Aerosol chemical dynamics

The arsenal of aerosol measurement methods has expanded dramatically over recent years, but a number of needs for fundamental research into the nature and origins of the atmospheric aerosol cannot be met by the current instrumentation. Instrumentation that has proven most valuable in the chemical characterization of the atmospheric aerosol is woefully inadequate either for following the chemical dynamics of aerosols because of the rapid changes that occur in homogeneous reacting systems or for unraveling the complexity of the aerosol products. 

In this section we focus on four specific environmental problems coal combustion aerosol formation, dynamics of atmospheric aerosols, the chemical characterization of particles, and the role of aerosols in clean room technology or so-called microcontamination control. For the reader interested in an introduction to aerosol science, we recommend three texts [6-8]. 

Further in.sighl into atmospheric aerosol dynamics can be obtained by analyzing variations in aerosol chemical composition with lime at a given sampling site. Many long-time... 

Several other chapters have been substantially rewritten to reflect the sharpened focus on aerosol dynamics. For example, the chapter on optical properties has been expanded to include more applications to polydisperse aerosols. It help.s support the chapter that follows on experimental methods in which coverage of instrumentation for rapid size distribution measurements has been augmented. Methods for the rapid on-line measurement of aerosol chemical characteristics are discussed in the chapters on optical properties and experimental methods. This chapter has been strongly influenced by the work of the Minnesota group (B. Y. H. Liu, D. Y. H, Pui, P, McMuny, and their colleagues and students) who continue to invent and perfect advanced aerosol instrumentation. Discussions of the effects of turbulence have been substantially expanded in chapters on coagulation and gas-to-particle conversion. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

FIG. 4 Time-resolved fluorescence Stokes shift of coumarin 343 in Aerosol OT reverse micelles, (a) normalized time-correlation functions, C i) = v(t) — v(oo)/v(0) — v(oo), and (b) unnormalized time-correlation functions, S i) = v i) — v(oo), showing the magnitude of the overall Stokes shift in addition to the dynamic response, wq = 1.1 ( ), 5 ( ), 7.5 ( ), 15 ( ), and 40 (O) and for bulk aqueous Na solution (A)- Points are data and lines that are multiexponential fits to the data. (Reprinted from Ref 38 with permission from the American Chemical Society.)... 

Pulmonary dynamics, the dimension and geometry of the respiratory tract and the structure of the lungs, together with the solubility and chemical reactivity of the inhalants greatly influence the magnitude of penetration, retention, and absorption of inhaled gases, vapors (Dahl, 1990), and aerosols (Raabe, 1982 Phalen, 1984). The quantity of an inhalant effectively retained in the pulmonary system constitutes the inhaled dose that causes pharmacotoxic responses. 

A different approach which also starts from the characteristics of the emissions is able to deal with some of these difficulties. Aerosol properties can be described by means of distribution functions with respect to particle size and chemical composition. The distribution functions change with time and space as a result of various atmospheric processes, and the dynamics of the aerosol can be described mathematically by certain equations which take into account particle growth, coagulation and sedimentation (1, Chap. 10). These equations can be solved if the wind field, particle deposition velocity and rates of gas-to-particle conversion are known, to predict the properties of the aerosol downwind from emission sources. This approach is known as dispersion modeling. 

The basic theoretical equation ( ) relating source contributions and chemical composition is a mass balance which requires no consideration of rate processes. In this paper, the theory is extended to the resolution of the visibility degrading components of the aerosol and to chemically reactive families of chemical compounds. These extensions require new theoretical analyses which take into account the dynamics of aerosol growth and chemical kinetics, respectively. The extension to these rate processes are the subject of this paper. 

Simulation of the Dynamical Response of the Arctic Vortex to Aerosol-Associated Chemical Perturbations in the Lower Stratosphere, Geophys. Res. Lett., 23, 1525-1528 (1996). 

Meng, Z., D. Dabdub, and J. H. Seinfeld, Size-Resolved and Chemically Resolved Model of Atmospheric Aerosol Dynamics, J. Geophys. Res., 103, 3419-3435 (1998). 

This theory, as originated from the early work of Smoluchowski [20], nowadays has numerous applications in several branches of chemistry, such as colloidal chemistry, aerosol dynamics, catalysis and the physical chemistry of solutions as well as in the physics and chemistry of the condensed state [21-24]. Until recently, its branch called standard chemical kinetics [12, 15, 16] based on the law of mass action seemed to be quite a complete and universal theory. However, because of their entirely phenomenological character, theories of this kind always operate with the reaction rates K which are postulated to be time-independent parameters. 

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