Aerosol Optical Characteristics in the Yellow Sand Events Observed in May, 1982 at Nagasaki-Part I Observations

Abstract

Optical thicknesses and volume spectra of aerosols were retrieved from spectral extinction and aureole measurements for the yellow sand events observed during 4-8 May 1982 at Nagasaki, Japan. The results showed a dominance of large particles of several micron radius and a reduction of submicron particles. The mode radius of the column volume spectrum obtained with the aureolemeter was larger than two microns during the yellow sand events. The aerosol optical thickness at a wavelength of 0.5*m and the Angstrom's exponent * took values of 0.5-1.0 and 0.1-0.5 in contrast with their normal values of 0.2-0.8 and 0.8-1.5, respectively. Trajectory analyses from the synoptic charts as well as the elemental composition, the number density and the scattering cross section of aerosols supported consistently the prevalence of the continental air mass associated with the frontal activity during the yellow sand events.

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

“…The refractive indices of the fine particle mode (radius 0.5 mm) were determined based on the chemical analyses (described in section 3.2): n = 1.53 + 10 À7 i (dry ammonium sulfate ((NH 4 ) 2 SO 4 ) [Toon et al, 1976]) or n = 1.46 + 0i (96 weight percent (wt%) of ammonium bisulfate (NH 4 HSO 4 ) solution [Tang and Munkelwitz, 1994]), depending on the height. The refractive index of the coarse particles mode (radius > 0.5 mm) was assumed, based on the SEM microanalysis (section 3.2), to be n = 1.55 + 0.005i (or 1.55 + 0.01i), obtained from previous studies of yellow sand (Asian mineral dust) measured in Japan Tanaka et al, 1989]. Mie theory was employed to compute the scattering intensities and the response curves of the OPCs.…”

“…To obtain the appropriate size distributions of the aerosols for this aircraft measurement, we used the size bins recalculated for the aerosol refractive indices (Figure 1) that were determined from the chemical analysis; we assumed a refractive index (n) of 1.46 + 0i (96 wt% ammonium bisulfate solution [Tang and Munkelwitz, 1994]) at q = 307 K and 301 K, n = 1.53 + 10 À7 i (ammonium sulfate [Toon et al, 1976]) at q = 293 K for particles of radius less than 0.5 mm, and n = 1.55 + 0.005i (typical value of mineral dust Tanaka et al, 1989]) for radii larger than 0.5 mm, over the height range of the measurement.…”

Aerosol Optical Characteristics in the Yellow Sand Events Observed in May, 1982 at Nagasaki-Part II Models

“…As described in Part I of our papers (Tanaka et al, 1989) we carried out measurements of solar radiation and aerosols during the period from 22 April to 12 May, 1982. We had two yellow sand events at Nagasaki, Japan during the period.…”

“…Measured phase functions were analyzed after subtracting the air molecule scattering, to retrieve the size distribution and refractive index of aerosols by the inversionlibrary method of Tanaka et al (1982). The po-lar nephelometer was set at the top of a building of Nagasaki University as well as other instruments described in Tanaka et al (1989). For the nephelometer, the air was sampled with a rate of 70l/min through an elephant tube of 50 mm diameter and 5 m long.…”

“…In this paper we study in sun measurements of the phase function of yellow sand particles using a polar nephelometer for the yellow sand events of 1982 (Tanaka et al, 1989). We describe some general features common in observed phase functions and try to fit the function using the semi-empirical theory of Pollack and Cuzzi (1980) or introducing a fictitious absorption into Mie particles.…”