Concentrations Of O-xylene Research Articles

An integrated system of biological and catalytic oxidation for the removal of o-xylene from exhaust

Biofiltration is an efficient technology for treatment of gaseous waste. Its disadvantages, however, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. Catalytic oxidation offers a high destructive efficiency at relatively low operating temperature and small unit. A bench scale system integrated with a biofilter and a catalytic oxidation unit for the treatment of gases containing o-xylene was investigated in this study. The catalytic oxidation unit was packed with Cu/Al2O3 catalyst. The results showed that 90% of o-xylene could be removed in the biofilter at the load below 38.2 g m(-3) h(-1). High o-xylene concentration in inlet gas resulted in an overload of the biofilter. Using the Cu/Al2O3 catalytic oxidation unit, the concentration of o-xylene could be reduced evidently. The combination of the chemical and microbial processes not only led to a high and stable efficiency of o-xylene conversion, but also improved capacity resisting the shock loads. The Cu/Al2O3 was studied for o-xylene oxidation in temperature range of 90-320 degrees C. The o-xylene conversion was improved correspondingly with the increasing of oxidation temperature. The reaction mechanism of o-xylene oxidation on Cu/Al2O3 was also investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). (C) 2007 Elsevier B.V. All rights reserved.

Roadside BTEX and other gaseous air pollutants in relation to emission sources

Abstract Hourly concentrations of benzene, toluene, ethylbenzene, m,p-xylenes, and o-xylene (BTEX) plus CO, NOx, SO2 were monitored at roadsides simultaneously with the traffic volume during the dry season of 2004, in Hanoi, Vietnam. The selected three streets included Truong Chinh (TC) with high traffic volume, Dien Bien Phu (DBP) with low traffic volume, and Nguyen Trai (NT) with high traffic volume running through an industrial estate. BTEX were sampled by SKC charcoal tubes and analyzed by GC–FID. Geometric means of hourly benzene, toluene, ethylbenzene, m,p-xylenes and o-xylene are, respectively, 65, 62, 15, 43, and 22 μg m−3 in TC street; 30, 38, 9, 26, and 13 μg m−3 in DBP street; and 123, 87, 24, 56, and 30 μg m−3 in NT street. Levels of other gaseous pollutants including CO, NOx, and SO2, measured by automatic instruments, were low and not exceeding the Vietnam national ambient air quality standards. BTEX levels were comparatively analyzed for different downwind distances (3–50 m) from the street, between peak hours and off-peak hours, as well as between weekdays and weekend. Results of principal component analysis suggest that the gaseous pollutants are associated with different vehicle types.

VOLATILE ORGANIC COMPOUNDS MEASUREMENT IN THE BOUNDARY OF WASTE TREATMENT FACILITIES

Concentrations of the principal volatile organic compounds, such as benzene, toluene, ethylbenzene, m,p,o-xylene, styrene, and chlorobenzene were measured at the solid waste treatment plants classified into four categories; municipal waste incinerator, municipal waste landfill site, industrial waste incinerator and industrial waste landfill site. The average concentration of VOCs in industrial waste treatment facilities was 33.43 ppb and was significantly higher than that measured at municipal waste treatment facilities (4.71 ppb). The average toluene concentrations measured at incinerators (13.05 ppb) were a little higher than those measured at landfill sites (11.54 ppb). The contribution of the waste treatment facilities to the concentration of benzene (0.35 ppb) and o-xylene (0.15 ppb) in the industrial area was relatively small. However, toluene measured in the industrial waste treatment facilities was the most abundant VOCs with the average concentration of 21.37 ppb. As a result of analyses of fingerprint, in cases of IISH and ILUS, a variety of compounds other than major VOCs were detected in high level. On the Pearson correlation analysis, the correlation was generally positive and some pairs of these VOCs were very strongly correlated (correlation coefficient > 0.75).

