Atmospheric chemistry mechanisms

Wang, S. W., P. G. Georgopoulos, G. Li, and H. Rabitz, Condensing Complex Atmospheric Chemistry Mechanisms. 1. The Direct Constrained Approximate Lumping (DCAL) Method Applied to Alkane Photochemistry, Environ. Sci. Technol, 32, 2018-2024 (1998). 

The mechanism of the hydroxyl radical-initiated oxidation of /i-pincnc in the presence of NO has been investigated using a discharge-flow system. Propagation of hydroxyl radicals was observed after the addition of O2 and NO, and the measured concentration profiles were compared with simulations based on both the master chemical mechanism and the regional atmospheric chemistry mechanism for /i-pinene oxidation.228... 

Geiger, H., I. Barnes, J. Bejan, T. Benter, and M. Spittler The tropospheric degradation of isoprene an updated module for the regional atmospheric chemistry mechanism. Atmospheric Environment, 37 (2003) 1503-1519. 

Gas-phase reactions play a fundamental role in nature, for example atmospheric chemistry [1, 2, 3, 4 and 5] and interstellar chemistry [6], as well as in many teclmical processes, for example combustion and exliaust fiime cleansing [7, 8 and 9], Apart from such practical aspects the study of gas-phase reactions has provided the basis for our understanding of chemical reaction mechanisms on a microscopic level. The typically small particle densities in the gas phase mean that reactions occur in well defined elementary steps, usually not involving more than three particles. 

Representation of Atmospheric Chemistry Through Chemical Mechanisms. A complete description of atmospheric chemistry within an air quaUty model would require tracking the kinetics of many hundreds of compounds through thousands of chemical reactions. Fortunately, in modeling the dynamics of reactive compounds such as peroxyacetyl nitrate [2278-22-0] (PAN), C2H2NO, O, and NO2, it is not necessary to foUow every compound. Instead, a compact representation of the atmospheric chemistry is used. Chemical mechanisms represent a compromise between an exhaustive description of the chemistry and computational tractabiUty. The level of chemical detail is balanced against computational time, which increases as the number of species and reactions increases. Instead of the hundreds of species present in the atmosphere, chemical mechanisms include on the order of 50 species and 100 reactions. 

Three different types of chemical mechanisms have evolved as attempts to simplify organic atmospheric chemistry surrogate (58,59), lumped (60—63), and carbon bond (64—66). These mechanisms were developed primarily to study the formation of and NO2 in photochemical smog, but can be extended to compute the concentrations of other pollutants, such as those leading to acid deposition (40,42). 

The mechanisms by which a jurisdiction develops its air pollution control strategies and episode control tactics are outlined in Fig. 5-1. Most of the boxes in the figure have already been discussed—sources, pollutant emitted, transport and diffusion, atmospheric chemistry, pollutant half-life, air quality, and air pollution effects. To complete an analysis of the elements of the air pollution system, it is necessary to explain the several boxes not vet discussed. 

Pandis, S. N., and J. H. Seinfeld, Sensitivity Analysis of a Chemical Mechanism for Aqueous-Phase Atmospheric Chemistry, 94, 1105-1126 (1989b). 

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... 

As we have seen, a great deal is known about emission sources and strengths, ambient levels, and mutagenic/carcinogenic properties of the particle-phase PAHs in airborne POM. However, because of the tremendous physical and chemical complexity of the aerosol surfaces on which photolysis, photooxidations, and gas-particle interactions take place in real polluted ambient air, much less is known about the structures, yields, and absolute rates and mechanisms of formation of PAH and PAC reaction products, especially for the more polar PACs. This is one area in which there exists a major gap in our knowledge of their atmospheric chemistry and toxicology. 

APPLICATIONS OF ATMOSPHERIC CHEMISTRY TABLE 16.2 Classification of Organics in the Carbon Bond IV Mechanism, Expanded Version" ... 

Barbara J. Finlayson-Pitts is Professor of Chemistry at the University of California, Irvine. Her research program focuses on laboratory studies of the kinetics and mechanisms of reactions in the atmosphere, especially those involving gases with liquids or solids of relevance in the troposphere. Reactions of sea salt particles to produce photochemically active halogen compounds and the subsequent fates of halogen atoms in the troposphere are particular areas of interest, as are reactions of oxides of nitrogen at aqueous and solid interfaces. Her research is currently supported by the National Science Foundation, the Department of Energy, the California Air Resources Board, the Dreyfus Foundation, and NATO. She has authored or coauthored more than 80 publications in this area, as well as a previous book, Atmospheric Chemistry Fundamentals and Experimental Techniques. 

