Fine aerosols

This arrangement provides a thin film of liquid sample solution flowing down to a narrow orifice (0.007-cm diameter) through which argon flows at high linear velocity (volume flow is about 0.5-1 1/min). A fine aerosol is produced. This particular nebulizer is efficient for solutions having a high concentration of analyte constituents. 

Aerosol-Based Direct Fluorination. A technology that works on Hter and half-Hter quantities has been introduced (40—42). This new aerosol technique, which functions on principles similar to LaMar direct fluorination (Fig. 5), uses fine aerosol particle surfaces rather than copper filings to maintain a high surface area for direct fluorination. The aerosol direct fluorination technique has been shown to be effective for the synthesis of bicycHc perfluorocarbon such as perfluoroadamantane, perfluoroketones, perfluoroethers, and highly branched perfluorocarbons. 

Continuous readings unaffected by clouds, night b i directly relatable to fine aerosol concentration at a point semiportable used in a number of previous studies sensitive models available automated... 

These generators vaporize a liquid (oil/mineral oil or glycol and water), which then condenses into a fine aerosol on contact with cooler air. The amount of smoke produced should be controllable by the liquid feed rate and the temperature of the heating chamber, but in practice the output is not ea.sy to control. They will, however, produce a large amount of smoke over a long periled, dhe generators are relatively expensive (several hundred ECUs), are bulky, are not generally portable, and require an electrical connection. 

Diffusion The mixing of substances by molecular motion to equalize a concentration gradient. Applicable to gases, fine aerosols and vapors. (See Brownian diffusion.)... 

The function of the nebuliser is to produce a mist or aerosol of the test solution. The solution to be nebulised is drawn up a capillary tube by the Venturi action of a jet of air blowing across the top of the capillary a gas flow at high pressure is necessary in order to produce a fine aerosol. 

Organic compormds constitirte abont 25-30 percent of the fine aerosol mass (the mass contained in particles smaller than 2.5 pm diameter) in trrban areas. They are of considerable interest becanse some of them, such as PAHs, are either suspected carcinogens or known mutagens. Still, little headway has been made... 

Aerosol concentrations, radon, and PAEC (in Working Levels) clearly peak in early hours after sunrise and at about the time of morning human use of the building which is coincident with the outdoor peak in radon and fine aerosols due to their overnight accumulation near ground level under local temperature inversions. ... 

Dry powders must be able to flow readily in order to leave the capsule or powder reservoir, but must also generate a fine aerosol enabling the patient to inhale a proper dose. These two requirements are often difficult to achieve simultaneously. Fine powders tend to be eohesive and have poor flow properties. Blending with a carrier phase, pelletization, and other approaches have been used to overcome these limitations. The featmes of blends and homogeneous powders are compared in Table 4 from a DPI device perspective ... 

The aerosol scattering coefficient distribution was calculated from the aerosol volume distribution, using the method described in Friedlander (] ] ). The resultant distribution is plotted in Figure 3. The contribution of the fine aerosol to visibility degradation at China Lake is seen in this figure. 

Figure 4. Normalized fine aerosol volume distribution, China Lake, CA (1979 average)—average of 254 measurements. The error bars are standard deviations. The distribution is normalized with respect to total aerosol volume concentration of particles less than 2 fim in diameter.

When only the fine aerosol (D <2 ym) is considered, it is seen that the calculated scattering coefficient, bgpi> agrees very well with the data. In a statistical analysis, bgo was very well correlated with the volume of fine particles, r = 0.81, but not with the total volume of particles smaller than 10 ym, r = 0.44. Similarly, Trijonis and Yuan 3) found that the total concentration was a poor indicator of visual range in Phoenix. 

Because the fine aerosol was found to be responsible for the bulk of light scattering at China Lake, this mode was examined to see if its normalized distribution remained constant throughout 1979. Figure 4 shows the 1979 average aerosol volume distribution at China Lake normalized with respect to the total volume of particles smaller than 2 ym. The error bars represent standard deviations in the 254 measurements. The particle volume distribution in the fine mode is seen to preserve its shape rather well. Over half the fine particle volume is due to particles of less than 0.3 ym diameter. 

Table 3 summarizes the 1979 annual average particle extinction coefficient and the mass concentrations of the fine aerosol chemical species estimated by statistical analysis of the 61 filter samples. Organics and sulfates dominated the chemically determined fine aerosol mass at China Lake in 1979. A linear least squares fit between molar concentrations of NHt and SO gave a zero intercept, a slope of 1.87 and a correlation coefficient of 0.98. It is therefore assumed that the fine sulfate aerosol was in the form of ammonium sulfate. The mass concentration of carbonaceous and sulfate aerosols were, on the average, comparable in magnitude. 

Fine Aerosol Species Concentrations, 1979, China Lake... 

To estimate the contribution of wind-blown dust of crustal origin to the fine aerosol concentration, elemental enrichment factors were calculated using the method of Macias et al. (20). The enrichment factor, EF., for an element i was calculated as follows ... 

