Calculation of Polydispersed Aerosol Optical Properties with Multicomponent Size Distribution and Different Mixture Type during Smog and Asian Dust Events in Korea

Abstract:

Aerosol optical properties depend on physico-chemical characteristics such as size distribution, chemical composition and mixture types. In this study, aerosol optical properties are investigated for different meteorological events such as smog and Asian dust.

In this study, PM2.5 and TSP measurement data are used for simulating bimodal aerosol size distribution. The Sampling was performed at Seoul, representative urban site, in Korea. Organic carbon as well as inorganic species were measured. OC and EC in sample filters were measured using a Sunset OC/EC analyzer (Sunset Laboratory, Tigard, OR, USA) based on a thermal/optical transmittance (TOT) method. Especially, water soluble organic carbon aerosols (WSOC) and water insoluble organic carbon aerosol (WISOC) are analyzed. Portions of the sample filters were extracted with 30 mL of ultrapure water in an ultrasonic bath for 45 min. The extracts were filtered with a 0.45 μm Teflon filter (Millipore, Billerica, MA, USA) and then divided two fractions for analysis of WSOC. The WSOC amounts were determined using a TOC analyzer (Shimadzu TOC-VCSH, Japan). During the sampling period, the smog and Asian dust events data were compared with normal days.

Based on these sampling data, the sensitivity of size distribution was simulated with different geometric mean diameter and geometric standard deviation using the size and composition dependent aerosol dynamic model and the optical properties are calculated from the Mie theory.

In order to testify the influence of the aerosol mixture on the optical properties, both the internal and external aerosol mixture was considered and the results were compared.

The calculated optical properties such as extinction coefficient, scattering and absorption coefficient were compared with Aerosol Optical Thickness (AOT) from AERONET remote sensing data and the results showed comparable trends.

Subsequently, this study estimated the contributions of each composition on the optical properties are estimated based on the chemical composition.