James N. Pitts, Jr., is a Research Chemist at the University of California, Irvine, and Professor Emeritus from the University of California, Riverside. He was Professor of Chemistry (1954-1988) and cofounder (1961) and Director of the Statewide Air Pollution Research Center (1970-1988) at the University of California, Riverside. His research has focused on the spectroscopy, kinetics, mechanisms, and photochemistry of species involved in a variety of homogeneous and heterogeneous atmospheric reactions, including those associated with the formation and fate of mutagenic and carcinogenic polycyclic aromatic compounds. He is the author or coauthor of more than 300 research publications and three books Atmospheric Chemistry Fundamentals and Experimental Techniques, Graduate School in the Sciences—Entrance, Survival and Careers, and Photochemistry. He has been coeditor of two series, Advances in Environmental Science and Technology and Advances in Photochemistry. He served on a number of panels in California, the United States, and internationally. These included several National Academy of Science panels and service as Chair of the State of California s Scientific Review Panel for Toxic Air Contaminants and as a member of the Scientific Advisory Committee on Acid Deposition. 

Michael Gery, who developed the OZIPR model, graciously provided advice on its use as well as electronic copies of the documentation. This model, which contains the two major chemical mechanism schemes for gas-phase, VOC-NC/ chemistry in use in atmospheric chemistry, is available on the Academic Press Web site (http //www.academicpress.com/pecs/down-load). A number of problems using this model are included in the book, and it is a valuable teaching tool for assessing the effects of various model input parameters on predicted concentrations of a wide variety of gas-phase species. His assistance and that of Marcia Dodge of the U.S. EPA in making it available are appreciated. 

For illustration, a number of high-temperature gas-phase processes are discussed in some detail in this and the following chapter. Low-temperature applications such as atmospheric chemistry are outside the scope of this book. High-temperature gas-phase reactions are important in combustion, incineration, flue gas-cleaning, petrochemical processes, as well certain processes in chemical synthesis and materials production. While the details of these systems may vary significantly, they share some characteristics that are common for all gas-phase reaction mechanisms. 

Because of the implications for atmospheric chemistry, chlorine reactions have been studied extensively at low temperatures. Despite the growing interest in incineration of toxic chemical waste involving chlorinated hydrocarbons, studies at high temperatures are still limited. Current mechanisms for high-temperature applications rely to a significant extent on extrapolation of low temperature data [355]. 

The approach taken in our laboratory combines both of these trends. Specifically, we have developed a new experiment that allows us to study, for the first time, the photodissociation spectroscopy and dynamics of an important class of molecules reactive free radicals. This work is motivated in part by the desire to obtain accurate bond dissociation energies for radicals, in order to better determine their possible role in complex chemical mechanisms such as typically occur in combustion or atmospheric chemistry. Moreover, since radicals are open-shell species, one expects many more low-lying electronic states than in closed-shell molecules of similar size and composition. Thus, the spectroscopy and dissociation dynamics of these excited states should, in many cases, be qualitatively different from that of closed-shell species. 

HO + HCHO. Despite the well-recognized, critical role of the HO + HCHO reaction in atmospheric chemistry [1,11], considerable uncertainty existed until recently concerning both the rate constant and the mechanism operative under tropospheric conditions. Namely, of the two exothermic reaction channels (6a) and (6b),... 

Over the past several years, the area of gas-phase transition metal ion chemistry has been gaining increasing attention from the scientific community [1-16]. Its appeal is manifold first, it has broad implications to a spectrum of other areas such as atmospheric chemistry, corrosion chemistry, solution organometallic chemistry, and surface chemistry secondly, an arsenal of gas phase techniques are available to study the thermochemistry, kinetics, and mechanisms of these "unusual" species in the absence of such complications as solvent and ligand... 

Hynes, A.J., Wine, P.H. (1996) The atmospheric chemistry of dimethylsulfoxide (DMSO) kinetics and mechanism of the OH + DMSO reaction. J. Atmos. Chem. 24, 23-37. 

Temperature units/conversions Periodic table Basic atomic structure Quantum mechanical model Atomic number and isotopes Atoms, molecules, and moles Unit conversions Chemical equations Stoichiometric calculations Week 3 Atmospheric chemistry... 

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