Formaldehyde and Aromatic Volatile Hydrocarbons in the Indoor Air of Egyptian Office Buildings

Indoor and outdoor measurements of formaldehyde and the aromatic hydrocarbons: benzene, toluene, ethylbenzene, m, p-xylene and o-xylene (BTEX) were conducted at six offices in a suburban area in Giza, Egypt, during the winter 2003-04 season. The mean indoor level of formaldehyde was 59.79ppb in offices where there was no smoking and 85.01ppb in offices where people smoked. The highest mean level of formalde-hyde in offices without smoking was in a new office, 90ppb, and the lowest, 36.16ppb, was in an old office. During the period of study, in 13.33%, 20% and 16.67% of samples from non-smoking, smoking and total offices, respectively, the level of formaldehyde exceeded the ASHRAE standard of 0.1ppm. The mean indoor concentrations of benzene, toluene, ethylbenzene, m, p-xylene and o-xylene were 4.32, 25.06, 3.60, 9.14 and 4.38ppb, respectively, in the six offices. The mean indoor levels in non-smoking offices were lower, and in offices with smoking, higher than the overall mean. The highest mean levels of BTEX in non-smoking offices were found in a new office, whereas the lowest concentrations were recorded in an old office. Significant positive correlations were found between the indoor concentrations of BTEX inside the six offices, except benzene in non-smoking offices. Benzene had only weak positive correlations with these compounds.

Reuse of Fly Ash–Amended Petroleum-Contaminated Soils in Highway Embankments

Remediation of contaminated soil and groundwater has been an important task for engineers and scientists in recent years. One of the sources of soil and groundwater contamination in the United States is petroleum spills. A laboratory study evaluated the geotechnical engineering properties and environmental suitability of remediated petroleum-contaminated soils for their possible use in highway construction. The laboratory test program included compaction, batch sorption, and long-term column leaching tests. Diesel fuel, naphthalene, and a model nonaqueous phase liquid (NAPL) were used as the pollutants; waste coal fly ash that included high carbon content was used to stabilize the contaminated soils. Compaction test results indicated that the maximum unit weights and optimum liquid contents of the stabilized soils satisfy the limits set for highway embankment construction. The results of the batch-scale adsorption tests conducted on the fly ash revealed that the ash has good naphthalene sorption properties because of the presence of high carbon content in its structure. Column leaching test results suggested that the naphthalene and o-xylene concentrations in the effluents collected from the fly ash–stabilized specimens were lower than those collected from the control specimens (i.e., borrow material). The findings indicate that the high carbon content fly ashes can be good sorptive agents for remediation of petroleum contaminated soils because of their low cost and presence of high carbon content. However, caution should be exercised when the laboratory results are carried to field conditions, because the level of contamination is likely to influence the leaching properties.

대구지역 대기 중 VOCs 농도 및 발생원 특성

In recent days, photochemical smog due to the rapid industry development and vehicle increasement has become a critical pollutant in the metropolitan area and the number of ozone alarm signal has increased every year. This research was performed to evaluate VOCs emission source characteristics and concentration of VOCs in Daegu. The site average concentration was observed in the following order: industrial area > commercial area > residential area. Most of the VOCs species except toluene showed variations with higher concentration during nighttime, and lower concentration during the daytime. The major VOCs of stationary emission source were BTEX(benzene, toluene, ethylbenzene. xylene) and methylene chloride, trichloroethene and styrene. Also, those of automobile exhaust were toluene and benzene. Also, the major VOCs concentration emited by the vehicle fuel was observed in the following order: gasoline > light oil > liquefied petroleum gas (L.P.G). Correlation coefficients values were estimated between major VOCs such as toluene, ethylbenzene, m,p-xylene, o-xylene. Results showed that correlation coefficient values were significant magnitude above 0.76. Also, there showed highly significant correlations among ethyl benzene, m,p-xylene, and o-xylene concentration(Pearson correlation coefficients, r=0.868-0.982). Calculated correlation coefficients among commercial area,industrial area and residential area were 0.934-0.981, they showed high correlation. There showed highly correlation between stationary emission source and industrial area, compared with commercial area and residential area. Also, calculated correlation coefficients among commercial area, industrial area, residential area and automobile exhaust were 0.732, 0.725, 0.777, respectively.

