Dust storms

Dust storms that entrain large amounts of particulate matter are a common natural source of air pollution in many parts of the world. Even a relatively small dust storm can result in suspended particulate matter read-... 

Gestbber, n. shower snowstorm dust storm, gestochen, p.p. (of stechen) stuck, etc. gestockt, p.p. (of stocken) stopped, etc, — a. 

Finally, increases in the intensity or variability of weather are considered another form of indirect evidence reflecting whether Earth is currently undergoing human-driven climate change. Predictions of increased incidence of extreme temperatures, tornadoes, thunderstorms, dust storms and fire-promoting weather have been drawn from basic global climate change theoiy. However, evidence has not so far borne out these predictions on a global scale. The IPCC concludes ... 

Denmark 1.5 days after the explosion. Air samples collected at Roskilde, Denmark on April 27-28, contained a mean air concentration of 241Am of 5.2 pBq/m3 (0.14 fCi/m3). In May 1986, the mean concentration was 11 pBq/m3 (0.30 fCi/m3) (Aarkrog 1988). Whereas debris from nuclear weapons testing is injected into the stratosphere, debris from Chernobyl was injected into the troposphere. As the mean residence time in the troposphere is 20-40 days, it would appear that the fallout would have decreased to very low levels by the end of 1986. However, from the levels of other radioactive elements, this was not the case. Sequential extraction studies were performed on aerosols collected in Lithuania after dust storms in September 1992 carried radioactive aerosols to the region from contaminated areas of the Ukraine and Belarus. The fraction distribution of241 Am in the aerosol samples was approximately (fraction, percent) organically-bound, 18% oxide-bound, 10% acid-soluble, 36% and residual, 32% (Lujaniene et al. 1999). Very little americium was found in the more readily extractable exchangeable and water soluble and specifically adsorbed fractions. 

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. 

The people who are most at risk for health problems from particulate exposure are those who already have some form of respiratory disorder or heart disease, the elderly, and children. Such problems begin to appear when the ambient concentration of pollutants reaches about 40 pg/m for PM25 particulates and about 150 pg/m for PM particulates. Such concentrations are observed during dust storms, along dusty unpaved roads, and in areas with high levels of motor vehicle traffic, for instance. Increasing concentrations of both PM2 5 and PMj particulates result in more serious health problems, including asthma, bronchitis, emphysema, and cardiac problems. 

The suspension of aerosols during dust storms from the Owens Dry Lake in California has been a subject of great concern to residents in the Owens Valley. 

In order to obtain quantitative data on particulate air quality in the Owens Valley, a study sponsored by the California Air Resources Board was conducted by the Air Quality Group at UCD. The primary objective was to determine the impact of the dry lake bed on the average particulate concentration and on the dust storm particulate concentrations in the valley. In order to accomplish this, it was necessary to determine the elemental composition of the dry lake bed and to determine the average weekly and dust storm concentration of aerosols. 

Weekly monitoring of particulate aerosols began on February 20, 1979, and ended on June 18, 1979. A total of seventeen weeks of monitoring were conducted during this period. Samplers were run for seven consecutive days each week at a flow rate of ten liters per minute, except during dust storm episodes. During dust storms, samples were collected dally at a flow rate of ten liters per minute. Samples during dust storms were collected on April 6,7,16,17,23,24, 1979. 

Effect of Dust Storm Episodes on the Average Weekly Aerosol Concentrations. The total and fine gravimetric mass averaged over all sites for each week, is depicted in Figure 6. The error bars for the Owens Valley curves represent the standard deviation of the mean. The errors on the Mono Lake curve represent the sampling system error of 15%. The mean weekly values do not include the three dust storm episodes sampled separately, but do include several additional dust storms. Table I lists all the dust storms reported by the sampler operators. 

These dust storm aerosol measurements are not Included in the weekly average concentration in Figure 7. 

Figures 4 and 7 indicate the spatial profile of total and fine aerosol mass for the weekly monitoring and the dust storm episode studies, respectively. The total mass concentration peaks at Keeler and declines sharply north of the lake bed.

As an indication of the effect of dust storm episodes on the aerosol concentration in the valley, the per cent Increase in the weekly total mass, coarse sulfur, chlorine, silicon, and iron concentration during a dust storm was computed. In addition, the absolute Increase in these quantities was also computed. The results of this analysis are shown in Table II. These data also indicate that a significant increase in aerosol concentration due to suspended lake bed materials occurs as far downwind as Independence. In order to quantify this effect, the sulfur to iron (S/Fe) and chlorine to iron (Cl/Fe) ratio at each site was examined. At Keeler, all the coarse sulfur and iron measured at the sampling site are suspended from the lake bed. At any site... 

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.

Figure 8. Mean concentrations of coarse and fine Si, coarse Fe, and total and fine S measured during the 3 dust storm periods. Error bars are standard error of the...

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. 

TABLE VI. TOTAL SULFATE CONCENTRATIONS DURING A DUST STORM... 

Error bars are standard error of the mean. Also included are profiles of total and fine Pb for the dust storm of April 13-14, 1979. Error bars are 15% measurement system... 

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