Semi-Continuous Aerosol Measurement for Visibility Variation Using an External Beam PIXE Method

Abstract

This study introduces the application of a semi-continuous monitoring and analytic technique to examine the elemental composition for a visibility-impairing aerosol. Semi-continuous measurements of the chemical composition for visibility-impairing aerosol were made during the spring period of 19 30 May 2007 in the urban area of Seoul, Korea. These included measurements of the aerosol elemental composition by a proton induced X-ray emission (PIXE) method, of the aerosol ionic composition by ion chromatography (IC) method and of the aerosol carbonaceous composition by a thermal optical transmittance (TOT) method. Light extinction, scattering and absorption coe cients were measured simultaneously with a transmissometer, a nephelometer and an aethalometer, respectively. The average light extinction coe cient and visual range were measured to be 343 186 Mm 1 and 11.8 4.2 km, respectively, during the intensive monitoring period. The average mass concentrations of PM1:0, PM2:5 and PM10 were measured to be 24.0 13.4, 44.6 30.6 and 77.0 56.1 g m 3 and the correlation coe cient r2 of submicron and ne particles to bext were calculated to be relatively higher values of 0.7835 and 0.7824, respectively. However, the value of r2 for coarse particles was a low value of 0.1261. The results revealed that visibility impairment in the urban atmosphere of Seoul was a ected by ne particles, including submicron particles, rather than coarse particles. On a clear day and a hazy day, the mass concentration of mineral dust was not sensitive to variations in bext. On an Asian dust event day, visibility degradation was dominantly caused by increases in the SO2 4 and the NO 3 components between 12:00 and 14:00, during which time they combined with a large loading of mineral dust caused severely reduced visibility. The ability to observe rapid changes in the aerosol composition using semi-continuous aerosol measurements and the PIXE method was helpful in understanding the diurnal variation of visibility.