Measurements Of Volatile Organic Compounds Research Articles

Unique Photoactivated Time-Resolved Response in 2D GeS for Selective Detection of Volatile Organic Compounds.

Volatile organic compounds (VOCs) sensors have a broad range of applications including healthcare, process control, and air quality analysis. There are a variety of techniques for detecting VOCs such as optical, acoustic, electrochemical, and chemiresistive sensors. However, existing commercial VOC detectors have drawbacks such as high cost, large size, or lack of selectivity. Herein, a new sensing mechanism is demonstrated based on surface interactions between VOC and UV-excited 2D germanium sulfide (GeS), which provides an effective solution to distinguish VOCs. The GeS sensor shows a unique time-resolved electrical response to different VOC species, facilitating identification and qualitative measurement of VOCs. Moreover, machine learning is utilized to distinguish VOC species from their dynamic response via visualization with high accuracy. The proposed approach demonstrates the potential of 2D GeS as a promising candidate for selective miniature VOCs sensors in critical applications such as non-invasive diagnosis of diseases and health monitoring.

Information fusion of stationary, mobile, and wearable consumer-grade sensors to confidently estimate bedroom ventilation rates

This study adds to the body of research investigating ventilation rates measured in residential dwellings. Using open-source Consumer-Grade Sensors (CGS), we measure Carbon Dioxide (CO2) to estimate ventilation rates under one of three conditions: CO2build-up when bedrooms were initially occupied, steady-state CO2 during the latter half of participants’ sleep episodes, and CO2decay after participants wake and vacate their bedroom. We do not ask participants to record their bedroom occupancy, but use information fusion to identify nightly occupied periods by cross-referencing home addresses to GPS measurements provided by their smartphones during sleep episodes identified by Fitbit wearable fitness trackers. We estimate 106 ventilation rates during build-up conditions which ranged from 0.04–1.36 h−1, 242 ventilation rates under steady-state conditions spanning 0.17–2.49 h−1, and 39 ventilation rates from decay conditions over a range of 0.06–1.05 h−1. In addition, we used occupied periods alongside times when GPS confirmed participants were away from home to label Indoor Air Quality (IAQ) data, and to train a Multi-Layer Perceptron (MLP) to classify occupancy based on CO2 and Total Volatile Organic Compound (TVOC) measurements. Using periods classified as occupied with at least 90% confidence, we estimated 116 additional steady-state ventilation rates spanning 0.25–2.49 h−1. Our results are consistent with more traditional and costly sensing approaches, and we conclude that information fusion of CGS is effective in measuring IAQ, detecting occupancy, and estimating ventilation rates.

Variations of Wintertime Ambient Volatile Organic Compounds in Beijing, China, from 2015 to 2019

Air quality in China significantly improved after strict regulations were put in place. To assess the efficacy of volatile organic compound (VOC) control strategies, online measurements of wintertime ambient VOCs at a Beijing urban location were taken in December and January from 2014 to 2019. We assessed the changes in mixing ratios of 81 VOC species and cancer risks of 10 hazard species. The impact of meteorology on VOC mixing ratios was decoupled using a machine-learning approach. The highest and lowest VOC mixing ratios were observed in wintertime 2017 (December 2016 and January 2017) and 2019 (December 2018 and January 2019), respectively, with a decrease in 63.5%. Both emission control policies and meteorological conditions helped reduce VOC mixing ratios in the winter in Beijing. Alkenes and alkynes decreased significantly from 2015 to 2019. In contrast, the contribution of aromatics increased considerably from 2015 to 2017, and many aromatics had higher mixing ratios in 2019 than in 2015, indicating that aromatics may be a key group for future air quality improvement. The cancer risks due to VOC exposure in the wintertime in Beijing in 2019 were lower than in other years but were still much higher than the safety level.

Influence of Wildfire on Urban Ozone: An Observationally Constrained Box Modeling Study at a Site in the Colorado Front Range.

