Gaseous Chemical Species Research Articles

140 GHz microwave spectrometer for the detection of gaseous chemical species

A sensitive microwave spectrometer for the detection of gaseous pollutants and other molecular species is described. The spectrometer operates in the vicinity of 140 GHz and employs a Fabry-Perot resonator as a sample cell and superheterodyne detection for high sensitivity. The instrument is capable of detecting a minimum concentration of 210 ppb of SO/sub 2/ diluted in air with a 1 sec time constant. For H/sub 2/CO diluted in air, the minimum detectable concentration is 130 ppb.

Atmospheric transport of visibility degrading pollutants into the California mojave desert

Three atmospheric tracer experiments using SF 6 and fine aerosol measurements were conducted in California to determine the relative impact of pollutant sources in the San Fernando Valley area of Los Angeles and the southern San Joaquin Valley on visibility in a portion of the Mojave Desert. Dilution ratios calculated for SF 6 and various gaseous and aerosol chemical species were used to indicate atmospheric transformation processes between source and receptor. The evolution of the aerosol sulfur mass distribution resulting from transport and transformation was measured. The SF 6 data were compared with predictions based upon the Gaussian dispersion model. SF 6 released in the San Fernando Valley was found to impact the southern Mojave Desert including the towns of Palmdale and Adelanto. SF 6 released at Oildale in the southern San Joaquin Valley was found to directly impact the northern Mojave Desert including the towns of Mojave and China Lake. Some SF 6 released in the San Joaquin Valley was also detected in the southern Mojave Desert. SF 6 was found to be diluted by factors of only 2–3 during passage over the mountains separating the source and receptor areas. The SF 6 dispersion during the San Fernando Valley experiment could be modeled with the Gaussian plume model if the experimentally determined mixing height, transport speed and plume trajectory were used, and the stability class was chosen to give good agreement with the data. A simple Gaussian plume model could not provide an adequate description of the San Joaquin Valley test because of the complexities of the wind reversal that occurred during the transition from morning to afternoon flow conditions during this test. Dilution ratios for conserved fine aerosols between Oildale and China Lake were found to be about 3. in excellent agreement with the SF 6 data. The timing of the diurnal degradation in visibility at China Lake was found to coincide with the arrival of SF 6, thus indicating that the southern San Joaquin Valley was the source of visibility degrading aerosol. The aerosol sulfur mass distribution was found to be essentially conserved between Oildale and China Lake and substantially different from Los Angeles-Palm Springs sulfur mass distributions. Our data indicate that pollutants from both the southern San Joaquin Valley and the Los Angeles Basin can impact the Mojave Desert during their transport eastward by the predominantly westerly summertime winds; consequently, both “plumes” should be taken into account when considering the impact of southern California pollutants upon the southwestern United States.

Hydrogen evolution from water using solid carbon and light energy

Using solar energy to decompose water and produce hydrogen for use in hydrogen energy systems has attracted much attention. Some semiconductors (such as TiO2 and SrTiO3) can decompose water to produce hydrogen and oxygen using the energy1 of light and the decomposition of water using powdered semiconductors has been reported2,3. One problem with powdered semiconductors is that when H2O decomposes into H2 and O2 in one cell an explosive gas is produced. Furthermore, although Schrauzer and Guth reported2 that traces of H2 and O2 were detected after the decomposition of water gas on TiO2, the reverse reaction will increase simultaneously as product is evolved. Hydrogen evolution stopped after a few hours. Hence the hydrogen or oxygen produced should be converted to more stable gaseous chemical species. The use of solid carbon is an interesting problem in relation to coal gasification and we have now examined the photocatalytic decomposition of water on TiO2 using solid carbon. We found that reactions (1) and (2) occur producing hydrogen gas from water vapour and solid carbon when mixed powders of TiO2, RuO2 and active carbon exposed to water vapour at room temperature ∼80 °C are illuminated. The free energies are increased by 63 and 92 kJ mol−1 respectively, utilising light energy.

Approche thermodynamique des conditions de dépôt chimique du bore sur substrat métallique

This paper deals with the thermodynamic study of the chemical compatibility of various metallic substrates (titanium, tantalum, tungsten and some of their borides) with the gaseous chemical species involved in the chemical vapour deposition of boron from BCl 3-H 2 mixtures. The method used is based on the minimization of the Gibbs free energy of the system. The results of this study lead to a classification of the metallic substrates. Thus, TiB 2 is chemically inert towards the gas phase whilst, of the three metals studied, tungsten is the one which has the best chemical compatibility with BCl 3-H 2 mixtures at 1300 – 1500 K, which justifies its use as a substrate in boron fibre production. The chemical compatibility of titanium with the gas phase is very poor. Nevertheless, high quality boron deposits can be obtained on titanium if the substrate is pretreated with BCl 3-doped hydrogen prior to boron deposition.

Concentrations of twenty gaseous chemical species in the flue gas of a municipal incinerator.

The body of information presented in this paper is directed to those professionals concerned with gaseous emissions from municipal incinerators and with incinerator testing and performance in general.