SO2 detection

Berger R, Fromm M., Chambaudet A., and Planade R., Tin dioxide-based gas sensors for SO2 detection A chemical interpretation of the increase in sensitivity obtained after a primary detection. Sens. Actuators B, 45, 175-181, 1997. 

Thamae, M., R Westbroek, and T. Nyokong (2002). pH study of the SO2 detection at a glassy carbon electrode modified with iron(It)tetrasutfophthalocyantne. Acta Microkim. Acta 140, 233-239. 

As a practical test for on-site application of the sensor for SO2 detection, a prototype probe sensor was fabricated. A sectional view of the probe sensor is illustrated in fig. 57 (Adachi and Imanaka 1991). In this type of probe, a mullite tube is utilized instead of the more expensive quartz tube. In order to prevent the chemical reaction between the sulfate electrolyte and the solid reference, an alumina plate was placed between them, as for the case of the SO2 sensor with the solid reference reservoir (sect. 5.6). The measurement was... 

In this case, the Na" concentration and the cell emf are related to the oxygen partial pressure sodium oxide should not be necessarily present as a separate phase, but Na20 activity should remain constant in order to provide stable emf. If the target species are not present in the ion-conducting phase, the measurements can be performed using so-called auxiliary electrodes, e.g., Na2S04 for SO2 detection ... 

Minayeva O. B. and Hopwood (. A. (2003) Microfabricated inductively coupled plasma-on-a-chip for molecular SO2 detection a comparison between global model and optical emission spectrometry, J. Anal. At. Spectrom. 18 856-863. 

Static sampling systems are defined as those that do not have an active air-moving component, such as the pump, to pull a sample to the collection medium. This type of sampling system has been used for over 100 years. Examples include the lead peroxide candle used to detect the presence of SO2 in the atmosphere and the dust-fall bucket and trays or slides coated with a viscous material used to detect particulate matter. This type of system suffers from inability to quantify the amount of pollutant present over a short period of time, i.e., less than 1 week. The potentially desirable characteristics of a static sampling system have led to further developments in this type of technology to provide quantitative information on pollutant concentrations over a fked period of time. Static sampling systems have been developed for use in the occupational environment and are also used to measure the exposure levels in the general community, e.g., radon gas in residences. 

Gaseous SO2 is an example. Very early procedures detected the presence of SO2 in ambient air by exposing a lead peroxide candle for a period of time and then measuring the amount of lead sulfate formed. Because the volume of air in contact with the candle was not measured, the technique could not quantify the amount of SO2 per unit volume of air. 

The continuous methods combine sample collection and the measurement technique in one automated process. The measurement methods used for continuous analyzers include conductometric, colorimetric, coulometric, and amperometric techniques for the determination of SO2 collected in a liquid medium (7). Other continuous methods utilize physicochemical techniques for detection of SO2 in a gas stream. These include flame photometric detection (described earlier) and fluorescence spectroscopy (8). Instruments based on all of these principles are available which meet standard performance specifications. 

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

Trifluorovinyltm derivatives have been reacted with SO2, however, only low yields of insertion into the tin-carbon bond of the Irifluorovinyl group were detected [20],... 

There has been considerable discussion about the extent of hydration of the proton and the hydroxide ion in aqueous solution. There is little doubt that this is variable (as for many other ions) and the hydration number derived depends both on the precise definition adopted for this quantity and on the experimental method used to determine it. H30" has definitely been detected by vibration spectroscopy, and by O nmr spectroscopy on a solution of HF/SbFs/Ha O in SO2 a quartet was observed at —15° which collapsed to a singlet on proton decoupling, 7( 0- H) 106 Hz. In crystalline hydrates there are a growing number of well-characterized hydrates of the series H3O+, H5O2+, H7O3+, H9O4+ and H13O6+, i.e. [H(0H2) ]+ n = 1-4, Thus... 

Weather conditions at the time of initial exposure of zinc and steel have a large influence on the protective nature of the initial corrosion products This can still be detected some months after initial exposure. Finally, rust on steel contains a proportion of ferrous sulphate which increases with increase in SO2 pollution of the atmosphere. The effect of this on corrosion rate is so strong that mild steel transferred from an industrial atmosphere to a rural one corrodes for some months as though it was still exposed to the industrial environment. ... 

