Natural organic matter in urban aerosols: Comparison between water and alkaline soluble components using excitationeemission matrix fluorescence spectroscopy and multiway data analysis Jo ~ ao T.V. Matos, Sandra M.S.C. Freire, Regina M.B.O. Duarte * , Armando C. Duarte Department of Chemistry & CESAM, University of Aveiro, 3810-193 Aveiro, Portugal highlights graphical abstract  EEM fluorescence spectroscopy was used to study organic aerosols.  Water and alkaline soluble compo- nents of organic aerosols have been compared.  The spectral intensity and their sea- sonal variability have been investigated.  PARAFAC was used to decompose EEM fluorescence spectra of organic aerosol fractions.  Possible sources of PARAFAC compo- nents from organic aerosols have been suggested. article info Article history: Received 15 July 2014 Received in revised form 18 November 2014 Accepted 21 November 2014 Available online 22 November 2014 Keywords: Water-soluble organic matter Alkaline-soluble organic matter Atmospheric aerosols Fluorescence spectroscopy Emissioneexcitation matrix PARAFAC-ALS abstract Understanding the complexity of Natural Organic Matter (NOM) in atmospheric aerosols has remained an important goal for the atmospheric research community. This work employs a Parallel Factor Model (PARAFAC) with Alternating Least Squares (ALS) algorithm to decompose and further compare sets of excitation-emission matrices fluorescence spectra of Water-soluble and Alkaline-soluble Organic Matter (WSOM and ASOM, respectively), sequentially extracted from urban aerosols collected during different seasons. The PARAFAC-ALS modelling identified three components in both WSOM and ASOM, whose maximum intensities follow a clear seasonal trend and which are likely to represent the dominant fluorescent moieties in NOM from urban aerosols. The PARAFAC-ALS modelling also indicated differences between the colder and warmer seasons in the fluorescence map of one WSOM component, which contrast with the results obtained for the ASOM, where the fluorescence signatures were found to be constant along the seasons, suggesting that the ASOM may have an in situ origin. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The fraction of natural organic matter (NOM) in atmospheric aerosols, often referred to as organic aerosols (OA), can be the predominant fraction of fine (diameter <2.5 mm) suspended matter, accounting for 20e90% of the total fine aerosol mass (Kanakidou et al., 2005; Jimenez et al., 2009). After more than a decade of * Corresponding author. E-mail address: regina.duarte@ua.pt (R.M.B.O. Duarte). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2014.11.042 1352-2310/© 2014 Elsevier Ltd. All rights reserved. Atmospheric Environment 102 (2015) 1e10