Initial NO2 concentration

Figure 12. Effect of initial NO2 concentration. A calculation with [NOg] = 0.01 ppm (dashed lines) is compared with the reference calculation, [NOg] = 0.05 ppm (solid lines).

Effect of Initial NO2 Concentration. In laboratory studies conducted to simulate atmospheric photochemical smog, a serious effort is usually made to start the experiment with low initial concentrations of NO2. In the data of Altshuller et al. studied here [N02]o was 0.05 ppm in other studies [N02]o had lower values (15, 16, 17, 18, 19, 20), and in most of the studies reported [N02]o was not even specified. The effect of reduc-... 

Experiment Number Initial NH4 Concentration (M) Initial NO2 Concentration (Al) 0 bserved Initial Rate (M/s)... 

A FIGURE 15.5 The same equilibrium mixture is produced regardless of the initial NO2 concentration. The... 

Then, having obtained the NO2 concentration at the specific time f = 2 h, we can use Equation 3.56 to calculate the initial NO2 concentration ... 

Figure 1. Experimental HO radical concentration data and model results as a function of added O2 concentration. Initial HO radical concentration - 5 x 1011 /cm3 at the SOj> port, NO2 concentration - 3.3 x 1012 molecule/cm3, SO2 added 115 ms from HO detection zone at concentration -1.1 x 1015 molecule/cm3, NO added 15 ms from HO detection zone at concentration - 1.2 x 1014 molecule/cm3 and 02 added 95 ms from HO detection zone at concentrations 0 - 2.2 x 10 5 molecule/cm3. The curves show the effect of varying the HOSO2 + O2 rate constant upper - 8.0 x Iff13 cm3/s, middle - 4.0 x 10"13 cm3/s and lower -2.0 x 10"13 cm3/s.

The rate coefficient for the reaction of CH3S with NO2 was measured in 40 torr to 200 torr of He, No, or O2. In He and N2 the rate coefficient was found to be (6.10 0.10) x 10"11 cm3 molec1 s 1, independent of the pressure, residence time in the reaction vessel and initial CH3S concentration. At low pressures of O2 a similar result was obtained, but as the amount of O2 was increased the apparent rate coefficient decreased, the value at an Oo pressure of 100 torr being 25% less than in the absence of O2. It is probable that this is due to... 

When NO was irradiated in the absence of CO and H2O at an initial NOa concentration of 5.3 ppm, NO2 reached a constant value of 1.15 ppm after about 4 hours of irradiation. The presence of water vapor at 53%... 

NO conversion was measured with respect to its initial effective concentration in the gas stream as determined from FT-IR analysis. The amount of NO flowing into the reaction line differed from that introduced in the mixture, due to the presence of high amounts of O2 that transformed part of the NO into NO2. The effective feed gas composition flowing into the reaction line was 2380 pm of NO, 600 ppm of NO2 and some amount of N2O. Conversion of NOx (NO plus NO2) corresponded to N2 production. 

The approximate initial reactant concentrations in both reactors (in ppmv units) were as follows NO2, 50-100 alkyl iodide 10-30 and 2-iodopropane 10-30 (1 ppmV = 2.46 x lo " molecule cm at 298 K and atmospheric pressure). The concentration-time behaviom of the alkyl iodides were monitored over a 15-30 min irradiation period in both the kinetic and product studies. 

Figure 17.25 shows typical variations with time of primary and secondary pollutants. Initially, the concentration of NO2 is quite low. As soon as solar radiation penetrates the atmosphere, more NO2 is formed from NO and O2. Note that the concentration of ozone remains fairly constant at a low level in the early morning hours. As the concentration of unbumed hydrocarbons and aldehydes increases in the air, the concentrations of NO2 and O3 also rise rapidly. The actual amounts, of course, depend on the location, traffic, and weather conditions, but their presence is always accompanied by haze (Figure 17.26). The oxidation of hydrocarbons produces various organic intermediates, such as alcohols and carboxylic acids, which are all less volatile than the...

In summary, the conversion between radical types occurs via reactions with NO, organics, and ozone. The initial OH attack on organics results in conversion to RO2 or HO2 radicals. RO2 then reacts with NO and is converted to HO2, which can react with NO or O3 to convert back to OH. It can be seen that conversion to OH depends greatly on the availability of NO. Together with the effect of NO2 concentration on HNO, formation, the overall... 

