Monitoring Of Volatile Organic Compounds Research Articles

Rapid and Visual Favor Analysis Using Gas Chromatography-Ion Mobility Spectrometry (GC-IMS) in Meat Products: Research Progress and Future Trends

The flavor profile of meat and its processed products is highly volatile and subject to significant changes during storage, processing, and transportation. It is therefore crucial to monitor the flavor of meat to evaluate sensory quality and protect consumer health and safety. Gas chromatography-ion mobility spectrometry (GC-IMS) has become increasingly popular due to its advantages of being nondestructive, rapid, and capable of trace detection. The analysis of volatile organic compounds (VOCs) using this technique is continuously applied in the assessment of food freshness, origin traceability, and adulteration detection. GC-IMS has emerged as a promising tool for accurate monitoring and characterization of VOCs in food, particularly in the field of meat flavor analysis. Its applications include meat product authentication, adulteration detection, processing and storage-related flavor changes, and freshness monitoring. This paper provides a comprehensive overview of the working principle of GC-IMS and its applications in meat flavor analysis, while exploring future trends and potential limitations associated with the technique.

A High-Precision Monitoring Method Based on SVM Regression for Multivariate Quantitative Analysis of PID Response to VOC Signals

In the moist environment of soil-water-air, there is a problem of low accuracy in monitoring volatile organic compounds (VOCs) using a photoionization detector (PID). This study is based on the PID water-soil-gas VOC online monitor developed by this group, online monitoring of the concentration of different constituents of VOCs in different production enterprises of the petroleum and chemical industries in Shandong Province, with the concentration of the laboratory test, to build a relevant model. The correlation coefficient about the PID test concentration and the actual concentration correlation coefficient was obtained through the collection of a large number of data trainings. Based on the application of PID in VOC monitoring, the establishment of a PID high-precision calibration model is important for the precise monitoring of VOCs. In this paper, multiple quantitative analyses were conducted, based on SVM regression of PID response to VOC signals, to study the high-precision VOC monitoring method. To select the response signals of PID under different concentrations of environmental VOCs measured by the research group, first, the PID response to VOC signals was modeled using the support vector machine principle to verify the effect of traditional SVM regression. For the problem of raw data redundancy, calculate the time-domain and frequency-domain characteristics of the PID signal, and conduct the principal component analysis of the time-domain of the PID signal. In order to make the SVM regression more generalized and robust, the selection of kernel function parameters and penalty factor of SVM is optimized by genetic algorithm. By comparing the accuracy of PID calibration models such as PID signal feature extraction, SVM regression, and principal component analysis SVM regression, the superiority of photoionization detector using the signal feature extraction PCA-GA-SVM method to monitor VOCs is verified.

Online headspace monitoring of volatile organic compounds using proton transfer reaction-mass spectrometry: Application to the multiphase atmospheric fate of 2,4-hexadienedial

