The Importance of Aerosols

Support for the importance of aerosols in maintaining chlorine in an active form during the maintenance period is found in Fig. 12.34. This shows the satellite-derived average total O, in the vortex as a function of... 

The importance of aerosol deposition, via precipitation and/or dry particle deposition, has received considerable attention in recent years, showing that dry and wet deposition of nutrients and metal contaminants are significant in biogeochemical budgets in wetlands and estuaries. 

Sections 3.04.6.1 and 3.04.6.2). Such work has contributed significantly to the development of our understanding of the importance of aerosols in chmate change, and has helped to unravel the natural variabihty from anthropogenic forcing. 

AgnewJE, Bateman JR, Watts M, Paramananda V, Pavia D, Clarke SW (1981) The importance of aerosol penetration for lung mucociliary clearance studies. Chest 80(Suppl) 843-84f>... 

The inspection of Table 6 shows that Na", K, NH/ and a trace of Rb" are present as cations in the aerosol. Rubidium is detected as a natural trace element in potassium salts. The densitometer readings provide approximate information on the relative abundances, although ammonium compounds may be underestimated due to some evaporation of their neutral components, especially at higher temperatures. The only anions detected in the aerosol are NOj", SO , HSO and Cl . The predominance of the nitrate ion is noteworthy, stressing the importance of aerosols as a sink for NO2 in the atmosphere. NO2 has been shown to react rapidly with NaCl to form NaNOj and NOCl as an intermediate of presumably short lifetime in the atmosphere. The product NaNOj is most abundantly observed in the aerosol, besides some unreacted NaCl. 

The choice of corrodents, their concentrations, and delivery rates are other important parameters to consider in laboratory tests. Despite the importance of aerosol particles, most tests so far reported have... 

Any discussion of chemical or biological weaponry must address the importance of aerosols for the delivery of toxic agents. (The very term aerosol was coined during World War I by F. G. Donnan, who was attempting to characterize the behavior of toxic smokes.) In terms of military efficiency, CW systems require substantial generation of aerosols—tiny liquid or solid particles suspended in air—to create the concentrations necessary to generate sufficient casualties. (We will have much more to say about aerosols and their behaviors in Part III, on biological weapons. For now, it is only necessary to treat this subject in brief.)... 

Fig. 9. Genesis of acid tain (13). From the oxidation of C, S, and N during the combustion of fossil fuels, there is a buildup in the atmosphere (gas phase, aerosol particles, raindrops, snowflakes, and fog) of CO2 and the oxides of S and N, which leads to acid—base interaction. The importance of absorption of gases into the various phases of gas, aerosol, and atmospheric water depends on a number of factors. The genesis of acid rain is shown on the upper right as an acid—base titration. The data given are representative of the environment in the vicinity of Zurich, Switzedand.

As stated earlier, inhalation is the main route of absorption for occupational exposure to chemicals. Absorption of gaseous substances depends on solubility ifi blood and tissues (as presented in Sections 2.3.3-2.3.5), blood flow, and pulmonary ventilation. Particle size has an important influence on the absorption of aerosols (see Sections 2.3.7 and 3.1.1). 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

Electrospray (ES) existed long before its application to mass spectrometry (MS). It is a method of considerable importance for the electrostatic dispersion of liquids and creation of aerosols. The interesting history and notable research advances in that field are very well described in Bailey s book Electrostatic Spraying of Liquids. 37 Much of the theory concerning the mechanism of the charged droplet formation was developed by researchers in this area. The latest works can be found in a special issue38 of the Journal of Aerosol Science devoted to ES. 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

The low rates of aqueous migration of many chemical species in Arid ecosystems and the accumulation of their water-soluble and dispersed forms in the uppermost soil layers play an important role in the geochemistry of aerosol formation and rainwater... 

Our knowledge of the chemical and physical processes that govern aerosol formation in the atmosphere is limited, and further research in the field is badly needed. Attention should be focused on laboratory studies of aerosol formation from aromatic hydrocarbons. The concentrations of aerosol precursors in the atmosphere should be determined more data on organic compounds in ambient aerosols are needed to estimate the relative importance of olefinic and aromatic hydrocarbons as aerosol precursors. 

Sin summary, both techniques present a qualitatively similar picture of the contributions of aerosol chemical species to bgp. Ammonium sulfate is the most important measured species, while the contributions of organics and crustal species are smaller, but not negligible. The species which could not be identified by chemical analysis also contributed to bsp. but roughly half of this contribution is statistically linked to sulfate. 

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 this paper we have shown that there is no simple answer to the question posed in the title of this paper. Primary carbon particles dominate the carbonaceous aerosol under certain conditions while substantial secondary carbon may be present at other times. However, the importance of secondary carbon contributions is much less obvious when 24-h samples are examined. With shorter time averaged samples (e.g. 6-h or less) the increase in secondary carbon formation can be more easily detected. Secondary carbon appears to be more important in the summer rather than winter, in the afternoon father than the early morning, and in LA rather than St. Louis. It should be noted that these conditions of increased secondary carbon aerosol formation are also more favorable conditions for photochemical reactions. Our detailed emission inventory Indicates that much more primary carbon exists in the urban aerosol than was thought previously. This is in agreement with the data. Our analysis shows that even on the very smoggy days in the ACHEX study there were times when primary carbon dominated the carbonaceous aerosol. 

Silicon and iron are generally considered to be tracers of resuspended soils. For this reason, they were included in the analysis to determine the importance of local soils on the measured aerosol concentration. 

In the case of S02, oxidation in the aqueous phase, present in the atmosphere in the form of aerosol particles, clouds, and fogs, is also important. Thus S02 from the gas phase dissolves in these water droplets and may be oxidized within the droplet by such species as H202, 03, 02, and free radicals. Oxidation of S02 on the surfaces of solids either present in the air or suspended in the water droplets is also possible. On the other hand, it is believed that HN03 is formed primarily by reaction (10) in the gas phase and subsequently dissolves in droplets. 

This chapter treats those aerosol phenomena that are known or believed to be important in atmospheric chemistry. For treatment of related, but specialized, topics, a number of excellent references are available. The classic works on aerosol physics are The Mechanics of Aerosols by the late N. A. Fuchs (1964) and Highly Dispersed Aerosols (Fuchs and Sutugin, 1970). The... 

Even taken qualitatively, these reactivity data have important toxicological as well as chemical implications regarding the composition of PAHs and PACs in and on the surfaces of aerosols in polluted air parcels, both near-source and during transport (downwind). Thus, under certain conditions (e.g., daytime, summer season, and high oxidant levels) over a period of hours BaP concentrations in ambient air could be expected to decay dramatically as a result of reactions, while those of the benzofluoranthenes and indeno[l,2,3-cabsolute concentrations also change as a result of dilution of the air parcel caused by increased mixing depth over time and transport. However, impacts of such physical processes are minimized if one considers ratios of concentrations of reactive to nonre-... 

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