Increasing trends in biomass burning emissions significantly impact air quality in North America. Enhanced mixing ratios of ozone (O3) in urban areas during smoke-impacted periods occur through transport of O3 produced within the smoke or through mixing of pyrogenic volatile organic compounds (PVOCs) with urban nitrogen oxides (NOx = NO + NO2) to enhance local O3 production. Here, we analyze a set of detailed chemical measurements, including carbon monoxide (CO), NOx, and speciated volatile organic compounds (VOCs), to evaluate the effects of smoke transported from relatively local and long-range fires on O3 measured at a site in Boulder, Colorado, during summer 2020. Relative to the smoke-free period, CO, background O3, OH reactivity, and total VOCs increased during both the local and long-range smoke periods, but NOx mixing ratios remained approximately constant. These observations are consistent with transport of PVOCs (comprised primarily of oxygenates) but not NOx with the smoke and with the influence of O3 produced within the smoke upwind of the urban area. Box-model calculations show that local O3 production during all three periods was in the NOx-sensitive regime. Consequently, this locally produced O3 was similar in all three periods and was relatively insensitive to the increase in PVOCs. However, calculated NOx sensitivities show that PVOCs substantially increase O3 production in the transition and NOx-saturated (VOC-sensitive) regimes. These results suggest that (1) O3 produced during smoke transport is the main driver for O3 increases in NOx-sensitive urban areas and (2) smoke may cause an additional increase in local O3 production in NOx-saturated (VOC-sensitive) urban areas. Additional detailed VOC and NOx measurements in smoke impacted urban areas are necessary to broadly quantify the effects of wildfire smoke on urban O3 and develop effective mitigation strategies.

Anthropogenic VOCs in the Long Island Sound, NY Airshed and their role in ozone production

Cities like New York and areas downwind have poor air quality due to pollution generated by human activity. Ozone (O3), a harmful pollutant, is produced in the atmosphere from photochemical reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx). Aircraft measurements of VOCs obtained during an O3 event in May 2017 over the New York City metropolitan area, Long Island Sound, and Connecticut show concentrations of O3 exceeding 100 ppb between ∼200 and 500 m above the surface. During this campaign, 35 whole air canisters were collected, and 50 VOC species were measured. Biogenic isoprene often dominates VOC reactivity in summer months, but analysis of the chemistry in the middle of the Planetary Boundary Layer (PBL) indicates that primary anthropogenic VOCs such as propylene and isopentane played a major, possibly dominant role in this Spring 2017 O3 event and are suitable targets for control.The most important measured anthropogenic VOCs ranked by OH reactivity were propylene and isopentane, with n-butane and 1-pentene also playing a substantial role. The most important anthropogenic VOCs ranked by Ozone Formation Potential (OFP) were again propylene and isopentane, but aromatic species like toluene were also large contributors. Isoprene ranked tenth in importance for OFP. For VOC species with short lifetimes, like isoprene and propylene, mixing of air parcels throughout the PBL means air above the surface may quickly become depleted of these VOCs, allowing longer-lived, anthropogenic VOCs to have a proportionally greater impact on photochemical O3 production aloft. Our observations indicate that VOC reactivity was much larger in the morning than in the afternoon, suggesting controls of propylene, isopentane, and aromatics overnight may be useful for reducing morning concentrations of VOCs and therefore possibly reduce maximum concentrations of O3 observed in the afternoon. Finally, because formaldehyde (HCHO) was not measured during these flights, and since oxygenates also contribute to O3 formation, we estimate the relative contribution of isoprene and propylene to HCHO formation using a box model. Propylene produces ∼25% and isoprene produces ∼4% of HCHO within the box model.

Multivariate data analysis strategy to monitor Trentingrana cheese real-scale production through volatile organic compounds profiling

Volatile organic compounds (VOCs) in cheese, as result of the chemical, physical and microbiological properties of the raw milk, are related to its sensory properties and consumer's acceptability. Measurement of VOCs can be related to the quality of the production process, highlighting changes in the raw materials or the process conditions. In the present study, we tested the suitability of ANOVA-Simultaneous Component Analysis (ASCA) to extract useful information from volatile organic compound data measured over two years of production of Trentingrana cheese in a real production context where several confounding factors are present.A total of 317 cheese wheels were collected from the 15 cooperative dairy factories every two months. The ASCA analysis indicates that the milk collection affects the VOC profiles. To deeper investigate this factor, an Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) model was developed to estimate the associations between VOCs and process characteristics of the dairy factory. Results showed that the milk collection procedure affects the content of organic acids, esters, and ketones of the cheeses.

