Monitoring Of Volatile Organic Compounds Research Articles

Ultra-fast detection and monitoring of cancerous volatile organic compounds in environment using graphene oxide modified CNT aerogel hybrid gas sensor

Ultra-fast detection of cancerous volatile organic compounds (VOCs) by carbon nanotube aerogel (CNT aerogel)-graphene oxide (GO) hybrid network has been studied in this paper. VOCs, especially non-polar compounds are difficult to detect due to their low electronegativity. A homogenous GO solution was drop cast on CNT aerogel film, both developed in-house, to obtain the CNT aerogel-GO composite. The CNT aerogel contains multi-directional porous CNT webs providing a stable and compact platform for GO adsorption. The loading concentration of GO and O/C ratios were optimized to obtain a highly sensitive CNT aerogel-GO hybrid sensor. The hybrid sensor could detect a range of non-polar VOCs like benzene, hexane, toluene, cyclohexane, and chlorobenzene with a limit of detection around 70 ppb. The optimized CNT aerogel-GO hybrid sensor showed 3 times better sensing performance than the bare CNT aerogel sensor. The principal component analysis (PCA) plot showed discrimination in all the VOCs as they all were distinct and spread over all four quadrants, indicating highly selective behavior of the sensor. Chemical and structural analysis by X-ray photoelectron spectroscopy and Raman spectrum showed that the oxygen loading could change the sp2 structure, making it ideal for sensing applications. The electron micrography images confirm the uniformity of the GO layer on the CNT aerogel. It is concluded that the concomitant formation of the CNT-GO junction can achieve better interaction and charge transfer during hybrid sensor fabrication. Subsequently, a sensitive, fast and durable CNT aerogel-GO hybrid sensor can be obtained for detection and continuous monitoring of cancerous VOCs.

Characteristics of Photochemical Reactions with VOCs Using Multivariate Statistical Techniques on Data from Photochemical Assessment Monitoring Stations

This study assesses the concentrations of the 54 ozone precursors (all being volatile organic compounds (VOCs)) detected at the four photochemical assessment monitoring stations that are part of the air quality monitoring network in the Kaohsiung-Pingtung area in Taiwan. Factor and cluster analyses of the multivariate statistical analysis are performed to explore the interrelationship among the 10 VOCs of relatively higher concentrations selected from the 54 ozone precursors to identify significant factors affecting ozone pollution levels in the study area. Moreover, the multivariate statistical analysis can faithfully reflect why the study area has been affected by photochemical pollution. First, results of the factor analysis suggest that the factors affecting how photochemical reactions occur in the study area can be divided into the following: “pollution from mobile sources”, “pollution from stationary sources”, and “pollution from energy sources”. Among them, mobile sources have the greatest impact on photochemical pollution levels. Second, the impacts of photochemical pollution on air quality in the study area can be classified into four clusters via cluster analysis. Each cluster represents how the 10 VOCs affect air quality, with different characteristics, and how they contribute to photochemical pollution in the study area. If there are more types and samples of photochemical pollutants when performing a multivariate statistical analysis, the analysis results will be more stable. This study adopts data on VOC monitoring over a period of nearly two years, which can effectively improve the validity and reliability of the factor analysis results, while helping environmental agencies review the effectiveness of air quality management in the future and serving as reference for the effectiveness of reducing photochemical pollution in the atmosphere.

Volatile Organic Compound Sampling through Rotor Unmanned Aerial Vehicle Technique for Environmental Monitoring

To improve the capacity to probe volatile chemical substances in the atmosphere, we designed an unmanned aerial vehicle system for volatile organic compound (VOC) monitoring and sampling. This environmental monitoring unmanned aerial vehicle (EMUAV) platform was equipped with a photoionization detector for continuous VOC monitoring and searching in a pollution air mass. Furthermore, a multifunction airborne microVOC sampler was loaded for sampling. An airbag and absorption tube were applied to collect air samples for further analyzing in the laboratory by GC-FID/MS or TD-GC/MS. By comparing the aerial samples derived from the microVOC sampler with the samples collected at a similar height to a building roof for chemical compositions, the sampling conditions, such as the sampling port location and sampling method, were optimized to ensure the representativeness of the air samples. The results of the sample comparison experiment showed that both the airbag method and the adsorption method could recover 70–130% for most VOC species. Through the aerial measurements, the advantages of this EMUAV system were demonstrated. Therefore, the developed EMUAV system would have immeasurable potential in the field of environment monitoring.

