Polycyclic aromatic hydrocarbons (PAHs) in ambient aerosols from Beijing: characterization of low volatile PAHs by positive-ion atmospheric pressure photoionization (APPI) coupled with Fourier transform ion cyclotron resonance

Associations between atmospheric PM2.5 exposure and carcinogenic health risks: Surveillance data from the year of lowest recorded levels in Beijing, China

Scant research has pinpointed the year of minimum PM2.5 concentration through extensive, uninterrupted monitoring, nor has it thoroughly assessed carcinogenic risks associated with analyzing numerous components during this nadir in Beijing. This study endeavored to delineate the atmospheric PM2.5 pollution in Beijing from 2015 to 2022 and to undertake comprehensive evaluation of carcinogenic risks associated with the composition of atmospheric PM2.5 during the year exhibiting the lowest concentration. PM2.5 concentrations were monitored gradually in 9 districts of Beijing for 7 consecutive days per month from 2015 to 2022, and 32 kinds of PM2.5 components collected in the lowest PM2.5 concentration year were analyzed. This comprehensive dataset served as the basis for carcinogenic risk assessment using Monte Carlo simulation. And we applied the Positive Matrix Factorization (PMF) method to identity the sources of atmospheric PM2.5. Furthermore, we integrated this source appointment model with risk assessment model to discern the origins of these risks. The findings revealed that the annual average PM2.5 concentration in 2022 stood at 43.1 μg/m3, marking the lowest level recorded. The mean carcinogenic risks of atmospheric PM2.5 exposure calculated at 6.30E-6 (empirical 95% CI 1.09E-6 to 2.25E-5) in 2022. The PMF model suggested that secondary sources (35.4%), coal combustion (25.6%), resuspended dust (15.1%), biomass combustion (14.1%), vehicle emissions (7.1%), industrial emissions (2.0%) and others (0.7%) were the main sources of atmospheric PM2.5 in Beijing. The mixed model revealed that coal combustion (2.41E-6), vehicle emissions (1.90E-6) and industrial emissions (1.32E-6) were the main sources of carcinogenic risks with caution. Despite a continual decrease in atmospheric PM2.5 concentration in recent years, the lowest concentration levels still pose non-negligible carcinogenic risks. Notably, the carcinogenic risks associated with metals and metalloids exceeded that of PAHs. And the distribution of risk sources did not align proportionally with the distribution of PM2.5 mass concentration.

Tracking the history of polycyclic aromatic compounds in London through a River Thames sediment core and ultrahigh resolution mass spectrometry

Polycyclic aromatic compounds (PACs), including polycyclic aromatic hydrocarbons (PAHs) and heteroatom-containing analogues, constitute an important environmental contaminant class. For decades, limited numbers of priority PAHs have been routinely targeted in pollution investigations, however, there is growing awareness for the potential occurrence of thousands of PACs in the environment. In this study, untargeted Fourier transform ion cyclotron resonance mass spectrometry was used for the molecular characterisation of PACs in a sediment core from Chiswick Ait, in the River Thames, London, UK. Using complex mixture analysis approaches, including aromaticity index calculations, the number of molecular PAC components was determined for eight core depths, extending back to the 1930s. A maximum of 1676 molecular compositions representing PACs was detected at the depth corresponding to the 1950s, and a decline in PAC numbers was observed up the core. A case linking the PACs to London's coal consumption history is presented, alongside other possible sources, with some data features indicating pyrogenic origins. The overall core profile trend in PAC components, including compounds with oxygen, sulfur, nitrogen, and chlorine atoms, is shown to broadly correspond to the 16 priority PAH concentration profile trend previously determined for this core. These findings have implications for other industry-impacted environments.

Distinct Photochemistry of Odd-Carbon PAHs from the Even-Carbon Ones During the Photoaging and Analysis of Soot

Polycyclic aromatic hydrocarbons (PAHs) are the primary organic carbons in soot. In addition to PAHs with even carbon numbers (PAHeven), substantial odd-carbon PAHs (PAHodd) have been widely observed in soot and ambient particles. Analyzing and understanding the photoaging of these compounds are essential for assessing their environmental effects. Here, using laser desorption ionization mass spectrometry (LDI-MS), we reveal the substantially different photoreactivity of PAHodd from PAHeven in the aging process and their MS detection through their distinct behaviors in the presence and absence of elemental carbon (EC) in soot. During direct photooxidation of organic carbon (OC) alone, the PAHeven are oxidized more rapidly than the PAHodd. However, the degradation of PAHodd becomes preponderant over PAHeven in the presence of EC during photoaging of the whole soot. All of these observations are proposed to originate from the more rapid hydrogen abstraction reaction from PAHodd in the EC-photosensitized reaction, owing to its unique structure of a single sp3-hybridized carbon site. Our findings reveal the photoreactivity and reaction mechanism of PAHodd for the first time, providing a comprehensive understanding of the oxidation of PAHs at a molecular level during soot aging and highlight the enhanced effect of EC on PAHodd ionization in LDI-MS analysis.

