Nitrogen dioxide sampling

The NO analyzer is based on the principles of chemiluminescence to determine continuously the NO concentration in the sample gas stream. The analyzer should contain a NOg-to-NO converter, which converts the nitrogen dioxide (NO9) in the sample gas to nitrogen oxide (NO). An NOg-to-NO converter is not necessary if data are presented to demonstrate that the NO9 portion of the exhaust gas is less than 5 percent of the total NO9 concentration. 

Consider what happens when a sample of N204, a colorless gas, is placed in a closed, evacuated container at 100°C. Instantly, a reddish-brown color develops. This color is due to nitrogen dioxide, NO2, harmed by decomposition of part of the N2O4 (Figure 12.1, p. 324) ... 

Nitrogen dioxide, a red-brown gas, is stable at room temperature. However, Figure 15-1 shows that reducing the temperature causes a sample of NO2 to become colorless. The color change that happens at low temperature occurs because two NO2 molecules combine to form one molecule of a colorless gas, N2 O4. ... 

The detailed chemistry describing the synthesis of ammonia Is complex, so we Introduce the principles of equilibrium using the chemistry of nitrogen dioxide. Molecules In a sample of nitrogen dioxide are always colliding with one another. As described in Chapter 15, a collision in the correct orientation can result In bond formation, producing an N2 O4 molecule 2 NO2 N2 O4... 

The feasibility of an optical fiber system was demonstrated for the differential absorption analysis of the car pollutant nitrogen dioxide. It absorbs in the visible and can be "sensed" using an Ar-ion laser27. The yellow metabolite bilirubin has been monitored in blood via fiber optic spectrometry in serum28. The tip of a fiber optic cable was inserted into a injection needle so to reach the blood sample, and absorbance (and later fluorescence) was acquired of a sample contained in the cavity at the tip of the fiber or needle. 

Electron-transfer activation. The observation of intense coloration upon mixing the solutions of hydroquinone ether MA and nitrogen dioxide at low temperature derives from the transient formation of MA+ cation radical, as confirmed by the spectral comparison with the authentic sample. The oxidation of MA to the corresponding cation radical is effected by the nitrosonium oxidant, which is spontaneously generated during the arene-induced disproportionation of nitrogen dioxide,239 i.e.,... 

In this metho d [ 124 ] nitrate, nitrate plus nitrite or nitrite alone are selectively reduced to nitric oxide, which is swept from the sample in a helium carrier gas flow. Nitric oxide is allowed to react with ozone in a nitrogen oxide analyser, where it forms nitrogen dioxide. The return of the nitrogen dioxide to the ground state is accompanied by release of a photon, which is detected by a photomultiplier. The integrated output of the photomultiplier over the time that the nitric oxide is pinged from the sample is proportional to the nitrite content of the sample. 

Before 1970, most of the data for nitrogen oxides were obtained by continuous measurements with a colorimetric analyzer that was similar in principle to the colorimetric oxidant analyzer shown in Figure 6-8. The scrubbing agent is a mixture of -(l-naphthyl)ethylenediamine, sulfanilic acid, and acetic acid in aqueous solution. The color is produced when both nitrogen dioxide and nitrites react with this reagent to form an azo dye. The color is not affected by nitric oxide in the air sample. 

Intersociety Committee. Tentative method of analysis for nitrogen dioxide content of the atmosphere (Griess-Sahzman Reaction), pp. 329-336. In Methods of Air Sampling and Analysis. Washington, D.C. American Public Health Association. 1972. 

Hisham, M. W. M., and D. Grosjean, Sampling of Atmospheric Nitrogen Dioxide Using Triethanolamine Interference from Per-oxyacetyl Nitrate, Atmos. Environ., 24, 2523-2525 (1990). 

Krochmal, D and L. Gorski, Determination of Nitrogen Dioxide in Ambient Air by Use of a Passive Sampling Technique and Triethanolamine as Absorbent, Environ. Sci. Technol., 25, 531-535 (1991). 

When a sample of N2O4, a colorless and poisonous gas, is placed in a closed container, a reddish-brown color develops due to the presence of nitrogen dioxide, NO2. As soon as some NO2 is formed, the reverse reaction can occur simultaneously with the forward reaction. 

Nitrogen dioxide permeation tubes were obtained from Metro-nics, Inc. These tubes were factory calibrated for use at 30.0°C. The permeation tubes were thermostated in a water bath and air passed over at a known flow rate (of at least 150 cc/min). Gas samples were drawn off at 80 cc/min. 

When the sample solution containing sodium nitrite was injected into the system, nitrogen dioxide was produced in the flow cell... 

Peng et a/.[45] reported the nitration of toluene with liquid nitrogen dioxide and oxygen in the presence of a variety of zeolites, and using toluene as reactant and solvent. The reactions were performed at room temperature over 22 h. In the absence of catalyst the reaction was highly unselective giving a mixture of MNTs, dinitrotoluenes, phenylnitromethane and benzaldehyde. In the presence of zeolites, HZSM-5 and HBeta, the selectivity to the p-nitrotoluene was enhanced. In contrast with the results reported by Smith et a/.,[14] HZSM-5 zeolite exhibited better selectivity than Beta zeolite (57 % and 46 %, respectively), which can be attributed to the absence of mediation of the chlorinated solvent molecules, as well as to the higher Si/Al of the HZSM-5 sample (Si/Al =1000). It was found that zeolites... 

Other observations of the reaction of hydrazine and nitrogen tetroxide substantiate the production of non-equilibrium combustion products. Non-equilibrium product concentrations were found in combustion gases extracted from a small rocket combustion chamber through a molecular beam sampling device with direct mass spec-trometric analysis (31) (39). Under oxidizer rich conditions excessive amounts of nitric oxide were found under fuel rich conditions excessive amounts of ammonia were found. A correlation between the experimentally observed characteristic velocity and nitric oxide concentration exists (40). Related kinetic effects are postulated to account for the two stage flame observed in the burning of hydrazine droplets in nitrogen dioxide atmospheres (41) (42). 

High efficiency denuders that concentrate atmospheric S02 were coupled to an ion chromatograph to yield detection limits on the order of 0.5 ppt (106). A newer approach has been introduced for the quantitative collection of aerosol particles to the submicrometer size (107). When interfaced to an inexpensive ion chromatograph for downstream analysis, the detection limit of the overall system for particulate sulfate, nitrite, and nitrate are 2.2,0.6, and 5.1 ng/m3, respectively, for an 8-min sample. A two-stage membrane sampling system coupled with an ion trap spectrometer has been utilized for the direct analysis of volatile compounds in air, with quantitation limits to low ppt levels (108). Toluene, carbon tetrachloride, tricholoroethane, and benzene were used in these studies. The measurement of nitrogen dioxide at ppb level in a liquid film droplet has been described (109) (see Air pollution). A number of elements in environmental samples have been determined by thermal ionization ms (Table 6). The detection limit for Pu was as low as 4 fg. 

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