The number concentrations and the water soluble ionic concentrations of PM2.5 have measured at Gosan site in Jeju, Korea, from March 2010 to December 2010, to clarify their characteristics. PM2.5 number concentrations vary from 22.57 to 975.65 particles/㎝3 with an average value of 240.41 particles/㎝3, which have been recorded evidently high in spring season as compared with those in other season. And the concentrations in small size ranges are greatly higher than those in large size ranges, so the number concentration in the size range 0.25∼0.45 ㎛ has more than 94% of the total number concentration of PM2.5. The major ionic components in PM2.5 are SO4 2-, NH4 + and NO3 -, which are mainly originated from anthropogenic sources, on the other hand, the concentrations of Cl-, K+, Ca2+ and Mg2+ are recorded relatively lower levels. The concentrations of the major ionic components are very high in spring season, but the concentration levels of the other components are recorded significantly high in winter season. On the other hand, in summer season, the lowest concentration levels are observed for overall components as well as the sum of them. The concentration ratios of nss-SO4 2-/SO4 2- and nss-Ca2+/Ca2+ are 98.1% and 88.9%. And the concentration ratio of SO4 2-/NO3 -(3.64) is greatly higher than the value in urban area due to no large NOx emission sources in the measurement. In addition, the correlation and the factor analysis for the number and the ionic concentrations of PM2.5 are performed to identify their sources. From the Pearson correlation analysis and the factor analysis, it can be suggested that the smaller parts(<0.5 ㎛) of PM2.5 is contributed by anthropogenic sources, but the sources of the remaining larger parts of PM2.5 are not able to be specified sources in this study.

Abstract
 1. Introduction
 2. Materials and Methods
  2.1. Measurement site
  2.2. Instruments and measurements
 3. Results and Discussion
  3.1. Characteristics of the PM2.5 number concentration
  3.2. Ionic composition of PM2.5
  3.3. Comparison of the number concentration andthe ionic composition
 4. Conclusions
 References

• Chang-Hee Kang(Department of Chemistry, Jeju National University)
• Chul-Goo Hu(Department of Environmental Engineering, Jeju National University) Corresponding author