Bimodal UV photoacoustic and fluorescence sensor for breath analysis

Breath analysis using spectroscopy techniques is coming up as one of the non-invasive methods for disease diagnosis. Among several spectroscopic methods, photoacoustic spectroscopy (PAS) and laser-induced fluorescence (LIF) are used to obtain information on sample's absorption and emission characteristics, respectively. In the present work, we present breath analysis results using a bimodal sensor using 266 nm UV laser, which can be used for both PAS and LIF measurements of volatile organic compounds (VOCs). The system is optimized using standard VOC samples to show limits of detection of the order of ppb-s. Preliminary breath analysis has been carried out for breath samples from Asthma patients and healthy volunteers. Principal component analysis has shown that the two sets of PAS and LIF data of Asthma and normal breath samples are discriminated from each other as distinct clusters enabling clear discrimination. Match/no match study using M-distance and spectral residual gives a sensitivity of 90 % and specificity of 96 % for PAS, and 85 % sensitivity and 86 % specificity for LIF, using optimized M-distance cutoff values. The receiver operating curve (ROC) and the area under the curve (AUC)-ROC shows that the method is quite suitable for applying bimodal spectroscopy for breath analysis. A comparison of the breath study of the same volunteers has been carried out using an E-nose to confirm the validity of UV laser-based PAS-LIF bimodal sensor.

Temperature dependence of volatile organic compound emissions from surface coatings: Inter-species difference observed in real indoor environments and mechanistic understanding

Coatings often cover two-thirds of the surfaces in indoor environments and represent important sources of indoor volatile organic compounds (VOCs). Temperature is known to affect VOC emission rates from coatings, yet inter-species difference in the temperature dependence still needs to be understood. Based on time-resolved VOC measurements in an indoor air campaign conducted in residences in Beijing, China, we identified dibasic ester (DBE), a solvent mixture often used in coatings, and found that the concentration ratios of DBE components exhibited strong temperature dependence in an apartment when the indoor temperature declined stepwise over a multiweek period. To interpret the observational results, we developed a simplified mechanistic model relating the temperature dependence of VOC emission rates from coated surfaces to the temperature dependence of the diffusion coefficient of the emitted VOCs in the coating layer and further to a predicable molecular property of the emitted VOCs, molar volumes at 0 K, based on the free-volume theory. This correlation was quantitatively verified using the DBE data as well as using the data of alkanes, another set of VOCs that might be emitted from coatings, observed in two apartments in the same campaign. Given that indoor temperature varies considerably over seasons and across regions, the correlation proposed herein may help better predict indoor VOC emissions from coatings.

Enigma of Urban Gaseous Oxygenated Organic Molecules: Precursor Type, Role of NOx, and Degree of Oxygenation.

Oxidation of volatile organic compounds (VOCs) forms oxygenated organic molecules (OOMs), which contribute to secondary pollution. Herein, we present measurement results of OOMs using chemical ionization mass spectrometry with nitrate as the reagent ion in Shanghai. Compared to those in forests and laboratory studies, OOMs detected at this urban site were of relatively lower degree of oxygenation. This was attributed to the high NOx concentrations (∼44 ppb), which overall showed a suppression on the propagation reactions. As another result, a large fraction of nitrogenous OOMs (75%) was observed, and this fraction further increased to 84% under a high NO/VOC ratio. By applying a novel framework on OOM categorization and supported by VOC measurements, 50 and 32% OOMs were attributed to aromatic and aliphatic precursors, respectively. Furthermore, aromatic OOMs are more oxygenated (effective oxygen number, nOeff = 4-6) than aliphatic ones (nOeff = 3-4), which can be partly explained by the difference in initiation mechanisms and points to possible discrimination in termination reactions. This study highlights the roles of NOx in OOM formation in urban areas, as well as the formation of nitrogenous products that might show discrimination between aromatic and aliphatic VOCs.

