Pollutant Particles in the Atmosphere

Atmospheric particles may consist of organic or inorganic materials or mixtures of both. Solid pollutant particles include very small combustion nuclei residues from fuel combustion, cement dust, silica dust from sandblasting, and soil dust mobilized by cultivation practices. Sulfuric acid droplets produced by oxidation of pollutant sulfur dioxide in the atmosphere are the most common kind of pollutant liquid droplets. Many kinds of particles are of biological origin and can be considered pollutants when they contribute to respiratory problems. These include bacteria, bacterial spores, fungal spores, and pollen. 

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Atmospheric chemical processes can influence meteorological phenomena. One of the most obvious examples of this influence is the formation of rain droplets around pollutant particles in the atmosphere. 

Pollutant particles in the atmosphere have both direct and indirect effects. The most obvious direct effects are reduction and distortion of visibility. The light scattering effects of particles in a size range of 0.1-1 jm are especially pronounced because of interference phenomena resulting from the particles being about the same size as the wavelengths of visible light. An indirect effect of particles is their ability to serve as reaction sites for atmospheric chemical reactions. They also act as nucle-ation bodies upon which water vapor condenses. 

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... 

The chemical composition of particulate pollutants is determined in two forms specific elements, or specific compounds or ions. Knowledge of their chemical composition is useful in determining the sources of airborne particles and in understanding the fate of particles in the atmosphere. Elemental analysis yields results in terms of the individual elements present in a sample such as a given quantity of sulfur, S. From elemental analysis techniques we do not obtain direct information about the chemical form of S in a sample such as sulfate (SO/ ) or sulfide. Two nondestructive techniques used for direct elemental analysis of particulate samples are X-ray fluorescence spectroscopy (XRF) and neutron activation analysis (NAA). 

The sources of particles in the atmosphere are of much current interest. This is true from the viewpoint of both the geo-atmospheric scientist and the pollution control specialist. For the atmospheric chemist or geochemist, the identities and the relative contributions of sources are important for understanding 1) atmospheric element cycles and budgets, and 2) the chemical content of precipitation. 

Mercury is a volatile toxic pollutant. The map shows Hg(0) concentrations in the air near Earth s surface. Mercury is also found as Hg(II)( y) in clouds and on particles in the atmosphere. 

The cloud chemistry simulation chamber (5,6) provides a controlled environment to simulate the ascent of a humid parcel of polluted air in the atmosphere. The cloud forms as the pressure and temperature of the moist air decreases. By controlling the physical conditions influencing cloud growth (i.e. initial temperature, relative humidity, cooling rate), and the size, composition, and concentration of suspended particles, chemical transformation rates of gases and particles to dissolved ions in the cloud water can be measured. These rates can be compared with those derived from physical/chemical models (7,9) which involve variables such as liquid water content, solute concentration, the gas/liquid interface, mass transfer, chemical equilibrium, temperature, and pressure. 

To what extent are current emissions of pollutants causing measurable increases or accumulations of aerosol particles in the atmosphere ... 

The consideration up to this point has been on pollutant molecules in the atmosphere. Air pollution, however, can also be hazardous in more confined areas, such as those found in outdoor areas with limited air circulation, in buildings, rooms, and in other tight indoor areas with limited circulation. Confined air pollutants can be vapors, aerosols, or particles... 

The description of a large variety of meteorological phenomena is also based on the analysis of motion of a collection of drops in air. The recent increase in atmosphere pollution is a serious problem, which requires understanding the transfer of mechanical, chemical, and radioactive particles in the atmosphere. 

Two commercially available aerosol mass concentration analyzers have been described for the determination of aerosols and particulates [18], The instruments are both portable and relatively rugged and operate on ordinary commercial power. A portable system utilizing an electrostatic precipitator was described for mass concentration measurements in the range of airborne dust particles smaller than 10 /Am [19]. Chuan [20] also described a typical commercial instrument based on the piezoelectric quartz crystal microbalance for the rapid assessment of particular mass concentrations in the atmosphere. The adhesive coating used in the device is non-hygroscopic and non-reactive to the usual concentrations of pollutant gases in the atmosphere, such as CO, SO2, NOjt, and hydrocarbons. 

Substances with very low volatility (high values of the Koa coefficient) and very low water solubility (high Kaw coefficient) are added on group C ( single hop ). These substances are so non-volatile and not water soluble that they can be transported only bond to the suspended particles in the atmosphere or in the water. Because of this they contaminate relatively small areas around the pollution sources. 

Bloch P, Adams E, Van Landuyt J and Van Goe-THEM L (1980) Morphological and chemical characterization of individual aerosol particles in the atmosphere. In Versino B, ed. Proceedings Symposium Physico-Chemical Behaviour of Atmospheric Pollutants. EUR 6621, ECSC-EEC-EAEC, Brussels, Luxembourg. 

Burtscher, H., Leonardi, A., Steiner, D., Baltensperger, U., and Weber, A. (1993) Aging of combustion particles in the atmosphere—results from a field study in Zurich, Water Air Soil Pollut., 68, 137-147. 

Small particles ranging in size from a few hundredths of a micron to several tenths of a micron in diameter have a long residence time as a function of their size and can thereby be transported over long distances of hundreds and possibly thousands of kilometers prior to deposition. Basically two mechanisms are responsible for the deposition of acidic pollutants carried in the atmosphere. Final deposition of the acidic aerosol may occur either directly via sedimentation and impaction (dry deposition) or indirectly as an acidic solution (wet deposition) which is formed during condensation of ati spheric water vapor prior to, or collected during, rain events. Segregation of the relative contribution of wet and drg deposition processes is difficult and must be carefully assessed ... 

Particulate matter is found near roads and some industries, in smoke and haze it can be directly emitted from sources such as forest fires, and it can be formed when gases emitted from power plants and automobiles react in the air. The NAAQSs for particulate matter, revised in 2006, are set at 150 xg/m as the 24-h average for coarse particulates (2.5- to 10-pm diameter) and are set at 35 pg/m as the 24-h average for fine particulates (. 5-pm diameter) [12], Particle pollution is controlled by reducing directly emitted particles and by reducing emissions of pollutants that are gases when emitted, but form particles in the atmosphere. In the United States in 2006, the average concentration of fine particulates amounted to about 13 xg/m [13]. 

In what sense is acid rain a secondary air pollutant What is the chemistry behind the formation of most acid rain constituents Explain how particles in the atmosphere may be either primary or secondary air pollutants ... 

Particles in the atmosphere, which range in size from about one-half millimeter (the size of sand or drizzle) down to molecular dimensions, are made up of an amazing variety of materials and discrete objects that may consist of either solids or liquid droplets (Table 15.1). Particulates is a term that has come to stand for particles in the atmosphere, although particulate matter or simply particles, is preferred usage. Particulate matter makes up the most visible and obvious form of air pollution. Atmospheric aerosols are solid or liquid particles smaller than 100 pm in diameter. Pollutant particles in the 0.001 to 10 pm range are commonly suspended in the air near sources of pollution, such as the urban atmosphere, industrial plants, highways, and power plants. 

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