Ozone chemiluminescence instruments

The calibration of a chemiluminescent analyzer using these standards is verified when both the nitrogen dioxide and nitric oxide channels respond similarly to charges from the (ylinder of diluted nitric oxide. Agreement with the response of the nitric oxide channel should also be obtained when the standard nitric oxide mixture is titrated with a previously established source of ozone. Chemiluminescent instruments have simplified monitoring of nitrogen oxides, but accurate calibration requires well-trained personnel. 

As an example, a recent intercomparison (37) included three N02 measurement techniques aTDLAS-based system and two chemical-based systems— the photolysis-ozone chemiluminescence system diagramed in Figure 7 and an instrument based on N02 plus luminol chemiluminescence. Above 2 ppbv the three instruments gave similar results, but at sub-ppbv the results from the three techniques became dissimilar. Tests on the prepared mixtures showed that the luminol results were affected by expected interferences from 03 and PAN. No interferences were found in the TDLAS system, but near the detection limit the data analysis procedures calculated levels of N02 that were too high. The outcome of this intercomparison was close to the ideal the sensitivity, specificity, accuracy, and precision of each instrument were objectively analyzed previous data sets taken by different systems can now be reliably evaluated and each investigator was able to perceive areas in which the technique could be improved. 

An instrument for measuring nitrogen oxides based on chemiluminescence is shown in Fig. 13.49. The ozone required for the reaction is produced in the ozone generator, which is part of rhe device. One of the reaction chamber walls is an optical filter through which a red-sensitive photomultiplier tube measures the chemiluminescence radiation intensity and converts it into a current signal. 

Instruments based on differential ultraviolet absorption still need to be evaluated, and possibly modified, before their acceptance for monitoring ozone in polluted atmospheres on a nationwide scale. The California Air Resources Board and other air pollution control agencies are evaluating ultraviolet absorption with both chemiluminescence and potassium iodide instruments. 

Differences in measurement methods include analyzer systems based both on the same and on different measurement principles. The average standard deviation in the performance of different chemiluminescent ozone instruments that are sampling the same ambient air both with and without an added ozone concentration of 0.(X)2-0.5 ppm is 6-10%. Field studies comparing an ultraviolet monitor with several chemiluminescent monitors showed correlation coefficients for hourly averages of 0.80-0.95 between various pairs of instruments. Hourly averages for about 500 pairs of values at ambient ozone concentrations of 0.005-0.100 ppm showed deviations of 3-23% between the average values for paired instruments. 

Continuous Measurement Methods for Trace Cases and Aerosols. Ozone. Three basic types of ozone instruments have been used in aircraft the ultraviolet photometric method and two chemiluminescent techniques measuring, respectively, light emitted from the reaction of 03 with ethylene and light emitted from the reaction of 03 with NO. Ultraviolet absorption photometry is one of the preferred methods for measuring 03 from aircraft because of the stability and reliability of commercially available instruments. The method is specific for 03 provided there are no immediate... 

More modern instrumental analysis has been used to improve sensitivity and response time. Shown in Figure 7 is a schematic diagram of an instrument that has been developed to measure NO and N02 (18). The detection scheme is based on the chemiluminescence produced when NO in the ambient air reacts with 1% ozone added as a reagent to the sampled airstream. 

ISO 1431-3 specifies that the calibration of the ozone meter is carried out in accordance with ISO 1396443 which is the general standard for determination of ozone concentration by UV photometry. The operation of UV meters is also to be in accordance with ISO 13964. The other allowed methods are electrochemical, chemiluminescence and wet chemical. Other instrumental methods are operated in accordance with the manufacturer s instructions (having been calibrated to ISO 13964) whilst the wet chemical methods are given in detail in an appendix. Although not referenced, there is also a general method using chemiluminescence44. 

Measurements were made in the travel of the Russian-German experiment TROICA-2 along Trans-Siberian railway during July-August 1996. Used instruments included a DASIBI-1008AH analyzer for ozone concentration measurements, a chemiluminescence gas analyzer AC-30M for NOx measurements, a solar radiation... 

Chemiluminescence. Chemiluminescence (262—265) is the emission of light during an exothermic chemical reaction, generaUy as fluorescence. It often occurs in oxidation processes, and enzyme-mediated bioluminescence has important analytical applications (241,262). Chemiluminescence analysis is highly specific and can reach ppb detection limits with relatively simple instrumentation. 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. 

Chemiluminescence techniques have been used for the determination of a variety or atmospheric pollutants [75], particularly ozone. Most the commercial instruments available for the determination of O3 are based on chemiluminscent reactions and use the Nederbragt et al. method [76], which utilizes the light emitted upon reaction of ozone with ethylene gas (Meloy OA 325-2R and OA... 

A sensitive and selective chemiluminescent detector that has made an appreciable impact on the analysis of nitrosamines in environmental samples in the last several years is the thermal energy analyzer or (TEA) (15-19). This detector utilizes an initial pyrolysis reaction that cleaves nitrosamines at the N-NO bond to produce nitric oxide. Although earlier instrumentation involved the use of a catalytic pyrolysis chamber (15,17,19), in current instruments, pyrolysis takes place in a heated quartz tube without a catalyst (20). The nitric oxide is then detected by its chemiluminescent ion react with ozone. The sequence of reactions can be depicted in Figure 1. A schematic of the TEA is shown in Figure 2 (17). Samples are introduced into the pyrolysis chamber by direct injection or by interfacing the detector with a gas chromatograph (15,17,21,22) or a liquid chromatograph (22-25). 

Instrumentation and Methods. A Sievers Sulfur Chemiluminescence Detector Model 350 was utilized for the selective detection of sulfur compounds. The electronics were set to integrate photon counts for 0.12 seconds. Supply air to the ozone generator was set at 8 psi., and the reaction vessel pressure was measured at 12-14 torr. 

The chemiluminescent detector is a mass-sensitive detector, which is highly selective for either sulfur (SCD) or nitrogen (NCD), depending on the instrumentation. The mechanism of detection is a two-step process with initial combustion followed by low-pressure reaction with ozone. The oxidation products emit a characteristic light, which is measured. The detection limit is about 0.5pgSs and 3 pg N s and the linearity is 10". One main use is the determination of sulfur compounds in petrochemical products. 

This analysis techniqne is illnstrative of chemiluminescence analysis in general. Chemiluminescence is an inherently desirable technique for the analysis of atmospheric pollutants because it avoids wet chemistry, is basically simple, and lends itself well to continuous monitoring and instrumental methods. Another chemiluminescence method, which is employed for the analysis of ozone, is described Section 18.20.5. 

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