Heterogeneous chemistry of ozone with floor cleaning agent: Implications of secondary VOCs in the indoor environment

Human daily activities such as cooking, and cleaning can affect the indoor air quality by releasing primary emitted volatile organic compounds (VOCs), as well as by the secondary product compounds formed through reactions with ozone (O3) and hydroxyl radicals (OH). However, our knowledge about the formation processes of the secondary VOCs is still incomplete. We performed real-time measurements of primary VOCs released by commercial floor-cleaning detergent and the secondary product compounds formed by heterogeneous reaction of O3 with the constituents of the cleaning agent by use of high-resolution mass spectrometry. We measured the uptake coefficients of O3 on the cleaning detergent at different relative humidities in dark and under different light intensities (320 nm < λ < 400 nm) relevant for the indoor environment. On the basis of the detected compounds we developed tentative reaction mechanisms describing the formation of the secondary VOCs. Intriguingly, under light irradiation the formation of valeraldehyde was observed based on the photosensitized chemistry of acetophenone which is a constituent of the cleaning agent. Finally, we modeled the observed mixing ratios of three aldehydes, glyoxal, methylglyoxal, and 4-oxopentanal with respect to real-life indoor environment. The results suggest that secondary VOCs initiated by ozone chemistry can additionally impact the indoor air pollution.

In Vivo Low-Temperature Plasma Ionization Mass Spectrometry (LTP-MS) Reveals Regulation of 6-Pentyl-2H-Pyran-2-One (6-PP) as a Physiological Variable during Plant-Fungal Interaction.

Volatile organic compounds (VOCs) comprises a broad class of small molecules (up to ~300 g/mol) produced by biological and non-biological sources. VOCs play a vital role in an organism's metabolism during its growth, defense, and reproduction. The well-known 6-pentyl-α-pyrone (6-PP) molecule is an example of a major volatile biosynthesized by Trichoderma atroviride that modulates the expression of PIN auxin-transport proteins in primary roots of Arabidopsis thaliana during their relationship. Their beneficial relation includes lateral root formation, defense induction, and increased plant biomass production. The role of 6-PP has been widely studied due to its relevance in this cross-kingdom relationship. Conventional VOCs measurements are often destructive; samples require further preparation, and the time resolution is low (around hours). Some techniques enable at-line or real-time analyses but are highly selective to defined compounds. Due to these technical constraints, it is difficult to acquire relevant information about the dynamics of VOCs in biological systems. Low-temperature plasma (LTP) ionization allows the analysis of a wide range of VOCs by mass spectrometry (MS). In addition, LTP-MS requires no sample preparation, is solvent-free, and enables the detection of 6-PP faster than conventional analytical methods. Applying static statistical methods such as Principal Component Analysis (PCA) and Discriminant Factorial Analysis (DFA) leads to a loss of information since the biological systems are dynamic. Thus, we applied a time series analysis to find patterns in the signal changes. Our results indicate that the 6-PP signal is constitutively emitted by T. atroviride only; the signal shows high skewness and kurtosis. In A. thaliana grown alone, no signal corresponding to 6-PP is detected above the white noise level. However, during T. atroviride-A. thaliana interaction, the signal performance showed reduced skewness and kurtosis with high autocorrelation. These results suggest that 6-PP is a physiological variable that promotes homeostasis during the plant-fungal relationship. Although the molecular mechanism of this cross-kingdom control is still unknown, our study indicates that 6-PP has to be regulated by A. thaliana during their interaction.

MOF-199-based coatings as SPME fiber for measurement of volatile organic compounds in air samples: Optimization of in situ deposition parameters

In this study MOF-199-based solid-phase microextraction coating was synthesized using an in situ solvothermal method on a stainless steel substrate. The effects of solvent, metal salt, chemical modulator, and batch composition on the physicochemical characteristics of the MOF-199 coating were studied. The thickness of the MOF-199 coating increased by 18% when 15.2 mmol of acetic acid was used as an additive. Using 99.9% butanol as the solvent improved homogeneity (smaller crystallite size) of the MOF coating and decreased coating thickness by 7.5 times compared to those of 75% ethanol. Using Cu(OAc)2·H2O as the metal precursor did not lead to the growth of the MOF-199 layer on stainless steel cores. Whilst the use of Cu(NO3)2·3H2O allowed to obtain 6-, 21-, 34-, 62-, 94- and 105 µm MOF-199 SPME coatings. Responses of 7 volatile organic compounds by 34-µm and 62-µm MOF-199-based fibers were 1.2–8.5 times higher than those of commercial PDMS/DVB. The method developed for the quantification of BTEX in the air was characterized by high linearity (R2 = 0.9909–0.9993), low limits of detection (0.03–0.09 μg/m3), and quantification (0.09–0.31 μg/m3), high repeatability (1.0–6.4%) and reproducibility (4.5–8.0%). The spike recoveries ranged from 73% to 108%.

