2.5. Methodology analysisPMF is a powerful and widely used source apportionment model and it can decomposes response data into major contributing factors and provides a profile for each factor (Pentti Paatero, 1994). In this application, EPA PMF 3.0 model was used to identify the source of PAHs and is described by equation. where Xij is concentrations of species j in sample i, fkj is fraction of species j in factor k, p is the number of factors, gik is a mass of factor k contributing to sample i, and eij is the residual of species j in sample i, defined as the sum of differences between observed and modeled concentrations. The residual eij value was calculated by the equation