Ozone measurement

The following section gives an overview of the different methods available to measure ozone in the gas and liquid phases. For quick reference the methods are summarized in Table 2-7 so that the reader can choose an analytical method that fits his or her system at a glance. All important information e. g. interference, detection limit, as well as the original reference with the detailed description of the method, necessary for its application can be found in this table. The methods are described in ascending order of their purchase costs. 

This method can be used for the determination of the ozone concentration in the gas and/or liquid phase. The measurement takes place in the liquid phase, though, so that to measure a process gas containing ozone, the gas must first be bubbled through a flask containing potassium iodide KI. For the measurement of the liquid ozone concentration, a water sample is mixed with a KI solution. The iodide F is oxidized by ozone. The reaction product iodine 12 is titrated immediately with sodium thiosulfate Na2S203 to a pale yellow color. With a starch indicator the endpoint of titration can be intensified (deep blue). The ozone concentration can be calculated by the consumption of Na2S203. 

The absorption maximum of ozone occurs at 254 nm, which is close to the wavelength of the mercury resonance line at 253.7 nm. The decrease of the UV intensity at X = 254 nm is proportional to the concentration of ozone based on the Lambert-Beer s law of absorption  

1 Intensity passing through the absorption cell containing the sample 

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If a nonattainment area is classified as serious, based on ambient ozone measurements, then the state must modify its SIP to bring the area into compliance in 9 years. The CAAA90 also specify the size and, therefore, the number of sources subject to regulatory control as a function of nonattainment classification. Table 24-3 illustrates these requirements for ozone nonattainment classifications of extreme and severe the state must include... 

For ozone, the recommended final standtird will be updated from 0.12 parts per million of ozone measured over one hour to a standard of 0.08 parts per million measured over eight hours, with the average fourth highest concentration over a three-year period determining whether an area is out of compliance. Details arc provided below. ... 

Volz, A. and Kley, D. (1988). Evaluation of the Montsouris series of ozone measurements made in the nineteenth century. Nature 332, 240-242. 

London. On the second day, the late afternoon peak exceeded 0.1 ppm. It is apparent that some conversion of nitric oxide to nitrogen dioxide was responsible for the ozone buildups, but it is not as clear a chemical pattern for London as it is for cities in the western United States. The paper did not mention the method of ozone measurement however, qualitative descriptions of the weather patterns suggest that the days of high ozone were characterized by light winds and considerable sunlight. 

A dramatic departure of ozone measurements from total oxidant measurements has b Mi reported for the Houston, Texas, area. Side-by-side measurements suggested that either method was a poor predictor of the other. Consideration was given to known interferences due to oxides of nitrogen, sulfur dioxide, or hydrogen sulfide, and the deviations still could not be accounted for. In the worst case, the ozone measurements exceeded the national ambient air quality standard for 3 h, and the potassium iodide instrument read less than 15 ppb for the 24-h period. Sulfur dioxide was measured at 0.01-0.04 ppm throughout the day. Even for a 1 1 molar influence of sulfur dioxide, this could not explain the low oxidant values. Regression analysis was carried out to support the conclusion that the ozone concentration is often much higher than the nonozone oxidant concentration. 

Severs, R. K. Simultaneous total oxidant and chemiluminescent ozone measurements in ambient air. J. Air Pollut. Control Assoc. 25 394-3%, 1975. 

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. 

For any event to be accurately recorded, it must persist for the pulse time of the instrument. This time is equal either to the rise time or to the time to 100% response, depending on the design of the instrument. For accurate data from aircraft sampling plumes, for example, it is necessary to obtain rise times of a few seconds or less. This is a very fast response for an analyzer and has only recently become possible for ozone measurements. 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

Hodgeson, J. A., C. L. Bennett, H. C. Kelly, and B. A. Mitehell. Ozone measurements by iodometiy, ultraviolet photometry and gas-phase titration. Paper Presented at the American Society for Testing and Materiak Conference on Calibration in Air Monitoring, Boulder, University of Cdorado, Aug. 5-7, 1975. 

