Evacuable smog chamber

As a result, some evacuable smog chambers have been designed and constructed to control both temperature and pressure. The one shown schematically in Fig. 16.3 is constructed with an aluminum alloy and the walls are coated with FEP Teflon. The end windows through which the mixture is irradiated are ultraviolet-... 

OH as a function of time when a VOC-NOx mixture was irradiated in the evacuable smog chamber shown in Fig. 16.3 (Carter et al., 1981, 1982). The rates of decay of propane and propene were used to estimate the concentration of OH shown by the horizontal bars in Fig. 16.12 as a function of reaction time. 

In later experiments, Izumi et al. (47, 48) examined aerosol formation during photooxidation of a variety of hydrocarbons in an evacuable smog chamber. No seed particles were used in these experiments, but good estimates of the yield of aerosol from photochemical oxidation of the hydrocarbon precursors were obtained by using EAA data. In some cases, the volumetric yield was found to decrease with decreasing precursor concentration (Figure 4), so the finite vapor pressure of the reaction products limited nucleation, particle growth, or both. 

Clearly, such adsorption-desorption processes on the surfaces of chambers potentially can have substantial effects on the observed levels of 03 and other trace pollutants and on their rates of formation. While such effects can be minimized using bake-out while pumping if the chamber is evacuable, relatively few smog chambers have such capabilities at present. Even for evacuable chambers, contamination from adsorption on, and desorption from, the walls occurs. How to correct the results for this and reliably extrapolate the data to real atmospheres remains problematical. 

Akimoto, H., M. Hoshino, G. Inoue, F. Sakamaki, N. Washida, and M. Okuda, Design and Characterization of the Evacuable and Bakable Photochemical Smog Chamber, Environ. Sci. Technol., 13, 471-475 (1979). 

Fig. 7.5 Evacuable photochemical smog chamber at National Institute for Environmental Studies, Tsukuba, Japan...

Akimoto, H., Hoshino, M., Inoue, G., Okuda, M. Reaction mechanism of the photooxidation of the toluene-N02-02-N2 system in the gas phase. Bull. Chem. Soc. Jpn. 51, 2496-2502 (1978) Akimoto, H., Hoshino, M., Inoue, G., Sakamaki, F., Washida, N., Okuda, M. Design and characterization of the evacuable and bakable photochemical smog chamber. Environ. Sci. Technol. 13, 471 75 (1979a)... 

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