Proton Transfer Reaction Mass Spectrometer Research Articles

Unveiling the hidden impact: How biodegradable microplastics influence CO2 and CH4 emissions and Volatile Organic Compounds (VOCs) profiles in soil ecosystems

Biodegradable plastics promise eco-friendliness, yet their transformation into microplastics (bio-MPs) raises environmental alarms. However, how those bio-MPs affect the greenhouse gases (GHGs) and volatile organic compounds (VOCs) in soil ecosystems remains largely unexplored. Here, we investigated the effects of diverse bio-MPs (PBAT, PBS, and PLA) on GHGs and VOCs emission in typical paddy or upland soils. We monitored the carbon dioxide (CO2) and methane (CH4) fluxes in-situ using the self-developed portable optical gas sensor and analyzed VOC profiles using a proton-transfer reaction mass spectrometer (PTR-MS). Our study has revealed that, despite their biodegradable nature, bio-MPs do not always promote soil GHG emissions as previously thought. Specifically, PBAT and PLA significantly increased CO2 and CH4 emissions up to 1.9–7.5 and 115.9–178.5 fold, respectively, compared to the control group. While PBS exhibited the opposite trend, causing a decrease of up to 39.9% for CO2 and up to 39.9% for CH4. In addition, different types of bio-MPs triggered distinct soil VOC emission patterns. According to the Mann-Whitney U-test and Partial Least Squares Discriminant Analysis (PLS-DA), a recognizable VOC pattern associated with different bio-MPs was revealed. This study claims the necessity of considering polymer-specific responses when assessing the environmental impact of Bio-MPs, and providing insights into their implications for climate change.

Deoxyxylulose 5-Phosphate Synthase Does Not Play a Major Role in Regulating the Methylerythritol 4-Phosphate Pathway in Poplar.

The plastidic 2-C-methylerythritol 4-phosphate (MEP) pathway supplies the precursors of a large variety of essential plant isoprenoids, but its regulation is still not well understood. Using metabolic control analysis (MCA), we examined the first enzyme of this pathway, 1-deoxyxylulose 5-phosphate synthase (DXS), in multiple grey poplar (Populus × canescens) lines modified in their DXS activity. Single leaves were dynamically labeled with 13CO2 in an illuminated, climate-controlled gas exchange cuvette coupled to a proton transfer reaction mass spectrometer, and the carbon flux through the MEP pathway was calculated. Carbon was rapidly assimilated into MEP pathway intermediates and labeled both the isoprene released and the IDP+DMADP pool by up to 90%. DXS activity was increased by 25% in lines overexpressing the DXS gene and reduced by 50% in RNA interference lines, while the carbon flux in the MEP pathway was 25-35% greater in overexpressing lines and unchanged in RNA interference lines. Isoprene emission was also not altered in these different genetic backgrounds. By correlating absolute flux to DXS activity under different conditions of light and temperature, the flux control coefficient was found to be low. Among isoprenoid end products, isoprene itself was unchanged in DXS transgenic lines, but the levels of the chlorophylls and most carotenoids measured were 20-30% less in RNA interference lines than in overexpression lines. Our data thus demonstrate that DXS in the isoprene-emitting grey poplar plays only a minor part in controlling flux through the MEP pathway.

Real Time Analysis of the CO2 Reduction Reaction Products in a Cu-Gde Setup

The electrochemical reduction of CO2 (CO2RR) on copper is widely regarded as one of the most promising topics in green-energy research, due to it´s potential to produce a wide array of building block chemicals while consuming CO2 and utilizing renewable energy sources. Contrary to traditional electrolysers that utilize dissolved CO2, a gas diffusion electrode (GDE) approach is capable of circumventing the CO2 diffusion dependency and hence reach economically relevant currents of >300 mA/cm². Although GDE brings eventual industrial application closer, such systems suffer from short-lived stability, mostly on account of catalyst layer deactivation and GDE flooding. As a consequence, most GDE based electrolysers are incapable of reaching a true steady-state, rendering batch-based analyses such as gas chromatography less useful when it comes to studying sensitive properties such as on-set potentials, catalyst deactivation and product selectivity shifts.In this work we present a novel set-up capable of exploring GDE-based systems and presenting both qualitative and quantitative response in real time. We base our system of a custom cell-design that is coupled to a proton transfer reaction mass spectrometer (PTR-MS) that analyses the liquid products and quadrupole mass spectrometer (QMS) for gaseous products analysis. As a proof of concept, we evaluate the CO2RR performance of copper based GDE´s in various electrolytes, showing how electrolyte´s pH influences properties such as product selectivity and on-set potentials. All experiments were conducted at industry-relevant currents of 200-600 mA/cm².

