Pollutants interactions with atmospheric

Models of chemical reactions of trace pollutants in groundwater must be based on experimental analysis of the kinetics of possible pollutant interactions with earth materials, much the same as smog chamber studies considered atmospheric photochemistry. Fundamental research could determine the surface chemistry of soil components and processes such as adsorption and desorption, pore diffusion, and biodegradation of contaminants. Hydrodynamic pollutant transport models should be upgraded to take into account chemical reactions at surfaces. 

The lifetime of these species in the atmosphere is relatively short and if they were distributed evenly their harmful effects would be minimal. Unfortunately these man-made effluents are usually concentrated in localized areas and their dispersion is limited by both meteorological and topographical factors. Furthermore, synergistic effects mean that the pollutants interact with each other in the presence of sunlight, carbon monoxide, nitrogen oxide(s), and unburned hydrocarbons lead to photochemical smog, while when sulfur dioxide concentrations become appreciable, sulfur oxide-based smog is formed. 

Air pollution can be considered to have three components sources, transport and transformations in the atmosphere, and receptors. The source emits airborne substances that, when released, are transported through the atmosphere. Some of the substances interact with sunlight or chemical species in the atmosphere and are transformed. Pollutants that are emitted directiy to the atmosphere are called primary pollutants pollutants that are formed in the atmosphere as a result of transformations are called secondary pollutants. The reactants that undergo transformation are referred to as precursors. An example of a secondary pollutant is O, and its precursors are NMHC and nitrogen oxides, NO, a combination of nitric oxide [10102-43-9] NO, and NO2. The receptor is the person, animal, plant, material, or ecosystem affected by the emissions. 

Dry Deposition. Dry deposition occurs in two steps the transport of pollutants to the earth s surface, and the physical and chemical interaction between the surface and the pollutant. The first is a fluid mechanical process (see Fluid mechanics), the second is primarily a chemical process, and neither is completely characterized at the present time. The problem is confounded by the interaction between the pollutants and biogenic surfaces where pollutant uptake is enhanced or retarded by plant activity that varies with time (47,48). It is very difficult to measure the depositional flux of pollutants from the atmosphere, though significant advances were made during the 1980s and early 1990s (49,50). 

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

Other elements of weather and outdoor exposure can interact with UV radiation to accelerate degradation in degradable types of plastics. They include humidity, salt spray, wind, industrial pollutants, and atmospheric impurities such as ozone, biological agents, and temperature. The wavelengths that have the most effect on plastics range from 290 to 400 nm (2,900 to 4,000 A). 

The different greenhouse gases can have complicated interactions. Carbon dioxide may cool the stratosphere which slows the process that destroys ozone. Stratospheric cooling can also create high altitude clouds which interact with chlorofluorocarbons to destroy ozone. Methane may be produced or destroyed in the lower atmosphere at various rates, which depend on the pollutants that are present. Methane can also affect chemicals that control ozone formation. 

Many of the processes responsible for isotope fractionations in the Earth s atmosphere may also occur in the atmospheres of other planetary systems, such as the atmospheric escape of atoms and molecules to outer space. Likely unique to Earth are isotope fractionations related to biological processes or to interactions with the ocean. One aspect of atmospheric research which has great potential for the application of stable isotope investigations is the study of anthropogenic pollution. 

Interactions of Gaseous Air Pollutants with Atmospheric Aqueous Solutions... 

The toxicology-based conclusion that the minimum concentration for 2-nitrofluoranthene to be an important human cell mutagen is 1 p.g/g, coupled with air quality sampling data showing its concentrations in respirable particles sampled from ambient air can in fact reach 10 pg/g, provides a useful example of a productive symbiotic interaction between atmospheric chemists and toxicologists. Such interactions are essential for reliable risk assessments of air pollution and human health effects of complex combustion-generated mixtures of gases and particles. 

Grosjean, D., K. Fung, and J. Harrison, Interactions of Polycyclic Aromatic Hydrocarbons with Atmospheric Pollutants, Environ. Sci. Technol., 17, 673-679(1983). 

The air emissions of fossil fuel combustion are dispersed and diluted within the atmosphere, eventually falling or migrating to the surface of the Earth or ocean at various rates. Until recently, most attention was focused on the so-called primary pollutants of fossil fuel combustion that are harmful to human health oxides of sulphur and nitrogen, carbon monoxide, suspended particles (including soot), heavy metals, and products of incomplete combustion. These pollutants are most concentrated in urban or industrialized areas close to large or multiple sources. However, the primary pollutants may interact with each other, and with atmospheric constituents and sunlight, forming secondary pollutants that disperse far beyond the urban-... 

Another debatable approach to pollution control involves the methods currently used to reduce hydrocarbons and CO in automotive exhausts. The need to control CO is based on its direct health effects while the need to control the hydrocarbons is based on their interactions with the N02 photolytic cycle which leads to elevated concentrations of N02, 03, peroxyacyl nitrates, and aerosols. The solution adopted was to increase the efficiency of the combustion process, thereby reducing hydrocarbon and CO emissions. Unfortunately, the method adopted also leads to dramatic increases in NO emissions. When this increase in NO was objected to, the answer came back that increased NO in the atmosphere is beneficial since it rapidly reacts with and destroys ozone, one of the very health-related substances requiring control. This is another example of failure to view the total air pollution system. Of course NO destroys 03, but one product of this reaction is N02 which is also detrimental to health. Furthermore, this N02 is the beginning point of sunlight absorption which leads to all the products of photochemical interactions. In a certain location excess NO will tend to reduce 03 levels. However, downstream of these locations excess N02 will promote more photochemical reactions and perhaps even higher ozone levels. In part this nonsolution to automotive pollution may be a major cause of the substantial increases in ozone in many areas during the past few years. This automotive example clearly illustrates the need for in-depth analysis when plans are made to change any part of the system of air pollution. Decisions based on such an analysis are all the more important because the tradeoffs involve human health and welfare. 

In the next section, you will see how gases in the atmosphere interact with the Sun s light. You will also find out about the dangers of gas pollution. 

Chlorofluorocarbons (CFCs) are an important class of polluting gases that are not usually caused by burning fossil fuels. CFCs are stable and harmless near the ground. When they make their way up into the atmosphere, however, they interact and interfere with atmospheric processes. In particular, these gases interfere with the production and reactions of ozone, 03. You will learn more about CFCs later in this section. 

Sulfur-35 was also used to determine the source of the sulfate in stream water in a highly polluted watershed in the Czech Republic (Novak et al., 2003). The sulfate input to this watershed has decreased over the past decade because of new controls on sulfur emissions, but the watershed continues to export sulfate far in excess of the atmospheric loading at the present time. Measurement of in runoff indicates that none of the recently deposited sulfate is exiting in the system. Apparently the atmospheric sulfate interacts with the soil layers and consequently takes more than a year to be removed from the watershed (Novak et al., 2003). 

Strong acids from atmospheric pollutants interact in the atmosphere with bases... 

---