Ozone in air

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

In addition to the specificity of the monitoring method, an important requirement for the measurement of atmospheric pollutants is the accuracy of the calibration technique. The calibration procedure for the measurement of oxidants or ozone utilizes a stable and reproducible sample of dilute ozone in air. The ozone concentration of this sample is established with a reference method that is not necessarily suitable for monitoring ambient air. This reference method must agree with the scientifically accurate measurement of ozone in the calibration sample. 

Most currently used oxidant and ozone monitors need to be calibrated with a predetermined concentration of ozone in air. Regardless of the principle used to measure ambient ozone or oxidant concentrations, the primary reference standard for calibrating each monitoring device or system should be identical everywhere. This requirement remains to be achieved in practice. Up to June 1975, at least seven calibration procedures were practiced in the United States. These are listed in Table 6-5... 

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. 

These iodometric calibration methods are based on the assumption that there is a stoichiometric reaction between ozone and the iodine in the various potassium iodide procedures. Three essentially independent methods have been used to test the accuracy of this assumption measuring the absorption of ultraviolet radiation at 254 nm by ozone in air, measuring the absorption of infrared radiation at 9,480 nm by ozone in air, and determining the ozone concentration in air by titration with nitric oxide. 

Determination of Ozone in Air by Titration with Nitric Oxide This calibration technique is based on the application of the rapid gas-phase reaction between nitric oxide and ozone to produce a stoichiometric quantity of nitrogen dioxide, according to the following reaction ... 

A diagram of a typical gas-phase (ozone-ethylene) chemiluminescent ozone analyzer is shown in Figure 6-10. The detector responds linearly to ozone concentrations between 0.003 and 30 ppm no interferences were initially observed. More recently, however, it has been established that, as the relative humidity goes from 0 to 60% and the temperature from 20° to 25° C, water vapor produces a small positive signal that results in an increase of about 8% in the ozone concentration measurement. This potential source of error can be minimized by using humidified, rather than dry, ozone in air streams when calibrating. 

The effect of the physical state of BaP and perylene adsorbed on fused-silica plates on their reaction rates with ozone in air was studied by Wu and co-workers (1984), who measured the fluorescence of the two PAHs... 

FIGURE 10.30 Percent conversion-time profiles for the decay of 5 PAHs in diesel exhaust particulate matter (Dp = 0.5 p.m) collected on glass fiber filters and exposed to 1.5 ppm of ozone in air under Hi-Vol sampling conditions. Half-lives (dotted line) decrease in order of the Nielsen (1984) electrophilic reactivity scale (Table 10.30) BaP, benzo[u]pyrene BghiP, benzo[ghi]pclyIcne BeP, benzolelpyrene IndP, indeno[l,2,3-cd]pyrene BkFI, benzolk]fluoranthene (adapted from Van Vaeck and Van Cauwenberghe, 1984). 

Ozone was generated at 250 mg/hour and 0.29% ozone in air passed through a reactor tube packed with dry fibrils at 1200ml/hour. The oxidation continued at ambient temperature for 3-45 hours and the product isolated. 

Oxidation photooxidation t/2 = 2.9-27.8 h, based on estimated rate constants for the reaction with hydroxyl radical and ozone in air (Atkinson Carter 1984 Atkinson 1987 quoted, Howard et al. 1991). 

Degradation of airborne pesticides is caused by absorption of light (direct photolysis), as well as by reaction with OH-radicals and ozone in air (indirect photolysis). 

Inhalation of ozone should be avoided. A threshold limit value of 0.1 p.p.m. of ozone in air has been adopted by the American Conference of Governmental Industrial Hygienists. This represents the concentration of ozone in air considered safe for an... 

Determination of Ozone in Air by Neutral and Alkaline Iodide Procedures... 

One per cent potassium iodide in neutral buffered or alkali solutions is more stable and useful than 20% potassium iodide in bubblers for collection and determination of ozone in air. Either 1 % solution may be used to determine low concentrations of ozone however, there is a difference in their stoichiometry. Over the range of 0.01 to 30 p.p.m. (v./v.) results by the alkaline procedure should be multiplied by 1.54 to correct for stoichiometry. The neutral reagent does not require acidification and has more nearly uniform stoichiometry. The alkaline procedure is preferable when final analysis may be delayed. Experiments with boric acid for acidification of samples in the alkaline reagent show that some mechanism other than oxidation of iodide to iodate or periodate is involved, possibly formation of hypoiodite. Preliminary experiments with gas phase titrations of nitrogen dioxide and nitric oxide against ozone confirm the stoichiometry of the neutral reagent as 1 mole of iodine released for each mole of ozone. 

Either neutral or alkaline iodide procedures may be applied for determination of ozone in air the latter procedure requires use of a correction factor for stoichiometry. 

For this experiment the three chemical systems were standardized to a 2% potassium iodide-monitored, ozone-in-air stream. Figure 8 presents the calibration curves used to calculate the atmospheric data. In the case of phenolphthalin, a somewhat... 

Possanzini M, Di Palo V. 1988. Simultaneous measurements of formaldehyde and ozone in air by annulardenuder - HPLC techniques. Chromatographia 25 895-898. 

Determination of ozone in air is based on its reaction with bis(terpyridyl)iron(Il) [24]. 

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