Jingle bells, what are those smells? Indoor VOC emissions from a live Christmas tree

Every year in the United States conifers are purchased to serve as Christmas trees in homes where they emit volatile organic compounds (VOCs) to the indoor environment. Although many studies have measured the ecosystem-level emissions of VOCs from conifers outdoors (characterizing monoterpene, isoprene, and aldehyde emissions), little is known about VOC emission rates once a conifer is brought indoors. Using a proton transfer reaction-mass spectrometer we characterized the VOCs emitted from a freshly cut Douglas Fir for 17 days in an environmentally controlled chamber. Ozone injections were also performed to analyze indoor chemistry that may occur. Introduction of the tree into the chamber increased the response of 52 mass spectra signals detected by the PTR-MS by at least 500 counts per second (cps) compared to background levels, with concentrations sharply decreasing after the first two days. Monoterpenes were emitted from the tree at a rate of 12.4 mg h−1 the first day and fell to 1 mg h−1 by day three. Overall, monoterpene emissions from this Douglas fir were initially comparable to other strong indoor monoterpene sources (fragranced products and air fresheners) but decayed quickly and, within days, were smaller than other common indoor sources. Addition of ozone to the chamber resulted in decreased monoterpene concentrations that coincided with modest increases in formaldehyde. Four other emitted VOCs were tentatively identified due to their large increase within the first few hours of the tree placed in the chamber, behavior during ozonation, or pattern of accumulation over time.

Air quality impacts from the development of unconventional oil and gas well pads: Air toxics and other volatile organic compounds

Unconventional oil and natural gas development (UOGD) has expanded rapidly across the United States in recent decades and raised concerns about associated air quality impacts. While significant effort has been made to quantify methane emissions, relatively few observations have been made of Volatile Organic Compounds (VOCs), especially during drilling and completion of new wells. Extensive air monitoring during development of several large, multi-well pads in Broomfield, Colorado, in the Denver-Julesburg Basin, provides a novel opportunity to examine changes in local air toxics and other VOC concentrations during well drilling and completions and production. These operations offer an especially useful case to study as several management practices were implemented to reduce emissions (e.g., electrified, grid-powered drill rigs and closed loop fluid handling systems to reduce truck traffic and limit fluid handling on the pad). With simultaneous measurements of methane and 50 VOCs from October 2018 to December 2022 at as many as 19 sites near well pads, in adjacent neighborhoods, and at a more distant reference location, we identify impacts from each phase of well development and production. Use of weekly, time-integrated canisters, a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous photoionization detectors (PID) to trigger canister collection upon detection of VOC-rich plumes, and an instrumented vehicle, provided a powerful suite of measurements to characterize both transient plumes and longer-term changes in air quality. Prior to the start of well development, VOC gradients were small across Broomfield. Once drilling commenced, concentrations of oil and gas (O&G) related VOCs, including alkanes and aromatics, increased around active well pads. Concentration increases were clearly apparent during certain operations, including drilling, coil tubing/millout operations, and production tubing installation. Emissions of C8–C10 n-alkanes during drilling operations highlighted the importance of VOC emissions from synthetic drilling mud chosen to reduce odor impacts. More than 90 samples were collected of transient plumes. Using composition measurements, meteorological data, and information about well pad activities, these plumes were connected with specific UOGD operations including drilling, flowback, and production equipment maintenance. The chemical signatures of these plumes differed by operation type (e.g., C8–C10 n-alkanes constituted a larger fraction of measured VOCs in drilling-related plumes). Concentrations of individual, oil and gas-related VOCs in these plumes were often several orders of magnitude higher than in background air, with maximum ethane and benzene concentrations of 79,600 and 819 ppbv, respectively. Because these plumes typically impact a monitoring site for just several minutes, they are easily missed by slower-responding instruments. Study measurements highlight future emission mitigation opportunities during UOGD operations, including better control of emissions from shakers that separate drill cuttings from drilling mud, production separator maintenance operations, and periodic emptying of sand cans during flowback operations.

