Long-range and local air pollution: what can we learn from chemical speciation of particulate matter at paired sites?
Authors: Pandolfi Marco , Mooibroek Dennis , Hopke Philip , van Pinxteren Dominik , Querol Xavier , Herrmann Hartmut , Alastuey Andrés , Favez Olivier , Hüglin Christoph , Perdrix Esperanza , Riffault Véronique , Sauvage Stéphane , van der Swaluw Eric , Tarasova Oksana , Colette Augustin 
Published: January 2020

Abstract. Here we report results of a detailed analysis of the urban and non-urban
contributions to particulate matter (PM) concentrations and source contributions in five European
cities, namely Schiedam (the Netherlands, NL), Lens (France, FR), Leipzig
(Germany, DE), Zurich (Switzerland, CH) and Barcelona (Spain, ES). PM
chemically speciated data from 12 European paired monitoring sites (one
traffic, five urban, five regional and one continental background) were analysed by
positive matrix factorisation (PMF) and Lenschow's approach to assign
measured PM and source contributions to the different spatial levels. Five
common sources were obtained at the 12 sites: sulfate-rich (SSA) and nitrate-rich (NSA) aerosols,
road traffic (RT), mineral matter (MM), and aged sea salt (SS). These sources explained from 55 % to 88 % of PM
mass at urban low-traffic-impact sites (UB) depending on the country. Three
additional common sources were identified at a subset of sites/countries,
namely biomass burning (BB) (FR, CH and DE), explaining an additional 9 %–13 % of PM
mass, and residual oil combustion (V–Ni) and primary industrial (IND) (NL and ES), together explaining an additional
11 %–15 % of PM mass. In all countries, the majority of PM measured at UB
sites was of a regional+continental (R+C) nature (64 %–74 %). The R+C PM
increments due to anthropogenic emissions in DE, NL, CH, ES and FR
represented around 66 %, 62 %, 52 %, 32 % and 23 %, respectively,
of UB PM mass. Overall, the R+C PM increments due to natural and
anthropogenic sources showed opposite seasonal profiles with the former
increasing in summer and the latter increasing in winter, even if exceptions
were observed. In ES, the anthropogenic R+C PM increment was higher in
summer due to high contributions from regional SSA and V–Ni sources, both
being mostly related to maritime shipping emissions at the Spanish sites.
Conversely, in the other countries, higher anthropogenic R+C PM increments
in winter were mostly due to high contributions from NSA and BB regional
sources during the cold season. On annual average, the sources showing
higher R+C increments were SSA (77 %–91 % of SSA source contribution at the
urban level), NSA (51 %–94 %), MM (58 %–80 %), BB (42 %–78 %) and IND (91 %
in NL). Other sources showing high R+C increments were photochemistry and coal combustion (97 %–99 %;
identified only in DE). The highest regional SSA increment was observed in
ES, especially in summer, and was related to ship emissions, enhanced
photochemistry and peculiar meteorological patterns of the Western
Mediterranean. The highest R+C and urban NSA increments were observed in
NL and associated with high availability of precursors such as NOx and
NH3. Conversely, on average, the sources showing higher local
increments were RT (62 %–90 % at all sites) and V–Ni (65 %–80 % in ES and
NL). The relationship between SSA and V–Ni indicated that the contribution
of ship emissions to the local sulfate concentrations in NL has strongly
decreased since 2007 thanks to the shift from high-sulfur- to low-sulfur-content fuel used by ships. An improvement of air quality in the five cities
included here could be achieved by further reducing local (urban) emissions
of PM, NOx and NH3 (from both traffic and non-traffic sources) but
also SO2 and PM (from maritime ships and ports) and giving high
relevance to non-urban contributions by further reducing emissions of
SO2 (maritime shipping) and NH3 (agriculture) and those from
industry, regional BB sources and coal combustion.