As we can see, the new equilibrium concentration of NO2 is greater than the initial equilibrium concentration (0.0475 M). Therefore, the gases should look darker]... 

The conclusion drawn that the first two steps in the decomposition of TNAZ involve NO2 loss agrees with the observation by Brill and coworkers [5] that gaseous NO2 was the most abundant species in the initial phases of the thermal decomposition of bulk TNAZ. That the NO2 concentration decreases from its initially observed level in the bulk study is evidence that this species is already undergoing significant secondary reactions at the time of its initial appearance yet the surmisal that the NO2 is a primary product is correct. Additionally, the observation that no methylene nitramine formation occurs agrees with the same conclusion drawn from the bulk study where the N2O/H2CO pair was not present. However, the absence of NO as an initial product in the molecular beam experiment, shows that the NO observed in the bulk decomposition study is not due to gas phase unimolecular nitro-nitrite isomerization followed by NO loss. 

Proceeding in the same way, the values of for the other samples are calculated. Note from Table 15.1 that the value for is constant (within the limits of experimental error) even though the initial concentrations vary. Furthermore, Experiment 4 shows that equilibrium can be achieved beginning with N2O4 rather than with NO2. That is, equilibrium can be approached from either direction. FIGURE 15.5 shows how Experiments 3 and 4 result in the same equilibrium mixture even though the two experiments start with very different NO2 concentrations. 

If gas cylinders are used to prepare simulated flue gas for exposure testing, many cylinders may be required to run long exposure periods. If a combustion source is used to supply flue gas, it is difficult to match the composition of flue gas from a large pulverized coal-fired boiler. Maintaining the proper ratio of NO to NO2 is a special problem because NO oxidation to NO2 is a function of the temperature, the initial NO concentration, the oxygen concentration, and the gas residence time in the exposure chamber. The usual procedure is to use simulated flue gas with the same SO2 concentration as actual flue gas, but with different concentrations of other species. This procedure can produce erroneous results. 

We have formulated a chemical kinetic model for the Thermal De-NOx process that satisfactorily predicts the NO removed and the N2O and NO2 produced by the process over a range of temperatures and initial oxygen concentrations. The new feature of the mechanism is that NO2 appears as an essential intermediate in the reaction scheme. It is formed as a consequence of NNH reacting with molecular oxygen,... 

Figure 6 Experimental and theoretical NO2 concentrations as a function of temperature for various initial O2 concentrations (flow reactor conditions of Kasuya et al [36]). Initial conditions NO = 500 ppm, NH3 = 1000 ppm, H2O = 5%, 62 concentrations as indicated, balance N2. Residence time = 88 K/T sec. (a) experimental results, (b) theoretical predictions. 

Fig. 12.8 NO2 TPD experiment at 200 °C over Cu-CHA. a The ratio of NO produced divided by NO2 consumed, b NO concentration in the initial part of the adsorption, c NO2 concentration in the initial part of the adsorption and d NO concentration during TPD [36]. Reprinted with permission from Colombo et al. [36]. Copyright (2012) Elsevier...

Recently Siflfert et al. obtained complete inactivation of clostripain by pure P-NO2-ZACK. The enzyme they used was four times more active (4.5 /tkat/mg) than that of Porter. It was activated for 2 hr at room temperature prior to the assay at a concentration of 20 fiM in 50 mAf Tris chloride at pH 7.4, containing 2.5 mAf DTT and 50 mAf CaCU- In inhibition experiments at an initial enzyme concentration of 10 /tAf, the rate of inactivation is extremely rapid a 4M excess of the reagent removes the activity completely in less than 2 min at room temperature. 

This reaction can account for the high initial abundance of NO found when the initial HONO concentration is also high [30]. Third, some nitramines we have studied also contain aliphatic C-NO2 groups. C-NO2 compounds are found to generate a considerable amount of NO [39,40], perhaps because of the approximately thermally neutral C-NO2 to C-ONO isomerization [41]. CO-NO homolysis leading to NO is facile in this isomerized state. Fourth, there is evidence that nitramines can form nitrosamines (R2W-NO) upon thermal decomposition in the condensed phase [42-44]. Fast thermal decomposition of nitrosamines also liberates NO [45]. 

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