Source Apportionment of PM_2.5 in Kumamoto Estimated by Receptor Models: Assessing Local and Regional Contributions by Comparison with Remote Sites

Abstract

The source apportionment of PM_2.5 in the central Kyushu area was conducted at five sites of roadside, urban and suburban sites in Kumamoto prefecture and at two remote sites in Nagasaki prefecture using the Positive Matrix Factorization (PMF) model and Chemical Mass Balance (CMB) model. The major sources at the five sites in FY2014 estimated by the PMF model were “Secondary sulfate” factor and “Carbonaceous aerosol” factor, with contributions of 19.8–33.1% and 39.9–56.9%, respectively. The major sources at the five sites in FY2014 estimated by the CMB model were “Secondary ammonium sulfate”, “Vehicle”, and “Secondary Organic Carbon” (SOC) with contributions of 34.3–40.1%, 10.9–21.5%, and 12.9–16.4%, respectively. A comparison with the model results at the remote sites suggested that the “Secondary sulfate” factor and “Secondary ammonium sulfate” were dominated by trans-boundary pollution, and the “Carbonaceous aerosol” factor, “Vehicle” and “SOC” were dominated by local pollution. These results suggested that local pollutions associated with traffic and SOC were influenced to exceedance of annual standard for PM_2.5. In addition, the models results and an analysis using NO_x indicated that emissions associated with traffic were the main cause of spatial variations in the PM_2.5 concentration at sites in Kumamoto prefecture.