This study focused on comparing the meteorological conditions in the Atmospheric Boundary Layer (ABL) on high-event days and non-event days in the Seoul Metropolitan Area (SMA). We utilized observed PM10 and meteorological variables at the surface as well as at the upper heights. The results showed that high-event days were consistently associated with lower wind speed, whereas wind direction showed no particular difference between high-event and non-event days with frequent westerlies and northwesterlies for both cases. During high-event days, the temperature was much warmer than the monthly normal values with a sharp increasing trend, and Relative Humidity (RH) was higher than the monthly normal, especially on high-event days in February. During high-event days in spring, a double inversion layer was present at surface and upper heights. This indicates that stability in the multi-layer is an important indicator of higher PM10 concentrations. Net radiation in spring and winter is also closely associated with higher PM10 concentrations. Strong net radiation resulted in large sensible heat, which in turn facilitated a deeper mixing height with diluted PM10 concentrations; in contrast, PM10 concentrations were higher when sensible heat in spring and winter was very low. We also confirmed that convective and friction velocity was higher on non-event days than on high-event days, and this was especially obvious in spring and winter. This indicated that thermal turbulence was dominant in spring, whereas in winter, mechanical turbulence was dominant over the SMA.

Abstract
1. Introduction
2. Materials and Methods
3. Results
    3.1. Characteristic of meteorological variables atsurface and upper heights
    3.2. Characteristic of turbulent parameters in theABL
4. Discussion
5. Conclusion
REFERENCES

• Moon-Soo Park(Department of Climate and Environment, Sejong University, Seoul 05006, Korea)
• Joonsuk Lee(Research Center for Atmospheric Environment, Hankuk University of Foreign Studies, Yongin 17035, Korea)
• Yu Woon Jang(Department of Environmental Sciences, Hankuk University of Foreign Studies, Yongin 17035, Korea)
• Il-Soo Park(Research Center for Atmospheric Environment, Hankuk University of Foreign Studies, Yongin 17035, Korea) Corresponding author