Temperature‐dependent kinetics of the gas‐phase reactions of Cl atoms with nopinone, ketolimonene, and myrtenal

AbstractIn this study, the gas phase reaction of chlorine atoms with three first‐generation oxidation products of monoterpene: (myrtenal C10H14O, nopinone C9H14O, and ketolimonene C9H14O) were investigated using a relative technique method. These compounds result from the atmospheric oxidation of monoterpene compounds such as α/β – pinene and limonene. Experiments were performed at temperature range 298–353 K and atmospheric pressure in synthetic air bath gas. Cl atoms were generated by UV photolysis of dichloride (Cl2). The reaction was followed using a proton‐transfer reaction mass spectrometer (PTR‐MS) and/or Fourier‐transform infrared spectroscopy (FTIR) to monitor the concentrations of the investigated species simultaneous with several reference compounds as a function of time. The rate constants were obtained and the Arrhenius expressions (cm3 molecule−1 s−1) obtained were established over the temperature range of 298–353 K:knopinone + Cl = (5.0 ± 1.2) × 10−10 exp ( − (406 ± 78) /T)kketolimonene + Cl = (8.88 ± 1.3) × 10−10 exp( − (246 ± 46)/T)kmyrtenal + Cl = (13.5 ± 6.4) × 10−10 exp( − (535 ± 153)/T)Based on rate constants, the atmospheric lifetimes (τ) of targeted compounds with respect to reaction with chlorine atoms were estimated and expected to be less than 1 day. There results led to conclude that the reaction with chlorine atoms can be an effective tropospheric loss pathway mainly in regions presenting relatively high chlorine concentrations.

Tempo-spacial variation and source apportionment of atmospheric formaldehyde in the Pearl River Delta, China

Formaldehyde (HCHO) plays an important role in atmospheric photochemistry and air quality. In this study, to investigate the sources and characteristics of formaldehyde pollution in different regions of southern China, formaldehyde online monitoring system and proton transfer reaction mass spectrometer were used to simultaneously monitor the level of HCHO and other non-methane hydrocarbons in the environment at urban site (HSTY) and rural site (NA) in the Pearl River Delta (PRD) of China. The results showed that formaldehyde concentrations were higher in autumn, with (4.46 ± 3.15 ppbv) and (2.13 ± 1.46 ppbv) for urban and rural sites, respectively, compared to (1.51 ± 0.80 ppbv) and (1.84 ± 0.93 ppbv) for winter. Continental air masses bring many secondary and biological species, with isoprene playing an important role in secondary HCHO generation. Using a photochemical age-based method to allocate HCHO, the highest proportion of secondary anthropogenic occurs at urban site (39.4%–42.5%), whereas biogenic contribute the most at rural site (39.1%–43.7%). Fewer human activities result in a lower proportion of primary anthropogenic at rural site (10.8%) compared to urban site (12.2%). These findings demonstrate the interplay between anthropogenic and biogenic sources, which would help understand the formation of photochemical pollution in the PRD.