Measuring the Effect of Photocatalytic Purifiers on Indoor Air Hydrocarbons and Carbonyl Pollutants

Laboratory tests of photocatalytic air purifiers are usually performed with a single pollutant, in the parts per million by volume domain and at airflow rates [H11349]0.1 m3/hr. Clearly, it is necessary to probe photocatalytic materials and apparatuses under real conditions or conditions closely mimicking reality. Photocatalytic prototypes were placed in an ordinary room. To collect hydrocarbons over a shorter period (15 min) than with adsorbent-containing cartridges, solid-phase microextraction (SPME) was used. Typically, concentrations in substituted benzene hydro-carbons and tetrachloroethene were decreased to 20–35% of initial values; toluene and m- [H11001] p-xylene concentrations dropped to 2–6 parts per billion by volume, and o-xylene and benzene concentrations were still lower. In the absence of appropriate, commercialized SPME fibers, carbonyl compounds (both formed and destroyed by photocatalysis) were extracted using cartridges containing 2,4- dinitrophenylhydrazine-coated silica. The concentration ranges (in parts per billion by volume) were shifted to higher values in treated air: from 9–15.5 to 12.5–18 for methanal, from 1.5–3 to 8–11.5 for ethanal, and from 4.5–19 to 8–26.5 for propanone with the prototype used; these unprecedented results do not exclude using photo-catalysis to treat air, but they illustrate that improvement is needed. Because these tests are time-consuming, preliminary tests are useful; results obtained with a 225-L closed-loop, airtight, photocatalytic reactor with an external turbine enabling the ambient air inside the reactor to be circulated through the purifier device at 15–450 m3/hr flow rates are reported.

Children’s Exposure to Volatile Organic Compounds as Determined by Longitudinal Measurements in Blood

Blood concentrations of 11 volatile organic compounds (VOCs) were measured up to four times over 2 years in a probability sample of more than 150 children from two poor, minority neighborhoods in Minneapolis, Minnesota. Blood levels of benzene, carbon tetrachloride, trichloroethene, and m-/p-xylene were comparable with those measured in selected adults from the Third National Health and Nutrition Examination Survey (NHANES III), whereas concentrations of ethylbenzene, tetrachloroethylene, toluene, 1,1,1-trichloroethane, and o-xylene were two or more times lower in the children. Blood levels of styrene were more than twice as high, and for about 10% of the children 1,4-dichlorobenzene levels were ≥10 times higher compared with NHANES III subjects. We observed strong statistical associations between numerous pairwise combinations of individual VOCs in blood (e.g., benzene and m-/p-xylene, m-/p-xylene and o-xylene, 1,1,1-trichloroethane and m-/p-xylene, and 1,1,1-trichloroethane and trichloroethene). Between-child variability was higher than within-child variability for 1,4-dichlorobenzene and tetrachloroethylene. Between- and within-child variability were approximately the same for ethylbenzene and 1,1,1-trichloroethane, and between-child was lower than within-child variability for the other seven compounds. Two-day, integrated personal air measurements explained almost 79% of the variance in blood levels for 1,4-dichlorobenzene and approximately 20% for tetrachloroethylene, toluene, m-/p-xylene, and o-xylene. Personal air measurements explained much less of the variance (between 0.5 and 8%) for trichloroethene, styrene, benzene, and ethylbenzene. We observed no significant statistical associations between total urinary cotinine (a biomarker for exposure to environmental tobacco smoke) and blood VOC concentrations. For siblings living in the same household, we found strong statistical associations between measured blood VOC concentrations.

Inhibition of anaerobic microbial o-xylene degradation by toluene in sulfidogenic sediment columns and pure cultures

It is frequently observed in aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene (BTEX)-contaminated aquifers that toluene degrades faster than xylenes and benzene. In sediment column experiments which were run with a mixture of BTEX compounds toluene degradation started after a lag period of several weeks. When we omitted toluene from the culture medium o-xylene degradation started. Xylene degradation could be inhibited by adding toluene back to the medium and could be recovered when toluene was omitted again. This was observed repeatedly when toluene concentrations higher than 20 microM were added. Two sulphate-reducing bacterial species, isolated from the column material, were used to investigate the degradation behaviour in detail. Strain TRM1 degraded exclusively toluene, strain OX39 degraded preferentially o-xylene and toluene only after an adaptation period of more than 90 days when added as the sole substrate. Growth and o-xylene degradation of strain OX39 were inhibited by toluene concentrations as low as 40 microM, whereas, in contrast, toluene degradation by strain TRM1 was not inhibited by o-xylene concentrations up to 0.5 mM. Both the column data and the batch experiments indicated that two organisms were responsible for the toluene/xylene degradation in the sediment column. One strain degraded only toluene and was not effected by xylene and the second degraded xylene and was inhibited by toluene. Our findings offer an explanation that the observed differential degradation of BTEX compounds in contaminated aquifers could originate from a partial metabolic inhibition of xylene-degrading organisms by toluene.