Chemical processes in clouds have been suggested to contribute significantly to the mass of organic aerosol particles in the atmosphere. Experimental and theoretical evidence suggest that organic mass production in clouds can be substantial and depends on the concentration of organic precursor compounds available in the gas phase. The present study aims at studying the aqueous phase reactivity of one of these overlooked precursors, i.e. 2,4-hexadienedial, an important and toxic intermediate in the atmospheric oxidation of aromatic species. Cautious synthesis and purification of 2,4-hexadienedial was performed. Its effective Henry's law constant was measured using a new simple and fast method based on online flow-injection analysis. The reactivity of 2,4-hexadienedial in the aqueous phase relevant to atmospheric conditions was studied, including hydrate formation, photolysis, ∙OH- and SO4∙--oxidation as well as reaction with NH3. The results revealed a low hydration constant compared to other dicarbonyls (Khyd1 = 7 × 10−2) and no dihydrate formation, indicating in an intermediate solubility (KH = 1.0 × 104 M atm−1) and high absorption cross sections (σ278nm > 10−16 cm2 molecule−1). Compared to its gas phase photolysis, its aqueous phase photolysis showed low quantum yields (Φ290–380nm = 0.9 %), and a significant red shift of the absorbance maximum, leading to a fast aqueous photolysis kinetics (Jaq,atm = 8.7 × 10−5 s−1) under atmospheric solar radiation, but no triplet state formation was detected. Radical oxidation experiments revealed extremely rapid oxidation kinetics (k∙OH = 1.10 × 1010 M−1 s−1 and kSO4∙- = 1.4 × 109 M−1 s−1) driven by fast addition of the radicals to the unsaturated bonds. In contrast, the reaction with aqueous NH3 (kNH3 = 2.6 × 10−3 M−1 s−1) was found slower than glyoxal and 2-butenedial, likely due to the hyperconjugation of 2,4-hexadienedial. Using these new data complemented with assumed aqueous phase kinetics (for NO3, 3C* and 1O2 reactions) and previous gas-phase kinetic ones, the multiphase atmospheric fate of 2,4-hexadienedial was established under atmospheric conditions reported from previous field measurements and models. The results revealed a short day lifetime (∼1 h) and a long night lifetime (>12 h). It was shown that daytime atmospheric chemistry of 2,4-hexadienedial can be influenced by aqueous-phase reactivity during cloud events, up to ∼50 % under thick cloud conditions (Liquid Water Content >2000 g/m3), indicating that even a compound of intermediate solubility can be strongly affected by condensed-phase reactivity. Besides its fast aqueous phase reactivity towards ∙OH and photolysis, its daytime condensed-phase reactivity may be driven by reactions with dissolved triplet states (3C*), up to 35 %, highlighting the need to study further the kinetics, the nature and concentrations of dissolved 3C* under various atmospheric conditions. In addition, the molecular properties and atmospheric behavior of 2,4-hexadienedial were found different from those of glyoxal and 2-butenedial, highlighting the need for detailed atmospheric reactivity studies of polyfunctional compounds, in particular unsaturated compounds.

Vortex Engineering on Oxide Bowl‐Coated Oxide/Gold Dual‐Layer Array for Dual Electrical/Spectroscopic Monitoring of Volatile Organic Compounds

AbstractIntegrating real‐time electrical gas sensing and highly identifiable surface‐enhanced Raman spectroscopy (SERS) for volatile organic compounds (VOCs) monitoring holds significant potential for safeguarding public health and safety. However, this technique remains in the proof‐of‐concept stage because the performance and reproducibility of devices fall short of meeting the practical application requirements. This work addresses this challenge by employing vortex engineering on a bifunctional dual‐layer array of Ni‐doped SnO2 (Ni‐SnO2) bowl‐coated on Ni‐SnO2/Au/SiO2 and developing highly reproducible device fabrication. In the dual‐layer array, vortices generated in upper Ni‐SnO2 bowls slow down the VOC flow and direct its delivery to gaps between lower Ni‐SnO2/Au/SiO2 units that are critical to SERS and electrical sensing. Experimental results show that the vortex effect in the array enables a low limit of detection of 10 ppb with a response and recovery in seconds. The excellent practicality of the array has been demonstrated through a ca. 100 hours of quantitative dual‐monitoring of styrene in a spacious environment (~60 m3) with a 5‐meter distance between the leakage source and the array. This work advances dual‐monitoring sensors for practical applications and offers insights for designing gas‐sensing materials and devices.

Eye-Readable and Wearable Colorimetric Sensor Arrays for In Situ Monitoring of Volatile Organic Compounds.

Wearable sensors utilize changes in color as a response to physiological stimuli, making them easily recognizable by the naked eye. These colorimetric wearable sensors offer benefits such as easy readability, rapid responsiveness, cost-effectiveness, and straightforward manufacturing techniques. However, their applications in detecting volatile organic compounds (VOCs) in situ have been limited due to the low concentration of complex VOCs and complicated external interferences. Aiming to address these challenges, we introduced readable and wearable colorimetric sensing arrays with a microchannel structure and highly gas-sensitive materials for in situ detection of complex VOCs. The highly gas-sensitive materials were designed by loading gas-sensitive dyes into the porous metal-organic frameworks and further depositing the composites on the electrospun nanofiber membrane. The colorimetric sensor arrays were fabricated using various gas-sensitive composites, including eight dye/MOF composites that respond to various VOCs and two Pd2+/dye/MOF composites that respond to ethylene. This enables the specific recognition of multiple characteristic VOCs. A microfluidic channel made of polydimethylsiloxane (PDMS) was integrated with different colorimetric elements to create a wearable sensor array. It was attached to the surface of fruits to collect and monitor VOCs using the DenseNet classification method. As a proof of concept, we demonstrated the feasibility of the wearable sensing system in monitoring the ripening process of fruits by continuously measuring the VOC emissions from the skin of the fruit.