Volatile Organic Compound Monitoring during Extreme Wildfires: Assessing the Potential of Sensors Based on LbL and Sputtering Films.

A new theory suggests that flammable gases generated by heated vegetation, in particular the volatile organic compounds (VOC) common to Mediterranean plants, may, under certain topographic and wind conditions, accumulate in locations where, after the arrival of the ignition source, they rapidly burst into flames as explosions. Hence, there is a need for the development of a system that can monitor the development of these compounds. In this work, a sensor’s array is proposed as a method for monitoring the amount of eucalyptol and α-pinene, the major VOC compounds of the Eucalyptus and Pine trees. The detection of the target compounds was assessed using the impedance spectroscopy response of thin films. Combinations of layers of polyelectrolytes, such as poly(allylamine hydrochloride) (PAH), polyethyleneimine (PEI), poly(sodium 4-sytrenesulfonate) (PSS) graphene oxide (GO), and non/functionalized multiwall nanotubes (MWCNT-COOH or MWCNT), namely, PAH/GO, PEI/PSS, PEI/GO, PAH/MWCNT, PAH/MWCNT-COOH, films, and TiO2 and ZnO sputtered films, were deposited onto ceramic supports coated with gold interdigitated electrodes. The results showed that concentrations of the target VOCs, within the range of 68 to 999 ppmv, can be easily distinguished by analyzing the impedance spectra, particularly in the case of the ZnO- and PAH/GO-film-based sensors, which showed the best results in the detection of the target compounds. Through principal component analysis (PCA), the best set of features attained for the ZnO and PAH/GO based sensor devices revealed a linear trend of the PCA’s first principal component with the concentration within the range 109 and 807 ppmv. Thus, the values of sensitivity to eucalyptol and α-pinene concentrations, which were (2.2 ± 0.3) × 10−4 and (5.0 ± 0.7) × 10−5 per decade, respectively, as well as resolutions of 118 and 136 ppbv, respectively, were identified.

Headset-type Ear Canal Gas Sensor for Monitoring of Volatile Organic Compounds in Human Blood

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High Sensitivity Monitoring of VOCs in Air through FTIR Spectroscopy Using a Multipass Gas Cell Setup.

Human exposure to Volatile Organic Compounds (VOCs) and their presence in indoor and working environments is recognized as a serious health risk, causing impairments of varying severities. Different detecting systems able to monitor VOCs are available in the market; however, they have significant limitations for both sensitivity and chemical discrimination capability. During the last years we studied systematically the use of Fourier Transform Infrared (FTIR) spectroscopy as an alternative, powerful tool for quantifying VOCs in air. We calibrated the method for a set of compounds (styrene, acetone, ethanol and isopropanol) by using both laboratory and portable infrared spectrometers. The aim was to develop a new, and highly sensitive sensor system for VOCs monitoring. In this paper, we improved the setup performance, testing the feasibility of using a multipass cell with the aim of extending the sensitivity of our system down to the part per million (ppm) level. Considering that multipass cells are now also available for portable instruments, this study opens the road for the design of new high-resolution devices for environmental monitoring.