Evaluation of primary calibration procedures applicable nationwide for ozone measurement. 

Figure 1.7 shows the total column ozone measured in October at one Antarctic location, Halley Bay, as a function of year. This includes the original Farman et al. (1985) data, as well as more recent data up to 1994 (Jones and Shanklin, 1995). It is clear that starting in the late 1970 s, there was a dramatic drop in total column ozone at the end of the polar winter when sunrise occurs. Observation of such a rapid change is unprecedented and quite remarkable. 

FIGURE 1.7 Average total column ozone measured in October at Halley Bay, Antarctica, from 1957 to 1994 (adapted from Jones and Shanklin, 1995). 

It was accepted for a number of years in the atmospheric chemistry community that so-called background ozone was typically around 30-40 ppb. However, starting in the mid-1980 s, a number of researchers examined the literature of a century earlier, shortly after ozone was discovered by Schonbein in 1839, and discovered several series of ozone measurements that had been made at different locations in the troposphere. Some of the papers describing this research include the papers by Bojkov (1986), Volz and Kley (1988), and Anfossi et al. (1991). 

Volz, A., and D. Kley, Evaluation of the Montsouris Series of Ozone Measurements Made in the Nineteenth Century, Nature, 332, 240-242 (1988). 

An unusual phenomenon was reported in the Arctic in the mid-1980s. Ozone measured at ground level was observed to decrease rapidly to small concentrations, at times near zero (Bottenheim et al., 1986 Oltmans and Komhyr, 1986). As seen in Fig. 6.37, an increase in bromide ion collected on filters (f-Br) was inversely correlated with the 03 decrease (Barrie et al., 1988 Oltmans et al., 1989 Sturges et al., 1993 Lehrer et al., 1997) this could reflect either particle bromide or a sticky gas such as HBr that could be collected on the filter simultaneously. This correlation suggested that the loss of ozone was due to gas-phase chain reactions... 

Brauer, M., and J. R. Brook, Personal and Fixed-Site Ozone Measurements with a Passive Sampler, Air Waste Manage. Assoc., 45, 529-537 (1995). 

Nardi, B T. Deshler, M. E. Hervig, and L. D. Oolman, Ozone Measurements over McMurdo Station, Antarctica during Spring 1994 and 1995, Geophys. Res. Lett., 24, 285-288 (1997). 

Cunnold, D. M H. Wang, W. P. Chu, and L. Froidevaux, Comparisons between Stratospheric Aerosol and Gas Experiment II and Microwave Limb Sounder Ozone Measurements and Aliasing of SAGE II Ozone Trends in the Lower Stratosphere, J. Geophys. Res., 101, 10061-10075 (1996). 

Kane, R. P Y. Sahai, and C. Casiccia, Latitude Dependence of the Quasi-Biennial Oscillation and Quasi-Triennial Oscillation Characteristics of Total Ozone Measured by TOMS, J. Geophys. Res., 103, 8477-8490 (1998). 

Madronich, S Implications of Recent Total Atmospheric Ozone Measurements for Biologically Active Ultraviolet Radiation Reaching the Earth s Surface, Geophys. Res. Lett., 19, 37-40... 

Ozone Measuring the dissolved ozone concentration may also be more complicated in three-phase systems. The analysis of dissolved ozone by the photometrical indigo method (Hoigne and Bader, 1981) is disturbed by compounds or materials that scatter or absorb... 

Ozone data collected by CASTNET are complementary to the larger ozone data sets gathered by the State and Local Air Monitoring Stations (SLAMS) and National Air Monitoring Stations (NAMS) networks. Most air-quality samples at SLAMS/NAMS sites are located in urban areas, while CASTNET sites are in rural locations. Hourly ozone measurements are taken at each of the 50 sites operated by EPA. Data from these sites provide information to help characterize ozone transport issues and ozone exposure levels. 

Oltmans, S.J., and Levy II, H. (1994) Surface ozone measurements from a global network, Atmos. Environ. 28,9-24. 

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