Molecular signatures and formation mechanisms of water-soluble chromophores in particulate matter from Karachi in Pakistan

Excitation-emission matrix (EEM) fluorescence spectroscopy is a widely-used method for characterizing the chemical components of brown carbon (BrC). However, the molecular basics and formation mechanisms of chromophores, which are decomposed by parallel factor (PARAFAC) analysis, are not yet fully understood. In this study, we characterized the water-soluble organic carbon (WSOC) in aerosols collected from Karachi, Pakistan, using EEM spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We identified three PARAFAC components, including two humic-like components (C1 and C2) and one phenolic-like species (C3). We determined the molecular families associated with each component by performing Spearman correlation analysis between FT-ICR MS peaks and PARAFAC component intensities. We found that the C1 and C2 components were associated with nitrogen-enriched compounds, where C2 with the longest emission wavelength exhibited a higher level of aromaticity, N content, and oxygenation than C1. The C3 associated formulas have fewer nitrogen-containing species, a lower unsaturation degree, and a lower oxidation state. An oxidation pathway was identified as an important process in the formation of C1 and C2 components at the molecular level, particularly for the assigned CHON compounds associated with the gas-phase oxidation process, despite their diverse precursor types. Numerous C2 formulas were found in the "potential BrC" region and overlapped with the BrC-associated formulas. It can be inferred that the compounds that fluoresce C2 contributed considerably to the light absorption of BrC. These findings are essential for future studies utilizing the EEM-PARAFAC method to explore the sources, processes, and compositions of atmospheric BrC.

Comparative analysis of organic chemical compositions in airborne particulate matter from Ulaanbaatar, Beijing, and Seoul using UPLC-FT-ICR-MS and artificial neural network

This paper presents comparative study on the composition and sources of PM2.5 in Ulaanbaatar, Beijing, and Seoul. Ultrahigh performance liquid chromatography (UPLC) combined with ultrahigh resolution mass spectrometry (UHR-MS) were employed to analyze 85 samples collected in winter. The obtained 340 spectra were interpreted with artificial neural network (ANN). PM2.5 mass concentrations in Ulaanbaatar were significantly higher than those in Beijing and Seoul. ANN based interpretation of UPLC UHR-MS data showed that aliphatic/lipid derived organo‑sulfur compounds, polycyclic aromatic and organo‑oxygen compounds were characteristic to Ulaanbaatar. Whereas, aliphatic/lipid-derived organo‑oxygen compounds were major components in Beijing and Seoul. Aromatic organo‑nitrogen compounds were the main contributors to differentiating the spectra obtained from Beijing from the other cities. Based on two-dimensional gas chromatography/high resolution mass spectrometric (GCxGC/HRMS) data, it was determined that the concentrations of the polycyclic aromatic hydrocarbon (PAH) and polycyclic aromatic sulfur heterocycle (PASH) containing sulfur were highest in Ulaanbaatar, followed by Beijing and Seoul. Coal/biomass combustion was identified as the primary source of contamination in Ulaanbaatar, while petroleum combustion was the main contributor to PM2.5 in Beijing and Seoul. The conclusion that diesel-powered heavy-duty trucks and buses are the main contributors to NOx emissions in Beijing is consistent with previous reports. This study provides a more comprehensive understanding of the composition and sources of PM2.5 in the three cities, with a focus on the differences in their atmospheric pollution profiles based on the UPLC UHR-MS and ANN analysis. It is notable that this study is the first to utilize this method on a large-scale sample set, providing a more detailed and molecular-level understanding of the compositional differences among PM2.5. Overall, the study contributes to a better understanding of the sources and composition of PM2.5 in Northeast Asia, which is essential for developing effective strategies to reduce air pollution and improve public health.

Oxidation treatment of shale gas produced water: Molecular changes in dissolved organic matter composition and toxicity evaluation

Produced water (PW) is the largest waste stream generated by hydraulic fracturing in an unconventional shale gas reservoir. Oxidation processes (OPs) are frequently used as advanced treatment method in highly complicated water matrix treatments. However, the degradation efficiency is the main focus of research, organic compounds and their toxicity have not been properly explored. Here, we obtained the characterization and transformation of dissolved organic matters of PW samples from the first shale gas field of China by two selected OPs using FT-ICR MS. CHO, CHON, CHOS, and CHONS heterocyclic compounds associated with lignins/CRAM-like, aliphatic/proteins, and carbohydrates compounds were the major organic compounds identified. Electrochemical Fe²⁺/HClO oxidation preferentially removed aromatic structures, unsaturated hydrocarbons, and tannin compounds with a double-bond equivalence (DBE) value below 7 to more saturated compounds. Nevertheless, Fe (VI) degradation manifested in CHOS compounds with low DBE values, especially single bond compounds. Oxygen- and Sulfur-containing substances, primarily O_4-11, S₁O₃-S₁O₁₂, N₁S₁O₄, and N₂S₁O₁₀ classes, were the main recalcitrant components in OPs. The toxicity assessment showed that the free-radical-formed Fe²⁺/HClO oxidation could cause significant DNA damage. Therefore, the toxicity response byproducts need spcial attention when conducting OPs. Our results led to discussions on designing appropriate treatment strategies and the development of PW discharge or reuse standards.

