Ozone chemical precursors

Intercontinental Transport and Chemical Transformation Inter-Tropical Convergence Zone International Tundra Experiment International Transport of Ozone and Precursors International Union for the Conservation of Nature and natural resources... 

Trichloroethane was a major solvent, particularly for cold and vapor degreasing. It was phased out for emissive uses in the United States in 1996 because of its ozone depletion potential. The only application left is as chemical precursor for HCFC-141b and HCFC-142b. However, both are subject to phaseout schedule of the Montreal Protocol,... 

Historically most attention has focused on SO2, and its oxidised wet form, sulphuric acid. Overall emissions of SO2 in the Community have declined in the last ten years and this trend may well continue. Without further abatement measures, this decline is not likely to be more than 15% by 2000. Recent investigations in Europe and work in the USA suggest that NOx emissions, which arise from both stationary and vehicle fossil fuel combustion and which are on a rising trend, may also contribute significantly to plant and tree damage. In particular ozone, of which NOx chemical precursor, can, at certain concentrations under summer climate conditions, cause damage or yield effects to some trees and plants, possibly in conjunction with SO2 and NOx ... 

VOCs react in the presence of sunlight to produce photochemical smog, a mixture of organic chemicals that can irritate the eyes and other mucous membranes. VOCs also constitute a major precursor chemical leading to ozone production. VOC levels across the United States fell, on average, by 20.4 percent between 1989 and 1998. 

Ultraviolet radiation (UVR) is a natural fraction of the solar radiation, and therefore has always influenced life in aquatic ecosystems. The development of oxygenic photosynthesis 2.5-2 J billion years ago (Holland 1984) led to drastic chemical changes in the Earth s oceans and atmosphere. The gradual increase in photosyn-thetically produced oxygen over millions of years was accompanied by a strong enrichment of it in the atmosphere, which ultimately acted as precursor for the ozone (03) layer in the stratosphere. 

There are a few reports on the combined application of ultrasound and ultraviolet light (UV) for the destruction of chemical pollutants. A study of the oxidation of humic acid and trihalomethane precursors with ozone revealed that the most effective destruction of the organic carbon compounds was achieved when both uv and ultrasound were used in combination with ozonation [35]. In other cases e. g. the removal of 1,1,1-tri-chloroethane from aqueous solutions, the combined application of ultrasound and UV proved to be more efficient than the use of either technique individually [36]. 

Developing control strategies for ozone is very different than for relatively unreactive species such as CO. In the latter case, the concentrations in air are a direct result of the emissions, and all things being equal, a reduction in emissions is expected to bring about an approximately proportional reduction in concentrations in ambient air. However, because O, is formed by chemical reactions in air, it does not necessarily respond in a proportional manner to reductions in the precursor emissions. Indeed, as we shall see, one can predict, using urban airshed or simple box models, that under some conditions, ozone levels at a particular... 

The continental biosphere is a large source of hydrocarbons. Quantification of these sources in toms of geophysical (e.g. temperature, humidity, light levels) and biogeochemical (soil physical and chemical properties, land use) parameters is much needed for inclusion in atmospheric models. The hydrocarbon oxidation mechanisms in the atmosphere should also be better understood, so that formation of ozone, carbon monoxide, partially oxidized gaseous hydrocarbons, and organic aerosol can be better quantified. The formation of organic aerosol from hydrocarbon precursors and then-capability to serve as cloud condensation nuclei are issues which need to be studied in depth. 

Glaze WH, Wallace JL, Wilcox D, Johansson KR, Scalf B, Noack R, Busch AW. Pilot scale evaluation of ozone-granular activated carbon combinations for trihalomethane precursor removal. McGuire MJ, Suffet IH eds. Advances in Chemistry Series, No. 202, Treatment of water by granular activated carbon. American Chemical Society, New York 1983 3 221-229. 

When the waste contains more complex molecules such as compounds refractory to oxidation with OH radicals, as well as in the presence of inorganic ions which can be precursor of long-life oxidants, the Faradic yield cannot be calculated by (8.3) and different alternatives have been proposed. Faouzi and co-worker (Faouzi et al. 2006) proposed a comparison between electrochemical oxidation at BDD anodes and Fenton and Ozone treatments for the removal of dyes a specific parameter OCC (oxygen-equivalent chemical-oxidation capacity) was proposed which is defined as the kg of 02 equivalent to the quantity of oxidant used in each AOP to treat 1 m3 of wastewater. As highlighted by the authors, the parameter OCC may only give information on the chemical efficiency of the oxidants, but it does not give any information related to the real cost of the treatment, as the oxidants can... 

Figure 3.3 and Table 3.1 are shown here to indicate the spread of available observations for model evaluation. Figure 3.3 shows a comparison of water vapor mixing ratio as predicted by WRF/Chem for the same time period, but compared to aircraft observations. Similar comparisons are available for other meteorological parameters as well as many chemical constituents, including Ozone, PM species and ozone precursors (Table 3.1). Detailed results are displayed on the WEB at http //www.al.noaa.gov/lCARTT/modeleval. 

Lurmann EW, Lloyd AC, Atkinson R (1986) A chemical mechanism for use in long-range transport/acid deposition computer modelling. J Geophys Res 91 10905-10936 Marcal V, Rivire ED, Held G, Cautenet S, Freitas S (2006) Modelling study of the impact of deep convection on the UTLS air composition - Part I analysis of ozone precursors. Atmos Chem Phys 6 1567-1584... 

The relation between ambient levels and precursor emissions is somewhat easier to identify for particulates than for ozone, because the chemical composition of individual particulates provides evidence for their origin sulfate particulates are associated with sulfur dioxide emissions organic particulates with specific VOCs, and so on. A variety of statistical methods have been used to identify source types for particulates based on chemical composition, especially in terms of trace metal components (e.g., Henry, 1992 Seinfeld and Pandis, 1998). This type of analysis requires sophisticated measurements of the chemical composition of individual particulates, rather than the more common measurement of summed concentrations. Statistical methods have also been used to gain information about ozone and ozone precursors (e.g., Buhr et al., 1995 Stehr et al., 2000). 

Regional scale episodes of elevated concentrations of photochemical oxidants occur every summer in Europe. During summertime, anticyclonic weather conditions, ozone concentrations steadily build up over several days and may exceed internationally-accepted criteria values (ref) set to protect human health, crops and trees [22]. There are no emissions of ozone into the atmosphere and all the ozone found close to the ground in pollution episodes has been formed there by chemical reactions involving the precursors, hydrocarbons and the nitrogen oxides, in the presence of sunlight. 

The main constituents of NOM in natural water are humic substances consisting of humic and fulvic acids. Humic substances are the precursors of THMs. These must be degraded before chlorine disinfection because once THMs are formed they cannot be removed by chemical oxidation. Ozonation can degrade humic substances into low molecular weight compounds that are less reactive toward chlorine, and hence can minimize the formation of... 

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