A novel VOC breath tracer method to evaluate indoor respiratory exposures in the near- and far-fields; implications for the spread of respiratory viruses

BackgroundSeveral studies suggest that far-field transmission (>6 ft) explains a significant number of COVID-19 superspreading outbreaks.ObjectiveTherefore, quantifying the ratio of near- and far-field exposure to emissions from a source is key to better understanding human-to-human airborne infectious disease transmission and associated risks.MethodsIn this study, we used an environmentally-controlled chamber to measure volatile organic compounds (VOCs) released from a healthy participant who consumed breath mints, which contained unique tracer compounds. Tracer measurements were made at 0.76 m (2.5 ft), 1.52 m (5 ft), 2.28 m (7.5 ft) from the participant, as well as in the exhaust plenum of the chamber.ResultsWe observed that 0.76 m (2.5 ft) trials had ~36–44% higher concentrations than other distances during the first 20 minutes of experiments, highlighting the importance of the near-field exposure relative to the far-field before virus-laden respiratory aerosol plumes are continuously mixed into the far-field. However, for the conditions studied, the concentrations of human-sourced tracers after 20 minutes and approaching the end of the 60-minute trials at 0.76 m, 1.52 m, and 2.28 m were only ~18%, ~11%, and ~7.5% higher than volume-averaged concentrations, respectively.SignificanceThis study suggests that for rooms with similar airflow parameters disease transmission risk is dominated by near-field exposures for shorter event durations (e.g., initial 20–25-minutes of event) whereas far-field exposures are critical throughout the entire event and are increasingly more important for longer event durations.Impact statementWe offer a novel methodology for studying the fate and transport of airborne bioaerosols in indoor spaces using VOCs as unique proxies for bioaerosols. We provide evidence that real-time measurement of VOCs can be applied in settings with human subjects to estimate the concentration of bioaerosol at different distances from the emitter. We also improve upon the conventional assumption that a well-mixed room exhibits instantaneous and perfect mixing by addressing spatial distances and mixing over time. We quantitatively assessed the exposure levels to breath tracers at alternate distances and provided more insights into the changes on “near-field to far-field” ratios over time. This method can be used in future to estimate the benefits of alternate environmental conditions and occupant behaviors.

The Relationship between Elemental Carbon and Volatile Organic Compounds in the Air of an Underground Metal Mine

Elemental carbon (EC) content in air is considered a proxy for the diesel exhaust impact at workplaces. This paper examines the possibility of estimating EC content in mine air on the basis of measurements of volatile organic compounds (VOC). The measurement study was carried out in an underground metal mine. Gas chromatography with mass spectrometry (GC/MS) was applied for VOC determination, and thermal-optical analysis (TOA) with an FID detector was utilized for EC measurements. A correlation was found between the measurements of EC and total VOC (TVOC) as well as the content of individual hydrocarbons C12–C14 in the air of an extraction zone in the mine. A regression model was developed which predicts EC based on C12, C13, and C14, considered individually, and the remaining VOCs detected with GC/MS taken in total. The model was statistically significant (p = 0.053), and it offered an EC prediction error of RMSE = 4.60 µg/sample. The obtained result confirms the possibility of using VOC measurements for the preliminary estimation of EC concentrations in mine air. This approach is feasible given the availability of portable GC/MS and offers easy and fast measurements providing qualitative and quantitative information.

