Application Of UNMIX-CMB Combined Model To Source Apportionment Of PAHs In Ambient Air

Atmospheric PAHs contamination is a matter of great public health concern of scientists and policy makers, so it is meaningful to identify certain kinds of sources and their contribution estimates. Several problems would rise when only one receptor model was applied. For example, the collinearity problem would result in the negative contributions when applying CMB model; certain sources would not be separated out when applying UNMIX model due to high correlation coefficients in time series between source contributions. In this study, the UNMIX-CMB combined model was attempted to resolve the problems, taking advantages of these receptor models. In addition, using synthetic datasets to evaluate the ability of receptor models as source apportionment tools was done in this study.The synthetic datasets reflected contributions to 16 PAHs from six sources:soil, road dust, cement, coal combustion, vehicle and an unknown source. CMB,UNMIX and UNMIX-CMB combined model were evaluated by applying them to source apportionment of synthetic datasets, separately. UNMIX-CMB combined model extracted source profiles and contributions that most closely represented the sources used to generate the synthetic datasets, and the value of AAE (average absolute error) was 23.73%. It shows that the accuracy of the UNMIX-CMB combined model for PAHs source apportionment and the feasibility of its dealing with the collinearity problem.The UNMIX-CMB combined model was applied to ambient dataset from Birmingham, UK, to test its practicability. Two step analysis get the source profiles of all sources and overall average percentage source contribution estimates for five source categories:diesel exhaust 61%, gasoline exhaust 18%, coal burning 16%, natural gas combustion 3% and wood smoke 2%. The result showed that diesel exhaust contributed the largest fraction to the total PAHs, and it was consistent with an earlier study.From the discussion above, the UNMIX-CMB combined model can be applied to the source apportionment of PAHs, especially for some relatively complicated receptor.