Aerosol storm concentration

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. 

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. 

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... 

Fig. 4.33 shows seasonal variations in nutrient concentrations within the aerosols (mol/kg, dry weight) (Zhang, 2004). At both sites, aerosols recorded high values of NOg- -N02 in winter due to the combustion of fossil fuels and a predominant northwest wind from the mainland, whereas low values were recorded in summer because of washing-out associated with frequent rain events. In spring, soil dust is the major source of aerosols because of frequent dust storms at this time of year over the East Asian mainland and the move-... 

The mechanism of sulfuric acid formation and scavenging in the Pasadena precipitation samples is also poorly understood. Aerosol sulfate measurements were too few for comparison with the excess sulfate concentrations, the sulfate in excess of that expected from sea salt. Sulfur dioxide concentrations during the storm were consistently 10 or 20 ppb with an uncertainty of 5 ppb. Gas scavenging of sulfur dioxide to form sulfite species and oxidation to sulfate before analysis of the sample could account for a large fraction of the excess sulfate. Equilibrium total sulfite was calculated from PSO2 i s sured at ground level and measured pH,by equations 17-20. 

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