Classification of PM10 distributions in Taiwan

Daily average PM10 concentrations of 71 stations in Taiwan in wintertime (October to March) and summertime periods (April to September) were fitted individually by a lognormal distribution for a 2 yr period (2001 to 2002). The distribution parameters (geometric mean and geometric standard deviation) in wintertime were used to determine the air-quality basins for PM10 by utilizing three clustering techniques, viz. of hierarchical clustering (Wardʹs method), non-hierarchical clustering (K-means) and two-level approach (self-organizing maps neural network, then K-means clustering). All three techniques suggested that 71 air-monitoring stations in Taiwan can be divided into five air-quality basins which are located in northern, central, eastern, southwestern and southern Taiwan, respectively. The sequence of PM10 pollution levels in the five basins is southern Taiwan>southwestern Taiwan>central Taiwan>northern Taiwan>eastern Taiwan. Geometric means and geometric standard deviations in each of the five air-quality basins were significantly different from each other for the two-level approach method by the Waller–Duncan k-ratio t-test (k=100, P=0.05), suggesting that the two-level approach method is best among the three clustering methods. The clustering results of five air-quality basins in Taiwan are useful to decide the corresponding control strategy at different air-quality basins.