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Abstract

Urban pollutants from megacities of western Taiwan region were found to be transported to mountain region of central Taiwan which are mixed with local and regional emission sources. The analysis of aerosol size distributions is a useful tool for understanding the sources and the processes influencing particulate matter pollution in urban areas. Four intensive measurements of particle size distribution (PSD) of submicron particles were conducted at a subtropical forest at Xitou located in the mountain area of central Taiwan from winter of 2013 to autumn of 2014. A k-mean cluster analysis has been applied to the PSD data and four clusters were identified which generally represent the pollution characteristics of i) NPF/local fresh vehicle emissions (C1: 7.6%), ii) particle growth (C2: 34.6%), iii) background condition (C3: 45%), and iv) regional/ aged pollution (C4: 12.8%) observed at the study site. In general, the aerosol size distributions modes obtained at different seasons were similar except that a broader peak of PSD was obtained for Cluster 1 during winter and spring season which is likely attributed to weaker new particle formation processes during cold seasons. Cluster 4 were often observed under the influence of the westerly wind which was associated with the transportation of urban pollutants from megacities in western Taiwan and other regional sources. The study investigated the seasonal variations of particle size distribution characteristics which provide insights into the critical factors attributing to the complex air pollution at the mountain area of central Taiwan.