Evolution of organic carbon in the laboratory oxidation of biomass-burning emissions

Abstract. Biomass burning (BB) is a major source of reactive organic carbon into the atmosphere. Once in the atmosphere, these organic BB emissions, in both the gas and particle phases, are subject to atmospheric oxidation, though the nature and impact of the chemical transformations are not currently well constrained. Here we describe experiments carried out as part of the FIREX FireLab campaign, in which smoke from the combustion of fuels typical of the western United States was sampled into an environmental chamber and exposed to high concentrations of OH, to simulate the equivalent of up to 2 d of atmospheric oxidation. The evolution of the organic mixture was monitored using three real-time time-of-flight mass spectrometric instruments (a proton transfer reaction mass spectrometer, an iodide chemical ionization mass spectrometer, and an aerosol mass spectrometer), providing measurements of both individual species and ensemble properties of the mixture. The combined measurements from these instruments achieve a reasonable degree of carbon closure (within 15 %–35 %), indicating that most of the reactive organic carbon is measured by these instruments. Consistent with our previous studies of the oxidation of individual organic species, atmospheric oxidation of the complex organic mixture leads to the formation of species that on average are smaller and more oxidized than those in the unoxidized emissions. In addition, the comparison of mass spectra from the different fuels indicates that the oxidative evolution of BB emissions proceeds largely independent of fuel type, with different fresh smoke mixtures ultimately converging into a common, aged distribution of gas-phase compounds. This distribution is characterized by high concentrations of several small, volatile oxygenates, formed from fragmentation reactions, as well as a complex pool of many minor oxidized species and secondary organic aerosol, likely formed via functionalization processes.

A signature of aged biogenic compounds detected from airborne VOC measurements in the high arctic atmosphere in March/April 2018

During the PAMARCMiP 2018 campaign (March and April 2018) a proton-transfer-reaction mass spectrometer (PTR-MS) was deployed onboard the POLAR 5 research aircraft and sampled the high Arctic atmosphere under Arctic haze conditions. More than 100 compounds exhibited levels above 1 pmol/mol in at least 25% of the measurements. We used acetone mixing ratios, ozone concentrations, and back trajectories to identify periods with and without long-range transport from continental sources. During two flights, surface ozone depletion events (ODE) were observed that coincided with enhanced levels of acetone, and methylethylketone, and ice nucleating particles (INP).Air masses with continental influence contained elevated levels of compounds associated with aged biogenic emissions and anthropogenic pollution (e.g., methanol, peroxyacetylnitrate (PAN), acetone, acetic acid, methylethylketone (MEK), proprionic acid, and pentanone). Almost half of all positively detected compounds (>100) in the high Arctic atmosphere can be associated with terpene oxidation products, likely produced from monoterpenes and sesquiterpenes emitted from boreal forests. We speculate that the transport of biogenic terpene emissions may constitute an important control of the High Arctic aerosol burden. The sum concentration of the detected aerosol forming vapours is ∼12 pmol/mol, which is of the same order than measured dimethylsulfide (DMS) mixing ratios and their mass density corresponds to approximately one fifth of the measured non-black-carbon particles.

Imaging VOC distribution and tracing emission sources in surface water by a mobile shipborne spray inlet proton transfer reaction mass spectrometry

Volatile organic compound (VOC) pollution in surface water can affect the growth of microorganisms and even cause damage to human health. Quickly obtaining VOC distribution and tracing emission sources are of great significance to ensure the security of water quality. In this study, we developed a mobile shipborne spray inlet proton transfer reaction mass spectrometry (S-SI-PTR-MS) instrument for rapid and on-line detection of volatile organic compounds (VOCs) in surface water. It mainly consists of a shipborne platform, a spray inlet system, a proton transfer reaction mass spectrometer, and geographic information software (GIS). During the navigation, VOCs in water can be quickly extracted to gaseous state by the SI system and transferred into the proton transfer reaction mass spectrometry (PTR-MS) for detection. The GIS can receive VOC and longitude-latitude data at the same time. And then the identification and concentration information can be shown on an electronic map in real time. The limit of detection and response time were 1.32 μg/L∼9.43 μg/L and 56 s∼114 s, respectively. The spatial resolution is 0.14 m in a common navigation experiment (5 km/h, dwell time=0.1 s), allowing for high-resolution monitoring of VOCs in water. Finally, field experiments were performed on the lower Nanfeihe River and some surfaces of Chaohu Lake in China. During tracing pollution in Nanfeihe River, two VOC emission sources in the downstream were located, nearing a sewage outlet and a wharf, respectively. During imaging VOC distribution in the Chaohu Lake, we found the areas with high-concentration VOCs were mainly along the ship channel. The newly developed S-SI-PTR-MS can monitor water quality in surface water in real time and has the potential to assist environmental protection enforcement.

