Air pollution is the introduction of chemicals, particulate matter, or microscopic organisms into the atmosphere; in particular, when concentrations of those substances cause adverse metabolic change to humans or other species. The most common and widespread air pollutants include carbon monoxide, sulfur dioxide, nitrogen oxides and particulate matter.
Presently, the greatest occurrences of air pollution are in China, India, Indonesia, South Africa, Brazil, Mexico and Argentina. Each year air pollution is the cause of millions of human deaths, and even larger numbers of respiratory, circulatory, and cancer-related disease occurrences. Also, indoor air pollution is a significant source of human death and disease—mortality and morbidity—through indoor burning of wood and charcoal (especially in developing countries), tobacco smoking, radon trapping and a host of chemical substances found in paints, printing supplies and cleaning products.
An increase of natural background concentrations to concentrations of a few micrograms per cubic meter of such common pollutants as sulfur dioxide, nitrogen oxides and ammonia may produce, for instance, increased growth of forests; however, higher levels of these chemicals produce such adverse effects on forests as decreased growth, greater susceptibility to diseases and pests, and ultimately to forest die-back.
Indoor air pollution refers to the occurrence of contaminants within a home, workplace (or other inhabited enclosure) arising from such sources as fuel combustion...
Earth's atmospheric airLast Updated on 2014-04-02 14:56:48The Earth's atmospheric air is a colorless, odorless and tasteless mixture of gases consisting mostly of nitrogen (N2) and oxygen (O2). It is the part of Earth's atmosphere that humans and all other animals breathe in order to obtain the oxygen needed to sustain life.
The Earth's atmosphere not only contains the air we breathe, it also holds clouds of moisture (water vapor) that become the water we drink. Furthermore, it protects us from meteors and harmful solar radiation and warms the Earth's surface by heat retention. In effect, the atmosphere is an envelope that protects all life on Earth.
The air may contain pollutants that originate from a variety of sources such as our industries and our vehicles, and can directly or indirectly affect our health and the natural environment. These effects may be experienced near the sources of air pollution and some air... More »
RespirationLast Updated on 2014-01-31 16:43:42Respiration is the gas exchange effected by living organisms for the purpose of sustaining vital metabolic processes. In the case of most animals, oxygen is taken into the organism, and carbon dioxide is expelled. In the case of plants, the inverse process occurs of consuming carbon dioxide and expelling oxygen as a waste gas.
Respiration may also be viewed at a cellular level, examining gas exchange at the cell wall; for very simple organisms, such as unicellular lifeforms, the process of gas exchange with the environment is simplified, so that cellular wall gas exchange is the totality of respiration for such an organism.
In the case of some bacteria and archaea, respiration sometimes occurs without any oxygen, and alternative molecular gases such as hydrogen sulfide or methane may participate in respiration and subsequent cellular metabolic reactions. Often such organisms are... More »
Carbon monoxideLast Updated on 2014-01-16 09:44:12Carbon monoxide (CO), also referred to as carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. Exposure to high levels of carbon monoxide is extremely toxic to humans and animals. Conversely, small amounts of carbon monoxide are produced in normal animal metabolism and it is thought to have some normal biological functions.
Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest member of the class of inorganic compounds known as oxocarbons which includes carbon dioxide (CO2), carbon suboxide (C3O2), mellitic anhydride (C12O9) and many others. When combined with a metal (i.e. an organometallic complex), the carbon monoxide is a ligand called carbonyl: for example, in nickel carbonyl with the formula Ni(CO)4.
Carbon monoxide is produced by the partial combustion of carbon-containing substances. It is produced... More »
Accidental release source termsLast Updated on 2013-12-18 14:53:28
Accidental release source terms are the mathematical equations that quantify the flow rate at which accidental releases of air pollutants into the ambient environment can occur at industrial facilities such as petroleum refineries, natural gas processing plants, petrochemical and chemical plants, oil and gas transportation pipelines, and many other industrial facilities. Accidental releases in such facilities may occur through acts of nature (e.g., floods, hurricanes or earthquakes), operational errors, faulty design or inadequate maintenance.
Governmental regulations in a many countries require that the probability of such accidental releases be analyzed and their quantitative impact upon the environment and human health be determined so that mitigating steps can be planned and implemented.
There are a number of mathematical calculation methods for determining the flow rate... More »
HydrodesulfurizationLast Updated on 2013-12-15 23:43:02Hydrodesulfurization (HDS) or Hydrotreating is a catalytic chemical process widely used to remove sulfur compounds from refined petroleum products such as gasoline or petrol, jet fuel, diesel fuel, and fuel oils. One purpose for removing the sulfur is to reduce the sulfur dioxide emissions resulting from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion.
Another important reason for removing sulfur from the intermediate product naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts platinum and rhenium in the catalytic reforming units that are subsequently used to upgrade the of the naphtha streams.
Hydrogenation of the sulfur compounds results in the formation of undesirable,... More »
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