Atmospheric chemistry Transformation

As discussed in Chapter 1, much of our understanding of the chemistry of our atmosphere is based on early studies of air pollution these are often treated in the context of an overall system. This approach starts with the various sources of anthropogenic and natural emissions and tracks the resulting pollutants through their atmospheric transport, transformations, and ambient concentrations—on local, regional, and global scales—to their ultimate chemical and physical fates, including their impacts on our health and environment. 

Over the past several decades there have been increasingly strong demands in Europe and the United States that atmospheric chemistry research be directly useful in developing scientific risk assessments and public policies. For example, one component of the EUROTRAC program (European Experiment on Transport and Transformation of Environmentally Relevant Trace Constituents in the Troposphere) ...is expected to assimilate the scientific results from EUROTRAC and present them in a condensed form, together with recommendations where appropriate, so that they are suitable for use by those responsible for environmental planning and management in Europe (EUROTRAC, 1993). 

Yokelson, R. J J. G. Goode, R. A. Susott, R. E. Babbitt, D. E. Ward, S. P. Baker, W. M. Hao, and D. W. T. Griffith, Smoke Chemistry Measurements by Airborne Fourier Transform Infrared Spectroscopy (AFTIR), IGAC International Symposium on Atmospheric Chemistry and Future Global Environment, Nagoya, Japan, November 11-13, 1997b. 

H. Niki, P. D. Maker, C. M. Savage, and L. P. Breitenbach, Fourier transform infrared spectroscopic studies of atmospheric chemistry, in Spectroscopy in Chemistry and Physics Modern Trends, F. J. Comes, A. Muller, and W. J. Orville-Thomas, Eds., Elsevier, New York, 1980 and J. Mol. Struct., 59, 1 (1980). 

Application of these procedures to future work will yield transformation rate data of known precision. Additional audits and protocols are necessary to derive data accuracy and validity. One of the shortcomings of previous experiments is they provide only a value of the observable while neglecting these three attributes. The institution of this methodology to chemical transformation data obtained with this system would yield results with known uncertainty for use in models of atmospheric chemistry and physics. Application of the general methodology which comprises the overall measurement process is important not only in the context of measured transformation rates but also in all experiments and programs where the collection of quality data is desired. 

In these discussions we will thus use the following explicit definition of a chemical measurement in the atmosphere the collection of a definable atmospheric phase as well as the determination of a specific chemical moiety with definable precision and accuracy. This definition is required since most atmospheric pollutants are not inert gaseous and aerosol species with atmospheric concentrations determined by source strength and physical dispersion processes alone. Instead they may undergo gas-phase, liquid-phase, or surface-mediated conversions (some reversible) and, in certain cases, mass transfer between phases may be kinetically limited. Analytical methods for chemical species in the atmosphere must transcend these complications from chemical transformations and microphysical processes in order to be useful adjuncts to atmospheric chemistry studies. 

Parisa Ariya was born in Tehran, the capital of Iran. She chose atmospheric chemistry for a career. Scientists in this field study the transformation of molecules in the atmosphere (the layer of gases surrounding Earth). They also study the atmosphere s interactions with oceans, land, and living things. After studying in several countries, Dr. Ariya became a professor at McGill University in Montreal. 

Quantum Chemistry can be utilized in atmospheric research in the same way as in other fields involving molecules and their transformations. Atmospheric chemistry is in fact much more favorable than the usual chemist s chemistry for applying quantum chemical methods since it occurs in the gas phase. From that point of view, of course, space chemistry, where temperature and pressure are very low, is even closer to the ideal conditions Quantum theory in atmospheric research can be useful in various areas i) pure spectroscopic calculations of frequencies and intensities, helping the identification and understanding of observations, ii) es-... 

The chemistry of the ozone layer in the tropics has not been extensively studied. We do not know the level of the ozone concentration with exactitude. We have demonstrated that termites do emit large quantities of methane in the tropics. The emitted methane is transformed into CO which can affect the ozone layer. Therefore, studies of ozone layer profile in the tropics would be an essential component towards our understanding of the atmospheric chemistry. 

Figure 9 Volcanic clouds are typically composed of gases and particles and diluted by the background atmosphere. Various chemical and physical processes and transformations acting during plume transport further modify plume composition. The chemical and physical form of plume components, their spatial and temporal distribution, and their deposition are therefore strongly controlled by atmospheric chemistry and transport of the plume.