Molecular characteristics, sources and transformation of water-insoluble organic matter in cloud water

Studies have shown that water-insoluble organic matter (WIOM) accounts for a large part of the organic components in cloud water and significantly contributes to brown carbon. However, the molecular characteristics of WIOM in cloud droplets remain unclear, hampering the understanding of their climate effects. In this study, cloud water was collected at a remote mountain site in South China during the winter of 2020, and WIOM was separated by membrane filtration, extracted by methanol, and characterized using Fourier transform ion cyclotron resonance mass spectrometry coupled with an electrospray ionization source. A total of 697-1637 molecules were identified in WIOM. WIOM is characterized by lower oxidation states of carbon atoms (-1.10 ∼ -0.84 in WIOM vs. -0.58 ∼ -0.51 in water-soluble organic matter (WSOM) on average), higher carbon number (14.12-20.59 vs. 9.87-10.56) and lower unsaturation (double-bond equivalent 4.55-4.95 vs. 4.84-5.23) relative to WSOM. More abundant lipid-like compounds (12.2-41.9% in WIOM vs. <2% in WSOM) but less highly oxygenated compounds (<7% vs. 28.6-35.3%) exist in WIOM. More than 30% of WIOM molecules in cloud water are common with interstitial particles, implying that WIOM in cloud water may originate from aerosol activation and/or collision. Some unique molecules in WIOM in cloud water are identified as aqueous-phase oligomerization products, indicating the aqueous-phase formation of WIOM. Further analysis of the intermolecular relationship shows that WIOM has the potential to transform into WSOM by partitioning into the dissolved phase, oxidation and functionalization by heteroatom-containing groups, representing a previously unidentified pathway for WSOM formation in cloud water. The results provide new insights into the in-cloud chemistry, which would assist in the understanding of the aqueous formation and evolution of WIOM.

Complementary Elucidation of the Molecular Characteristics of Groundwater Dissolved Organic Matter Using Ultrahigh-Resolution Mass Spectrometry Coupled with Negative- and Positive-Ion Electrospray Ionization

The formula assignment of the Fourier transform ion cyclotron resonance mass spectrometry coupled with positive-ion electrospray ionization [ESI(+)-FT-ICR MS] is challenging because of the extensive occurrence of adducts. However, there is a paucity of automated formula assignment methods for ESI(+)-FT-ICR MS spectra. The novel automated formula assignment algorithm for ESI(+)-FT-ICR MS spectra developed herein has been applied to elucidate the composition of dissolved organic matter (DOM) in groundwater during air-induced ferrous [Fe(II)] oxidation. The ESI(+)-FT-ICR MS spectra of groundwater DOM were profoundly impacted by [M + Na]⁺ adducts and, to a lesser extent, [M + K]⁺ adducts. Oxygen-poor and N-containing compounds were frequently detected when the FT-ICR MS was operated in the ESI(+) mode, while the components with higher carbon oxidation states were preferentially ionized in the negative-ion electrospray ionization [ESI(-)] mode. Values for the difference between double-bond equivalents and the number of oxygen atoms from -13 to 13 are proposed for the formula assignment of the ESI(+)-FT-ICR MS spectra of aquatic DOM. Furthermore, for the first time, the Fe(II)-mediated formation of highly toxic organic iodine species was reported in groundwater rich in Fe(II), iodide, and DOM. The results of this study not only shed light on the further algorithm development for comprehensive characterization of DOM by ESI(-)-FT-ICR MS and ESI(+)-FT-ICR MS but also highlight the importance of appropriate treatment of specific groundwater prior to use.