Iron was chosen as the reference element because its major source is likely to be soil and it is measured with good accuracy and precision by FIXE. Crustal abundances were taken from Mason (21). Enrichment factors greater than 1 indicate an enrichment of that element relative to crustal abundances values less than 1 indicate a depletion. The results of this calculation are shown in Table 4. For this calculation it was assumed that ammonium and nitrate accounted for all aerosol nitrogen. It is seen that Si and Ca are near their crustal abundance, indicating a probable soil dust source. The low EF for Al is probably due to a systematic error in the Al measurement rather than a true depletion. Potassium, although present in small concentrations, is slightly enriched relative to crust. The other fine aerosol species, C, N, S, and Pb are enriched by factors of thousands over their natural crustal abundance, indicating that they are not due to wind-blown dust. 

Fine Aerosol Species Mass Balance, China Lake, California... 

On the average, the requirements for application of the statistical technique to filter data were met. Analysis of the 254 measured particle size distributions in 1979 indicates that the fine aerosol volume distribution preserved its shape. The measured sulfur mass distribution followed that of the total submicron volume. By difference, it was assumed that the organics did the same. The low relative humidity at China Lake minimized the formation of aqueous solutions due to water condensation on the particles. Therefore, it is expected that the statistical technique can be used with some success with the China Lake filter data. 

As a first cut, univariate regression was used to see relationships between pairs of measured variables. The results are summarized in Table 6. It is seen that the particle scattering coefficient is highly correlated with the total fine aerosol mass concentrations, sulfate, and ammonium. To a lesser degree it is correlated with the particle absorption coefficient, potassium, and the unaccounted mass concentration. My. The correlations between the particle scattering coefficient and the nitrate, total carbon (Ct) and crustal species are poor. The poor correlation, r=0.6J, between bgp and the soot concentration is probably an indication of the error in the soot measurement. Although the sulfate and the unaccounted mass are highly correlated with the total mass, they are not well correlated with each other (r=0.49). 

On the basis of a preliminary regression analysis in which it was found that the crustal species, e.g., Fe, Ca, and Si, were well correlated with each other, the fine aerosol was grouped into four species sulfates, organics, crustal species, and the unaccounted species. The concentrations of these four species were calculated in the following manner ... 

In summary, the variance in the measured fine particle scattering coefficient, bgp was dominated by sulfate concentrations. Organics and crustal species were much less important statistically. The inferred mass scattering effeciency for sulfates was intermediate between other desert values and Los Angeles. The statistical results for China Lake are quite similar to those by other investigators at other locations, even though only the fine aerosol was sampled at China Lake. 

Fine Aerosol Scattering Coefficient Balances Statistical and theoretical Results... 

Multiple regression analysis was applied to the measured particle scattering coefficient and fine aerosol species mass concentrations from 61 filter samples collected at China Lake, California in 1979. Contributions of various aerosol species to the particle scattering coefficient were estimated. 

It was found that the requirements were satisfied for application of the linear regression technique to species mass concentrations in a multicomponent aerosol. The results of 254 particle size distributions measured at China Lake in 1979 indicate that the normalized fine aerosol volume distribution remained approximately constant. The agreement between the calculated and measrued fine particle scattering coefficients was excellent. The measured aerosol sulfur mass distribution usually followed the total distribution for particles less than 1 ym. It was assumed that organic aerosol also followed the total submicron distribution. 

The measured fine aerosol species were grouped into sulfates, organics, and crustal species, each having annual average mass concentrations of about 2-2.5 micrograms per cubic meter. An... 

The quality of statistically inferred species extinction balances can be enhanced with proper aerosol sampling. Due to its important role in light scattering, only the fine aerosol should be sampled. A mass balance should account for all major fine particle species. Ideally the particle scattering coefficient should be measured directly at the location where aerosol is sampled by the filters. The importance of soot and other carbonaceous aerosol contributions to light extinction in arid regions should not be overlooked. 

In previous studies we found that improved emission-control devices (such as hot-side electrostatic precipitaters and wet-scrubber systems) now being installed on modern pulverized-coal-fired power plants modify the quantity, chemical composition, and distribution characteristics of fine aerosol emissions (12,13). Such modifications must be understood to adequately assess human health and environmental hazards, and to apportion the contributions of sources to urban pollutant inventories. 

Finally, corrosion of internal metal surfaces, constituents of the absorbing and water-conditioning agents, and condensation of vapor components further contribute to the concentrations of Cr and Mn, Ca and P, and Se and S in the scrubbing solution and lead to their enrichment in fine aerosol emissions. 

Fine Aerosol Mass Balance. The temporal variations of fine particle mass, total carbon, elemental carbon, nitrogen, sulfur and for a typical summer period (August 4-10, 1979) and... 

We have also looked for the presence of increased secondary organic aerosol by calculating the fine aerosol mass balance in both summer and winter during periods of high and low sulfate concentrations. Formation of secondary sulfate aerosol can cause elevated levels of sulfates and has been linked to periods of regional scale haziness in the eastern U.S. (17). 

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