Atmospheric Environment 38 (2004) 1313–1323 Aerosol optical depth during episodes of Asian dust storms and biomass burning at Kwangju, South Korea K.O. Ogunjobi*, Z. He, K.W. Kim, Y.J. Kim Advanced Environmental Monitoring Research Center (ADMRC), Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology, No. 1, Oryong-Dong, Buk-Ku, Kwangju 500-712, South Korea Received 18 June 2003; received in revised form 18 November 2003; accepted 27 November 2003 Abstract Spectraldailyaerosolopticaldepths(t al )estimatedfromamulti-filterradiometeroverKwangjuwereanalyzedfrom January 1999 to August 2001 (total of 277 days). Optical depths obtained showed a pronounced temporal trend, with maximum dust loading observed during spring time and biomass burning aerosol in early summer and autumn of each year. Result indicates that t a501nm increased from spring average of 0.4570.02tovalues>0.7on7April2000,and13 April2001.Dailymeanspectralvariationsinthe ( Angstr . omexponents a werealsocomputedforvariousepisodeperiods under consideration. A dramatic change in a value is noted especially at high aerosol optical depth when coarse mode aerosol dominates over the influence of accumulation-mode aerosol. High values of t al associatedwithhighvaluesof a in early June and October are characteristics of smoke aerosol predominantly from biomass burning aerosol. Also, volume size distribution is investigated for different pollution episodes with result indicating that the peak in the distributionofthecoarsemodevolumeradiusandfinemodeparticlesofdustandbiomass-burningaerosolrespectively increases as aerosol optical depth increases at Kwangju. Air-mass trajectory were developed on 7–8 April and 19–20 October, 2000 to explain the transport of Asian dust particle and biomass burning to Kwangju. r 2003 Elsevier Ltd. All rights reserved. Keywords: Yellow sand; Visibility; Aerosol optical depths; Trajectory; Volume size distribution 1. Introduction Troposphere aerosol optical depth (AOD) is an important parameter for studying atmospheric pollution visibility degradation, aerosol radiation–climate effects, and atmospheric corrections in remote sensing among others. The passive spectral extinction method has proofed to be one of the most reliable methods for the measurements of aerosol optical depth (Qiu, 1998). The extinction method uses a sun-photometer to detect narrowband direct solar radiation and then estimate atmospheric t al from the irradiance measurements (King et al., 1978; Vaughan et al., 2001). This paper has employed similar method to determine aerosol optical depth from total direct solar irradiance measure- ments taken by a multi-filter radiometer (MFR-7). Dust storms from inland China causes seasonal peaks in dust pollution over Korea peninsula and the rest of Northeast Asia region. Each year Asian dust storms (often called yellow sand) is transported to Korea from March to April (Chung and Yoon, 1996). Dust storms in deserts of Asia also tend to cause major aerosoleventswellbeyondtheAsiancontinentstoasfar as the eastern shores of USA (Mizohata and Mamuro, 1978; Iwasakaetal.,1983; Husaretal.,2001; Choietal., 2001). The importance of the aerosol optical depths, Angstromparametersandthesizedistributionfunctions in atmospheric and remote sensing studies point out the needforextensivemeasurementsandanalysisofspectral optical depths and turbidity parameters at as many ARTICLE IN PRESS AE International – Asia *Corresponding author. E-mail address: kenog@kjist.ac.kr (K.O. Ogunjobi). 1352-2310/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2003.11.031