Ozone emission

Public concern about risk ranges from earthquakes, fires, and hurricanes to asbestos, radon emissions, ozone depletion, toxins in our food and water, and so on. Many of the public s worries are out of proportion, because the fear is eidier overestimated or at times underestimated The risks given die most publicity and attention receive the greatest coiicem, while the ones diat are more familiar and accepted are given less thought. 

When a monitoring site is selected, it is important to take account of environmental features. For example, ozone measured in or near automotive traffic can drop to 50% of the areawide value, owing to reaction with the nitric oxide firom exhaust emission. Ozone measured 7.5 m from a large tree in green leaf can drop to 70% of the areawide value, but it may also be reduced within 1 m of shrubs and grass. Paint, asphalt, concrete, dry soil, and dead vegetation are not as reactive and so have less effect. Peak ozone values observed in sunlit windscreened. 

In the review by Armor [1] a variety of pollutants are discussed with a focus on commercially applied processes using catalysis as a solution. Issues such as the removal of NO.v, SO.v, chlorofluorohydrocarbons (CFC), VOC, carbon monoxide, auto exhaust emission, ozone, nitrous oxide, byproducts from chemicals production, odor control, and toxic gas removal are discussed. In another review Armor [2] discusses specific topics such as monolith technology, new catalytic materials, and specific processes. Additionally, key suggestions for future research effort are given. 

The methodology for impact assessment is widely accepted and ISO standards have been established to compare and quantify the various weighing factors. The assessment consists of weighing the classes to integrate the environmental profiles such as effects on GHG emission, ozone depletion, acidification, or eutrophication. It is however unrealistic to desire unification into one environmental impact number for widely diverse ecological and economical effects. 

Cradle-to-gate non Type of waste GHG emissions Ozone Acidification Eutrophication non-renewable energy treatment assumed (kgC02cq./ precursors (gS02eq.) (gP04eq.)... 

The sample is burned in oxygen at 1000°C. Nitrogen oxide, NO, is formed and transformed into NO2 by ozone, the NO2 thus formed being in an excited state NO. The return to the normal state of the molecule is accompanied by the emission of photons which are detected by photometry. This type of apparatus is very common today and is capable of reaching detectable limits of about 0.5 ppm. 

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances. 

Lowi, A. and W.P.L. Carter (1990), A method lor evaluating the atmosphere ozone impact of actual vehicle emissions . SAE paper No. 90-0710, International congress and exposition, Detroit, MI. 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

Emissions from methanol vehicles are expected to produce lower HC and CO emissions than equivalent gasoline engines. However, methanol combustion produces significant amounts of formaldehyde (qv), a partial oxidation product of methanol. Eormaldehyde is classified as an air toxic and its emissions should be minimized. Eormaldehyde is also very reactive in the atmosphere and contributes to the formation of ozone. Emissions of NO may also pose a problem, especiaHy if the engine mns lean, a regime in which the standard three-way catalyst is not effective for NO reduction. 

Confirmation of the destmetion of ozone by chlorine and bromine from halofluorocarbons has led to international efforts to reduce emissions of ozone-destroying CPCs and Halons into the atmosphere. The 1987 Montreal Protocol on Substances That Deplete the Ozone Layer (150) (and its 1990 and 1992 revisions) calls for an end to the production of Halons in 1994 and CPCs, carbon tetrachloride, and methylchloroform byjanuary 1, 1996. In 1993, worldwide production of CPCs was reduced to 50% of 1986 levels of 1.13 x 10 and decreases in growth rates of CPC-11 and CPC-12 have been observed (151). 

Although the naturally occurring concentration of ozone at the earth s surface is low, the distribution has been altered by the emission of pollutants, primarily by automobiles but also from industrial sources which lead to the formation of ozone. The strategy for controlling ambient ozone concentrations arising from automobile exhaust emissions is based on the control of hydrocarbons, CO, and NO via catalytic converters. As a result, peak ozone levels in Los Angeles, for instance, have decreased from 0.58 ppm in 1970 to 0.33 ppm in 1990, despite a 66% increase in the number of vehicles. 

Because of the necessity to comply with national standards for ground-level ozone, some states are planning another phase of more stringent NO emissions limits which may take place in the eady 2000s. These additional post-RACT reductions may affect plants of all sizes and types, but are likely to focus on major sources. The deadline for compliance in the most extreme areas is 2010. For severe nonattainment areas (O levels 0.181—0.280 ppm), including many coastal areas in the Northeast, from northern Virginia to southern Maine, compliance must be achieved by November 2005 to November 2007. Serious ozone nonattainment areas (O levels 0.161—0.180 ppm) are expected to be in compliance by November 1999. Moderate noncompHance areas must comply by November 1996. 

VOC Emissions Reduction Approach. The Rule 66-type approach focuses on solvent composition further developments have led to regulatory approaches that emphasize overall VOC emission reduction. Even though the more reactive solvents react near their emission point, all VOC compounds eventually react to form ozone pollution. This may occur some distance downwind, increasing ozone levels in areas which have low artificial emissions. 

VOC Emissions Reduction/Ozone Attainment. Tide I of the 1990 Amendments continues the process of diminishing VOC emissions from all sources to reduce o2one concentrations. A compliance timetable by category has been estabUshed, which depends on the level of current o2one concentration. The definition of a major source also depends on the o2one nonattainment category ... 

Chemiluminescence. Chemiluminescence (262—265) is the emission of light duting an exothermic chemical reaction, generaUy as fluorescence. It often occurs ia oxidation processes, and enzyme-mediated bioluminescence has important analytical appHcations (241,262). Chemiluminescence analysis is highly specific and can reach ppb detection limits with relatively simple iastmmentation. Nitric oxide has been so analyzed from reaction with ozone (266—268), and ozone can be detected by the emission at 585 nm from reaction with ethylene. 

The demand for trichloroethylene grew steadily until 1970. Since that time trichloroethylene has been a less desirable solvent because of restrictions on emissions under air pollution legislation and the passage of the Occupational Safety and Health Act. Whereas previously the principal use of trichloroethylene was for vapor degreasing, currentiy 1,1,1-trichloroethane is the most used solvent for vapor degreasing. The restrictions on production of 1,1,1-trichloroethane [71-55-6] from the 1990 Amendments to the Montreal Protocol on substances that deplete the stratospheric ozone and the U.S. 

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