Characteristics, sources of volatile organic compounds, and their contributions to secondary air pollution during different periods in Beijing, China

Continuous measurements of volatile organic compounds (VOCs), ozone (O3), fine particulate matter (PM2.5), and related parameters were conducted between April 2020 and March 2021 in Beijing, China, to characterize potential sources of VOCs and their impacts on secondary organic aerosols (SOAs) and O3 levels. The annual average mixing ratio of VOCs was 17.4 ± 10.1 ppbv, with monthly averages ranging from 11.6 to 25.2 ppbv. According to the empirical kinetic modeling approach (EKMA), O3 formation during O3 season was “VOCs-limited”, while it was in a “transition” regime during O3 pollution episodes. In the O3 season, higher ozone formation potential (OFP) of m/p-xylene, o-xylene, toluene, isopentane, and n-butane were evident during O3 pollution episodes, in line with the increasing contributions of solvent usage and coating, as well as gasoline evaporation to OFP obtained through a matrix factorization model (PMF). Aromatics contributed the most to the secondary organic aerosol formation potential (SOAFP). In the non-O3 season, the contribution of vehicle exhaust to SOAFP elevated on hazy days, thereby revealing the importance of traffic-derived VOCs for PM2.5 pollution. Our results indicate that the prior control of different VOC sources should vary by season, thereby facilitating the synergistic control of O3 and PM2.5 in Beijing.

Source apportionment of VOCs based on photochemical loss in summer at a suburban site in Beijing

Volatile organic compounds (VOCs) are critical precursors of photochemical smog. Quantitatively evaluating the VOC sources and their contributions to ozone formation provides valuable information for photochemical pollution abatement. However, due to the fast oxidization of VOCs during transport in the atmosphere, source apportionment via receptor models using measured VOC data inevitably has a systematic deviation. In this study, we conducted a field measurement of VOCs at a suburban site in Beijing and evaluated the influences of photochemical oxidization on VOC source contributions. The initial VOC concentration, defined as the sum of measured VOC concentration and their photochemical losses. The real-time photochemical age-based parameterization method and a sequential reaction model were applied to characterize the photochemical loss of VOCs. Also, the photochemical loss of VOCs was considered in the he positive matrix factorization (PMF) model. Photochemical losses, on average, accounted for 5.6% of total VOCs (TVOCs) and 59.2% of alkenes, indicating that the impact of photochemical reaction cannot be ignored. Alkanes were the most significant contributors to both measured and initial TVOCs, while the alkenes and oxygenated volatile organic compounds (OVOCs), especially ethylene and isoprene, contributed the most to ozone formation potential. By adopting the positive matrix factorization model, seven VOC sources were identified for both measured and initial TVOCs. Vehicular emissions, industrial sources, and biomass burning were the top three contributors to ambient TVOC. Photochemistry significantly influenced the results of source apportionment, e.g., the contribution of biogenic sources (+4.4%), industrial emissions (+2.5%) and solvent usage (+2.5%) based on initial VOCs were larger than that of measured VOCs, while the contribution of gasoline vehicular emissions (−9.9%) was lower than that of measured VOCs. Our results highlight the necessity of adequately considering the photochemical loss of VOCs for accurately apportioning the emission sources.

Two-year online measurements of volatile organic compounds (VOCs) at four sites in a Chinese city: Significant impact of petrochemical industry

Volatile organic compounds (VOCs) management has been recently given a high priority in China to mitigate ozone (O3) air pollution. However, there is a relatively poor understanding of VOCs due to their complexity and fewer observations. To better understand the pollution characteristics of VOCs and their impact on O3 pollution, two-year continuous measurements were conducted at four representative sites in Ji'nan, eastern China. These four sites cover urban, background, and industrial areas (within a petroleum refinery). Ambient VOCs showed higher concentrations at industrial site than at urban and background sites, owing to intensive emissions from petrochemical industry. The VOCs compositions present spatial heterogeneity with alkenes dominated in total reactivity at urban and background sites, while alkenes and aromatics together dominated at industrial site. The VOCs emission profile from petrochemical industry was calculated based on observational data, which revealed a huge impact on light alkanes (C2–C5), light alkenes (ethene), and aromatics (toluene and m/p-xylene). The positive matrix factorization (PMF) model analysis further refined the impact of different petrochemical industrial processes. Alkanes and alkenes dominated the emissions during refining process, while aromatics dominated during solvent usage process. Analysis by an observation-based model indicated stronger in-situ O3 production and higher sensitivity to nitrogen oxides at industrial site compared to urban and background sites. The reduction of VOCs emissions from petrochemical industry would significantly reduce the O3 concentrations. The analyses underline the significant impact of petrochemical industry on VOCs and O3 pollution, and provide important reference for the formulation of refined and effective control strategies.