Understanding the early-stage release of volatile organic compounds from rapeseed oil during deep-frying of tubers by targeted and omics-inspired approaches using PTR-MS and gas chromatography

During deep-frying, a plethora of volatile products is emitted with the fumes. These compounds could act as oil quality indicators and change the indoor air composition leading to health risks for occupants. The presented experiments focus on deep-frying of different tubers in rapeseed oil at different frying temperatures. Here, two scenarios for real-time monitoring of volatile organic compounds (VOCs) using proton transfer reaction mass spectrometry (PTR-MS) were proposed. The first, targeted, involved the application of gas chromatography with a flame ionization detector (GC-FID). The second, omics-inspired, involved the use of solid-phase microextraction (SPME) along with gas chromatography-mass spectrometry (GC-MS) and molecular networking algorithm as a complementary tool to the PTR-MS analysis. In a targeted approach, it was shown that the emission profile of pentanal and hexanal depends on the frying temperature and as the temperature increases, a sudden release of these compounds can be observed in the first minutes of frying. Meanwhile, using an omics-inspired protocol enables finding the relation between 1,4-heptadienal and 2-heptanone, octanal and limonene emissions. Using both approaches it was possible to record real-time changes in emission profiles of various oils’ degradation products. It was also observed that the emission profiles of VOCs are strictly related to the frying temperature and the type of fried tuber.

Control of pollutants in the atmospheric air on the example of an automated monitoring system in St. Petersburg

Assessment of air quality is an integral part of the strategy to improve the quality of life and health of the population. According to the recommendations of the World Health Organization, carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, and particulate matter are subject to monitoring. Of particular interest are nitrogen oxides and ozone, which are characterized by an inverse correlation. The study is aimed at establishing the degree of this relationship according to the data of an automated monitoring system and assessing the level of air pollution in St. Petersburg, Russia. In addition, it is necessary to control the content of various specific compounds, including volatile organic compounds (VOCs). This is because public health impacts include exposure to both the VOCs themselves and secondary air pollutants resulting from chemical reactions between VOCs and other components. Thus, these substances are constantly monitored at observation stations in St. Petersburg. VOC monitoring provides for qualitative and quantitative analysis on measuring equipment with preliminary sampling and their preparation. Sampling uses various methods and devices. Based on the results of the theoretical and experimental studies, the authors propose the use of sampling devices, which differ from analogues in their design, metrological and operational characteristics.

Vehicle Underway Mobile Monitoring of Volatile Organic Compounds Using Online Mass Spectrometry: Application in an Industrial Park

The environmental problem of volatile organic compounds (VOCs) pollution in industrial parks is becoming increasingly serious. Rapid and large-scale monitoring of the overall pollution in the area and identification of pollution sources are keys to efficient pollution control. However, traditional detection methods cannot achieve rapid detection, let alone accurately pinpoint the source of pollution. In this study, an online VOC mobile monitoring system based on time-of-flight mass spectrometry was used to monitor an industrial park and successfully obtain the VOC distribution image of the industrial park. Two polluted areas (A and B) were pinpointed by examining the image, and the ΣVOCs concentration ranges were 74–421 μg/m3 and 51–577 μg/m3. Eight abnormal sites with concentration peaks exceeding the standard were found, and the pollution source of one abnormal site was analyzed. The correlation between the pollution source factor of the abnormal site and the emission enterprise was as high as 0.91, and the pollution source of the abnormal site was identified. To explore whether it was affected by other surrounding enterprises, a positive matrix factorization model was further used to analyze the receptor data of abnormal site. Three pollution sources were analyzed and compared with enterprise emission sources. Combined with the location of the abnormal site and emission sources, we found that the abnormal sites were not only affected by the emission sources of surrounding enterprises but also by the emission sources of enterprises in the northeast. This approach offers rapid and large-scale monitoring of the overall pollution in an area and quickly pinpointed the location of the pollution sources. This method solves the shortcomings of traditional methods that cannot identify the location of pollution source and provides an effective technical means for the rapid detection of the pollution distribution in industrial parks for efficient screening of pollution sources.