The species S3 (absorbing at 420 nm) and S4 (absorbing at 530 nm) have been detected by reflection spectra in the condensate but the formation of S4 is unexplained [16]. S3 and SO2 have also been observed by Raman spectroscopy in such samples [15] (the expected S4 Raman line at 678 cm was probably obscured by the SS stretching mode of S2O at 673 cm but a shoulder at the high-frequency side of the S2O line indicates that some S4 may have been present). While the reddish colors turn yellow on warming at about -120 °C, the sulfur radicals could be observed by ESR spectroscopy up to 0 °C [10]. If the condensation of S2O gas is performed very slowly at -196 °C the condensate is almost colorless and turns red only if the temperature is allowed to increase slowly. Hence, it has been suspected that S2O is actually colorless like SO2. 

If gaseous S2O-SO2 mixtures are dissolved in dry solvents such as CS2, CCI4, CHCI3, CH2CI2, and liquid SO2 at temperatures between -75 and -1-25 °C, intense yellow solutions of polysulfuroxides are obtained which have been characterized only very poorly [19]. In contrast to the opinion of some authors [20], S2O cannot be detected in such solutions, e.g., by infrared spectroscopy. Most probably, mixtures of cyclic polysulfuroxides are present besides SO2 (see below, in particular the preparation of S5O), e.g. ... 

On exposure to air, the initially clear orange crystals of the adduct turn cloudy within 1 min as a result of the loss of CS2, and ultimately form a yellow oil. In CS2 solution the adduct decomposes fairly rapidly at room temperature the decomposition products SOCI2, SO2, Sg, and SbCls are already detectable after 10 min. The SO stretching vibrations of Si202-2SbCl5 occur at 940 cm in the infrared spectrum (in CS2) [61]. Free S12O2 has not been prepared yet. 

In reaction condition C, Figure 5 shows that the optimed molar ratio of O2/H2S is 0.6, different from the stoichiometric ratio obtained under water-free condition. While COS was detected for the ratios less than 0.6, SO2 was detected for ratios greater than 0.6. 

Konovalov and colleagues " studied the chemical shifts of the CH2 protons for a series of derivatives of arylsulfonylacetic acids and ) -disulfones in DMSO or CDCI3. The transmission of electronic effects through the SO2 bridge was detected and attributed to the possibility of participation of the 3d orbitals of sulfur in the formation of the S=0 bond and to the existence of d7t-p7t conjugation . The paper contains various references to related (mainly Soviet) work. 

In dibenzothiophene-S,S-dioxide the S atom is in a ring, and hence more constrained. The yield of SO2 in the radiolysis is linear with the dose to about 13 Mrad after which it levels off as in p,p -ditolyl sulfone. However, the yield of SO2 in this case is much lower (a factor of 25) than in the case of p,p -ditolyl sulfone (G = 0.002 compared to G = 0.05). This stability of the dibenzothiophene sulfone could be partially due to back reaction to reform the parent sulfone and partially due to more efficient energy delocalization. The expected biphenylene product was not detected due to limitations of the analytical method. Bowmer and O Donneir studied the volatile products in y-radiolysis of dialkyl, alkyl aryl and diaryl sulfones. Table 2 gives the radiolytic yields of SO2 and of the hydrocarbon products of the alkyl or aryl radicals. The hydrocarbon products are those obtained either by H atom abstraction or by radical combination. The authors suggested the mechanism... 

The SSI (solid-state imaging) camera on board the Galileo spacecraft transmitted impressive high-resolution pictures of Io s volcanic activity. Active lava lakes, lava curtains , calderas, mountains and plateaus can be seen (McEwen et al., 2000). The Hubble telescope detected both S2 gas and SO2 in a SO2 to S2 ratio of 1 4 in the smoke trail of the volcano Pele. This value suggests an equilibrium between silicate magmas in the neighbourhood of the quartz-fayalite-magnetite buffer (see Sect. 7.2.2). 

Finally, three additional individual data matrices were obtained for soil (so1 so2, and so3), in this case with the same number of samples (rows) for each of them. A new soil data matrix (SO) was obtained after individual matrix concatenation containing 36 samples in total (12 samples analyzed in 3 sampling campaigns) (see Fig. 7). Fifteen variables (all of them detected in SE as well) were measured in every sample PAHs (acenaphtylene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(a)pyrene, indeno (l,2,3-cd)pyrene, dibenzo(a,h)anthracene, and benzo(g,h,i)perylene), an organophosphate compound (tributylphosphate), and an OC (4,4 -DDE). 

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