PM2.5-mediated photochemical reaction of typical toluene in real air matrix with identification of products by isotopic tracing and FT-ICR MS

The sight into photoconversion of toluene, a ubiquitous typical pollutant, attentively by the involvement of PM2.5 in the real air environment is crucial for controlling haze pollution. Compared with the large-size PM2.5 on normal day (PM2.5-ND), the PM2.5 on haze day (PM2.5-HD) formed of small particle agglomerates featured greater oxidation capability, evidenced by the valence distribution of sulfur species. Notably, PM2.5-HD had abundant O₂^-• and •OH and participated in the photochemical reaction of toluene, giving it a greater toluene conversion with a first-order kinetic rate constant of 0.4 d^-1 on haze day than on normal day (0.2 d^-1). During the toluene photoconversion, isotopic labelling traced small molecules including benzene and newfound pentane, ethylbenzene, 1,3,8-p-menthatriene and 4-methyl-1-pentanone benzene that could be formed by methyl breakage, ring opening, fragmentation reforming and addition reaction of toluene. Given ADMET properties, 1,3,8-p-menthatriene was assigned high priority since it had poor metabolism, low excretion and severe toxicity, while benzene and 4-methyl-1-pentanone benzene should also be noticeable. FT-ICR MS results indicated that toluene could create multiple macromolecular products that are more sensitive to SOA generation in haze air matrix with broader carbon number and O/C, more oxygenated substitution with CHO/CHON occupying by 81.4%, lower DBE_average at 4.66 and higher OS_C‾ at -1.60 than normal air matrix. Accordingly, a photochemical reaction mechanism for toluene in real air atmosphere was proposed. The stronger oxidation property of PM2.5 not only facilitated toluene to generate small molecules but also boosted the conversion of intermediates to oxygenated macromolecular products, contributing to the formation of SOA.

Responses of dissolved organic matter (DOM) characteristics in eutrophic lake to water diversion from external watershed

Eutrophication is an important water environment issue facing global lakes. Diversion of water from external watersheds into lakes is considered as effective in ameliorating eutrophication and reducing algal blooms. Nevertheless, the changes in lake water environment caused by external water diversion, especially the influence of water diversion on the characteristics of dissolved organic matters (DOM), are still poorly understood. We therefore used a combination of EEM-PARAFAC, Principal Component Analysis (PCA), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate the effects of water diversion from the Niulan River on DOM characteristics in Lake Dianchi. The results showed that the water diversion from the Niulan River significantly improved the water quality of Lake Dianchi, the concentrations of TN, TP, COD and Chla decreased rapidly, and the degree of humification of dissolved organic matter (DOM) increased, which was in sharp contrast with that of pre-implementation. Firstly, the diversion of water from the Niulan River mainly led to changes in the structure of pollution sources. The load of influent rivers and sewage treatment plants rich in lignin and tannins increased, and the input of terrestrial humus increased. Second, the improved water quality reduced algal enrichment and frequency of blooms, and reduced the release of lipid- and protein-riched algal-derived DOM. Finally, the hydraulic retention time of Lake Dianchi caused by water diversion was shortened, the hydrodynamic conditions were significantly improved, and the dissolved oxygen (DO) level gradually recovered, which played a positive role in improving the humification degree of DOM. Our findings provide new insights for exploring the improvement of eutrophic lake eco-environmental quality caused by water diversion projects.

Molecular characteristics, sources and environmental risk of aromatic compounds in particulate matter during COVID-2019: Nontarget screening by ultra-high resolution mass spectrometry and comprehensive two-dimensional gas chromatography

Aromatic compounds, including many polycyclic aromatic hydrocarbons (PAHs), are suspected carcinogens and may originate from different sources. To investigate the impact of anthropogenic emission reductions on unknown aromatic compounds in particulate matter, we collected samples during the pre-COVID period in 2020, the COVID-19 lockdown period in 2020, and the same period as the lockdown in 2019. Besides the 16 PAHs, other aromatic compounds were analyzed by Fourier transform ion cyclotron resonance mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. Four main compound classes were identified: CH, CHO, CHNO, and CHOS. Hierarchical cluster analysis showed the aromatic compounds varied during the different periods. Compared with before the pandemic, the relative abundances of aromatic compounds with low degrees of unsaturation and long alkyl chains (e.g., alkylbenzenes) increased. These compounds probably mainly arose from fossil fuel combustion and petrochemical industry emissions. The CHO compounds, which were dominated by those with high degrees of oxidation, might originate from secondary organic aerosols. Aromatic aldehydes (e.g., cyclamen aldehyde) and benzoates (e.g., 2-ethylhexyl benzoate) probably with high toxicity deserve more attention. During lockdown, nitro derivatives of condensed PAHs were the main CHNO compounds, and the numbers of homologs decreased perhaps because of significant reductions in NO_x and PAHs. CHOS compounds with long carbon chains and low degrees of unsaturation were predominant and the numbers of homologs increased. Five compounds (e.g. 1,3-dimethyl pyrene) were predicted to possibly exhibit persistent and bio-accumulated by EPI Suite model, which need further research. The results provide insight on aromatic compounds and their source appointment in atmospheric particulate matter.