Characteristics and sources of volatile organic compounds (VOCs) in Xinxiang, China, during the 2021 summer ozone pollution control

Real-time monitoring of volatile organic compounds (VOCs) was conducted in Xinxiang, China, during the implementation of Xinxiang's ozone pollution control period (CP) in June 2021. To evaluate the effectiveness of the control measures, three study periods were determined by combining meteorological conditions and the implementation time of the control measures: before, during, and after the CP of ozone pollution (BCP, CP, and ACP, respectively). The average concentrations of VOCs during the three periods were 41.20 ± 4.99 ppbv, 33.64 ± 5.65 ppbv, and 37.42 ± 2.59 ppbv, respectively, with the same top three components, namely oxygenated VOCs (OVOCs), alkanes, and halogenated hydrocarbons (XVOCs). However, the concentrations of these three components decreased substantially during the CP (by 19 %, 18 %, and 11 %, respectively). The ozone formation potential (OFP) during the BCP was 144.47 ppbv, which was 1.2 times and 1.3 times higher than those during the ACP and CP periods, respectively. During the CP, the proportion of alkenes that contributed to the OFP decreased significantly by 24 %. Five types of VOCs sources were determined by positive matrix factorization (PMF): (1) solvent use, (2) biogenic, (3) secondary formation, (4) industrial process, and (5) vehicle exhaust and fuel evaporation sources. The VOCs emissions from industrial processes decreased by 54 % during the CP, whereas those from vehicle exhaust and fuel evaporation sources decreased by 36 %, indicating the effectiveness of emission control measures and the importance of these two sources for VOCs control in Xinxiang. In terms of regional transport, the results of the spatial analysis revealed that Hebi and Anyang in the northeast and Zhengzhou and Pingdingshan in the southwest, affected significantly the VOCs of Xinxiang. These results highlight the importance of controlling VOCs emissions in Xinxiang. Furthermore, attention should be paid to controlling the regional transport of surrounding cities.

Volatile Organic Compounds and Physiological Parameters as Markers of Potato (Solanum tuberosum L.) Infection with Phytopathogens.

The feasibility of early disease detection in potato seeds storage monitoring of volatile organic compounds (VOCs) and plant physiological markers was evaluated using 10 fungal and bacterial pathogens of potato in laboratory-scale experiments. Data analysis of HS-SPME-GC-MS revealed 130 compounds released from infected potatoes, including sesquiterpenes, dimethyl disulfide, 1,2,4-trimethylbenzene, 2,6,11-trimethyldodecane, benzothiazole, 3-octanol, and 2-butanol, which may have been associated with the activity of Fusarium sambucinum, Alternaria tenuissima and Pectobacterium carotovorum. In turn, acetic acid was detected in all infected samples. The criteria of selection for volatiles for possible use as incipient disease indicators were discussed in terms of potato physiology. The established physiological markers proved to demonstrate a negative effect of phytopathogens infecting seed potatoes not only on the kinetics of stem and root growth and the development of the entire root system, but also on gas exchange, chlorophyll content in leaves, and yield. The negative effect of phytopathogens on plant growth was dependent on the time of planting after infection. The research also showed different usefulness of VOCs and physiological markers as the indicators of the toxic effect of inoculated phytopathogens at different stages of plant development and their individual organs.

Dynamic Supervision and Control of VOCs Emission From China’s Furniture Manufacturing Based on Big Data and IoT

How to effectively monitor and prevent volatile organic compounds (VOCs) in furniture manufacturing has become the key to solving the dilemma between furniture industry development and public health. Based on the combination of VOCs emission standards and prevention policies of China’s furniture manufacturing, this article explores the path of dynamic monitoring, intelligent prevention, and control of VOCs embedded in furniture manufacturing with big data and IoT and puts forward feasible VOCs control technologies in the whole process of China’s furniture manufacturing, including source, process, and end. Herein, dynamic monitoring, intelligent prevention, and control of VOCs in furniture manufacturing have important reference significance for the prevention and control of VOCs in other industries, such as coal chemical industry, rubber products, engineering machinery, and coiled materials.

