Volatile organic compounds, atmospheric importance

Pollutant Distribution. Of particular importance for the aquatic ecosystem is the distribution of volatile substances, eg, gases and volatile organic compounds, between the atmosphere and water, and the sorption of compounds at soHd surfaces, eg, settling suspended matter, biological particles, sediments, and soils (41,42). 

Emissions to the atmosphere from ammonia plants include sulfur dioxide (SOj), nitrogen oxides (NOJ, carbon monoxide (CO), carbon dioxide (COj), hydrogen sulfide (HjS), volatile organic compounds (VOCs), particulate matter, methane, hydrogen cyanide, and ammonia. The two primary sources of pollutants, with typical reported values, in kilograms per ton (kg/t) for the important pollutants, are as follows ... 

For gas-phase sensors, both remarkable selectivity and very low LOD are important. Sensors featuring MIP recognition combined with SAW transduction can meet these requirements. The MIP-PZ chemosensors operating in gases are devised for two main applications, namely for indoor gas inspection and online monitoring of volatile organic compounds. The latter is essential to protect humans from threats of environmental atmospheric pollutants. 

Various other workers have reported on the determination of volatile organic compounds in soils [186,187] and landfill soils [188]. Soil fumigants such as methyl bromide have also been determined by this technique [189]. Trifluoroacetic acid is a breakdown product of hydrofluorocarbons and hydrochlorofluorocarbon refrigerant products in the atmosphere and, as such, due to the known toxicity of trifluoroacetic acid, it is important to be able to determine it in the atmosphere, water and in soil from an environmental point of view [190]. In this method the trifluoroacetic acid is extracted from the soil sample by sulfuric acid and methanol, which is then followed by the derivatisation of it to the methyl ester. The highly volatile methyl ester is then analysed with a recovery of 87% using headspace gas chromatography. Levels of trifluoroacetic acid in soil down to 0.2 ng/g can be determined by the procedure. 

Because of their electrical, optical, and redox properties as well as the thermal and chemical stability, the Pcs also have been tried in the detection of volatile organic compounds and poisonous gases, which is very important for environment and human health. In the past decades, the possible applications of Pc thin film as sensor for atmospheric gaseous pollutants have been extensively studied [73, 74], Langmuir-Blodgett films of some multinuclear and multidouble-decker lutetium Pcs have also been used for those measurements [75,76], More details about conductivity and sensing properties of Pcs can be found elsewhere [77,78]. 

So what are nitrogen oxides Where does they come from And why is there a concern about the amount that enters the atmosphere Nitrogen dioxide (NO2) is a brownish, highly reactive gas that is present in all urban atmospheres. N02 can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. Nitrogen oxides are an important precursor both to ozone (Oj) and acid rain, and may affect both terrestrial and aquatic ecosystems. The major mechanism for the formation of NO2 in the atmosphere is the oxidation of the primary air pollutant, nitric oxide (NO). NOx plays a major role, together with VOCs (Volatile Organic Compounds), in the atmospheric... 

Complete oxidation of hydrocarbons in air is a useful method for atmospheric purification, and has been sucessfully applied in automotive exhaust control. An important new area is the catalytic control of the emissions of volatile organic compounds (VOC) in a more general sense [1]. Many sources, low concentrations and wide temperature ranges can be involved. 

Gas-phase, solution-phase, and heterogeneous reactions all play important roles in atmospheric chemistry. The mean atmospheric composition is given in Table 1. N2, O2, and Ar comprise 99.9% of the atmosphere and, for all practical purposes, the relative proportion of these gases is constant in the lower 100 km of the atmosphere. We are concerned here with the fate of pollutants such as CO, volatile organic compounds, halocarbons, sulfur compounds, and nitrogen oxides, which are present in trace amounts and whose concentrations vary significantly both spatially and temporally. 

The American 1970 Clean Air Act defined ambient air quality standards (NAAQS) in the United States for atmospheric ozone, NO, lead, carbon monoxide, sulfur oxides, and PM-10 (particulate matter less than 10 p.m). The strategy to reduce levels of lead, NOx, PM-10, and to some extent carbon monoxide was to control emissions from automobiles that included the phasing-out of leaded fuel. As previously noted, ozone is a product of the photochemical reaction of volatile organic compounds with NOx (photochemical smog), so the balance between organic compounds and NOx pollutants is important in meeting target ozone levels (e.g., 0.12 ppm). Emissions from stationary sources is an important factor, and limits have been set for them. Because of low pressure drop requirements, coated monolithic catalysts... 

Volatile organic compounds, VOC s, are an Important class of air pollutants usually found in the atmosphere of all urban and Industrial areas. Toluene is one of these compounds and, due to Its noxious nature, several strategies have been Identified in order to reduce Its presence In indoor and Industrial emissions. 

Aldehydes are emitted directly into the atmosphere from a variety of natural and anthropogenic sources and are also formed in situ from the atmospheric degradation of volatile organic compounds (VOCs). The atmospheric fate of aldehydes is controlled by photolysis and reaction with hydroxyl (OH) or nitrate (NO3) radicals and, in the case of unsaturated compounds, reaction with ozone (Atkinson, 1994). The photolysis of aldehydes is of particular importance because it is a source of free radicals in the troposphere, and thus may significantly influence the oxidizing capacity of the lower atmosphere (Finlayson-Pitts and Pitts, 1986). 

Small carbonyl compounds are formed during the photochemical oxidation of many volatile organic compounds (VOC s), in urban as well as in rural areas. Photolysis and reaction with the OH radical are the most important initiation reactions for the atmospheric degradation of these compounds, and lead to the formation of peroxy radicals in the former case and either stable molecules and/or free radicals in the latter case (Finlayson-Pitts and Pitts, 1999). 

In this work atmospheric concentrations of a large number of non-methane volatile organic compounds (NMVOCs) emitted by different anthropogenic sources, in particular from traffic exhaust and solvent use, have been investigated. The results from the studies should provide more information about the relative importance of road traffic and solvent use to the total NMVOC emission in Europe. 

Low-molecular mass carbonyls are among the most abundant and ubiquitous volatile organic compounds in the atmosphere. They are produced from industrial activity and incomplete combustion of fossil fuels and biomass. Many aldehydes are also emitted indoors (plastic, foam insulation, lacquers, etc.). As a source of free radicals, aldehydes play an important role in the ozone formation, in urban smog events, as well as in the photochemistry of the unpolluted troposphere. Aldehydes are recognized irritants of the eye and respiratory tract, and often, carcinogenic and mutagenic characteristics are also attributed to them. 

The primary purpose of NO, controls under Title I is to reduce ambient concentrations of ozone. Tropospheric ozone pollution occurs at ground level and is the major component of urban smog. Ozone is a secondary pollutant formed in the atmosphere by reactions of volatile organic compounds (VOCs) and NO, in the presence of sunlight. The EPA established a national ambient air quality standard (NAAQS) for ozone in order to protect the public health and welfare. After two decades of efforts to reduce ozone concentrations, primarily through reductions in emissions of VOCs, tropospheric ozone remains a widespread and important problem. A recent study by the National Academy of Sciences and EPA concludes that NO. control is necessary for effective reduction of ozone in many areas. 

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