Large contribution of non-priority PAHs in atmospheric fine particles: Insights from time-resolved measurement and nontarget analysis

Polycyclic aromatic hydrocarbons (PAHs), detrimental to human health, are key components contributing to the carcinogenicity of fine particles. The 16 priority PAHs listed by the United States Environment Protection Agency have been studied extensively. However, other than them, there is a large diversity of PAH species, whose atmospheric concentrations, risks, and variations remain elusive. Here, we carried out a time-resolved nontarget measurement in atmospheric PM_2.5 using an improved comprehensive two-dimensional gas chromatography mass spectrometry. The measurement conducted during a 5-day pollution episode at an urban site of Beijing with a time resolution of 2 h. The nontarget analysis of time-resolved chromatographic data was performed for screening PAHs. A total number of 85 PAHs were identified and quantified. We found that other than 16 EPA PAHs, other screened PAHs contributed 43.3% of the total PAH mass concentration and 40.8% poential health risks. Dynamic variations of mass concentrations and their potential health risks of the screened PAHs were captured during a short-term heavy pollution episode, during which the instantaneous PAHs concentrations were much higher than their average concentrations. This study shows the potential for application of nontarget analysis for online comprehensive two-dimensional gas chromatography mass spectrometry and highlights the importance of time-resolved measurement of PAHs in PM_2.5 and attention on extended PAHs species other than 16 EPA PAHs.

Identification of emerging organic pollutants from solid waste incinerations by FT-ICR-MS and GC/Q-TOF-MS and their potential toxicities

Emissions from the incineration of solid waste are a global public health concern, but little attention has been paid to previously unrecognized chemical compounds that are generated by waste incineration and released into the atmosphere. We conducted nontarget analysis of organic chemicals formed during waste incineration by Fourier-transform ion cyclotron resonance mass spectrometry and gas chromatography-quadrupole time-of-flight mass spectrometry. Using toxicity data in the ToxCast library and predicted toxicity data for traditional priority polycyclic aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin, we prioritized 13 compounds including hexachloro-1,3-butadiene, 9 of which are reported here for the first time as constituents of emissions from the incineration of solid waste and hexachloro-1,3-butadiene was included in the Stockholm Convention in 2017. The predicted activity of these pollutants to androgen receptors and to the aryl hydrocarbon receptor were comparable to, or higher than, the 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo[a]pyrene. In addition, some alkylated polycyclic aromatic hydrocarbons and heteroatom polycyclic aromatic hydrocarbons were also identified in solid waste incineration processes, peak areas of which were 1-2 orders of magnitude higher than dioxins and 1-3 orders of magnitude lower than their parent polycyclic aromatic hydrocarbons. Our study can provide information for better recognizing and regulating the emissions of organic pollutants formed by the incineration of solid waste.

Molecular characterization of organic aerosol in winter from Beijing using UHPLC-Orbitrap MS

The urban organic aerosol (OA) may pose a serious threat to human health and ecological environment. In order to understand the molecular characteristics of organic compounds in aerosols, atmospheric PM_2.5 samples were collected in Beijing and the extracts were analyzed by liquid chromatography-Orbitrap mass spectrometry combined with negative-ion electrospray ionization, positive-ion electrospray ionization, and positive-ion atmospheric pressure photoionization sources. The combination of multiple ionization sources realized the comprehensive molecular characterization of organic compounds in OA, and 1976 (+APPI), 3038 (-ESI), and 4376 (+ESI) molecular formulas were identified in this study. Significant differences in the species, abundance, and number of subgroups (CHO, CHN, CHON, CHONS, CHOS, and CH compounds) were clarified. Chemical fingerprinting of organics in the PM_2.5 extract were investigated by high-throughput non-target compound analytical methods. Structure induction of organic compounds was realized through fragmentation prediction of MS/MS spectra with Sirius software. Furthermore, a total of 50 nitroaromatic formulas, 285 organosulfates (OS) formulas, 57 nitrooxy-OS formulas, 228 CHO- formulas with carboxyl groups, and 36 monoketone formulas were determined based on diagnostic fragmentation filtering. Our results provide important insights into the molecular composition and structural characteristics of OA, and establish foundation for exploring the interaction between composition and physicochemical properties.

Determination of anthropogenic organics in dichlomethane extracts of aerosol particulate matter collected from four different locations in China and Republic of Korea by GC-MS and FTICR-MS

In this study, the hypothesis that particulate matter in east of Korea peninsula would be significantly influenced by particulate matter originated from east of China was evaluated. To test the hypothesis, water-insoluble compounds in particulate matter samples collected from three different locations in Korea and one in China were characterized by atmospheric pressure photoionization (APPI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and gas chromatography mass spectrometry (GC-MS). Each sample was collected twice, in winter and in spring. The GC-MS data revealed the presence of high levels of polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]anthracene in the samples from Tianjin, China. The sample collected in the winter from Baengnyeong Island, which is the location in Korea that is geographically closest to the east coast of China was also rich in aromatic compounds. Meanwhile, the APPI FTICR-MS data showed that polycondensed PAHs and two- to four-ring PAHs with long alkyl chains were abundant in the winter samples from Tianjin and Baengnyeong Island which stems most likely from coal combustion in the eastern China. In contrast, nonaromatic compounds with a biogenic origin were mostly observed in samples collected from islands located in eastern (Ulleung Island) and southern (Jeju Island) Korea. A principal component analysis by FTICR-MS and GC-MS also showed that the samples from Tianjin and those collected from Baengnyeong Island in the winter are strongly associated with coal combustion, whereas the other samples are mainly influenced by vehicle emissions. Therefore, it is concluded that the atmosphere from east of China has significant influence over atmosphere in west of Korea peninsula.