Abnormal Respiratory Symptoms of Workers and Sampling of Organic Vapors Using Solid-phase Microextraction Devices in a Golf Ball Manufacturing Factory

The ink that is used in the mark printing, and the protective paints that are sprayed on golf balls as surface and primer layers are the main sources of volatile organic compounds (VOCs) in a golf ball manufacturing factory. In this investigation, workers’ exposures to VOCs were evaluated using a needle trap sampler (NTS), which is a micro sampling device, and the results of an analysis using a gas chromatography mass spectrometer were compared to the samples that were collected in charcoal adsorption tubes with respect to VOC content. Ethyl acetate and n-butyl acetate are main compounds that are emitted in the painting and printing of golf ball. The highest worker time weighted average exposure concentration of n-butyl acetate was 16.92 ppm, and that for ethyl acetate was 19.69 ppm, as measured in a closed spray room. Painters’ and printers’ symptoms of respiratory tract abnormalities (RTA) were strongly correlated with their exposures to organic solvents as determined from the answers to a questionnaire survey on workers’ RTA symptoms. An NTS can be used as an alternative to charcoal tubes for sampling organic solvents to which workers are exposed, based on the differences in the limiting VOC analysis concentrations of both sampling devices. Due to lighter weight and lower cost than the traditional charcoal tube, which has to be connected to a sampling pump, therefore, NTS should be promoted as a routine VOC monitoring device in the workplace.

High-Performance VOC Quantification for IAQ Monitoring Using Advanced Sensor Systems and Deep Learning

With air quality being one target in the sustainable development goals set by the United Nations, accurate monitoring also of indoor air quality is more important than ever. Chemiresistive gas sensors are an inexpensive and promising solution for the monitoring of volatile organic compounds, which are of high concern indoors. To fully exploit the potential of these sensors, advanced operating modes, calibration, and data evaluation methods are required. This contribution outlines a systematic approach based on dynamic operation (temperature-cycled operation), randomized calibration (Latin hypercube sampling), and the use of advances in deep neural networks originally developed for natural language processing and computer vision, applying this approach to volatile organic compound measurements for indoor air quality monitoring. This paper discusses the pros and cons of deep neural networks for volatile organic compound monitoring in a laboratory environment by comparing the quantification accuracy of state-of-the-art data evaluation methods with a 10-layer deep convolutional neural network (TCOCNN). The overall performance of both methods was compared for complex gas mixtures with several volatile organic compounds, as well as interfering gases and changing ambient humidity in a comprehensive lab evaluation. Furthermore, both were tested under realistic conditions in the field with additional release tests of volatile organic compounds. The results obtained during field testing were compared with analytical measurements, namely the gold standard gas chromatography mass spectrometry analysis based on Tenax sampling, as well as two mobile systems, a gas chromatograph with photo-ionization detection for volatile organic compound monitoring and a gas chromatograph with a reducing compound photometer for the monitoring of hydrogen. The results showed that the TCOCNN outperforms state-of-the-art data evaluation methods, for example for critical pollutants such as formaldehyde, achieving an uncertainty of around 11 ppb even in complex mixtures, and offers a more robust volatile organic compound quantification in a laboratory environment, as well as in real ambient air for most targets.

Selective detection of VOCs using microfluidic gas sensor with embedded cylindrical microfeatures coated with graphene oxide

Volatile organic compounds (VOCs) are major environmental pollutants. Exposure to VOCs has been associated with adverse health outcomes. The monitoring of hazardous VOCs is a vital step towards identifying their presence and preventing the risk of acute or chronic exposure and polluting the environment. One of the challenges associated with monitoring VOCs is selectivity of the sensor. Microfluidic gas sensors offer selective and sensitive detection capabilities that have been recently applied for detection of VOCs. In this study, we achieve improved selectivity for detection of a range of VOCs by adding micro- and nanofeatures to the microchannel of microfluidic gas sensors. First, microfeatures are embedded into the microchannel and their geometries are optimized using Taguchi design of experiment method. In the next step the microfeatures embedded microchannel is coated with graphene oxide, to increase the surface to volume ratio by introducing nanofeatures to the surfaces. The nano- and microfeatures are characterized by SEM, XPS, and water contact angle measurement. Finally, the changes in the sensor response are compared to plain microfluidic gas sensor, the results show an average of 64.4% and 120.9% improvement in the selectivity of the sensor with microfeatures and both nano- and microfeatures, respectively

