Environmental Inorganic Chemistry. Properties, Processes, and Estimation Methods

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Collecting fibres as air pollutants is important since asbestos has been classified as a confirmed carcinogenic material. Measurement procedures for fibrous materials consist of counting, under the microscope, fibres that have been separated on filters.

Only electron microscopic procedures can be considered for outside air measurements. The fibres are separated on gold-coated porous filters. Prior to assessment in an electron scan microscope, the sample is freed of organic substances through plasma incineration right on the filter. The fibres are counted on part of the filter surface, randomly chosen and classified by geometry and type of fibre.

With the help of energy dispersive x-ray analysis EDXA , asbestos fibres, calcium sulphate fibres and other inorganic fibres can be differentiated on the basis of elemental composition. The entire procedure is extremely expensive and requires the greatest care to achieve reliable results. Soot in the form of particles emitted by diesel motors has become relevant since diesel soot was also classified as carcinogenic. Because of its changing and complex composition and because of the fact that various constituents are also emitted from other sources, there is no measurement procedure specific to diesel soot.

Nevertheless, in order to say something concrete about the concentrations in ambient air, soot is conventionally defined as elemental carbon, as a part of total carbon. Determination of the carbon content ensues through burning in an oxygen stream and coulometric titration or non-dispersive IR detection of the carbon dioxide formed in the process. The so-called aethalometer and the photoelectric aerosol sensor are also used for measuring soot, in principle.

Together with dry deposition, wet deposition in rain, snow, fog and dew constitute the most important means by which harmful materials enter the ground, water or plant surfaces from the air. With rain sensors, which mostly work on the principle of conductivity changes, the cover is opened when it starts to rain and closed again when the rain stops.

The samples are transferred through a funnel open area approx. In general, analysing the collected water for inorganic components can be done without sample preparation. The water should be centrifuged or filtered if it is visibly cloudy. Organic compounds are extracted from rain water with, for example, dichloromethane, or blown out with argon and adsorbed with Tenax tubes only highly volatile materials. Dry deposition correlates directly with ambient air concentrations.

The concentration differences of airborne harmful materials in rain, however, are relatively small, so that for measuring wet deposition, wide-mesh measuring networks are adequate. Examples include the European EMEP measurement network, in which the entry of sulphate and nitrate ions, certain cations and precipitation pH values are collected in approximately 90 stations. There are also extensive measurement networks in North America.

Whereas the procedures described up to now catch air pollution at one point, optical long-distance measuring procedures measure in an integrated manner over light paths of several kilometres or they determine the spatial distribution.

They use the absorption characteristics of gases in the atmosphere in the UV, visible or IR spectral range and are based on the Lambert-Beer law, according to which the product of light path and concentration are proportional to the measured extinction. If the sender and receiver of the measuring installation change the wavelength, several components can be measured in parallel or sequentially with one device. In practice, the measurement systems identified in table IR range approx.

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The measurement of air pollution containing organic components is complicated primarily by the range of materials in this class of compounds. Especially due to the great differences in potential impact, collecting relevant individual components has more and more taken the place of previously used summation procedures e. The FID method, however, has retained a certain significance in connection with a short separation column to separate out methane, which is photochemically not very reactive, and for collecting the precursor volatile organic compounds VOC for the formation of photo-oxidants.

The frequent necessity of separating the complex mixtures of the organic compounds into relevant individual components makes measuring it virtually an exercise in applied chromatography.

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Chromatographic procedures are the methods of choice when the organic compounds are sufficiently stable, thermally and chemically. Examples include using amines to convert aldehydes to hydrazones, with subsequent photometric measurement; derivatization with 2,4-dinitrophenylhydrazine and separation of the 2,4-hydrazone that is formed; or forming azo-dyes with p- nitroaniline for detecting phenols and cresols. Among chromatographic procedures, gas chromatography GC and high-pressure liquid chromatography HPLC are most frequently employed for separating the often complex mixtures.

For gas chromatography, separation columns with very narrow diameters approx. The HPLC uses special through-flow detectors which, for example, are designed as the through-flow cuvette of a UV spectrometer. Especially effective, but also especially expensive, is the use of a mass spectrometer as a detector. Really certain identification, especially with unknown mixtures of compounds, is often possible only through the mass spectrum of the organic compound. The qualitative information of the so-called retention time time the material remains in the column that is contained in the chromatogram with conventional detectors is supplemented with the specific detection of the individual components by mass fragmentograms with high detection sensitivity.

Sampling must be considered before the actual analysis. The choice of sampling method is determined primarily by volatility, but also by expected concentration range, polarity and chemical stability. Furthermore, with non-volatile compounds, a choice must be made between concentration and deposition measurements.

Deposition measurements of organic compounds with low volatility e. Since food is the main source of human intake, airborne material transferred onto food plants is of great significance. There is, however, evidence that material transfer by way of particulate deposition is less important than dry deposition of quasi-gaseous compounds. For measuring total deposition, standardized devices for dust precipitation are used e.

