Comparison of multivariate source apportionment of urban PM2.5 with chemical mass closure

In the lack of comparisons of different source apportionment methods, we resolved daily contributions of five source categories to PM 2.5 by applying principal component analysis and multiple linear regression to air pollution data from Helsinki, Finland. From the same data we estimated mass concentrations of four major components of PM 2.5 using a chemical mass closure model. Multiple linear regression analysis suggested that secondary and other long-range transported particles contributed 58% to total PM 2.5 , on the average, while traffic and mixed local combustion sources accounted for 19%, oil combustion for 14%, crustal source for 4.9% and salt for 2.4%. Mass closure suggested average contributions of 50%, 34%, 4.5% and 1.2% from ammonium sulphate, combustion-related particles, crustal material and sea salt, respectively. The crustal source and salt were apportioned similar amounts of PM 2.5 whereas results from the two methods were less comparable for the long-range transported and secondary particles, and the combustion-related source components.