The Recovery of Volatile Organic Compounds and Volatile Sulfur Compounds in Fused-Silica Lined Canisters, Polyvinyl Fluoride/Tedlar Bags, and Foil-Lined Bags

Accurate and precise monitoring of volatile organic compounds (VOCs) and volatile sulfur compounds (VSCs) is critical to protect individuals against occupational and environmental exposure. Whole-air sampling containers are commonly employed in monitoring, such as fused-silica lined (FSL) canisters, polyvinyl fluoride (PVF) bags, and foil-lined bags. However, these containers have not yet been fully validated, and previous recovery studies are weakened by contradictory findings, short study time, no humidified samples, and unfeasibly high concentrations of VOCs and VSCs. This study evaluated FSL canisters, PVF bags, and foil-lined bags for the recovery of VOCs and VSCs over a period of 20 and 14 days, respectively. This recovery evaluation aimed to quantify the recovery over time of 64 VOCs and 14 VSCs at practical concentrations in the previously specified containers. To better represent field samples, sample containers were prepared at a relative humidity (RH) of 40%, with each set prepared at a “high” (20 ppb for VOCs and 500 ppb for VSCs) and “low” concentration (1 ppb for VOCs and 7 ppb for VSCs). Containers were analyzed intermittently throughout the evaluation period, and sample results were modeled using a first-order natural decay model. From the findings, modeling constants were determined by regression, and a majority (70%) of VOC and VSC models were found to be a good fit (R2 > 0.8). PVF bags were found to have higher recoveries for many VSCs than foil-lined bags, and were stable for periods similar to or longer than previously believed. FSL canisters showed a full recovery (>90%) for all VOCs and VSCs over the entire length of the evaluation (20 days for VOCs, 14 days for VSCs). Foil-lined bags were found to have lower recoveries for all VSCs compared to PVF bags.

A Low-Power Wearable E-Nose System Based on a Capacitive Micromachined Ultrasonic Transducer (CMUT) Array for Indoor VOC Monitoring

Volatile organic compounds (VOCs) are pervasive in the environment and their real-time continuous monitoring can facilitate better understanding of their effects on human health by combining environmental factors with physiological conditions. The scope of wearable sensors for detection of VOCs is evident as the accuracy of the sensor prediction depends on its proximity to the VOC source along with the sensitivity and selectivity of the sensor itself. In this paper, we present a low-power wearable e-nose system based on a capacitive micromachined ultrasonic transducer (CMUT) array. CMUTs offer inherent benefits of excellent mass resolution, easy array fabrication, and integration with electronics, which make them an appropriate choice as a transducer element for gravimetric e-nose systems. A 5-channel CMUT sensor array was chemically functionalized and used for the detection of four volatiles, ethanol, toluene, p-xylene, and styrene. All the channels of the sensor array achieved a resolution below 10 ppm within 0.2–3% of OSHA-PEL time-weighted average (TWA) for each volatile. For each test cycle, the maximum frequency shift, the rate of adsorption, and the rate of desorption were extracted as features. Linear discriminant analysis (LDA) was applied to visualize the discrimination performance of the sensor array. The system performance was characterized using an automated testing system. The presented sensor system can be used for identification of volatiles with suitable pattern-recognition techniques.

Nature of Volatile Organic Matter in Lake Sediments as a Reflection of Paleoclimate Changes Occurring at 4 ka in the Central Qaidam Basin