Traceability tagging of volatile organic compound sources and their contributions to ozone formation in Suzhou using vehicle-based portable single-photon ionization mass spectrometry

BackgroundIn recent decades, there has been an increasing global preoccupation with atmospheric volatile organic compounds (VOCs). Given the significant impact of VOCs as pollutants and essential precursors of ozone (O3) in urban and industrial areas, it is imperative to identify and quantify the sources of their emissions to facilitate the development and implementation of effective environmental control strategies.MethodsA mobile laboratory vehicle equipped with a single-photon ionization–time-of-flight mass spectrometer (SPI–TOFMS) and a navigation system was employed to establish the traceability of VOCs that contribute to the formation of ozone in Suzhou Industrial Park. The method exhibited a favorable detection limit of 0.090 ppbv, accompanied by a mass resolution of 1500 for the instrument and a correlation coefficient ≥ 0.990. A positive matrix factorization (PMF) model was utilized to determine the source appointment of the VOCs.ResultsThe study tentatively traced and identified the VOCs emissions source and their contribution to ozone formation in Suzhou. Using the PMF model, the sources of VOCs were profiled: three primary sources of VOCs were identified, namely, vehicular emissions, an industrial solvent, and biofuel combustion. Alkanes groups were found to be the most abundant VOCs species, accounting for 60% of the total VOCs, followed by aromatics and alkenes. Maximum incremental reactivity (MIR) quantifies the impact of photochemical reaction mechanism on the potential ozone formation.ConclusionsThe findings of this study complement existing knowledge on the pollution status of atmospheric VOCs and highlight the correlation with ozone formation potential in Suzhou. The aforementioned sources were identified as the primary factors responsible for the pollution in Suzhou. The successful implementation of SPI–TOFMS has demonstrated a promising methodology that is well-suited for the real-time and online monitoring of VOCs in the atmosphere. In addition, a library for identifying VOC fingerprints from the same plant was established. This library serves as a comprehensive resource for establishing on-site VOC traceability, estimating source apportionment, and evaluating their impact on ozone formation.

Discrimination of the geographical origin of peaches by the monitoring of volatile organic compounds by gas chromatography with mass spectrometry and chemometric tools

The peach is one of the most popular and widely consumed fruits in Europe. Spain is the largest peach-producing country in the world with several growing areas recognised by consumers. This work focuses on the development, optimisation and validation of a non-targeted metabolomics strategy for the determination of peach volatile organic compounds from different origins by headspace gas chromatography coupled to mass spectrometry (HS–GC–MS). The volatil profile found in each sample is used to classify peaches according to their origin. The results obtained were processed using MS-DIAL software and 279 features were detected, of which 102 volatile compounds were tentatively identified and 30 of them could also be quantified. In addition, the areas of all the features were used to build models based on orthogonal partial least squares discriminant analysis (OPLS-DA) to differentiate peaches according to their geographical origin. A very promising model was obtained, with a validation rate of 90.32%, which means that it could be used to guarantee the Protected Designation of Origin of different peaches with a simple analysis.

Practical organic electronic noses using semi-permeable polymer membranes

Electronic noses (E-noses) mimic olfactory organs and quantify volatile organic compounds (VOCs), emulating the sense of smell, with applications in real-time monitoring of VOCs in food, healthcare, and law enforcement industries. Organic field-effect transistor (OFET) based sensors can be fabricated in large arrays by economical processes, however, lack the selectivity necessary to differentiate wide varieties of VOCs. Here, we explore the use of permeable polymer membranes with OFET sensors to improve their selectivity. Acylated poly(vinyl alcohol) (PVA) derivatives were synthesized, characterized, and evaluated in OFET vapor sensors as tunable membranes. Sensors with and without acylated PVA membranes were tested with VOC analytes. By monitoring drain current over time, we found that membranes dramatically changed responses to different analytes. We show that VOCs including methanol, ethanol, hexane, toluene, tetrahydrofuran, methyl ethyl ketone, and ethyl acetate can all be detected and differentiated with much greater selectivity than sensors without membranes. In particular, methanol and ethanol, which are difficult to differentiate in vapor sensors, showed significant quantitative differences in the initial slope (0.0403 s−1 vs 0.0192 s−1 respectively; 6 σ) and decay constants (5.5 s vs 15.9 s respectively; 26 σ) of their current vs time responses, allowing methanol and ethanol to be differentiated with 100 % confidence. This approach enables the economical fabrication of large varieties of unique organic vapor sensors by simply changing the membrane layer and results in an outstanding level of selectivity for OFET vapor sensors.