Gas-phase hydrogenation of o-xylene over Pt/alumina catalyst, activity, and stereoselectivity

The kinetics of the gas-phase hydrogenation of o-xylene over Pt/alumina catalysts was studied at 430–520 K, a hydrogen partial pressure of 0.19–0.36, and an o-xylene partial pressure of 0.04–0.10. The catalysts were characterized by H2/o-xylene TPD, H2 chemisorption, energy-dispersive X-ray analysis, and XPS. The stereoisomers, cis- and trans-1,2-dimethylcyclohexane, were the only reaction products. A reversible maximum in the o-xylene hydrogenation activity vs temperature was observed; it was explained by a decrease in the surface concentration of o-xylene at higher temperatures. The hydrogenation rate was independent of the o-xylene concentration, whereas the reaction orders with respect to hydrogen varied from 0.9 to 3 in the temperature range investigated. The stereoselectivity of the products was found to depend on temperature, reactant concentrations, and platinum precursor. The catalyst prepared from a chlorine-containing precursor exhibited a lower hydrogenation activity and selectivity toward the trans isomer. Chlorine remained on the catalyst surface, even after reduction at 673 K. Dehydrogenation and configurational isomerization of cis- to trans-1,2-dimethylcyclohexane took place at the same time as hydrogenation. Dehydrogenation and configurational isomerization reactions are enhanced by the presence of residual chlorine on the catalyst surface. The reaction pathway is proposed.

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o-xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m,p-xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o-xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable.

The catalytic performance of Cs-doped V/Ti/O catalysts in the oxidation of o-xylene to phthalic anhydride: a TPR/TPO and reactivity study

Abstract Titania-supported vanadia (V/Ti/O) systems were modified by addition of cesium oxide for application as catalysts in the selective oxidation of o -xylene to phthalic anhydride (PA). Catalytic tests demonstrated that cesium is a strong promoter of the activity and selectivity to PA, but this effect is evident only under well-defined reaction conditions. Samples with a Cs content lower than 0.35 wt.% Cs 2 O exhibited a considerable increase in conversion as compared with the undoped V/Ti/O system. Catalytic tests made with varying o -xylene and oxygen concentrations in the feed demonstrated that in Cs-doped V/Ti/O catalysts the rate-determining step is the re-oxidation of vanadium by molecular oxygen. Thermal-programmed reduction (TPR) and thermal-programmed re-oxidation (TPO) tests evidenced that the addition of Cs decreases the vanadium reducibility and increases the re-oxidizability of the reduced vanadium sites. The positive effect of Cs on selectivity to PA was evident only for o -xylene concentrations in feed lower than 1.5 mol%.

Investigations on flammability models and zones for o-xylene under various initial pressures, temperatures and oxygen concentrations

Abstract The main purpose of this study is to investigate various initial temperatures (100–230 °C) and pressures (760–2,280 mmHg) for fire and explosion characteristics of o-xylene (OX)/air mixtures, which are commercially used in the production of phthalic anhydride (PA), so that empirical flammability models can be established and used in calculations for flammability zones. According to the results of the experiment, while the experimental condition of OX is controlled by the same oxygen concentration, if the initial temperature is increased, the upper explosion limit (UEL), flammability zones of OX are correspondingly increased, but the maximum explosion pressure (Pmax) gas or vapour explosion constant (Kg) of OX is decreased. In addition, if the initial pressure is increased, the explosion characteristic parameters are all increased. However, while OX is controlled by the same oxygen concentration, if the initial temperature is increased, the lower explosion limit (LEL) of OX is decreased. Nevertheless, if the initial pressure is increased, the LEL has various changes under various temperatures. In general, the LEL of OX has little change at higher temperature. From the experimental results, the minimum oxygen concentration (MOC) does not significantly vary while the initial temperature is increased, whereas it will be decreased by enhancing initial pressure. Therefore, the MOC of OX is determined by initial pressure instead of initial temperature. It is crucially important that if the initial temperature is lower than the normal boiling point of OX (144 °C), then the UEL, Pmax and Kg of OX are higher under 100 °C than 150 °C and even higher temperatures. Consequently, the liquid–vapour co-existing phase will demonstrate higher degree of hazard. Therefore, it is important that the loading of the volume concentration of OX should not fall into the flammability zone.

