Source apportionment of fine PM and sub-micron particle number concentrations at a regional background site in the western Mediterranean: a 2.5 yr study
Authors: Cusack M. , Pérez N. , Pey J. , Alastuey A. , Querol X. 
Published: February 2013

Abstract. The chemical composition and sources of ambient fine particulate matter (PM1) over a period of 2.5 yr for a regional background site in the western Mediterranean are presented in this work. Major components (such as SO12−, NO3−, NH4+, organic and elemental carbon) and trace elements were analysed and the emission sources affecting PM1 were determined using Positive Matrix Factorisation (PMF). Furthermore, sub-micron particle number concentrations and the sources of these particles are also presented. Sources of sub-micron particles were determined by Principal Component Analysis (PCA). The mean PM1 concentration for the measurement period was 8.9 μg m−3, with organic matter (OM) and sulphate comprising most of the mass (3.2 and 1.5 μg m−3). A clear seasonal variation was recorded with higher PM1 concentrations in summer (11.2 μg m−3) compared to winter (6.6 μg m−3). This summer increase was due to elevated levels of sulphate and OM. Six sources were identified by PMF: secondary organic aerosol, secondary nitrate, industrial, traffic + biomass burning, fuel oil combustion and secondary sulphate. The daily variations of these sources were also determined, whereby the typically anthropogenic sources displayed elevated concentrations during the week with reductions at weekends. Nitrate levels were elevated in winter and negligible in summer, whereas secondary sulphate levels underwent a contrasting seasonal evolution with highest concentrations in summer, similar to the fuel oil combustion source. The SOA source was influenced by episodes of sustained pollution as a result of anticyclonic conditions occurring during winter, giving rise to thermal inversions and the accumulation of pollutants in the mixing layer. Increased levels in summer were owing to higher biogenic emissions and regional recirculation of air masses. The industrial source decreased in August due to decreased emissions during the vacation period. Increases in the traffic + biomass burning source were recorded in January, April and October, which were attributed to the occurrence of the aforementioned pollution episodes and local biomass burning emission sources, which include agriculture and domestic heating systems. Average particle number concentrations (N9–825 nm) from 5 November 2010 to 1 June 2011 and from 15 October 2011 to 18 December 2011 reached 3097 cm−3. Five emission sources of particles were identified by PCA; industrial + traffic + biomass burning, new particle formation + growth, secondary sulphate + fuel oil combustion, crustal material and secondary nitrate. Multilinear regression analysis was applied to the dataset to quantify the contribution of each source to the sub-micron particle number concentration. The new particle formation + growth source dominated the particle number concentration (56% of total particle number concentration), especially for particles <100 nm, followed by industrial + traffic + biomass burning (13%). Secondary sulphate + fuel oil combustion (8%), nitrate (9%) and crustal material (2%) were dominant for particles of larger diameter (>100 nm) and thus did not influence the particle number concentration significantly.