Dedicated odor-taste stimulation design for fMRI flavor studies

BackgroundFlavor is a mental representation that results from the brain’s integration of at least odor and taste, and fMRI can highlight brain-related areas. However, delivering stimuli during fMRI can be challenging especially when administrating liquid stimuli in supine position. It remains unclear how and when odorants are released in the nose and how to improve odorant release. New methodWe used a proton transfer reaction mass spectrometer (PTR-MS) to monitor the in vivo release of odorants via the retronasal pathway during retronasal odor-taste stimulation in a supine position. We tested techniques to improve odorant release, including avoiding or delaying swallowing and velum open training (VOT). ResultsOdorant release was observed during retronasal stimulation, before swallowing, and in a supine position. VOT did not improve odorant release. Odorant release during stimulation had a latency more optimal for fitting with BOLD timing than after swallowing. Comparison with existing method(s)Previous in vivo measurements of odorant release under fMRI-like conditions showed that odorant release occurred only after swallowing. On the contrary, a second study found that aroma release could occur before swallowing, but participants were sitting. ConclusionOur method shows optimal odorant release during the stimulation phase, meeting the criteria for high-quality brain imaging of flavor processing without swallowing-related motion artifacts. These findings provide an important advancement in understanding the mechanisms underlying flavor processing in the brain.

Bleach Emissions Interact Substantially with Surgical and KN95 Mask Surfaces.

Mask wearing and bleach disinfectants became commonplace during the COVID-19 pandemic. Bleach generates toxic species including hypochlorous acid (HOCl), chlorine (Cl2), and chloramines. Their reaction with organic species can generate additional toxic compounds. To understand interactions between masks and bleach disinfection, bleach was injected into a ventilated chamber containing a manikin with a breathing system and wearing a surgical or KN95 mask. Concentrations inside the chamber and behind the mask were measured by a chemical ionization mass spectrometer (CIMS) and a Vocus proton transfer reaction mass spectrometer (Vocus PTRMS). HOCl, Cl2, and chloramines were observed during disinfection and concentrations inside the chamber are 2-20 times greater than those behind the mask, driven by losses to the mask surface. After bleach injection, many species decay more slowly behind the mask by a factor of 0.5-0.7 as they desorb or form on the mask. Mass transfer modeling confirms the transition of the mask from a sink during disinfection to a source persisting >4 h after disinfection. Humidifying the mask increases reactive formation of chloramines, likely related to uptake of ammonia and HOCl. These experiments indicate that masks are a source of chemical exposure after cleaning events occur.

High emission rates and strong temperature response make boreal wetlands a large source of isoprene and terpenes

