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Critical Load
In the study of air pollution, a critical load is defined as "a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge". Air pollution research in relation to critical loads has focused on nitrogen and sulfur pollutants. After these pollutants are emitted into the atmosphere, they are subsequently deposited into ecosystems. Both sulfur and nitrogen deposition can acidify surface waters and soils. As added acidity lowers the pH of water, fish and invertebrate health are negatively impacted.Greaver, T. L., T. J. Sullivan, J. D. Herrick, M. C. Barber, J. S. Baron, B. J. Cosby, M. E. Deerhake, R. L. Dennis, J.-J. B. Dubois, C. L. Goodale, A. T. Herlihy, G. B. Lawrence, L. Liu, J. A. Lynch, and K. J. Novak. 2012. Ecological effects of nitrogen and sulfur air pollution in the US: what do we know? Frontiers in Ecology and the Environment 10:365-37 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Air Pollution
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types of air pollutants, such as gases (including ammonia, carbon monoxide, sulfur dioxide, nitrous oxides, methane, carbon dioxide and chlorofluorocarbons), particulates (both organic and inorganic), and biological molecules. Air pollution can cause diseases, allergies, and even death to humans; it can also cause harm to other living organisms such as animals and food crops, and may damage the natural environment (for example, climate change, ozone depletion or habitat degradation) or built environment (for example, acid rain). Air pollution can be caused by both human activities and natural phenomena. Air pollution is a significant risk factor for a number of pollution-related diseases, including respiratory infections, heart disease, COPD ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Level
The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the density is so low that the molecules are essentially collisionless. In the case of bodies with substantial atmospheres, such as Earth's atmosphere, the exosphere is the uppermost layer, where the atmosphere thins out and merges with outer space. It is located directly above the thermosphere. Very little is known about it due to lack of research. Mercury, the Moon, Ceres, Europa, and Ganymede have surface boundary exospheres, which are exospheres without a denser atmosphere underneath. The Earth's exosphere is mostly hydrogen and helium, with some heavier atoms and molecules near the base. Surface boundary exosphere Mercury, Ceres and several large natural satellites, such as the Moon, Europa, and Ganymede, have exospheres without a denser atmo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tropospheric Ozone
Ground-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer (2 to 8 parts per million ozone) exists which is located between 10 and 50 kilometers above the Earth's surface. The troposphere extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. Ground-level or tropospheric ozone is created by chemical reactions between NOx gases (oxides of nitrogen produced by combustion) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Non-methane Volatile Organic Compound
Non-methane volatile organic compounds (NMVOCs) are a set of organic compounds that are typically photochemically reactive in the atmosphere—marked by the exclusion of methane. NMVOCs include a large variety of chemically different compounds, such as benzene, ethanol, formaldehyde, cyclohexane, 1,1,1-trichloroethane and acetone. Essentially, NMVOCs are identical to volatile organic compounds (VOCs), but with methane excluded. Methane is excluded in air-pollution contexts because it is not toxic. It is however a very potent greenhouse gas, with low reactivity and thus a long lifetime in the atmosphere. An important subset of NMVOCs are the non-methane hydrocarbons (NMHCs). Sometimes NMVOC is also used as a sum parameter for emissions, where all NMVOC emissions are added up ''per weight'' into one figure. In absence of more detailed data, this can be a very coarse parameter for pollution (e.g. for summer smog or indoor air pollution). The major sources of NMVOCs include vegeta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrogen Oxide
Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide * Nitrogen trioxide (), or nitrate radical *Nitrous oxide (), nitrogen(0,II) oxide *Dinitrogen dioxide (), nitrogen(II) oxide dimer *Dinitrogen trioxide (), nitrogen(II,IV) oxide *Dinitrogen tetroxide (), nitrogen(IV) oxide dimer *Dinitrogen pentoxide (), nitrogen(V) oxide, or nitronium nitrate *Nitrosyl azide (), nitrogen(−I,0,I,II) oxide * Nitryl azide () *Oxatetrazole () *Trinitramide ( or ), nitrogen(0,IV) oxide Anions *Nitroxide () * Nitrite ( or ) *Nitrate () *Peroxynitrite ( or ) *Peroxynitrate ( or ) *Orthonitrate (, analogous to phosphate ) *Hyponitrite ( or ) *Trioxodinitrate or hyponitrate ( or ) *Nitroxylate ( or ) * Dinitramide ( or ) Cations * Nitrosonium ( or ) * Nitronium ( or ) Atmospheric sciences In atmospheric chemistry: * (or NO''x'') refe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to 45% of the world's food and fertilizers. Around 70% of ammonia is used to make fertilisers in various forms and composition, such as urea and Diammonium phosphate. Ammonia in pure form is also applied directly into the soil. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products. It is mainly collected by downward displacement of both air and water. Although common in nature—both terrestrially and in the outer planets of the Solar System—and in wide use, ammonia is both caust ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfur Dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activity and is produced as a by-product of copper extraction and the burning of sulfur- bearing fossil fuels. Structure and bonding SO2 is a bent molecule with ''C''2v symmetry point group. A valence bond theory approach considering just ''s'' and ''p'' orbitals would describe the bonding in terms of resonance between two resonance structures. The sulfur–oxygen bond has a bond order of 1.5. There is support for this simple approach that does not invoke ''d'' orbital participation. In terms of electron-counting formalism, the sulfur atom has an oxidation state of +4 and a formal charge of +1. Occurrence Sulfur dioxide is found on Earth and exists in very small concentrations and in the atmosphere at about 1 ppm. On other planets, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lower atmosphere to (dioxygen). Ozone is formed from dioxygen by the action of ultraviolet (UV) light and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the latter, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation. Ozone's odour is reminiscent of chlorine, and detectable by many people at concentrations of as little as in air. Ozone's O3 structure was determined in 1865. The molecule was later proven to have a bent structure and to be weakly diamagnetic. In standard conditions, ozone is a pale blue gas that condenses at cryogenic temperatures to a dark blue liquid and finally a violet-black soli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplankton productivity". Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions. Eutrophication can affect freshwater or salt water systems. In freshwater ecosystems it is almost always caused by excess phosphorus. In coastal waters on the other hand, the main contributing nutrient is more likely to be nitrogen, or nitrogen and phosphorus together. This depends on the location and other factors. When occurring naturally, eutrophication is a very slow process in which nutrients, especially phosphorus compounds and organic matter, accumulate in water bodies. These nutrients deriv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soil Acidification
Soil acidification is the buildup of hydrogen cations, which reduces the soil pH. Chemically, this happens when a proton donor gets added to the soil. The donor can be an acid, such as nitric acid, sulfuric acid, or carbonic acid. It can also be a compound such as aluminium sulfate, which reacts in the soil to release protons. Acidification also occurs when base cations such as calcium, magnesium, potassium and sodium are leached from the soil. Soil acidification naturally occurs as lichens and algae begin to break down rock surfaces. Acids continue with this dissolution as soil develops. With time and weathering, soils become more acidic in natural ecosystems. Soil acidification rates can vary, and increase with certain factors such as acid rain, agriculture, and pollution. Causes Acid rain Rainfall is naturally acidic due to carbonic acid forming from carbon dioxide in the atmosphere. This compound causes rainfall pH to be around 5.0-5.5. When rainfall has a lower pH than na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequence of database operations that satisfies the ACID properties (which can be perceived as a single logical operation on the data) is called a ''transaction''. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. In 1983, Andreas Reuter and Theo Härder coined the acronym ''ACID'', building on earlier work by Jim Gray who named atomicity, consistency, and durability, but not isolation, when characterizing the transaction concept. These four properties are the major guarantees of the transaction paradigm, which has influenced many aspects of development in database systems. According to Gray and Reuter, the IBM Informa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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