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Most chemical analytical techniques rely on the analyte being present in solution. This chapter examines extraction and dissolution techniques from solids to solubilize the components of interest. The analysis can then proceed by the
Analysis of Land, Solids and Waste
instrumental techniques which have already been discussed in earlier chapters. Solids which are of importance in studying the environment include animal and plant specimens, soils, contaminated land and waste and landfill sites, sediments and sewage sludge, and atmospheric particulates. Specific extraction and dissolution procedures have been discussed for each type of solid, except for atmospheric particulates. In some instances (particularly for landfill sites), the sampling and analysis of associated liquids and gases is also described. Atmospheric particulates are dealt with later in Chapter 7, after discussion of the gaseous components of the atmosphere in the next chapter.
Introduction to Environmental Analysis Roger Reeve
Copyright © 2002 John Wiley & Sons Ltd ISBNs: 0-471-49294-9 (Hardback); 0-470-84578-3 (Electronic)
Atmospheric Analysis - Gases
• To be able to list the major components in external atmospheres and appreciate the need for analytical monitoring.
• To understand the difference in type and concentration of pollutants in external and internal environments and the difference in approach needed for their analysis.
• To realize the importance of personal sampling.
• To be able to describe, compare and contrast the analytical methods available for external and internal atmospheres.
• To understand simple methods of flue gas analysis.
• To appreciate the availability of portable instruments for gas analysis and the possibilities of remote sensing.
From your previous knowledge and from the earlier chapters in this present text you should have some idea of the major components of the atmosphere.
List the components of clean dry air and give an indication of their approximate concentrations.
These components and their typical concentrations are shown in Figure 6.1 below.
Introduction to Environmental Analysis
Figure 6.1 Gaseous constituents of the atmosphere.
You will probably have included the major components, but many of the minor components might be a surprise to you. You may have considered some of these to be anthropogenic pollutants. There are few of the common gases (chlorofluoro-carbons being possibly the only example) which are not found in the atmosphere from natural sources. Non-localized atmospheric pollution problems are mainly concerned with increases in concentrations of naturally occurring compounds above the unpolluted clean-air levels.
We have previously mentioned in Chapter 1 the problems due to acid rain which contains high concentrations of sulfur and nitrogen oxides. The compounds are oxidized over periods of hours or days to sulfuric and nitric acids by reactions which may include other atmospheric components (e.g. ozone and particulates). Global warming was also discussed with increasing carbon dioxide levels being a major contributing factor. The problem arises from the increased absorption of infrared radiation by carbon dioxide. Introduction of other covalent compounds into the atmosphere can add to the problem, particularly if they absorb at wavelengths which would otherwise not be absorbed by the atmosphere (window regions). This can occur with compounds containing C-H, C-Cl or C-Br bonds.
Concern over specific compounds includes the rising concentrations of methane (another greenhouse gas) and of ground-level ozone (an oxidant, which produces
Atmospheric Analysis - Gases
breathing difficulties) which is increasing even in non-industrialized areas. Localized problems in urban or industrial areas can be more complex, not only due to the introduction of a large number of other pollutants but also from atmospheric reactions producing new species. A good example of this is the complex series of reactions which occur each day in large cities in hot climates throughout the world. Under specific meteorological conditions (thermal inversion where layers of hot light air are found above cold dense air, producing a stable atmospheric condition), pollutants build up in the atmosphere without dispersal. Gases given off by vehicles (CO, NO, NO2, unburnt hydrocarbons, etc.) inter-react to produce a range of oxidants including ozone and peroxyacetyl nitrate (PAN). The chemical changes that occur throughout a typical day are shown in Figure 6.2. These reactions produce a haze over a city, known as photochemical smog, and the compounds produced can cause respiratory problems. There is a more general concern over the emission of all volatile organic compounds (VOCs) into the atmosphere. Many are toxic in their own right, all are greenhouse gases, and they may contribute to the atmospheric chemical reactions discussed above.