FT-ICR mass spectrometry for molecular characterization of water-insoluble organic compounds in winter atmospheric fine particulate matters

Water-insoluble organic compounds (WIOCs) are an important fraction of atmospheric fine particulate matters (PM_2.5), which could affect the climate system and threaten human health potentially. In this study, molecular characterization of WIOCs in PM_2.5 were investigated by 15 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with atmospheric pressure photoionization (APPI) source in positive ion mode. A total of 2573 and 1875 molecular formulas were identified in WIOCs extracted by dichloromethane, which were collected in hazy and normal days, respectively. The identified molecular formulas were further classified into four major subgroups, including CH, CHN, CHO and CHNO compounds. CHO compounds predominated in WIOCs, accounting for more than 60% in both samples. CHNO compounds (26.6%) and CH compounds (16.1%) were the second highest subgroups in WIOCs from the hazy days and normal days, respectively. The relative abundance and number of nitro-substituted aromatic compounds were significantly higher in hazy days than in normal days. The molecular composition of WIOCs was more complex in hazy days while more aromatic compounds were identified in normal days.

Defining Blood Plasma and Serum Metabolome by GC-MS

Metabolomics uses advanced analytical chemistry methods to analyze metabolites in biological samples. The most intensively studied samples are blood and its liquid components: plasma and serum. Armed with advanced equipment and progressive software solutions, the scientific community has shown that small molecules’ roles in living systems are not limited to traditional “building blocks” or “just fuel” for cellular energy. As a result, the conclusions based on studying the metabolome are finding practical reflection in molecular medicine and a better understanding of fundamental biochemical processes in living systems. This review is not a detailed protocol of metabolomic analysis. However, it should support the reader with information about the achievements in the whole process of metabolic exploration of human plasma and serum using mass spectrometry combined with gas chromatography.

In Situ Construction of COF-Based Paper Serving as a Plasmonic Substrate for Enhanced PSI-MS Detection of Polycyclic Aromatic Hydrocarbons

Accurate detection, quantitation, and differentiation of polycyclic aromatic hydrocarbons (PAHs) and their isomers in diverse samples is elusive for paper spray ionization mass spectrometry (PSI-MS). To address these issues, herein, for the first time, we propose to fabricate a novel, flexible, and stable paper substrate based on covalent organic frameworks (COFs) via an in situ method under room temperature in air. After embedding gold nanoparticles (AuNPs), this paper substrate (COFs-paper) could further serve as a multifunctional plasmonic matrix (AuNPs-COFs-paper) for dual-wavelength laser-assisted PSI-MS detection of PAHs and feasible paper surface-enhanced Raman scattering (pSERS)-aided isomer discrimination. Taking advantage of the synergistic effect between the AuNPs and COFs present on the novel AuNP-embedded COFs-paper substrate, a satisfied LOD of 0.50 ng/μL for phenanthrene was realized, which improved almost 300 times compared with the naked-paper matrix, and the regression coefficient R² was up to 0.999. Real sample corn oil-containing PAHs can be efficiently detected and identified using this technique. The established platform has promising potential for on-site chemical analysis with portable PSI-MS and pSERS instruments.

Detection of organosulfates and nitrooxy-organosulfates in Arctic and Antarctic atmospheric aerosols, using ultra-high resolution FT-ICR mass spectrometry

Organosulfates (OSs) are recognized as important secondary organic aerosols (SOAs) in recent years. Due to their amphipathy and light absorptive capacity, OSs may potentially impact climate. Moreover, OSs can serve as molecular tracers for precursors and multiple processes leading to the generation of SOA. However, studies on OSs are lacking in the polar regions which limits our understanding of both their formation pathways and impacts on the polar environment. Here we present the first investigation into OSs in both the Arctic and Antarctic. Organic compounds in aerosol samples collected from the polar regions during the 2013/2014 Chinese National Arctic/Antarctic Research Expedition (CHINARE) were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) coupled with negative ion mode electrospray ionization (ESI(-)). Hundreds to thousands of OSs were detected at the polar sampling sites. The estimated total concentrations of OSs were in the range of 46-670 ng/m³ in the Arctic sampling area, and 47-260 ng/m³ in the Antarctic sampling area, accounting for 1-16% of total OM. OSs were found to have undergone a high degree of oxidation in the aerosol samples, which might be due to the combined effects of enhanced photo-oxidation in summertime or continuous oxidation during transport to the polar region. The potential appointment of OS precursors highlights the important role of long-range air-mass transport on the OSs derived from biogenic precursors and a notably large contribution from anthropogenic emissions, suggesting that human activities have significant impacts in remote polar environments. The results of this study provide important insights into the characteristics of OSs in the polar atmosphere. However, the need for further research focusing on the quantification, formation mechanisms and impacts of OSs on climate is emphasized.

