Ozone sources

Ozone decay was measured in an office, a home, and several metal test facilities. Measurements were carried out with a Mast ozone meter and an MEC chemiluminescence ozone detector. The latter was calibrated with a stable ozone source and the epa neutral buffered potasaum iodide procedure. (It was noted over a wide range of concentrations that the mec meter measurements were consistently higher than those of the Mast meter by a factor of 1.3. That this is essentially identical with the findings of the DeMore committee is interesting.) Ozone generated by a positive corona ionizer was introduced into the test facilities. Ozone decay in a metal-walled room was found to be first-order, with the rate constant... 

FIGURE 6-2 Ozone source and manifold system. Adapted from Hodgesonet al. 

For reliable calibrations, it was necessary to develop a stable and reproducible ozone source that could produce ozone in air at concentrations smaller than parts per million. After this was accomplished, several different versions were engineered they are now available commercially from vendors of most ozone-monitoring instruments. The factors affecting the production and survival of oxygen species other than ozone are discussed in Chapter 12. Care must be taken to prevent these species from creating interference when ozone is generated for instrument calibration. 

Hodgeson, J. A., R. K. Stevens, and B. E. Martin. A stable ozone source applicable as a secondary standard for calibration of atmospheric monhens, pp. 149-158. In J. Scales, Ed. Air Quality InstrumentatkMi. Vol. 1. Selected Papers from International Symposia Presented by the Instrument Society of America. Pittsburgh Instrument Society of America. 1972. 

To begin investigations we need to define the reaction system more exactly. This consists of at least an ozone source, a water to be ozonated with one or more compounds of interest M, and a reaction vessel (a reactor). The reactor could be a stirred tank reactor and could look like Figure 1 -2. Some of the parameters necessary to characterize the system are summarized in Table 1-1 ... 

Since ozone is an unstable molecule, ozone has to be generated on-site. The various methods of ozone production differ in their working principles and ozone sources. The methods and their differences are summarized in Table 2-2. 

Method of Ozone generation Working Principle Ozone Source Field of Application... 

Ozone source - air or 02 high-purity feed-water, conductivity < 20 pS cm 1... 

In this study we will present aspects of STE in relation with the budget and concentrations of ozone in the troposphere, specifically in the Northern Hemisphere. Firstly, we present ozone observations in the tropopause region from the measurement campaign MOZAIC, and discuss their correlation with potential vorticity. The results have been used to improve the parameterization of stratospheric ozone in a coupled tropospheric chemistry - general circulation model. We will show examples of the performance of the model regarding the simulation of ozone in the tropopause region, and present the simulated seasonality of cross-tropopause ozone transport in relation to other tropospheric ozone sources and sinks. Finally, we will examine and compare the influence of cross-tropopause transports to surface ozone concentrations for simulations with contemporary, pre-industrial, and future emission scenarios. 

General Ozonolysis. A Welsbach T-23 ozonator was used as the ozone source. Its sample stream output was 0.5 mmole 03/minute. 

The dried oxygen is introduced into the ozone source under a pressure of 8 p.s.i. (415 mm. Hg) and with a voltage of 110 5 volts applied to the ozone instrument. The flow valve indicating the rate of flow for ozone is set at 0.1 standard cubic feet per minute (2.8 l./minute). The nitrogen-(IV) oxide is taken from the tank as a slow gas stream by... 

This is the source of ozone, tlirough the reaction q, + q. One obtains a pronounced dependence of the... 

Effect of Nitric Oxide on Ozone Depletion. Nitrous oxide is injected into the atmosphere from natural sources on earth about 10% is converted to nitric oxide (N20 + 0( D) — 2 NO), which in turn can catalyze the destmction of ozone (11,32,75). The two main cycles are 1 and 2. Rate constant data are given in Reference 11. 

Removal of Refractory Organics. Ozone reacts slowly or insignificantly with certain micropoUutants in some source waters such as carbon tetrachloride, trichlorethylene (TCE), and perchlorethylene (PCE), as well as in chlorinated waters, ie, ttihalomethanes, THMs (eg, chloroform and bromoform), and haloacetic acids (HAAs) (eg, trichloroacetic acid). Some removal of these compounds occurs in the ozone contactor as a result of volatilization (115). Air-stripping in a packed column is effective for removing some THMs, but not CHBr. THMs can be adsorbed on granular activated carbon (GAG) but the adsorption efficiency is low. 

A smaller factor in ozone depletion is the rising levels of N2O in the atmosphere from combustion and the use of nitrogen-rich fertilizers, since they ate the sources of NO in the stratosphere that can destroy ozone catalyticaHy. Another concern in the depletion of ozone layer, under study by the National Aeronautics and Space Administration (NASA), is a proposed fleet of supersonic aircraft that can inject additional nitrogen oxides, as weU as sulfur dioxide and moisture, into the stratosphere via their exhaust gases (155). Although sulfate aerosols can suppress the amount of nitrogen oxides in the stratosphere... 

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. 

The CAAA also estabHshed a requirement that major new or modified sources of PMIO or carbon monoxide (CO) located in ozone nonattainment... 

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 ... 

Nonattainment area classification One-hour ozone concentration design value, ppm Attainment date Major source threshold level, tons VOGs/yr Offset ratio for new/modified sources... 

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