Pollution Characteristics，Source Analysis，and Activity Analysis of Atmospheric VOCs During Winter and Summer Pollution in Zhengzhou

In order to study the pollution characteristics of volatile organic compounds （VOCs）， continuous monitoring of VOCs in two pollution processes was conducted in June and December 2021 in Zhengzhou. Combined with meteorological conditions， the pollution characteristics， source contributions， and reactivity of VOCs in winter and summer were compared and analyzed. The results showed that the volume fraction of atmospheric VOCs in two episodes were （27.92±12.68）×10-9 and （24.30±5.93）×10-9， respectively. The volume fraction of atmospheric VOCs in the haze pollution process in winter was larger than that in the ozone pollution process in summer. The analysis results of winter sources were as follows： industrial source （27.0%）， motor vehicle source （22.5%）， combustion source （20.1%）， solvent use source （16.3%）， and oil and gas volatilization source （14.1%）. The analysis results of summer sources were as follows： motor vehicle source （24.8%）， industrial source （24.1%）， solvent source （17.4%）， oil and gas volatilization source （14.2%）， combustion source （11.2%）， and plant source （8.4%）. The results of the smog production model showed that the proportion of days in the synergistic control zone of VOCs during the two pollution processes in summer （66.7%） was smaller than that in winter （100.0%）. The secondary reaction activity results showed that the average ·OH loss rate （L·OH） values in winter and summer were 4.12 s-1 and 4.75 s-1， respectively. The average ozone formation potential （OFP） values in summer were 108.36 μg·m-3. The olefins were dominant in the top ten species due to L·OH and OFP contributions in summer. The total SOAFP values in winter in Zhengzhou were 54.38 μg·m-3. Among the top ten species contributing to SOAFP in winter， nine were aromatic hydrocarbons.

Direct Online Monitoring of Mouse Exhaled Breath for Diabetes Assessment Using Corona Ionization Mass Spectrometry

Since certain types of diabetes are reversible and curable in the early stages, early detection is crucial for effective treatment. Exhaled breath analysis, a noninvasive technique, is increasingly recognized for its potential in health monitoring, providing insights into an organism’s metabolic state more directly than blood glucose tests. This work developed an in situ method utilizing corona ion source mass spectrometry for real-time direct monitoring of volatile organic compounds (VOCs) in mouse exhaled breath. The method was used to track breath changes in two mouse models with streptozotocin-induced diabetes throughout disease progression. Notably, variations in certain VOCs in exhaled breath correlated with blood glucose levels (BGLs) during diabetes development. For instance, in the type 1 diabetes model, acetone levels remained stable within 8 days after hyperglycemia (not significant, n.s.) compared to those in controls but showed a significant increase after 10 days (p < 0.001). In the type 2 diabetes model, isopropanol levels decreased (p < 0.001) during the prediabetes phase, when BGL changes were not significant (n.s.) compared to those in the healthy state. These results indicate that specific substances in exhaled breath change prior to noticeable BGL alterations. This study thus established the viability of direct online mass spectrometry for breath analysis in early diabetes detection and showed that this technique has potential for identifying clear clinical markers for early diabetes screening.

Real-Time and Online Monitoring of Hazardous Volatile Organic Compounds in Environmental Water by an Unmanned Shipborne Mass Spectrometer System.

