Impact of aerosol particle sources on optical properties at urban, regional and remote levels in the north-western Mediterranean

10 Further research is needed to reduce the existing uncertainties on the effect that specific aerosol particle sources have on light extinction and consequently on climate. This study presents a new approach aiming at quantifying the mass scattering and absorption efficiencies (MSE and MAE) of different aerosol sources at urban (Barcelona-BCN), regional (Montseny-MSY) and remote (Montsec-MSA) background sites in the northwestern (NW) Mediterranean. An analysis of source apportionment to the measured multi-wavelength light scattering (σsp) and absorption (σap) coefficients was performed by 15 means of a multilinear regression (MLR) model for the periods 2009-2014, 2010-2014 and 2011-2014 at BCN, MSY and MSA, respectively. The source contributions to PM10 mass concentration, identified by means of the Positive Matrix Factorization (PMF) model, were used as dependent variables in the MLR model. With this approach we addressed both, the effect that aerosol sources have on air quality and their potential effect on light extinction through the determination of their MSE and MAE. An advantage of the presented approach is that the calculated MSE and MAE take into account the internal 20 mixing of atmospheric particles. Seven aerosol sources were identified at MSA and MSY, and eight sources at BCN. Mineral, Aged marine, Secondary sulfate, Secondary nitrate and V-Ni bearing sources were common at the three sites. Traffic, Industrial/metallurgy and Road dust resuspension sources were isolated at BCN, whereas mixed Industrial/Traffic and Aged organics sources were identified at MSY and MSA. The highest MSE were observed for Secondary sulfate (4.5 and 10.7 m 2 g -1 , at MSY and MSA, 25 respectively), Secondary nitrate (8.8 and 7.8 m 2 g -1 ) and V-Ni bearing source (8 and 3.5 m 2 g -1 ). These sources dominated the scattering throughout the year with marked seasonal trends. The V-Ni bearing source, originating mainly from shipping in the area under study, simultaneously contributed to both σsp and σap, being the second most efficient light-absorbing source in BCN (MAE=0.9 m 2 g -1 ). The Traffic source at BCN and the Industrial/Traffic at MSY exhibited the highest MAE (1.7 and 0.9 m 2 g -1 , respectively). These sources were the major contributors to σap at BCN and MSY, however at MSA, Secondary 30