Ionic Strength Effect Triggers Brown Carbon Formation through Heterogeneous Ozone Processing of Ortho-Vanillin

Methoxyphenols are an important class of compounds emerging from biomass combustion, and their reactions with ozone can generate secondary organic aerosols in the atmosphere. Here, we use a vertical wetted wall flow tube reactor to evaluate the effect of ionic strength on the heterogeneous reaction of gas-phase ozone (O₃) with a liquid film of o-vanillin (o-VL) (2-hydroxy-3-methoxybenzaldehyde), as a proxy for methoxyphenols. Typical for moderately acidic aerosols, at fixed pH = 5.6, the uptake coefficients (γ) of O₃ on o-VL ([o-VL] = 1 × 10^-5 mol L^-1) increase from γ = (1.9 ± 0.1) × 10^-7 in the absence of Na₂SO₄ to γ = (6.8 ± 0.3) × 10^-7 at I = 0.2 mol L^-1, and then, it decreases again. The addition of NO₃^- ions only slightly decreases the uptakes of O₃. Ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) reveals that the formation of multicore aromatic compounds is favored upon heterogeneous O₃ reaction with o-VL, in the presence of SO₄^2- and NO₃^- ions. The addition of NO₃^- ions favors the formation of nitrooxy (-ONO₂) or oxygenated nitrooxy group of organonitrates, which are components of brown carbon that can affect both climate and air quality.

Recognition of the molecular characterization and mechanisms of heterogeneously formed organic pollutants from metallurgical industries by FT-ICR-MS and GC/Q-TOF-MS

Emissions of numerous targeted and non-targeted organic pollutants from industrial activities are one of the major contributors to the global air pollution. However, comprehensive recognition of their molecular characterization and real industrial scale mechanisms have never been achieved. Herein, by using high resolution mass spectrometry, we firstly give an insight into the molecular characterization and mechanisms of organic pollutants formed on fly ashes from secondary smelting of Al, Cu, Pb, and Zn and electric arc furnace steel-making. We found that lipid-like, unsaturated hydrocarbon and carboxyl-rich alicyclic molecule-like structures were the major chemical classes. Methylation- and oxidation-related reactions were suggested to be the major formation mechanisms. The predominance of carboxyl-rich structures in the fly ash further proved the contribution of metallurgical industrial emissions to air pollution. Findings in this study could be significant for further understanding the contribution of industrial emissions to air pollutions and conducting their source emission control.

Nontarget Screening of Polycyclic Aromatic Compounds in Atmospheric Particulate Matter Using Ultrahigh Resolution Mass Spectrometry and Comprehensive Two-Dimensional Gas Chromatography

Polycyclic aromatic hydrocarbons (PAHs) are mutagenic and carcinogenic. 16 PAHs as priority pollutants listed by the US Environmental Protection Agency were usually monitored. Therefore, multiple potentially toxic polycyclic aromatic compounds (PACs) are not monitored. In this study, atmospheric particulate matter samples from Beijing were analyzed using atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight (GC × GC-TOF) mass spectrometry. The FT-ICR data detected high molecular weight PAHs, alkylated PAHs (APAHs) and heteroatom PAHs. The GC × GC-TOF data tentatively identified 386 PACs in five categories of identification confidence. Twenty-one spectra in the unknown class were manually resolved. Eighty-two PACs with high identification confidence were proposed for further research. The identities of five PAHs and five APAHs that are currently not regulated were confirmed using available standards and quantified in some samples. Some of these PACs, such as dibenzo[a,e]pyrene (C₂₂H₁₄) and 1-methylpyrene (C₁₇H₁₂), should be of concern because of their contamination levels and the high toxicities of themselves and/or their derivatives. This study highlights the possibility of expanding the traditional lists of PAHs to improve pollution control and risk assessment accuracy.