A wide range of structurally diverse compounds is produced during incineration. These include PAHs and related compounds, azaarenes, and chlorinated PAHs from combustion of fossil fuels and natural wildfires. Organic compounds in the atmosphere may exist both in the free (gaseous) state or on particles of various dimensions. Recent concern has been directed to the occurrence in aerosols both of the compounds themselves and of their transformation products (secondary aerosols) (1) for their role in atmospheric chemistry and as determinants of climate (Andreae and Crutzen 1997) and (2) due to health risks since aerosol formation facilitates the transport into and sorption by the lungs. 

James G. Anderson is Philip S. Weld Professor of Atmospheric Chemistry at Harvard University. He received his B.S. in physics from the University of Washington and his Ph.D. in physics-astrogeophysics from the University of Colorado. His research addresses three domains within physical chemistry (1) chemical reactivity viewed from the microscopic perspective of electron structure, molecular orbitals, and reactivities of radical-radical and radical-molecule systems (2) chemical catalysis sustained by free-radical chain reactions that dictate the macroscopic rate of chemical transformation in the Earth s stratosphere and troposphere and (3) mechanistic links between chemistry, radiation, and dynamics in the atmosphere that control climate. Studies are carried out both in the laboratory, where elementary processes can be isolated, and within natural systems, in which reaction networks and transport patterns are dissected by establishing cause and effect using simultaneous, in situ detection of free radicals, reactive intermediates, and long-lived tracers. Professor Anderson is a member of the National Academy of Sciences. 

Table II gives typical ozone and oxides of nitrogen levels in these four regions. Urban- and regional-scale atmospheric chemistry is characterized by the definitive influence of anthropogenic emissions. The goals of a study of urban- and regional-scale atmospheric chemistry are to understand the atmospheric transformations of emitted species to be able to predict the formation of ozone and other pollutants, and to predict the pathways of removal of emitted species and their transformation products from the atmosphere.

Atmospheric chemistry deals with chemical compounds in the atmosphere, their distribution, origin, chemical transformation into other compounds, and finally, their removal from the atmospheric domain. These substances may occur as gases, liquids, or solids. The composition of the atmosphere is dominated by the gases nitrogen and oxygen in proportions that have been found invariable in time and space at altitudes up to 100 km. All other components are minor ones with many of them occurring only in traces. Atmospheric chemistry thus deals primarily with trace substances. 

Although much emphasis has been placed on characterisation of the organic compounds in atmosphere, recent research suggests that a substantial fraction of both gas-phase and aerosol atmospheric organics have not been, or have very rarely been, determined. A major challenge in atmospheric chemistry research will be to elucidate the sources, structure, transformation and formation processes, and fate of the clearly ubiquitous, yet poorly constrained, organic atmospheric constituents. 

The chemical composition of air depends on the natural and man-made sources of the constituents (their distribution and source strength in time and space) as well the physical (e. g. radiation, temperature, humidity, wind) and chemical conditions (other trace species) which determine transportation and transformation. Thus, atmospheric chemistry is not a pure chemistry and also includes other disciplines which are important for describing the interaction between atmosphere and other surrounding reservoirs (biosphere, hydrosphere, etc.). Measurements of chemical and physical parameters in air will always contain a geographical component, i. e., the particularities of the locality. That is why the terms chemical weather and chemical climate have been introduced. For example, diurnal variation of the concentration of a substance may occur for different reasons. Therefore general conclusions or transfer of results to other sites should be done with care. On the other hand, it is a basic task in atmospheric chemistry not only to present local results of chemical composition and its variation in time, but also to find general relationships between pollutants and their behavior under different conditions. 

The composition of single aerosol particles in the micrometer range is important for assessing their environmental health hazard and for studying the atmospheric chemistry of particle formation and transformation during atmospheric transport. Both... 

The sensitivity analysis method was employed successfully for studying the mechatrisms of a great number of complex chemical transformations, such as reactions on combustion [33-36], pyrolysis [37,38], the self-oscillation reaction of Belousov-Zhabotinsky [39,40], atmospheric chemistry [41-44], as well as in many other fields of natural science, such as physics, economy, sociology, population science, etc. [7,45,46]. 

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