Analysis of VOC emissions and O3 control strategies in the Fenhe Plain cities, China

Long-term continuous hourly measurements of ambient volatile organic compounds (VOCs) are scarce at the regional scale. In this study, a one-year hourly measurement campaign of VOCs was performed in Lvliang, Linfen, and Yuncheng in the heavily polluted Fenhe Plain region in China. The VOC average (±standard deviation, std) concentrations in Lvliang, Linfen, and Yuncheng were 44.4 ± 24.9, 45.7 ± 24.9, and 37.5 ± 25.0 ppbv, respectively. Compared to published data from the past two decades in China, the observed VOCs were at high concentration levels. VOCs in the Fenhe Plain cities were significantly impacted by industrial sources according to calculated emission ratios but were less affected by liquefied petroleum gas and natural gas (LPG/NG) and traffic emissions than those in megacities abroad. The emission inventories and observation data were combined for verification and identification of the key VOC species and sources controlling ozone (O3). Industrial emissions were the largest source of VOCs, accounting for 65%–79% of the total VOC emissions, while the coking industry accounted for 45.2%–66.0%. The emission inventories significantly underestimated oxygenated VOC (OVOC) emissions through the verification of VOC emission ratios. O3 control scenarios were analyzed by changing VOC/NOX reduction ratios through a photochemical box model. O3 control strategies were formulated considering local pollution control plans, emission inventories, and O3 formation regimes. The O3 reduction of reactivity-control measures was comparable with emission-control measures, ranging from 16% to 41%, which was contrary to the general perception that ozone formation potential (OFP)-based measures were more efficient for O3 reduction. Sources with high VOC emissions are accompanied by high OFP on the Fenhe Plain, indicating that the control of high-emission sources can effectively mitigate O3 pollution on this region.

Highly Time-Resolved and Nontargeted Characterization of Volatile Organic Compound Emissions from Face Masks

Face covering by masks has become a lifeline for humans to prevent the airborne transmission of highly infectious SARS-CoV-2. One of the side effects, however, is the release of volatile organic compounds (VOCs), which can hardly be fully understood based on traditional offline measurements. Here, for the first time, we performed highly time-resolved and nontargeted measurements of VOCs emitted from face masks using an ultrasensitive proton transfer-reaction quadrupole-interface time-of-flight mass spectrometer. We found diverse VOC species, some of which are toxic. The chemical structures of the major VOC species were identified to be from the chemicals and processes involved in mask production. High concentrations of VOCs emitted from surgical masks (predominant mask type) were all concentrated in the initial 1 h and then dropped rapidly to an acceptable level after a process of naturally airing out. Higher emissions from a surgical mask for children are likely due to their colorful cartoon patterns. Despite the lowest emissions, the N95 respirator with an active carbon layer required 6 h to remove the toxic methanol. We support mask wearing to curtail the COVID-19 pandemic, but our results highlight the importance of naturally airing out masks to reduce zero-distance inhalation of mask-emitted VOCs.

The Effect of Human Occupancy on Indoor Air Quality through Real-Time Measurements of Key Pollutants.

The primarily emitted compounds by human presence, e.g., skin and volatile organic compounds (VOCs) in breath, can react with typical indoor air oxidants, ozone (O3), and hydroxyl radicals (OH), leading to secondary organic compounds. Nevertheless, our understanding about the formation processes of the compounds through reactions of indoor air oxidants with primary emitted pollutants is still incomplete. In this study we performed real-time measurements of nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), O3, and VOCs to investigate the contribution of human presence and human activity, e.g., mopping the floor, to secondary organic compounds. During human occupancy a significant increase was observed of 1-butene, isoprene, and d-limonene exhaled by the four adults in the room and an increase of methyl vinyl ketone/methacrolein, methylglyoxal, and 3-methylfuran, formed as secondary compounds through reactions of OH radicals with isoprene. Intriguingly, the level of some compounds (e.g., m/z 126, 6-methyl-5-hepten-2-one, m/z 152, dihydrocarvone, and m/z 194, geranyl acetone) formed through reactions of O3 with the primary compounds was higher in the presence of four adults than during the period of mopping the floor with commercial detergent. These results indicate that human presence can additionally degrade the indoor air quality.