Calculations smog chamber

The success of these computer simulations must be rated as quite good. Figure 2-8 compares concentration-time measurements from a smog-chamber study of NO,-propylene-air with computer-calculated results based on the same initial conditions. The time dependences and absolute concentrations agree fairly well, but not perfectly. Note that the... 

However, the number of concentrations being fitted is fairly small, compared with the number of parameters going into the model. The computer calculations can be used to predict the concentrations of other trace compounds that should be present in smog chambers. If these compounds are later found at approximately the predicted concentrations, the model will be strengthened. If not, changes will have to be made in the model. A more stringent test of the model will occur when it becomes... 

TABLE 13-4 Calculated Concentrations of Oxidant Species in Smog Chambers ... 

Calculated coocentratioas for oxidants in smog chamber under conditions outlined in Chapter 2 for 60-niin irradiation (see Table 2-2). 

It is apparent from (VIII- 18a) that a rapid conversion of NO to N02 is needed for the buildup of O, concentration levels. It was recognized that the conversion rate of NO to N02, observed in the real atmosphere, was several hundred times as fast as the rate of the reaction 2NO + 02 — 2NOz in the range of NO concentrations of 0.05 to 0.5 ppm. Furthermore, in simulated smog chamber experiments it was found that the rate of butene consumption by illumination of a NO- N02-H20-butene mixture in air was much faster than that calculated on the basis of reactions of O(3P) atoms and 02 with butene. Apparently a new mechanism based on radical chain reactions was needed to explain these observations. Two groups of scientists, Heicklen and coworkers and Weinstock and coworkers, were the first to propose independently the following sequence of reactions in 1970. 

Application of Fade Approximants to Smog Chamber Calculations. The chemical model described previously is implemented in rate equations which must be integrated numerically. Because of the widely... 

About 580 actinic flux spectra recorded under different meteorological conditions (clear sky, partially cloudy or overcast) in the EUPHORE smog chambers, have been used to calculate the photolysis frequencies for various small carbonyl compounds that are considered to be important from the atmospheric chemistry point of view. The results are presented here. 

Further studies within the DIFUSO project studies exhibited that the influence of diesel soot on the ozone formation is negligible under the conditions of the smog chamber experiments performed. The present simulations using a simple gas-phase model leading to good agreement of experimental and calculated data confirmed this observation. 

Recently there Is evidence from both smog chamber data (47, 140) and from theoretical calculations (47, 48) that the Isomerization of the alkoxy radicals ( C4) can be competitive with unlmolecular decomposition and with reaction with O2. 

Odum et al. (1996) formulated an easy approach to calculate the aerosol yield of various precursor compounds with unknown oxidation products by smog chamber experiments. He defined two viitual products a non-volatile and a semivolatile product and fitted a curve through various smog chamber experiments to obtain the fraction of the product a, and its partitioning coefficient Ap, . 

Aromatic hydrocarbons (benzene, toluene, xylene isomers) are a major class of organic compounds associated with the urban environment and model calculations appear to indicate that they might contribute more than 30 % of the photo-oxidant formation in urban areas. However, the mechanisms currently used in models of tropospheric chemistry to describe the photo-oxidation of aromatic compounds are highly speculative. Studies within LACTOZ have involved both direct and smog chamber investigations and have provided data on many different aspects of the mechanisms for oxidation of aromatic compounds related to tropospheric ozone and oxidant formation. Most of this work was carried out by four of the LACTOZ groups (Becker, Devolder, Kerr, Zetzsch). 

Table 2 Ratios decomp / ( (02)-10 cm obtained from smog chamber data [5] compared to those calculated with our absolute rate constants (300 K).

More recently. Topping developed a methodology for an analytical solution to calculate the movement of organic material from the bulk to a surface layer, requiring only surface tension parameters from binary systems [265]. He found that the method was computationally efficient, but it must be validated by comparisons with laboratory experimental data, and then further with ambient studies and smog chambers. 

Fig. 7.2 Comparison of experimental loss rate of CaH in the irradiation of a mixture of C3H6 and NOx in air in a smog chamber with the calculated loss rate by the reaction with O atom and O3...

Fig. 7.9 The dependence of the maximum ozone mixing ratio [OaJmax as a function of the square root of initial mixing ratio of NOx, [NOxlo, in the irradiation of the mixture of CaHg and NO in air in the smog chamber. The abscissa axis is in a square root scale. The initial concentration of CaHg is 500 ppbv (O, ) and 100 ppbv (A, A). Experimental (open symbols) and model-calculated (filled symbols) values are compared (Sakamaki et al. 1982)...

Nitro compounds may be photoreduced by suitable hydrogen donors under sunlight. For example, nitrobenzene was reduced by toluene to yield aniline, 4-amino phenol, azoxy benzene, and benzoic acid. Alkyl aromatics that can form benzyl-type radicals were efficient hydrogen donors for this reaction. The sorption of nitrobenzene to humus with increased residence time and reaction sites will likely make this pathway play a significant role in the fate of nitrobenzene. Half-life of toluene calculated from smog chamber experi-... 

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