Worker exposure to aromatic volatile organic compounds in dry cleaning stores.

This study evaluated worker exposure to aromatic compounds and perchloroethylene (PERC) in dry cleaning stores relative to four different solvents. For benzene and toluene, there was no significant difference among the indoor air concentrations of the four different solvents. For ethylbenzene, m,p-xylene, and o-xylene, the air concentrations were significantly higher in the dry cleaning stores using Solvent V, YuClean, and Super New Cleaner than in those using a PERC mixture. Breath concentrations measured prior to and immediately after work were not significantly different for benzene and toluene, whereas breath concentrations of ethylbenzene, m,p-xylene, and o-xylene were significantly higher (p<0.05) in the samples collected immediately after work compared with those collected prior to work. The breath concentrations of benzene and toluene both prior to and immediately after work showed no upward or downward trend for 7 consecutive days excluding Sunday, starting from Monday. In contrast, the breath concentrations of ethylbenzene, m,p-xylene, and o-xylene measured immediately after work showed a slight upward trend in three subjects. However, this trend was most likely not due to an accumulated body burden from repeated daily work, but rather was the result of the amount of solvent used each day. It is concluded that dry cleaning workers using the aromatics-contained solvents are exposed to elevated levels of some aromatic compounds compared with the dry cleaning workers using PERC. Further study is recommended to examine the presence of other air toxics inside dry cleaning stores using these solvents.

The Biofiltration of Indoor Air: Air Flux and Temperature Influences the Removal of Toluene, Ethylbenzene, and Xylene

An alternative approach to maintaining indoor air quality may be the biofiltration of air circulated within the space. A biofilter with living botanical matter as the packing medium reduced concentrations of toluene, ethylbenzene, and o-xylene concurrently present at parts per billion (volume) in indoor air. The greatest reduction in concentrations per pass was under the slowest influent air flux (0.025 m s(-1)); however, the maximum amount removed per unit time occurred under the most rapid flux (0.2 m s(-1)). There was little difference between the different compounds with removal capacities of between 1.3 and 2.4 micromol m(-3) biofilter s(-1) (between 0.5 and 0.9 g m(-3) biofilter h(-1)) depending on influent flux and temperature. Contrary to biofilters subjected to higher influent concentrations, the optimal temperatures for removal by this biofilter decreased to less than 20 degrees C at the most rapid flux for all three compounds. Microbial activity was decreased at these cooler temperatures suggesting the biofilter was not microbially limited but rather was limited by the availability of substrate. The cooler temperatures allowed greater partitioning of the VOCs into the water column which had a greater impact on removal than its reduction in microbial activity.

Effect of the reaction bath temperature in a fixed-bed reactor for oxidation of oxylene over V2O5/TiO2 catalysts

The effects of the reaction variables in the operation of a fixed-bed reactor for oxidation ofo-xylene over V2O5/TiO2 catalysts were studied experimentally using a bench reactor. Reaction temperature, feed flow rate and feed concentration ofo-xylene were found to have significant effects on the product distribution and the temperature profile in the reactor. Drastic enhancements ofo-xylene oxidation reaction were observed at some conditions, which was ascribed to the effect of heat accumulated in the bed and indicated a possible way to increase the productivity in the industrial condition.

Concentrations of volatile organic compounds in the passenger side and the back seat of automobiles.

