Predicting changes of glass optical properties in polluted atmospheric environment by a neural network model A. Verney-Carron * , A.L. Dutot, T. Lombardo, A. Chabas Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, UPEC, UPD, 61 avenue du Général de Gaulle, 94010 Créteil Cedex, France article info Article history: Received 1 October 2011 Received in revised form 7 February 2012 Accepted 27 February 2012 Keywords: Soiling Glass Neural network Atmospheric pollution Doseeresponse function abstract Soiling results from the deposition of pollutants on materials. On glass, it leads to an alteration of its intrinsic optical properties. The nature and intensity of this phenomenon mirrors the pollution of an environment. This paper proposes a new statistical model in order to predict the evolution of haze (H) (i.e. diffuse/direct transmitted light ratio) as a function of time and major pollutant concentrations in the atmosphere (SO 2 , NO 2 , and PM 10 (Particulate Matter < 10 mm)). The model was parameterized by using a large set of data collected in European cities (especially, Paris and its suburbs, Athens, Krakow, Prague, and Rome) during field exposure campaigns (French, European, and international programs). This statistical model, called NEUROPT-Glass, comes from an artificial neural network with two hidden layers and uses a non-linear parametric regression named Multilayer Perceptron (MLP). The results display a high determination coefficient (R 2 ¼ 0.88) between the measured and the predicted hazes and mini- mizes the dispersion of data compared to existing multilinear doseeresponse functions. Therefore, this model can be used with a great confidence in order to predict the soiling of glass as a function of time in world cities with different levels of pollution or to assess the effect of pollution reduction policies on glass soiling problems in urban environments. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Soiling is caused by the deposition of pollutants on materials. For the glass it results in a degradation of its intrinsic optical properties (transparency loss) and leads to a visual and aesthetical impairment. This phenomenon is generally quantified using haze (transmittance) or reflectance change (Brooks and Schwar, 1987; Schwar, 1998; Sharples et al., 2001; Adams et al., 2002; Chabas and Lefèvre, 2002; Lombardo et al., 2005a,b, 2010; Favez et al., 2006; Ionescu et al., 2006; Chabas et al., 2008, 2010). As glass is a transparent material, transmittance measurements are generally preferred to reflectance measurements which require the use of a standard (white paper behind the sample). However, several studies have shown evident correlations between transmittance and reflectance for aerosols (Saucier and Sansone, 1972 and refer- ences therein). Beyond the aesthetical and economic (maintenance costs) aspects, the soiling of glass reflects the pollution of the atmospheric environment. The deposition on glass is mainly composed of insoluble parti- cles (terrigenous or anthropogenic metallic debris), salts, particulate organic matter (biogenic and organic compounds) and elemental carbon (soots). The insoluble part represents a high fraction (between 25 and 66 %) of the total mass of the deposition and the fraction of salts, organic matter, and black carbon are 18e29%, 8e36%, and 4e12%, respectively (Lombardo et al., 2005a; Favez et al., 2006; Chabas et al., 2008). Moreover, the nature of the deposition is relatively representative of the airborne particles. The fraction of organic matter can slightly decrease on glass due to the oxidative degradation, whereas the salts fraction can increase as salts are deposited on the glass but also formed in situ from water and gases interactions (Favez et al., 2006; Chabas et al., 2008). The role of each kind of components on the glass optical properties is not completely clear. Black carbon is known to be responsible of light absorption (Lanting, 1986; Horvath, 1993) and blackening of materials (e.g., Brimblecombe and Grossi, 2005 for stone). Favez et al. (2006) have also found correlations between black carbon mass and light absorption and between ions mass and diffuse transmittance on glass. Soiling is therefore a consequence of natural elements present in the atmosphere (contribution of terrigenous particles and soluble ions), but also of the anthropic pollution (especially soots, salts formed from gaseous pollutants such as SO 2 and NO x , and metallic particles). The respective contribution of natural and anthropic elements remains difficult to be assessed, especially for organic * Corresponding author. Tel.: þ33 1 45 17 66 08; fax: þ33 145 17 15 64. E-mail address: aurelie.verney@lisa.u-pec.fr (A. Verney-Carron). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2012.02.093 Atmospheric Environment 54 (2012) 141e148