Ozone levels

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. 

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. 

The discovery of ozone holes over Antarctica in the mid-1980s was strong observational evidence to support the Rowland and Molina hypothesis. The atmosphere over the south pole is complex because of the long periods of total darkness and sunlight and the presence of a polar vortex and polar stratospheric clouds. However, researchers have found evidence to support the role of CIO in the rapid depletion of stratospheric ozone over the south pole. Figure 11-3 shows the profile of ozone and CIO measured at an altitude of 18 km on an aircraft flight from southern Chile toward the south pole on September 21, 1987. One month earlier the ozone levels were fairly uniform around 2 ppm (vol). 

The updtitcd stmidard recognizes the current scientific view that exposure to ozone levels at and below the current standard causes significant adverse health clTccts in cliildrcn and in healthy adults engaged in outdoor activities... 

Ozone levels and peak power for Southern California Edison versus 4 P.M. temperature in Los Angeles as a predictor of smog. 

Mario Molina and Sherwood Rowland used Crutzen s work and other data in 1974 to build a model of the stratosphere that explained how chlorofluorocarbons could threaten the ozone layer. In 1985, ozone levels over Antarctica were indeed found to be decreasing and had dropped to the lowest ever observed by the year 2000, the hole had reached Chile. These losses are now known to be global in extent and it has been postulated that they may be contributing to global warming in the Southern Hemisphere. 

It is only recently that a decrease in stratospheric ozone levels attributable to the CFCs has been observed. In spite of the relatively large natural... 

The downward spectral irradiance data [Ed(X), the ambient UV radiation] were generated with the atmospheric model of Frederick and Lubin (27) and ozone levels measured during the course of this study (J.E. Frederick, pers. commun.). The relative degree of UV enhancement (%ENH) for each chamber was calculated as follows ... 

Based solely on this relationship, it has been predicted that the ozone concentration should be about 2 pphm at solar noon in the United States. Indeed [7], in unpolluted environments, ozone concentrations are usually in the range of 2-5 pphm. However, in polluted urban areas, ozone concentrations can be as high as 50 pphm. Peroxy radicals formed from hydrocarbon emissions cause this enhanced ozone concentration. These radicals oxidize nitric oxide to nitrogen dioxide, thereby shifting the above steady-state relationship to higher ozone levels. 

Since ozone is generated by photolytic reactions, anything which affects available sunhght will affect the ozone concentration. Consequently, ozone levels are the highest in the summer months, when the days are longer and the sun is more intense [42]. Similarly, ozone levels are highest near midday and decrease almost to zero at night [43]. Temperature has little effect on ozone formation. 

The length and amount of cracks is assessed according to the Bayer method [72,73]. The ISO standard ozone test conditions involve a test temperature of 40°C zE 1°C and an ozone level of 50 5 pphm, with a test duration of 72 h. Testing is done under static [72] and/or dynamic strain [73]. These are accelerated tests and should be used for the relative comparison of compounds, rather than for the prediction of long-term service life. The method is rather complicated and demands a long duration of ozone exposure. Therefore, in some cases the rate constants of the antiozonants reaction with ozone in solution are used instead to evaluate the efficiency of different antiozonants [74]. 

Fifteen tire brand-vehicle combinations were collected from Phoenix, AZ Los Angeles, CA Detroit, MI and Hartford, CT. Six different vehicle types and three different tire manufacturers were studied as detailed in Table 34.1. Vehicle-brand combinations are denoted by the vehicle type followed by the letter denoting the specific manufacturer, e.g., SUV/Minivan-A. The geographic locations were chosen based on ambient temperature and ozone level. Both on-road and full-size spare tires were collected ranging in age from two weeks to six years old. In total, over 1500 tires were analyzed in this study. A small number of tires from Miami, FI and Denver, CO were collected to evaluate the effects for road roughness on aging. No significant effect was observed and these tires were not included in the analysis. 

The revealed preference method is an indirect approach that is used in order to monetize use values. This method observes the real choice between money and the environmental goods. Methods often include observations of consumers or producers behaviour or actions, such as the hedonic price method and the production function method. The hedonic price method determines values from actual market transactions. These transactions are used to see how the price of a market commodity varies when a related environmental good changes, such as the effects of noise or air pollution on house prices. The production function method is used to estimate the value of the environmental effects on production. This method is suitable when consumption or production of a private good is affected by the environmental good. An example is the valuation of ground-level ozone levels by valuing the impact on the production of wheat or timber, which has market prices. The problem with the revealed preference method is that it does not contain all the individuals values that affect the WTP. 

Ozone layer depletion, stratospheric, 21 525-529 Ozone level, reduction in, 21 528 Ozone molecules, vibrationally excited, 27 774... 

Although the Chapman mechanism models the general shape of the profile of stratospheric ozone correctly, it seriously overestimates its concentration. To account for this discrepancy, a catalytic process which increases the rate of step 4 occurs (Figure 7.12). Trace amounts of radicals present in the stratosphere reduce natural ozone levels below those predicted by the Chapman scheme ... 

Evans, L. S. Bean leaf growth response to moderate ozone levels. Environ. Pbllut. 4 17-26, 1973. 

Walker, i. T., and J. C. Barlow. Response of indkator plants to ozone levels in Georgia. Phytopathology 64 1122-1127, 1974. 

The U.S. EPA defines as unhealthy ambient air containing 125 parts per biUion (ppb) of ozone. (This means the ordinary air we breathe.) In different regions of the United States, ozone alerts are issued when the ozone level is both higher and lower than this standard. Most regions have their own standards that range from 100 ppb to 350 ppb. 

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