Aerosol Optical Properties with Polydisperse Size Distribution and Mixture Types during Smog and Asian Dust Events in Seoul, South Korea

This study investigates the optical properties of aerosol for different meteorological events and deals with smog and Asian dust. Sampling was performed in Seoul, a representative urban site in Korea during March, 2012. Organic Carbon (OC) and inorganic species were measured, and the Water Soluble Organic carbon (WSOC), Water Insoluble Organic carbon (WISOC) and Elemental Carbon (EC) in the sample filters were analyzed using the thermal/optical transmittance (TOT) method. During the sampling period, data from the smog and Asian dust events were compared with those from normal days. Based on the measurement data, the sensitivity of optical properties according to the size distribution was simulated with different geometric mean diameter (0.1-1.0 mm) and geometric standard deviation (1.3-2.2). The optical properties are calculated from the Mie theory combined with the aerosol dynamic model for multicomponent polydispered size distribution. The influence of the aerosol mixture on the optical properties was compared for both the internal and external aerosol mixture.

The calculated optical properties were compared with the aerosol optical thickness (AOT) obtained from AERONET remote sensing data and the results showed comparable trends. From the comparison, it can be deduced that organic aerosol and water contents are important in estimating the aerosol optical properties.

Analysis of the sampled data also showed that the water-soluble components of organic matter increased on smog days, whereas crustal elements increased on dust days. The water content significantly influenced the optical properties of aerosols during the smog days becasue of high relative humidity and an increase in the water-soluble component. The absorption coefficients depended on the aerosol mixture type and the aerosol size distributions. Subsequently, this study showed that accurate measurements of aerosols, such as size distribution, composition, and mixture type, under different meteorological conditions are required in order to improve our knowledge on radiative impacts of aerosols, especially the regional impacts of aerosols in East Asia.