Abstract. Wetlands cover only 3 % of the global land surface area, but boreal wetlands are experiencing an unprecedented warming of four times the global average. These wetlands emit isoprene and terpenes (including monoterpenes (MT), sesquiterpenes (SQT), and diterpenes (DT)), which are climate-relevant highly reactive biogenic volatile organic compounds (BVOCs) with an exponential dependence on temperature. In this study, we present ecosystem-scale eddy covariance (EC) fluxes of isoprene, MT, SQT, and DT (hereafter referred to together as terpenes) at Siikaneva, a boreal fen in southern Finland, from the start to the peak of the growing season of 2021 (19 May 2021 to 28 June 2021). These are the first EC fluxes reported using the novel state-of-the-art Vocus proton transfer reaction mass spectrometer (Vocus-PTR) and the first-ever fluxes reported for DTs from a wetland. Isoprene was the dominant compound emitted by the wetland, followed by MTs, SQTs, and DTs, and they all exhibited a strong exponential temperature dependence. The Q10 values, the factor by which terpene emissions increases for every 10 ∘C rise in temperature, were up to five times higher than those used in most BVOC models. During the campaign, the air temperature peaked above 31 ∘C on 21–22 June 2021, which is abnormally high for boreal environments, and the maximum flux for all terpenes coincided with this period. We observed that terpene emissions were elevated after this abnormally “high-temperature stress period”, indicating that past temperatures alter emissions significantly. The standardized emission factor (EF) of the fen for isoprene (EFiso) was 11.1 ± 0.3 nmol m−2 s−1, which is at least two times higher than in previous studies and as high as the emission factors typical for broadleaf and other forests in the lower latitudes. We observed EFMT of 2.4 ± 0.1 nmol m−2 s−1, EFSQT of 1.3 ± 0.03 nmol m−2 s−1, higher than typical for needle leaf and broadleaf tree functional types, and EFDT of 0.011 ± 0.001 nmol m−2 s−1. We also compared the landscape average emissions to the model of emissions of gases and aerosols from nature (MEGAN) v2.1 and found that the emissions were underestimated by over 9 times for isoprene, over 300 times for MTs, and 800 times for SQTs. Our results show that due to very high EFs and high sensitivity to increasing temperatures, these high-latitude ecosystems can be a large source of terpenes to the atmosphere, and anthropogenic global warming could induce much higher BVOC emissions from wetlands in the future.

Volatile Compound Emissions from Stereolithography Three-Dimensional Printed Cured Resin Models for Biomedical Applications.

Stereolithography three-dimensional printing is used increasingly in biomedical applications to create components for use in healthcare and therapy. The exposure of patients to volatile organic compounds (VOCs) emitted from cured resins represents an element of concern in such applications. Here, we investigate the biocompatibility in relation to inhalation exposure of volatile emissions of three different cured commercial resins for use in printing a mouthpiece adapter for sampling exhaled breath. VOC emission rates were estimated based on direct analysis using a microchamber/thermal extractor coupled to a proton transfer reaction-mass spectrometer. Complementary analyses using comprehensive gas chromatography-mass spectrometry aided compound identification. Major VOCs emitted from the cured resins were associated with polymerization agents, additives, and postprocessing procedures and included alcohols, aldehydes, ketones, hydrocarbons, esters, and terpenes. Total VOC emissions from cubes printed using the general-purpose resin were approximately an order of magnitude higher than those of the cubes printed using resins dedicated to biomedical applications at the respective test temperatures (40 and 25 °C). Daily inhalation exposures were estimated and compared with daily tolerable intake levels or standard thresholds of toxicological concerns. The two resins intended for biomedical applications were deemed suitable for fabricating an adapter mouthpiece for use in breath research. The general-purpose resin was unsuitable, with daily inhalation exposures for breath sampling applications at 40 °C estimated at 310 μg day-1 for propylene glycol (tolerable intake (TI) limit of 190 μg day-1) and 1254 μg day-1 for methyl acrylate (TI of 43 μg day-1).

Online Volatile Compound Emissions Analysis Using a Microchamber/Thermal Extractor Coupled to Proton Transfer Reaction-Mass Spectrometry.

Indoor air is a complex and dynamic mixture comprising manifold volatile organic compounds (VOCs) that may cause physiological and/or psychological discomfort, depending on the nature of exposure. This technical note presents a novel approach to analyze VOC emissions by coupling a microchamber/thermal extractor (μ-CTE) system to a proton transfer reaction-mass spectrometer (PTR-MS). This configuration provides an alternative to conventional emissions testing of small objects. The dynamic emission profiles of VOCs from a representative 3D-printed model are presented as a proof-of-concept analysis. Emission profiles are related to the target compound volatility, whereby 2-propanol and acetaldehyde exhibited the highest emissions and most rapid changes compared to the less volatile vinyl crotonate, 2-hydroxymethyl methacrylate, and mesitaldehyde, which were present at lower concentrations and showed different dynamics. Comparative measurements of the emission profiles of these compounds either with or without prior static equilibration yielded stark differences in their dynamics, albeit converging to similar values after 15 min of sampling time. Further, the utility of this system to determine the time required to capture a specific proportion of volatile emissions over the sampling period was demonstrated, with a mean duration of 8.4 ± 0.3 min to sample 50% of emissions across all compounds. This novel configuration provides a means to characterize the dynamic nature of VOC emissions from small objects and is especially suited to measuring highly volatile compounds, which can present a challenge for conventional sampling and analysis approaches. Further, it represents an opportunity for rapid, targeted emissions analyses of products to screen for potentially harmful volatiles.

