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Hourly-resolved aerosol chemical speciation data can be a highly powerful tool to determine the source origin of atmospheric pollutants in urban environments. Aerosol mass concentrations of seventeen elements (Na, Mg, Al, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Sr and Pb) were obtained by time (1 h) and size (PM2.5 particulate matter <2.5 μm) resolved aerosol samples analysed by Particle Induced X-ray Emission (PIXE) measurements. In the Marie Curie European Union framework of SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies), the approach used is the simultaneous sampling at two monitoring sites in Barcelona (Spain) during September-October 2010: an urban background site (UB) and a street canyon traffic road site (RS). Elements related to primary nonexhaust traffic emission (Fe, Cu), dust resuspension (Ca) and anthropogenic Cl were found enhanced at the RS, whereas industrial related trace metals (Zn, Pb, Mn) were found at higher concentrations at the more ventilated UB site. When receptor modelling was performed with positive matrix factorization (PMF), nine different aerosol sources were identified at both sites: three types of regional aerosols (regional sulphate (S) - 27 %, biomass burning (K) - 5 %, sea salt (Na- Mg) - 17 %), three types of dust aerosols (soil dust (Al-Ti) - 17 %, urban crustal dust (Ca) - 6 %, and primary traffic non-exhaust brake dust (Fe-Cu) - 7 %), and three types of industrial aerosol plumes-like events (shipping oil combustion (V-Ni) - 17 %, industrial smelters (Zn-Mn) - 3 %, and industrial combustion (Pb-Cl) - 5 %, percentages presented are average source contributions to the total elemental mass measured). The validity of the PMF solution of the PIXE data is supported by very good correlations with external single particle mass spectrometry measurements. Some important conclusions can be drawn about the PM2.5 mass fraction simultaneously measured at the UB and RS sites: (1) the regional aerosol sources impact both monitoring sites at similar concentrations regardless their different ventilation conditions; (2) by contrast, local industrial aerosol plumes associated with shipping oil combustion and smelters activities have a higher impact on the more ventilated UB site; (3) a unique source of Pb-Cl (associated with combustion emissions) is found to be the major (82 %) source of fine Cl in the urban agglomerate; (4) the mean diurnal variation of PM 2.5 primary traffic non-exhaust brake dust (Fe-Cu) suggests that this source is mainly emitted and not resuspended, whereas PM2.5 urban dust (Ca) is found mainly resuspended by both traffic vortex and sea breeze; (5) urban dust (Ca) is found the aerosol source most affected by land wetness, reduced by a factor of eight during rainy days and suggesting that wet roads may be a solution for reducing urban dust concentrations. © Author(s) 2013. ; FP7-PEOPLE-2009-IEF, Project number 254773, SAPUSS – Solving 25 Aerosol Problems Using Synergistic Strategies (Marie Curie Actions – Intra European Fellow- ships. Mr. Manuel Dall'Osto). This study was previously supported by research projects from the D.G. de Calidad y Evaluacion Ambiental (Spanish Ministry of the Environment) and the Plan Nacional de I + D (Spanish Ministry of Science and Innovation [CGL2010-19464 (VAMOS) andCSD2007-00067 (GRACCIE)]), a collaboration agreement CSIC-JRC, and the Departaments of Medi Ambient from the Generalitat de Catalunya and Diputacio of Barcelona. The University of Birmingham (UK) and the University of Cork (Ireland) SAPUSS ATOFMS teams are also 5 acknowledged. ; Peer Reviewed

Thermal-optical analysis is currently under consideration by the European standardization body (CEN) as the reference method to quantitatively determine organic carbon (OC) and elemental carbon (EC) in ambient air. This paper presents an overview of the critical parameters related to the thermal-optical analysis including thermal protocols, critical factors and interferences of the methods examined, method inter-comparisons, inter-laboratory exercises, biases and artifacts, and reference materials. The most commonly used thermal protocols include NIOSH-like, IMPROVE_A and EUSAAR_2 protocols either with light transmittance or reflectance correction for charring. All thermal evolution protocols are comparable for total carbon (TC) concentrations but the results vary significantly concerning OC and especially EC concentrations. Thermal protocols with a rather low peak temperature in the inert mode like IMPROVE_A and EUSAAR_2 tend to classify more carbon as EC compared to NIOSH-like protocols, while charring correction based on transmittance usually leads to smaller EC values compared to reflectance. The difference between reflectance and transmittance correction tends to be larger than the difference between different thermal protocols. Nevertheless, thermal protocols seem to correlate better when reflectance is used as charring correction method. The difference between EC values as determined by the different protocols is not only dependent on the optical pyrolysis correction method, but also on the chemical properties of the samples due to different contributions from various sources. The overall conclusion from this literature review is that it is not possible to identify the "best" thermal-optical protocol based on literature data only, although differences attributed to the methods have been quantified when possible. ; This work was undertaken under Mandate M/503 "Standardisation mandate to CEN, CENELEC and ETSI in support of the implementation of the Ambient Air Quality Legislation", ENX "Ambient air – Measurement of airborne lemental carbon (EC) and organic carbon (OC) in PM 2.5 deposited on filters". ; EUR 1,920 APC fee funded by the EC FP7 Post-Grant Open Access Pilot ; Peer reviewed