Development into Atmospheric Chemistry

Acid rain has been significantly reduced over the past decade as new mechanisms for trapping nonmetal oxides before they get into the atmosphere have been developed. Read the Chemistry and Society feature for more information about this type of air pollution. 

Munson and Field reported in 1966 on a technique of ionizing molecules by gas phase ion-molecule reactions, which they called chemical ionization (Cl). In this way, break-up of the molecules can be greatly reduced or even avoided. Thus, measured ion currents can be correlated with the densities of the respective parent neutral compounds, allowing for on-line monitoring of rather complex gas mixtures. The fundamental principles of gas phase ion chemistry on which Cl is based, as well as the instrumentation for Cl, have been reviewed in great detail by Harrison." The wide variety of Cl methods that has been developed includes Medium Pressure Mass Spectrometry, Fourier Transform Mass Spectrometry, Quadrupole Ion Trap Mass Spectrometry, Pulsed Positive Ion-Negative Ion Chemical Ionization, and Atmospheric Pressure Ionization Mass Spectrometry (API-MS). Of these, API-MS has developed into a very reliable and widely used technique for analysis of VOCs in flavor release studies and human breath. A variety of API-MS applications in these fields of research has been described in a recent volume by Roberts and Taylor. ... 

Direct Measurement of HO, in the Troposphere. Techniques to measure tropospheric concentrations of HO have been reviewed (O Brien Hard, submitted to Advances in Chemistry, 1991) so only a summary will be given here. The most extensively researched technique for [HO ] measurement in the troposphere is based on laser-induced fluorescence (LIF) of HO. This approach has been developed in many configurations directing the laser into the free atmosphere and collecting fluorescence back scatter (LIDAR) (105,106,107) LIF of air sampled at atmospheric pressure... 

Explicit mechanisms attempt to include all nonmethane hydrocarbons believed present in the system with an explicit representation of their known chemical reactions. Atmospheric simulation experiments with controlled NMHC concentrations can be used to develop explicit mechanisms. Examples of these are Leone and Seinfeld (164), Hough (165) and Atkinson et al (169). Rate constants for homogeneous (gas-phase) reactions and photolytic processes are fairly well established for many NMHC. Most of the lower alkanes and alkenes have been extensively studied, and the reactions of the higher family members, although little studied, should be comparable to the lower members of the family. Terpenes and aromatic hydrocarbons, on the other hand, are still inadequately understood, in spite of considerable experimental effort. Parameterization of NMHC chemistry results when NMHC s known to be present in the atmosphere are not explicitly incorporated into the mechanism, but rather are assigned to augment the concentration of NMHC s of similar chemical nature which the... 

Models of atmospheric phenomena are similar to those of combustion and involve the coupling of exceedingly complex chemistry and physics with three-dimensional hydrodynamics. The distribution and transport of chemicals introduced into groundwater also involve a coupling of chemical reactions and transports through porous solid media. The development of groundwater models is critical to understanding the effects of land disposal of toxic waste (see Chapter 7). 

The story of research into the depletion of atmospheric ozone is just one example of how scientific understanding and theories develop. The fundamental theories and laws of chemistry that we present In this text all went through similar intense scrutiny and study. 

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