Increasing role of phenolic oxidative branch in daytime oxidation process of aromatics in Chinese haze period

To understand the photooxidation mechanisms of aromatic compounds in the NOx-rich atmosphere, gaseous aromatics and their oxidization products (i.e., methyl glyoxal (MGLY), and nitrated phenols (NPs) including nitrophenols (NPhs) and methylnitrophenols (MNPs)) were measured with a 1-h time resolution on Chongming Island, a downwind region of the Yangtze River Delta (YRD) metropolitans of China in winter 2019 by using a proton-transfer-reaction mass spectrometer (PTR-MS). During the entire observation period, concentrations of the measured VOCs were 9.6 ± 7.1 ppbv for aromatics, 118 ± 59 pptv for MGLY, 36 ± 10 pptv for NPhs, and 9.3 ± 2.8 pptv for MNPs, respectively. Secondary NPs (SNPs) accounted for only 19–24 % of the total nitrated phenols during the clean and transition periods but increased to 44 % of the total on the hazy days. Moreover, the daytime mixing ratios of SNPs increased along with an increasing NO2 concentration during the clean and transition periods, but in the haze period the daytime SNPs first increased along with the increasing NO2 levels and then increased much more sharply when NO2 was >25 ppbv. Such highly proportional and sharply increased daytime SNPs in the haze period indicated an enhanced phenolic oxidation under the high NOx conditions. In addition, the lack of correlations between aromatics and MGLY, increased MGLYaro (MGLY produced by aromatics), and sharply increased ΔSNPs / Δ(benzene + toluene) further suggested that such an increasing role of the phenolic oxidative branch in the daytime oxidation process of aromatics during the YRD haze period was caused by the strong atmospheric oxidation capacity and the high level of NOx.

Volatile Dimethyl Disulfide from Guava Plants Regulate Developmental Performance of Asian Citrus Psyllid through Activation of Defense Responses in Neighboring Orange Plants.

Intercropping with guava (Psidium guajava L.) can assist with the management of Asian citrus psyllid (ACP, Diaphorina citri Kuwayama), the insect vector of the huanglongbing pathogen, in citrus orchards. Sulfur volatiles have a repellent activity and physiological effects, as well as being important components of guava volatiles. In this study, we tested whether the sulfur volatiles emitted by guava plants play a role in plant–plant communications and trigger anti-herbivore activities against ACP in sweet orange plants (Citrus sinensis L. Osbeck). Real-time determination using a proton-transfer-reaction mass spectrometer (PTR-MS) showed that guava plants continuously release methanethiol, dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), and the contents increased rapidly after mechanical damage. The exposure of orange plants to DMDS resulted in the suppression of the developmental performance of ACP. The differential elevation of salicylic acid (SA) levels; the expression of phenylalanine ammonia lyase (PAL), salicylate-O-methyl transferase (SMT), and pathogenesis-related (PR1) genes; the activities of defense-related enzymes PAL, polyphenol oxidase (PPO), and peroxidase (POD); and the total polyphenol content were observed in DMDS-exposed orange plants. The emission of volatiles including myrcene, nonanal, decanal, and methyl salicylate (MeSA) was increased. In addition, phenylpropanoid and flavonoid biosynthesis, and aromatic amino acid (such as phenylalanine, tyrosine, and tryptophan) metabolic pathways were induced. Altogether, our results indicated that DMDS from guava plants can activate defense responses in eavesdropping orange plants and boost their herbivore resistance to ACP, which suggests the possibility of using DMDS as a novel approach for the management of ACP in citrus orchards.

