at urban–traffic and regional–remote sites. In some cases, al., 2017) or even the Copernicus Atmosphere Monitoring (e.g. Spain, ES) these measurements were continuously per- Service (CAMS) policy service (http://policy.atmosphere. formed over long periods, whereas in other cases the mea- copernicus.eu, last access: 13 July 2019). In various ways, surements were performed for a limited time period. The pe- these tools propose a quantification of the priority activity riods presented here were comparable in Switzerland (CH, sectors and scale for actions that must be targeted when de- 2008–2009) and the Netherlands (NL, 2007–2008), whereas Atmos.