The concentration characteristics of four aerosol chemical components (water-soluble, insoluble, black carbon (BC), and sea-salt) and their direct radiative forcing (DRF) were analyzed using the daily or hourly data (PM2.5) measured at urban (Yeonsan, Gwangbok, Hakjang, and Gijang in Busan) and background sites (Aewol in Jeju Island) during haze events, based on a modeling approach. Overall, the concentrations of water-soluble component and its impact on the DRF were predominant over all other components at most of the sites (especially at Aewol, Gwangbok and/or Hakjang). The DRFs at the surface (DRFSFC), top of the atmosphere (DRFTOA), and the atmosphere (DRFATM) for most aerosol components (except for BC) at most of the sites (except for Yeonsan) were high in spring or winter and low in summer or fall. Meanwhile, the DRFs at Yeonsan were highest in summer (for DRFTOA) or fall (for DRFSFC) and lowest in spring (for both). These seasonal DRF characteristics in the study sites might be closely related to the seasonal patterns of aerosol component concentrations and/ or meteorological conditions (e.g., relative humidity). In addition, the positive DRFATM of BC in the study sites was highest among the all aerosol components due to strong radiative absorption. The differences in DRFs for water-soluble component between haze and non-haze periods were largest in the all study sites. In particular, the DRFTOA (and DRFSFC) of water-soluble at the sites of Gwangbok and Aewol during the haze periods were higher by a factor of 1.8 and 2.3 (and a factor of 1.9 and 2.4) than those during the non-haze periods.

The optical properties and direct aerosol radiative forcing (DARF) of different aerosol components in PM2.5 (water-soluble, insoluble, black carbon (BC), and sea-salt) were estimated using the hourly resolution data measured at Aewol intensive air monitoring site on Jeju Island during 2013, based on a modeling approach. In general, the water-soluble component was predominant over all other components with respect to its impact on the optical properties (except for absorbing BC) and DARF. The annual mean aerosol optical depth (AOD) at 500 nm for the water-soluble component was 0.14 +/- 0.14 (0.04 +/- 0.01 for BC). The total DARF at the surface (DARF(SFC)) and top of the atmosphere (DARF(TOA)), and in the atmosphere (DARF(ATM)) for most aerosol components (except for sea-salt) during the daytime were highest in spring and lowest in fall and/or summer. The maximum DARF(SFC) of most aerosol components occurred around noon (12:00 similar to 14:00 LST) during all seasons, while the maximum DARF(TOA) occurred in the afternoon (13:00 similar to 16:00 LST) during most seasons (except for spring). In addition, the estimated DARF(SFC) and DARF(ATM) of the water-soluble component were -20 to -59 W/m(2) and +3.5 to +14 W/m(2), respectively, while those of BC were -18 to -29 W/m(2) and +23 to +37 W/m(2), respectively.