Spectral optical properties of long-range transport Asian dust and pollution particle observed in Northeast Asia

As a part of the IGAC Mega-cities program, aerosol optical and chemical properties were continuously measured from April 2007 to March 2008 at an urban site (37.57°N, 126.94°E) in Seoul, Korea. Aerosol light scattering and column integrated aerosol optical thickness (AOT) were measured by a nephelometer and a sky-radiometer, respectively. Particulate organic carbon (OC) and elemental carbon (EC) were also measured by a semi-continuous OC/EC monitor. Black carbon (BC) was also measured by a 7-wavelength aethalometer. Multiple scattering correction factor for aethalometer instrument was determined for each measurement date. Mixing state of EC was indirectly determined based on the BC/EC ratio in order to retrieve absorption coefficient of EC, babs from the aethalometer BC data. Mass absorption efficiency of EC at 550nm wavelength has been determined to be 9.1, 9.6, 10.0, and 10.0 m2/g during spring, summer, fall, and winter, respectively. Since the measurement site is located in the downwind area of Asian continental outflow, long-range transport Asian dust (AD) and pollution (LTP) particles frequently affect the local air quality. Ångström exponent of aerosol light extinction coefficient between 550 ~ 1020nm was determined to be <0.2 and >1.4 during AD and LTP periods, respectively. Based on the spectral optical scattering and absorption coefficients obtained, single scattering albedo (SSA) was determined as a function of wavelength for different seasons. This measured spectral signature of SSA can provide information about the chemical characteristics of atmospheric aerosol.