Hazardous volatile organic compounds (VOCs) are one of the critical concerns in environmental water due to their toxicity to aquatic organisms and drinking water. Therefore, rapid detection of hazardous VOCs in environmental water is highly needed as many analytical methods are limited to on-site monitoring. In this work, we designed a novel unmanned shipborne mass spectrometer (US-MS) system for the real-time and online monitoring of hazardous VOCs in environmental water. The US-MS system consists of a miniaturized mass spectrometer, an automatic sampling device, a robust unmanned ship, and other monitoring and control devices. Along with the navigation route of the US-MS system, environmental water was continuously introduced into the MS system for the online and real-time detection of hazardous VOCs via a liquid/gas exchange membrane. Analytical performances of the US-MS system were investigated by a mixture of 10 VOCs showing low limits of detection (LODs: 0.31-1.26 ng/mL), good reproducibility (RSDs: 2.93-11.03%, n = 7), and excellent quantitative ability (R2 > 0.99). Furthermore, on-site detection and online monitoring of hazardous volatile contaminants such as benzene, chloroprene, and toluene in different aquatic environments such as rivers and lakes were successfully demonstrated, showing excellent field applicability of the US-MS system. Overall, the newly developed US-MS system could perform on-site, online, and real-time monitoring of complex VOCs in environmental water, showing good performances and versatile applications in water analysis.

Advances in the Application of Direct Injection Mass Spectrometry Techniques to the Analysis of Grape, Wine and Other Alcoholic Beverages.

Direct injection mass spectrometry (DIMS) entails the direct introduction of a gaseous sample into a mass analyser without prior treatment or separation. DIMS techniques offer the opportunity to monitor processes in time, with limits of detection as low as 0.5 parts per trillion in volume (for a 1 s measurement time) while providing results with high informational content. This review provides insight into current and promising future developments of DIMS in the analysis of grape, wine and other alcoholic beverages. Thanks to its unique characteristics, DIMS allows the online monitoring of volatile organic compounds (VOCs) released by grapes during fermentative bioprocesses or by wine directly from the glass headspace or during drinking. A DIMS-based approach can also be adopted to perform quality control and high-throughput analysis, allowing us to characterise the volatile profile of large sample sets rapidly and in a comprehensive fashion. Furthermore, DIMS presents several characteristic elements of green analytical chemistry approaches, catalysing an interest linked to the development of sustainable paths in research and development activities in the field of viticulture and oenology.

Advanced tetra amino (ATA-100) cobalt(II) phthalocyanine-based metallo-covalent organic polymer for sensitively detecting volatile organic compounds.

The synthesis and characterization of a novel covalent organic polymer cobalt (II) phthalocyanine (ATA-100) including tetra amino group is described for the first time. This covalent organic polymer (COP) is characterized by FTIR, TGA, RAMAN, PXRD, and SEM-EDS. The developed sensor is tested for acetone, ethyl butyrate, n-hexane, chloroform, and n-butyraldehyde in a range of 80-10,900 ppm. ATA-100 showed the highest sensitivity for ethyl butyrate. The results have confirmed the possibility of utilizing ATA-100 COP-based surface acoustic wave (SAW) sensors for a wide variety of applications, including indoor air quality and environmental monitoring of volatile organic compounds (VOCs).

A turn-on type vapofluorochromic methoxybenzylidene methanone Schiff base applied to wearable VOC sensor and smartphone-based detection

This study presents the synthesis, crystallographic data and photophysical properties of a donor-acceptor (D-A) compound, methoxybenzylidene methanone Schiff base (HMPPM). It shows remarkable vapofluorochromism, embodied as turn-on red fluorescence in response to volatile organic compounds (VOCs), with fast response and high signal contrast. HMPPM is further developed into a cellulose sensor via dip-dying method for VOCs detection. We further use RGB and CIELAB color spaces to quantify the vapofluorochromic fluorescence. The limits of detection (LOD) of the sensor reach ppm level. Furthermore, it was fabricated into a wearable VOC sensor, with the introduction of an endogenous/exogenous reference, which conduces to high accuracy and visual identification. The cellulose sensor can be tailored into diversified patterns, with controllable shape and size, which facilitated the encapsulation into various wearables, including shoes, hat and smart band, etc., succeeding in scenario-based VOCs detection. In addition, we built a smartphone-based sensing platform based on HMPPM, which achieves a ppm-level LOD in VOCs monitoring.

