1.空气污染.doc

Causes of Air PollutionAir pollution is the introduction of chemicals, particulate matter(，颗粒物， ), or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere。Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants into the atmosphere. These sources can be classified into two major categories which are:.Anthropogenic sources (human activity) mostly related to burning different kinds of fuel。1.Industrial Emissions工业排放 Manufacturing facilities, power plants, and waste incinerators (垃圾焚烧炉 ) are all industries that emit high levels of carbon monoxide, organic compounds(有机化合物), and chemicals into the atmosphere, just to name a few. Possibly the most devastating thing about this particular cause is that it effects every single corner of the globe. There is not an ecosystem that isnt exposed to industrial emissions in some way shape or form. There have been efforts to limit the amount of harmful particulates and filter the materials which are produced by these facilities. However, there is a good amount of research that states that the damage has already been done and the regulations that are now being passed are too little too late.In addition to these typical industrial emission contributors, there are also a number of other culprits. Petroleum refineries release a variety of particulates and hydrocarbons(碳氢化合物) into the Earths atmosphere. Also, though a bit more rare, radioactive fallout(放射性沉降物 )from nuclear facilities is also one of the causes of air pollution.2 。Transport Burning the petroleum products to run automotive transport vehicles is the main cause of air pollution. The main pollutants like SO2, CO, CO2 are main gases being released into air due to transport vehicles.But, the extent of pollution due to transport vehicles is directly dependent upon the level of urbanisation城市化 density of vehiclesAs the urban development increases, the necessity of transport vehicles becomes inevitable. As the dependence on vehicle increases, the density of vehicle increases.Cities with very high population have recorded high level of air pollution due to vehicles. Vehicular pollution in many agglomerates like Delhi, Bombay, Calcutta, Bangalore, Pune is so high that a natural air with its natural composition has become rare.Some socially relevant issues related to vehicular pollution have been recently raised in public debates: Although vehicular transport is inevitable in cities, is it possible that individual ownership of vehicle could be avoided and public transport system could be more efficiently used. Is it necessary that a single travelling person use a four wheeler? Can we not partially replace the transport needs by electrically operated public transport systems than present petroleum dependent vehicles? Is there any possibility using electricity operated vehicles? 3. Chemicals, dust and controlled burn practices in agriculture and forestry management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement(温室气体减排). Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the germination (萌发) of some desirable forest trees, thus renewing the forest. 4. Fumes from paint, hair spray(发胶), varnish(油漆), aerosol sprays(喷雾剂) and other solvents(溶剂) 5 Waste deposition in landfills(堆填区), which generate methane.(甲烷) Methane is not toxic(窒息剂); however, it is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement 6 Military, such as nuclear weapons, toxic gases, germ warfare and rocketryNatural sources1 Dust from natural sources, usually large areas of land with little or no vegetation 2 Methane, emitted by the digestion of food by animals, for example cattle 3 Radon (氡)gas from radioactive decay(放射性衰变) within the Earths crust. Radon is a colorless, odorless, naturally occurring, radioactive noble gas(放射性惰性气体) that is formed from the decay of radium(镭衰变). It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking 4 Smoke and carbon monoxide from wildfiresAll forest fires emit carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and particulate matter. Carbon monoxide, which is a poisonous gas, can be emitted in large amounts during forest fires. Particulates, which are mixtures of soot, tars, and volatile organic substances, either solid or liquid, are emitted in large quantities from forest fires. The particulates, which can be smaller than 2.5 micrometers in diameter, if deeply inhaled into the lungs, can damage lung tissues and cause respiratory and cardiovascular problems. Nitrogen oxides are released at temperatures greater than 1,500 degree centigrade. Therefore nitrogen oxides are released in significant quantities only during the most severe fires. Sulfur dioxide emissions are significantly less serious with forest fires, as concentration of the dioxide in most forest fuels is usually less than 0.2 percent. However, forest fire sites with peat and muck soil may be exceptions. There are many other air pollution causes like wind erosion, pollen dispersal, evaporation of organic compounds, and natural radioactivity. However, these causes are usually not significant. Although there is no doubt that the impact of natural causes for air pollution can sometimes be drastic, take for example volcanic eruptions, but they are usually not frequent. Rather, the more significant air pollution causes are in fact caused by human activities, such as through the combustion of fuel by vehicles and power stations, waste incineration, etc. In other words, we have mainly ourselves to blame for our dirty air! 5 Vegetation, in some regions, emits environmentally significant amounts of VOCs(挥发性有机化合物) on warmer days. These VOCs react with primary anthropogenic pollutantsspecifically, NOx, SO2, and anthropogenic organic carbon compounds(化合物)to produce a seasonal haze of secondary pollutants. 6 Volcanicactivity, which produce sulfur硫，, chlorine氯, and ash particulates(灰烬污染)One of the most important natural causes of air pollution is volcanic eruption. The most problematic gases emi