An alternative way to determine the size distribution of airborne particulate matter Eleonora Cuccia a , Vera Bernardoni b , Dario Massabò a , Paolo Prati a, * , Gianluigi Valli b , Roberta Vecchi b a Dipartimento di Fisica and INFN, Università di Genova, via Dodecaneso 33,16146 Genova, Italy b Dipartimento di Fisica and INFN, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy article info Article history: Received 19 March 2010 Received in revised form 21 May 2010 Accepted 24 May 2010 Keywords: Particulate matter Size distribution Optical counter Positive matrix factorization abstract We developed and tested a methodology to extract both the size-segregated source apportionment of atmospheric aerosol and the size distribution of each detected element. The experiment is based on the parallel use of a standard low-volume sampler to collect Particulate Matter (PM) and an Optical Particle Counter (OPC). The approach is complementary to size-segregated PM sampling, and it was tested versus a 12-stage cascade impactor. Samples were collected inside the urban area of Genoa (Italy) and their elemental composition was measured by Energy Dispersive-X Ray Fluorescence (ED-XRF). Positive Matrix Factorization (PMF) was applied to time series of elemental concentrations to identify major PM sources, and both PM mass concentration and size-segregated particle number concentration were apportioned. Source profiles and temporal trends extracted by PMF were analyzed together with the OPC data to obtain the size distribution for several elements. The new methodology proved to be reliable for the PM apportionment as well as in providing the elemental concentrations in PM10, PM2.5, and PM1 (PM with aerodynamic diameter, D ae < 10, 2.5, and 1 mm, respectively). The elemental size distributions are in good agreement with those obtained by the cascade impactor for several elements but some discrepancies, in particular for traffic emissions, are stressed and discussed in the text. The new methodology has two main advantages: it only requires standard semi-automatic sampling equipment and compositional analysis and it provides size-segregated information averaged over quite long periods (typically several months). This is particularly important since campaigns with cascade impactors are generally laborious and thus limited to short periods. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The comprehensive characterization of atmospheric aerosols requires much information, such as the temporal behaviour of PM, its composition, and the particle number concentration in different size bins with high-time resolution (i.e., from minutes to hours, especially in urban and/or industrial areas) as well as the size-segregated PM mass and composition. All these features help both in the source characterization through receptor models (Gordon, 1988) and in the assessment of health effects (HEI, 2002; Pope et al., 2002; Balásházy et al., 2003). In some studies (Wichmann and Peters, 2000; and references therein), it has been claimed a correlation between morbidity and particle number concentration, in particular for particles with diameter < 1 mm, and it is therefore of interest to single out the relationship among size fractions and specific sources of PM. Several devices have been manufactured and are commercially available to count particles and to obtain their size distribution with high-time resolution (e.g. Knutson and Whitby, 1975; Fissan et al., 1984; Büttner, 1990; Winklmayr et al., 1991) while the assessment of the size distribution of single elements and/or compounds is still quite complex, in particular for mineral matter (time-of-flight mass spectrometers allow the single particle real-time chemical characterization of a number of organic and inorganic species but not mineral dust components, see Canagaratna et al., 2007). Size- segregated elemental concentration is commonly measured by cascade impactors (Hillamo and Kauppinen, 1991; Marple et al., 1991; Maenhaut et al., 1996) but very hardly these samplers can be used to obtain long temporal trends since each set of collecting media is usually kept under sampling for a few hours and then manually changed. Sampling campaigns with multi-stage cascade impactors usually last few days with a quite limited number of collected samples (Salma et al., 2005). In a previous work (Mazzei et al., 2007), we introduced a method to obtain a size-segregated source apportionment by the combined use of a two-stage continuous streaker sampler (Annegarn et al., 1988) and an optical particle counter (OPC). The streaker is a rotating sampler which collects continuously the PM10 coarse and fine fraction * Corresponding author. E-mail address: prati@ge.infn.it (P. Prati). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.05.045 Atmospheric Environment 44 (2010) 3304e3313