Mid-infrared self-difference frequency generation via random quasi-phase-matching in Cr:ZnSe laser

This study presents the first ever demonstration of self-difference frequency generation (DFG) under random quasi-phase-matching (RQPM) in a polycrystalline Cr:ZnSe gain medium. An RQPM-based self-DFG Cr:ZnSe laser was developed with broad vibronic spectroscopic properties along with a wide phase-matching spectral bandwidth, offering ultrabroad tunability of nanosecond mid-infrared pulses in the 7.6–16 µm spectral range by pumping with a Tm:YAG laser at 2.013 µm. Trace detection of N2O was performed by multi-pass absorption spectroscopy using an electronically tuned self-DFG output, controlled by an acousto-optic tunable filter. The proposed laser source is expected to find applications in the real-time monitoring of volatile organic compounds through differential absorption spectroscopy.

Comparison of anthocyanin and volatile organic compounds in juices and fruit wines made from blood oranges (Citrus sinensis L. Osbeck) at different maturity stages

The variation in profiles of anthocyanins and volatile organic compounds (VOCs) in juices and in the corresponding fruit wines made from blood oranges ripened at different maturity stages were investigated. The compositions of sugars and organic acids were monitored, as well. Original findings have been reported for the maturity effect on blood orange juices, while the impact of fruit ripening on wine is explored for the first time. Using UPLC-DAD-ESI-Q-TOF-MS, based on elution order, UV–vis spectra, fragmentation pattern, and authentic standards, thirteen individual anthocyanins were identified, nine common to unfermented and fermented blood orange samples, while four (identified as hydroxyphenyl-pyranoanthocyanins) generated from fermentation. The total anthocyanin content in unfermented blood orange juice showed dramatic increases during maturation, especially in the late maturity stage, while fermentation resulted in significant reductions. The monitoring of VOCs in blood orange and wines was provided via a combination approach of HS-GC-IMS and HS-SPME-GC-MS for the first time. Forty-five and ninety-one VOCs were identified by GC-IMS and GC-MS, respectively. The concentrations of alcohols, ketones, and terpenes decreased with maturity, while that of esters increased significantly during this period. Fermentation enhanced the complexity and intensity of VOCs, with all VOC categories except ketones showing 2.1−94.3 times increase after fermentation. This work improves the knowledge on the processing management of blood orange juice and wine in order to obtain superior quality products.

Supported fluorine-free ionic liquids with highly sensitive gas-sensing performance

Monitoring volatile organic compounds (VOCs) is of increasing significance in the fields of environmental protection, health and safety, economic issues in industries, etc. Ionic liquids (ILs) arouse a great interest as potential sensing materials for VOCs. Here, the gas-sensing ability of fluorine-free ILs such as [N4,4,4,4][MEEA], [P6,6,6,14][MEEA], and [P6,6,6,14][TpA] have been thoroughly investigated. These ILs with phosphonium and ammonium cations as well as fluorine-free anions were successfully supported on carboxyl and amino groups terminated surfaces (denoted as COOH and NH2) as electrical gas sensors to tailor the response to the electronic resistance after sensing of VOCs. The [P6,6,6,14][MEEA] IL supported by either COOH or NH2 exhibits the strongest electrical sensing response within five cycles at a 150 ppm concentration of acetone or toluene, followed by [P6,6,6,14][TpA], and [N4,4,4,4][MEEA] with the shorter ammonium cation exhibiting the weakest response. The achieved higher gas sensing capability of the supported [P6,6,6,14][MEEA] is strongly associated with the accelerated ion mobility reflected from the smaller friction coefficient (μ), while [N4,4,4,4][MEEA] possesses the highest μ and [P6,6,6,14][TpA] in between. The reduced friction coefficient of the supported [P6,6,6,14][MEEA] IL originates from the observed more ordered ion layering, speeding up the kinetics of gaseous molecules in the supported IL. The monitoring of VOCs in these supported ILs offers an excellent opportunity in e-nose sensing devices to easily and cost-effectively detect VOCs at ppm concentrations.