Bridging the Analytical Gap Between Gas Treatment and Reactor Plants in Carbon2Chem®

The use of purified process gases as feedstock for subsequent processes requires a detailed verification of the gas purity to ensure long lifetimes of applied catalysts. Herein, the analytical infrastructure for the measurements of the cleaned gases is presented. An overview of all sampling points for the off- and on-line analysis is given. The detailed decryption of the composition of the cleaned blast furnace gas, its main components as well as its traces are presented. Thereby, over 99 % of the overall signal strength of this complex gas matrix measured with a proton transfer reaction mass spectrometer with H3O+ as reagent ion could be revealed. Furthermore, by the example of the catalyst poison H2S, the necessity of monitoring continuously the gas matrix for certain compounds was proven.

Evolution of source attributed organic aerosols and gases in a megacity of central China

Abstract. The secondary production of oxygenated organic aerosol (OOA) impacts air quality, climate, and human health. The importance of various sources in contributing to the OOA loading and associated different ageing mechanisms remains to be elucidated. Here we present a concurrent observation and factorization analysis on the mass spectra of organic aerosol (OA) by a high-resolution aerosol mass spectrometer and volatile organic compounds (VOCs) by a proton transfer reaction mass spectrometer in Wuhan, a megacity in central China, during autumn. The full mass spectra of organics with two principle anthropogenic sources were identified as the traffic and cooking sources, for their primary emission profiles in aerosol and gas phases, the evolutions, and their respective roles in producing OOA and secondary VOCs. Primary emissions in gas and aerosol phases both contributed to the production of OOA. The photooxidation of traffic sources from the morning rush hour caused a 2.5 fold increase in OOA mass in a higher oxidation state (oxygen-to-carbon ratio as O/C =0.72), co-producing gas phase carboxylic acids, while, at night, cooking aerosols and VOCs (particularly acrolein and hexanal) importantly caused the nocturnal formation of oxygenated intermediate VOCs, increasing OOA mass by a factor of 1.7 (O/C =0.42). The daytime and nighttime formation of secondary aerosols, as contributed by different sources, was found to be modulated by solar radiation and air moisture, respectively. The environmental policy should, therefore, consider the primary emissions and their respective ageing mechanisms influenced by meteorological conditions.

A versatile vacuum ultraviolet ion source for reduced pressure bipolar chemical ionization mass spectrometry

Abstract. We present the development of a chemical ionization mass spectrometer ion source specifically designed for in situ measurements of trace gases in the upper troposphere and lower stratosphere. The ion source utilizes a commercially available photoionization krypton lamp, primarily emitting photons in the vacuum ultraviolet (VUV) region at wavelengths of 124 and 117 nm (corresponding to energies of 10 and 10.6 eV, respectively), coupled to a commercially available Vocus proton transfer reaction mass spectrometer. The VUV ion source can produce both negative and positive reagent ions; however, here we primarily focus on generating iodide anions (I−). The instrument's drift tube (also known as ion–molecule reactor) operates at pressures between 2 and 10 mbar, which facilitates ambient sampling at atmospheric pressures as low as 50 mbar. The low operating pressure reduces secondary ion chemistry that can occur in iodide chemical ionization mass spectrometry (CIMS). It also allows the addition of water vapor to the drift tube to exceed typical ambient humidity by more than 1 order of magnitude, significantly reducing ambient humidity dependence of sensitivities. An additional benefit of this ion source and drift tube is a 10- to 100-fold reduction in nitrogen consumed during operation relative to standard I− ion sources, resulting in significantly reduced instrument weight and operational costs. In iodide mode, sensitivities of 76 cps ppt−1 for nitric acid, 35 cps ppt−1 for Br2 and 8.9 cps ppt−1 for Cl2 were achieved. Lastly, we demonstrate that this ion source can generate benzene (C6H6+) and ammonium (NH4+) reagent ions to expand the number of detected atmospheric trace gases.