Pollutants gaseous

Gaseous pollutants commonly present in polluted atmospheres are carbon dioxide (CO2), sulphur dioxide (SO2), and nitrogen oxides (NO , ). Locally, depending on the type of 

Sulphur dioxide originates essentially from the combustion of gas oil and coal. Sources are, therefore, thermal power stations generating electricity, central or individual heating plants and industrial plants. Transport (cars, industrial vehicles) is not a significant source of sulphur dioxide, especially since in Europe the sulphur concentration in diesel fuel has been decreased from 0.20 to 0.05%. 

The concentration of sulphur dioxide (SO2) in the atmosphere varies within a very wide range, depending on the activity of the site, the type of collective or individual heating, the means of transport and the main wind direction. For typical atmospheres, the usual concentrations are 

The sulphur dioxide concentration of the atmosphere of large cities varies within a wide range (Table C.2.3). 

Sulphur dioxide is highly soluble in water (Table C.2.4) and dissolves easily in the moisture film present on the surface of the metal. With water, it forms sulphuric anhydride (H2SO3) and then sulphuric acid (H2SO4). This reaction is catalysed by soot and certain dusts. The medium becomes acidic pH values of 3 or 4 are often found. 

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Incineration. Incinerators were discussed in Sec. 11.1. When incinerators are used to treat gaseous pollutants in relatively low concentration, auxiliary firing from fuel or other waste material normally will be necessary. The capital and operating costs may be high. In addition, long duct lines are often necessary. 

The short-term exposure of humans, animals, and plants to gaseous pollutants is more severe than that for pollutants in other matrices. Since the composition of atmospheric gases can show a substantial variation over a time, the continuous monitoring of atmospheric gases such as O3, CO, SO2, NH3, H2O2, and NO2 by in situ sampling is important. 

Sampling of Gaseous Pollutants. Gaseous poUutant detection is dependent upon the chemistry of the material involved. 

W. Ruch, ed.. Chemical Detection of Gaseous Pollutants, Ann Arbor Science PubHshers, Inc., Ann Arbor, Mich., 1966. 

R. Gdsar, H. Preier, G. Schmidtke, and G. ResteUi, eds.. Monitoring of Gaseous Pollutants by Tunable Diode Lasers, D. Reidel Publishing Co., Dordrecht, Germany, 1987. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

Gaseous Pollutants Gaseous pollutants may be classified as inorganic or organic. Inorganic pollutants consist of ... 

The most common gaseous pollutants and their major sources and significance are presented in Table 25-11. 

TABLE 25-11 Typical Gaseous Pollutants and Their Principal Sources and Significance... 

Some of the more common plume-rise equations have been summarized by Buonicore and Theodore (Industrial Control Equipment for Gaseous Pollutants, vol. 2, CRC Press, Boca Raton, Florida, 1975) and include ... 

In most processes involving the absorption of a gaseous pollutant from an effluent gas stream, the gas stream is the processed fluid hence, its inlet condition (flow rate, composition, and temperature) are usually known. The temperature and composition of the inlet liq-... 

Of the three categories, the packed column is by far the most commonly used for the absorption of gaseous pollutants. Miscellaneous gas-absorption equipment could include acid gas scrubbers that are commonly classified as either wet or diy. In wet scrubber systems, the absorption tower uses a hme-based sorbent liquor that reacts with the acid gases to form a wet/solid by-product. Diy scrubbers can be grouped into three catagories (1) spray diyers (2) circulating spray diyers and (3) dry injection. Each of these systems yields a diy product that can be captured with a fabric filter baghouse downstream and... 

Although the continuous-countercurrent type of operation has found limited application in the removal of gaseous pollutants from process streams (Tor example, the removal of carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide), by far the most common type of operation presently in use is the fixed-bed adsorber. The relatively high cost of continuously transporting solid particles as required in steady-state operations makes fixed-bed adsorption an attractive, economical alternative. If intermittent or batch operation is practical, a simple one-bed system, cycling alternately between the adsorption and regeneration phases, 1 suffice. 

FIG. 25-9 Eq uilibrium partial pressures for certain gases on molecular sieves. (A. ]. Buonicore and L. Theodore, Industrial Control Equipment for Gaseous Pollutants,-oo/. I, CRC Fress, Boca Raton, Fla., 1975.)... 

Particulates Procedures for testing a particulate source are more detailed than those used for sampling gases. Because particulates exhibit inertial effects and are not uniformly distributed within a stack, sampling to obtain a representative sample is more complex than for gaseous pollutants. EPA Method 5 (as shown in Fig. 25-32) is the most widely used procedure for determination of particulate emissions from a stationary source. In-stack samphng guidehnes are presented in EPA Method 17. 

What are the two primary gaseous pollutants that transform to fine-particle form during long-range transport ... 

Gaseous pollutant Monitoring site % days 1 hr 1 day 1 month 1 ytjM... 

Pollutant effects on the atmosphere include increased parhculate matter, which decreases visibility and inhibits incoming solar radiahon, and increased gaseous pollutant concentrations, which absorb longwave radiation and increase surface temperatures. For a detailed discussion of visibility effects, see Chapter 10. 

One of the methods of controlling air pollution mentioned in the previous chapter was pollution removal. For pollution removal to be accomplished, the polluted carrier gas must pass through a control device or system, which collects or destroys the pollutant and releases the cleaned carrier gas to the atmosphere. The control device or system selected must be specific for the pollutant of concern. If the pollutant is an aerosol, the device used will, in most cases, be different from the one used for a gaseous pollutant. If the aerosol is a dry solid, a different device must be used than for liquid droplets. 

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