The in-vehicle volatile organic compound (VOC) concentrations during commutes have previously been measured in only one single interior sampling location, considering a sample collected in the single interior location as representative of overall VOC concentrations within an automobile. The present study evaluated if the potential differences in VOC concentrations occur in the automobiles' interior during idling and commuting under different driving conditions associated with the use of air cleaning devices (ACDs) and interior fan. The experiments were conducted under the low ventilation condition with the windows and the vent closed and the fan off. The difference of VOC concentrations between passenger side and back seat during idling was small. The variability of VOC concentrations with location inside automobiles while commuting was not significant at p < 0.05, regardless of the use of ACDs and/or the interior fan, while inter-vehicle variability was significant at p < 0.05. In addition, currently available ACDs equipped with activated carbon filters in Korea were ineffective at removing VOCs from the interior of automobiles. The concentrations of the two lightest ones of the target compounds, benzene and toluene, were significantly higher inside two vehicles than in the roadway air at p < 0.05, while the in-vehicle and roadway concentrations of the other target compounds did not differ significantly at p < 0.05 for both vehicles. The concentrations of all target VOCs, except benzene, were significantly higher (p < 0.05) in the interior of older car than of newer car. Median in-vehicle concentrations of benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene were 38.3, 107, 9.2, 7.8, 16.9, and 10.7 micrograms/m3, respectively.

The effect of deactivation of a V 2O 5/TiO 2 (anatase) industrial catalyst on reactor behaviour during the partial oxidation of o-xylene to phthalic anhydride

Abstract It is well known that during the partial oxidation of o -xylene to phthalic anhydride, on a V 2 O 5 /TiO 2 (anatase) catalyst under industrial conditions, the catalyst can experience both reversible and irreversible deactivation. Experimental evidence presented here suggests that the reversible deactivation can be attributed to the deposition of some carbonaceous compounds. Experiments were carried out in both a microreactor and an industrial-scale pilot-plant reactor. Catalyst samples from the microreactor were analysed by elemental C–H–N analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). These analyses suggest that the decrease in the disappearance rate of o -xylene at high o -xylene concentrations, which the standard redox model cannot predict, is most likely to be caused by the deposition of carbonaceous compounds rather than by the over-reduction of the catalyst. Two types of reversible deactivation are postulated from the experimental results: (1) by easily removable and (2) by strongly adsorbed carbonaceous compounds. Experiments on the pilot-plant reactor exhibited some unusual dynamic behaviour such as multiple steady-state operation, travelling hot spots and decreased catalyst activity, following an attempted reactivation process at a low temperature. These were all found to be consistent with a model based upon the postulated deactivation mechanism and kinetics; corresponding models based upon constant activity profiles could not reproduce the observed results.

Concentrations of volatile organic compounds in automobiles' cabins while commuting along a Korean urban area

This study examined in-vehicle concentrations of selected gasoline-derived volatile organic compounds (VOCs) on 115 commutes along a Korean urban route. Median in-vehicle concentrations of benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene were 38.3, 107, 9.2, 7.8, 16.9, and 10.7 μg/m 3 , respectively. The concentrations of benzene and toluene were significantly higher inside the two vehicles than in the roadway air at p<0.05, while the concentrations of the other target compounds did not differ significantly. The concentrations of all target VOCs except benzene were significantly higher (p<0.05) in the interior of older cars than of newer cars. The concentration differences between the passenger's side and the back seat during a single run were not significant at p<0.05 for all driving conditions associated with the use of an air cleaning device (ACD) which was equipped with an activated carbon filter and the fan. The in-vehicle concentrations of target compounds were not significantly different between ACD on and ACD off conditions, and between the interior fan on and the interior fan off conditions.

The Response of the Intoxilyzer 5000® to Five Potential Interfering Substances

A study was conducted of potential vapor phase interferents which could be present on human breath and also be capable of inducing a false-positive response for ethanol on the evidential infrared-based breath testing device, the Intoxilyzer-5000. This involved preparation and validation of a range of vapor standards, which were introduced to the instrument using a dynamic flow double-bubbler system. Potential interferents were chosen on the basis of both their infrared signatures and their general availability, and included toluene, m-xylene, o-xylene, methanol and isopropanol. All compounds tested were found to be capable of inducing false-positive readings for ethanol in a highly reproducible manner, as a result of which it has been possible to derive precise least-squares equations describing the ethanol readout expected for any given blood concentration of toluene, m-xylene, o-xylene, methanol and isopropanol. The likelihood of an interference compromising the integrity of the analysis is related to both the toxicological significance and prevalence of a given blood concentration of each solvent, and the point at which the instrumental interference light is triggered in each case.