Brine Volatilome Changes Along the Spontaneous Fermentation of Spanish-Style cv. Chalkidiki Green Olives Under High and Low NaCl Conditions

Table olives are essential components of the Mediterranean diet. Yet, their contribution to salt intake has prompted efforts to reformulate traditional products via safe interventions, mainly focused on the fermentation step. The volatilomics approach is an important tool to assess the complex table olives fermentation. However, extensive data related to monitoring of volatile organic compounds (VOCs) in manufacturing process of Spanish-style cv. Chalkidiki green table olives are scarce in the literature. The present work systematically examines VOCs profile in brines during spontaneous fermentation of cv. Chalkidiki olives under high (8% w/v) and 50% lower NaCl content using selected combinations of chloride salts (NaCl, KCl, CaCl2) in pilot scale for two consecutive periods. VOCs were determined by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. Changes in the population of the dominant microbial groups, pH, and titratable acidity values were also investigated. A total of 56 VOCs were identified, including acids, alcohols, carbonyls, esters, and phenols. Multivariate data analysis explored the links between volatile metabolites, microbial groups, and fermentation stages under different NaCl conditions. The evolution of propanoic acid and 2-butanol was intriguing for monitoring a fermentation dominated by lactic acid bacteria under low NaCl conditions, while 3-methyl-1-butanol was indicative of yeast prevalence arising from seasonal variation and/or high NaCl processing. Τhe important contribution of acetic acid to the overall VOCs profile at a late fermentation stage was typical in low NaCl brines. The complete results could be beneficial for marker-assisted monitoring of the fermentation processes in the future.

A DFT Study of Volatile Organic Compounds Detection on Pristine and Pt-Decorated SnS Monolayers.

Real-time monitoring of volatile organic compounds (VOCs) is crucial for both industrial production and daily life. However, the non-reactive nature of VOCs and their low concentrations pose a significant challenge for developing sensors. In this study, we investigated the adsorption behaviors of typical VOCs (C2H4, C2H6, and C6H6), on pristine and Pt-decorated SnS monolayers using density functional theory (DFT) calculations. Pristine SnS monolayers have limited charge transfer and long adsorption distances to VOC molecules, resulting in VOC insensitivity. The introduction of Pt atoms promotes charge transfer, creates new energy levels, and increases the overlap of the density of states, thereby enhancing electron excitation and improving gas sensitivity. Pt-decorated SnS monolayers exhibited high sensitivities of 241,921.7%, 35.7%, and 74.3% towards C2H4, C2H6, and C6H6, respectively. These values are 142,306.9, 23.8, and 82.6 times higher than those of pristine SnS monolayers, respectively. Moreover, the moderate adsorption energies of adsorbing C2H6 and C6H6 molecules ensure that Pt-decorated SnS monolayers possess good reversibility with a short recovery time at 298 K. When heated to 498 K, C2H4 molecules desorbs from the surface of Pt-decorated SnS monolayer in 162.33 s. Our results indicate that Pt-decorated SnS monolayers could be superior candidates for sensing VOCs with high selectivity, sensitivity, and reversibility.

A Comparative Study of Ground-Gridded and Satellite-Derived Formaldehyde during Ozone Episodes in the Chinese Greater Bay Area

Formaldehyde (HCHO) plays an important role in atmospheric photochemical reactions. Comparative studies between ground-based and satellite observations are necessary to assess and promote the potential use of column HCHO as a proxy for surface HCHO and volatile organic compound (VOC) oxidation. Previous studies have only validated temporal and vertical profile variations at one point, with limited studies comparing horizontal spatial variations due to sparse monitoring sites. The photochemistry-active Chinese Greater Bay Area (GBA) is a typical megacity cluster as well as a large hotspot of HCHO globally, which recorded a high incidence of ozone (O3) pollution. Here, we conducted the first comparative study of ground-gridded (HCHOgg) and satellite-derived (HCHOsd) HCHO during typical O3 episodes in the GBA. Our results revealed a good correlation between HCHOgg and HCHOsd, with a correlation coefficient higher than 0.5. Cloud coverage and ground pixel sizes were found to be the dominant factors affecting the quality of HCHOsd and contributing to the varying satellite pixel density. Daily averages of HCHOsd effectively improved the HCHOsd accuracy, except in areas with low satellite pixel density. Furthermore, a new quality control procedure was established to improve HCHOsd from Level 2 to Level 3, which demonstrated good application performance in O3 sensitivity analysis. Our findings indicate that the correlation between satellite observations and surface air quality can be optimized by spatiotemporal averaging of hourly HCHOsd, given the advent of geostationary satellites. Considering the representative range of sampling sites in this comparative study, we recommend establishing VOC monitoring stations within a 50 km radius in the GBA to further analyze and control photochemical pollution.