Dust storm particles

In the case of mixing process between crustal and anthropogenic components, it is suggested that the incorporation of anthropogenic components into dust storm particles may occur at the industrial areas in China, Jeju Island in Korea, and at the receptor area in Japan. The coalescence of two cloud droplets which are containing different particles (e.g. dust and man-made particles) is also considered as other aging mechanisms of dust particles with man-made components. 

Figure 4.21. Micro-PIXE spectrum of a coarse particle (> 1.17 pm) collected during an Asian dust storm. Beam 2.5MeVH+, current 70pA, irradiation time 30min. (Kasahara et al. 2001.)...

The particles and droplets that make up particulate matter range widely in size. Some are large enough to he seen, such as the tiny particles of sand stirred up in a dust storm. Others are so small as to be invisible to the naked eye. In general, these particles and droplets are divided into two major categories, based on their size. Particles designated as PM2 5 have diameters less than or equal to 2.5 p (microns or micrometers) in diameter. Particles with diameters between 2.5 p and 10 p are designated as PMj particulates. The terms fine and coarse are sometimes used to described PM2 5 and PMjq particulates, respectively. 

Figure 7. Total mass (particles less than 15 fUn) and fine mass (particles less than 2.5 fjm) measured during 3 dust storms April 6-7, April 16-17, and April 23-24, 1979. Error bars are 15% measurement system error.

The Owens Lake brine analysis of Table V Indicates that the Na/S ratio should be approximately 3.8 for lake bed materials, which agrees quite well with the ambient ratio measured at Keeler. The above data suggests that airborne sulfur aerosols measured in the Owens Valley are in the form of sulfates which are suspended from the efflorescent crust on the Owens Lake bed. Therefore, if we assume that all the sulfur measured at each site is in the form of sulfate, then during a dust storm, the sulfate standard for the state of California (25pg/m ) is violated near the Owens Lake. It should be noted that the sulfate standard was developed for very fine acidic aerosols. The sulfates measured here are larger and basic particles, so their toxicity may be different from particles for which the standard was written. The calculated sulfate levels at each site during a dust storm are listed in Table VI. 

For example, in some areas dust storms are prevalent and extremely high particle concentrations along with unique elemental signatures result. One such case is in central California, where particle concentrations from Owens (dry) Lake are highest in the United... 

A complete theory of turbulence is still lacking, so we must restrict our discussions to two general cases of interest to us (a) the diffusion of particles from point or line sources where the turbulence may be said to be isotropic, and (b) the behavior of particles near large land surfaces— as for example, dust storms. We shall begin our discussion with an explanation of the meaning of eddy-diffusion, which is characteristic of the conditions to be more fully discussed later. 

An aerosol cloud consisting of dust (sand) particles, soot and smoke coming with south-west air flows was registered by flic Teplokluchenka station on March 20. The day before, a heavy sand storm occurred in the region of military actions. Maximum backscattering ratio R higher than 100 was observed at die wavelength of 1064 nm (Chen et al., 2004). 

Individual dust storms from the Sahara desert have been shown to transfer material from the northwest coast of Africa, across the Atlantic, to the east coast of the United States (Ott et al., 1991). For example, Prospero et al. (1987) suggested that enough Saharan dust is carried into the Miami area to significantly reduce visibility during the summer months. Similar dust transport occurs from the deserts of Asia across the Pacific Ocean (Prospero, 1995). While particles as large as 100 /im in diameter are found in the source regions, only particles smaller than 10 /im are transported over long distances, often further than 5000 km. 

The value of PM2.5/PM10 was lower than 0.5 in most cases due to the abundance of coarse particles originating from frequent dust storms in the region. 

Dust storms originating from the Saharan desert occur in autumn, winter and spring lead to the increase in coarse particles. In the summer, levels of fine particles are enhanced as a result of increased humidity, photochemically and induced secondary PM, and long-range transport of sulfur. 

A common size rai e definition for dust aerosol particles is greater than 0.5 im as stated however, in practise, dust aerosols such as desert dust storm aerosols, exhibit particles ranging from about 1 nm to over 100 pm in diameter. 

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