This study explores the paleoclimate changes around the 4 ka BP period in the central Qaidam Basin (QB), assessing the differences in spectral characteristics and organic composition of salt lake sediments under different climate change conditions. Sediment samples (10-m-depth profile) were collected from the middle of dry salt flats in East Taijinar Lake (China). Sediment organic matter (SOM) was assessed by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). Results showed a significant difference in the TOC content of sediments with different lithological characteristics. A lower TOC content in salt-bearing strata was attributed to the extreme sedimentary environment with minimal exogenous inputs. FTIR spectroscopy revealed that the SOM in sediments included aliphatic C, ketones and alcohols. Sediments of salt-bearing strata generally exhibited a rise in the content of ketone C=O groups and a decrease in aliphatic C, with an equal content of alcohols compared with silty sand. Therefore, exogenous OM and the content of TOC in silty sand strata are higher than in salt-bearing strata, indicating that the paleoclimate became warmer and wetter after 4 ka BP. GC-MS analysis showed a significant difference between the phenol and aldehyde content in different strata, further indicating that the paleoclimate changed from dry to relatively warm around 4 ka BP. Seven organic compound types were identified in SOM, including aldehydes, hydrocarbons, phenols, esters, ketones, alcohols, and furans. Different strata exhibited different distributions of organic compounds, with particularly high concentrations of aldehydes in salt-bearing strata and phenols in silty sand. Correlation analysis was performed between detrital minerals and OM types in all samples. Results showed a strong positive correlation between detrital minerals and phenols and a strong negative correlation between detrital minerals and aldehydes, with a negative correlation also identified between detrital minerals and ketones. Overall, the reduction in volatile organic compounds demonstrates that the paleoclimate changed from cooler and dry to wet and warm around the 4 ka BP period in the central QB, with the carbon preference index and n-alkane values further demonstrating these results. This study also confirms the importance of volatile organic compound monitoring to assess paleoclimate changes.

Field evaluation of a low-uptake VOC passive sampler suitable for long-term deployments

Passive samplers have proven to be effective for continuous monitoring of volatile organic compounds (VOCs) in ambient air in remote, urban and industrial environments. Thermal desorption tubes fitted with endcaps that facilitate passive uptake through diffusion are now routinely used for monitoring fugitive benzene emissions from refineries and petrochemical facilities across North America (EPA Method 325A/B). However, deployment periods of 14 days are typically employed to minimize the risk of poor retention, requiring 26 deployments per year to return an annual average concentration for comparison with chronic exposure health-based standards. Here, we explore extending the deployment duration of these passive samplers to one, two and three months by limiting VOC uptake rates using an alternative diffusive endcap featuring a smaller cross-sectional area. Field testing was performed beside a major highway during two separate three-month campaigns. Uptake rates for benzene, toluene, ethylbenzene and xylenes (BTEX) were observed to remain linear for deployments of up to three months when using the low-uptake endcaps. Application of the low-uptake endcaps and the uptake rates determined here will enable annual average concentrations of BTEX to be calculated using only four tube deployments per year. The cost savings associated with this decreased deployment frequency will facilitate increased spatial resolution during future exposure assessment studies. The stability of selected air toxics within the tubes was also assessed and the results suggest that while aromatic VOCs are stable for storage times of at least 70 days, chloroform and trichloroethylene begin to degrade within two weeks of sampling.

Photoionization-induced NO+ chemical ionization time-of-flight mass spectrometry for rapid measurement of aldehydes and benzenes in vehicles

In-vehicle air pollution has become a major concern to public health in recent years. The traditional analytical methods for detection of volatile organic compounds (VOCs) pollutants in air are based on gas chromatography - mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC), including complicated pretreatment and separation procedures, which are not only time-consuming and labor-intensive, but also incapable of simultaneously measuring both aldehydes and benzenes. In this work, a new photoionization-induced NO+ chemical ionization time-of-flight mass spectrometry (PNCI-TOFMS) was developed for real-time and continuous measurement of aldehydes and benzenes in vehicles. High-intensity NO+ reactant ions could be generated by photoionization of NO reagent gas, and efficient chemical ionization between NO+ reactant ions and analyte molecules occurred to produce adduct ions M·NO+ at an elevated ion source pressure of 800 Pa. Consequently, the achieved LODs for aldehydes and benzenes were down to sub-ppbv within 60 s. The analytical capacity of this system was demonstrated by continuous and online monitoring of in-vehicle VOCs in a used car, exhibiting broad potential applications of the PNCI-TOFMS in air pollutants monitoring and in-vehicle air quality analysis.