Important technical measurement problems, such as the resuspension of already separated particles, evaporation or possible photolytic decomposition, are now being systematically researched in order to improve the less-than-optimal sampling procedures for organic compounds. Olfactometric immission investigations are used in monitoring to quantify odour complaints and to determine baseline pollution in licensing procedures. They serve primarily to assess whether existing or anticipated odours should be classified as significant.

The first possibility combines emission measurement with modelling and, strictly speaking, cannot be classified under the term air quality monitoring. In the third method, the human nose is used as the detector with significantly reduced precision as compared to physical-chemical methods. Details of inspections, measurement plans and assessing the results are contained, for example, in the environmental protection regulations of some German states.

Simplified measurement procedures are sometimes used for preparatory studies screening. Examples include passive samplers, test tubes and biological procedures. With passive diffusive samplers, the material to be tested is collected with freely flowing processes such as diffusion, permeation or adsorption in simple forms of collectors tubes, plaques and enriched in impregnated filters, meshes or other adsorption media. So-called active sampling sucking the sample air through a pump thus does not occur. The enriched quantity of material, analytically determined according to definite exposure time, is converted into concentration units on the basis of physical laws e.

The methodology stems from the field of occupational health personal sampling and indoor air measurement, but it is increasingly being used for ambient air pollutant concentration measurements. An overview can be found in Brown Detector tubes are often used for sampling and quick preparatory analysis of gases.

A certain test air volume is sucked through a glass tube that is filled with an adsorptive reagent that corresponds with the test objective. The contents of the tube change colour depending on the concentration of the material to be determined that is present in the test air. Small testing tubes are often used in the field of workplace monitoring or as a quick procedure in cases of accidents, such as fires. They are not used for routine ambient air pollutant concentration measurements due to the generally too high detection limits and too limited selectivity.

Detector testing tubes are available for numerous materials in various concentration ranges. Among the biological procedures, two methods have become accepted in routine monitoring.

Voices of Inorganic Chemistry - Harry B. Gray

With the standardized lichen exposure procedure, the mortality rate of the lichen is determined over the exposure time of days. Then the amount of growth is determined. Both procedures serve as summary determinations of air pollutant concentration effects. Around the world, the most varied types of air quality networks are utilized.

A distinction should be drawn between measurement networks, consisting of automatic, computer-controlled measuring stations measurement containers , and virtual measurement networks, which only define the measurement locations for various types of air pollutant concentration measurements in the form of a preset grid. Tasks and conceptions of measurement networks were discussed above. Continuously operating measurement networks are based on automatic measuring stations, and serve primarily for air quality monitoring of urban areas. Measured are air pollutants such as sulphur dioxide SO 2 , dust, nitrogen monoxide NO , nitrogen dioxide NO 2 , carbon monoxide CO , ozone O 3 , and to an extent also the sum of the hydrocarbons free methane, C n H m or individual organic components e.

In addition, depending on need, meteorological parameters such as wind direction, wind speed, air temperature, relative humidity, precipitation, global radiation or radiation balance are included.

The measuring equipment operated in measurement stations generally consists of an analyser, a calibration unit, and control and steering electronics, which monitors the whole measuring equipment and contains a standardized interface for data collection. In addition to the measurement values, the measuring equipment supplies so-called status signals on errors and the operating status. The calibration of the devices is automatically checked by computer at regular intervals. As a rule, the measurement stations are connected with fixed data lines, dial connections or other data transfer systems to a computer process computer, workstation or PC, depending on the scope of the system in which the measurement results are entered, processed and displayed.

The measurement network computers and, if necessary, specially trained personnel monitor continuously whether various threshold limits are exceeded. In this manner critical air quality situations can be recognized at any time.

Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences

This is very important, especially for monitoring critical smog situations in winter and summer photo-oxidants and for current public information. Beyond the telemetric measurement network, other measuring systems for monitoring air quality are used to varying extents. Examples include occasionally partially automated measurement networks to determine:. A series of substances measured in this manner have been classified as carcinogens, such as cadmium compounds, PAHs or benzene.

Monitoring them is therefore particularly important. To provide an example of a comprehensive programme, table The objective of a manager of an air pollution control system is to ensure that excessive concentrations of air pollutants do not reach a susceptible target. Targets could include people, plants, animals and materials. In all cases we should be concerned with the most sensitive of each of these groups.

Air pollutants could include gases, vapours, aerosols and, in some cases, biohazardous materials. A well designed system will prevent a target from receiving a harmful concentration of a pollutant.

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Most air pollution control systems involve a combination of several control techniques, usually a combination of technological controls and administrative controls, and in larger or more complex sources there may be more than one type of technological control. Ideally, the selection of the appropriate controls will be made in the context of the problem to be solved. What is the most susceptible target?

Step 1: Define emissions. The first part is to determine what will be released from the stack. All potentially harmful emissions must be listed.