Atmospheric light extinction reconstructed from the size-resolved aerosol composition using PIXE analysis

Abstract

Intensive visibility monitoring was performed in the urban atmosphere of Seoul from 2007 to 2009. Using optical and chemical measurement data and the well-known reconstruction light extinction equations, contributions of size-resolved aerosols to light extinction were calculated. Composite variables for visibility impairing aerosols were reconstructed with elemental and ionic concentrations determined by particle induced X-ray emission and ion chromatography methods. Three types of reconstruction equations were introduced in this study. The first equation is the early reconstruction equation mainly based on fine particles. The second equation considers light scattering by sulfates and sea salt aerosol components in the coarse particle regime. The third equation provides information on light scattering by sulfates, nitrates, and organics for PM_1.0 and particles between PM_1.0 and PM_2.5 and the hygroscopic function of sea salt aerosol. Visibility conditions were classified into four categories of clear, moderate, hazy, and Asian dust storm event. The contributions of sulfates and nitrates particles to light extinction increased significantly under the hazy event. The light extinction budget for sulfate particles, including coarse sulfates, increased approximately 1.5% compared to the results from the first equation. Sulfates, nitrates, and organic aerosols in the large particle size mode were responsible for 18.7 ∼ 28.6%, 3.2 ∼ 5.1%, and 6.4 ∼ 8.4% of total light extinction, and they were 1.8, 1.3, and 1.5 times larger than those in the small particles size mode, respectively. During Asian dust storm events, they were 59.1, 9.1, and 1.3%, respectively. The major visibility impairing aerosol species of sulfates, nitrates, organics, and elemental carbon accounted for 77.1 ∼ 78.2% of the total light extinction according to estimation resulting from the three reconstruction equations.