Amount and State of Mineral Particles in the Upper Mixed Layer and the Lower Free Troposphere over Mt. Raizan, Southwestern Japan: Unmanned Airplane Measurements in the Spring of 2003

Abstract

The number fractions of mineral particles mixed with sea salt of all the mineral particles in the mixed layer were much higher than those in the free troposphere. These results suggest that mineral particles mixed with sea salt were formed in the marine boundary layer. The weather record suggests that the formation process through the clouds, which has previously been considered an efficient formation process for mixed particles, cannot explain sufficiently the observed abundance of mineral particles internally mixed with sea salt. IntroductionAeolian dust, drifting from the arid and semiarid regions of the center of the Asian continent, is known to cause dust storms and dust events. The aeolian dust is transported effectively by the westerly wind in the free troposphere and dispersed widely over East Asia and the Northwest Pacific (e.g., Iwasaka et al. 1983). Dust storms cause not only significant damage to agriculture and other human activities in these regions, but also have an impact on the global climate through direct and indirect effects on the radiation budget of the atmosphere. So far, estimation of the effects of green house gases and some kinds of aerosol species have been accomplished, but there remains many uncertainties about the effect of mineral particles, such as aeolian dust, owing principally to a lack of field observations (e.g., IPCC 2001). To fully estimate the influence of aeolian dust on the radiation budget, information is required on the temporal and spatial distributions of mineral particles, as well as size distribution, composition, and shape (Mishchenko et al. 1997;Sokolik and Toon 1999;Mikami et al. 2002).Several observations of aeolian dust both at ground and sea level have been made during dust events in the eastern part of China (e.g., Fan et al. 1996;Zhang et al. 2003a), in Japan (e.g., Niimura et al. 1994; Zhang et al. 2003b), and in the North Pacific Ocean (e.g., Duce et al. 1980;Uematsu et al. 1983). As aeolian dust floats in the atmosphere, in-situ observation within the upper atmosphere is desirable. Although observations from aircraft and balloons are useful for this purpose, it is difficult to make observation frequently because of the cost and, in the case of balloon, it is difficult to recover the instruments and the samples.We have developed an unmanned radiocontrolled airplane system suitable for frequent observation of aerosols in the lower atmosphere, for example in the mixed layer . Using this system, in-situ observations of size distribution and number mixing ratios, and sampling of aerosol particles were carried out in the spring of 2003 over Mt. Raizan, SW Japan (Fig. 1). The aim of this paper is to show the results of these observations including the elemental composition of the aerosol particles in the upper mixed layer and lower free troposphere, and to discuss

CCN Ability of Asian Mineral Dust Particles and Their Effects on Cloud Droplet Formation

“…Mineral dust particles over East Asia may be modified and become internally mixed particles through the adsorption of gases or coagulation with other kinds of aerosol particles during their transport. The internally mixed particles of dust and sea salt were often found in the boundary layer over Japan in the spring and its fraction often exceeded 80% of total dust particles (e.g., Zhang et al 2003Zhang et al , 2006Yamashita et al 2005). Although it is possible that the CCN ability of the mineral dust particles changes with such modifications, few studies have addressed this issue.…”

Aeolian dust experiment on climate impact: An overview of Japan–China joint project ADEC

“…During the ADEC IOPs, analyses were made using a Scanning Electron Microscope with an EnergyDispersive X-ray analyzer (SEM-EDX) for samples collected at Dunhuang (a dust source region), Beijing and Nagoya (central Japan; Iwasaka et al, 2003b;Matsuki et al, 2005), and at Mt. Raizan (southwestern Japan; Yamashita et al, 2005).…”

“…A positive correlation was also found with the number of sulfate containing particles and the relative humidity. Yamashita et al (2005) carried out an in situ sampling of aerosol particles from 800 to 2000 m altitude over Mt. Raizan (33.5°N, 130.2°E) from March to April 2003 using an unmanned radio-controlled airplane.…”

Atmospheric Aging of Asian Dust Particles During Long Range Transport

“…A simple calculation indicated that the Brownian coagulation time of 1 µm dust particles with ∼2 µm sea-salt particles was about 2.6 weeks (i.e., much longer coagulation time compared to the lifetime of dust particles) (the coagulation time is defined as the time for the initial number concentrations of the dust particles to decrease by half, and the initial number concentrations of the dust particles and sea-salt particles are assumed to be 1,000 and 100 #/cm 3 , respectively) (Hinds 1999;Baron and Willeke 2001). However, the possibility of direct coagulation of dust particles and sea-salt particles cannot be completely ruled out (Zhang et al 2003;Yamashita et al 2005).…”