Photoinduced Uptake and Oxidation of SO2 on Beijing Urban PM2.5

Sulfate, as a major component of aerosol particles, greatly contributes to haze formation and affects global climate change. Although formation pathways of sulfate aerosols from the conversion of SO₂ have been extensively studied, the discrepancy between field observations and model simulations suggests that there are still unknown sulfate sources. Herein, we report for the first time a photoinduced SO₂ uptake and oxidation pathway in Beijing urban PM_2.5 aerosols. In comparison with the NO₂- and O₃-induced SO₂ oxidation pathways, this SO₂ photo-oxidation in Beijing urban PM_2.5 could make an important contribution to the daytime sulfate formation. Reactive species, such as ^•OH radicals and H₂O₂, are the major oxidants leading to sulfate formation in PM_2.5. The water-soluble matter (WSM) and water-insoluble organic matter (WISOM) in PM_2.5 were identified as the main photo-oxidant producers. Our work highlights an important daytime sulfate source in the atmosphere and provides new insight into the photochemical aging of ambient aerosols.

Fractionation and Characterization of Petroleum Asphaltene: Focus on Metalopetroleomics

Asphaltenes, as the heaviest and most polar fraction of petroleum, have been characterized by various analytical techniques. A variety of fractionation methods have been carried out to separate asphaltenes into multiple subfractions for further investigation, and some of them have important reference significance. The goal of the current review article is to offer insight into the multitudinous analytical techniques and fractionation methods of asphaltene analysis, following an introduction with regard to the morphologies of metals and heteroatoms in asphaltenes, as well their functions on asphaltene aggregation. Learned lessons and suggestions on possible future work conclude the present review article.

Assessment of PM2.5-bound nitrogen-containing organic compounds (NOCs) during winter at urban sites in China and Korea

In this study, ambient fine particles (PM_2.5) were collected in two urban cities in China and Korea (Beijing and Gwangju, respectively) simultaneously in January 2018. Analysis of the nonpolar and semipolar organic matter (OM) using atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that compounds containing only C, H, and O (CHO) and those containing C, H, O, and N (CHON) accounted for more than 90% of the total intensity of the OM peaks. Higher proportions of CHON compounds were observed during days with abnormally high PM_2.5 concentrations at both sites than on regular or non-event days. The proportion of CHON species at the Beijing site was not correlated with secondary ionic species (i.e., NO₃^-, SO₄^2-, and NH₄⁺) or gaseous components (i.e., O₃, NO₂, and SO₂). In contrast, the proportion of CHON species at the Gwangju site was positively correlated with the concentrations of particulate nitrate and ammonium ions, assuming that ambient ammonium nitrate plays a role in the atmospheric formation of nitrogen-containing organic compounds (NOCs) at the Gwangju site and that Gwangju is more strongly influenced by secondary aerosols than Beijing is. In particular, a significant proportion of the compounds observed at the Beijing site contained only C, H and N (CHN), while negligible amounts of CHN were detected at the Gwangju site. The CHN species in Beijing were identified as quinoline compounds and the corresponding -CH₂ homologous series using complementary GC × GC-TOF MS analysis. These results suggest that NOCs and their -CH₂ homologous series from primary emissions may be significant contributors to nonpolar and semipolar OM during winter in Beijing, while NOCs with high oxidation states, likely formed via ambient-phase nitrate-mediated reactions, may be the dominant OM constituents in Gwangju.

Ambient PM2.5 and PM10 bound PAHs in Islamabad, Pakistan: Concentration, source and health risk assessment

Polycyclic aromatic hydrocarbons (PAHs) in ambient particulate matter contribute considerably to human health risk. Simultaneous sampling of ambient PM_2.5/PM₁₀ was done to analyze the Ʃ16PAH across the four seasons of 2017 in Islamabad, Pakistan. The average Ʃ16PAH concentrations in PM_2.5 and PM₁₀ were 25.69 and 40.69 ng m^-3_, respectively. For both PM_2.5 and PM₁₀, the highest PAHs concentration was in winter (45.14, 67.10 ng m^-3), while the lowest was in summer (16.40, 28.18 ng m^-3). Source appointment indicated that vehicular exhaust, i.e., diesel, gasoline and alternatively fuel liquid natural gas (LNG), and compressed natural gas (CNG) combustion was the primary PAHs contributor, whereas biomass burning and fuel combustion (coal, biomass, wood, CNG) from stationary sources were another important sources. Health risk assessment showed that the lifetime cancer risk (LCR) values of PAHs were higher than the acceptable level in all four seasons. LCR values were the highest in winter (9.23 × 10^-4 for PAHs in PM_2.5 and 13.98 × 10^-4 for PAHs in PM₁₀) which were 9 and 13 times higher than tolerable cancer risk level respectively, and they were 2-3 times higher than the acceptable values in other seasons.

Monitoring of Anthracene Using Nanoscale Au-Cu Bimetallic Alloy Nanoparticles Synthesized with Various Compositions

Bimetallic alloy Au-Cu nanoparticles (Au-Cu alloy NPs) were synthesized using a chemical reduction method for sensing applications. Electronic absorption spectroscopy (UV-visible spectroscopy), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used for the confirmation and morphological studies of the synthesized nanoparticles. The composition of Au-Cu alloy NPs was studied by energy-dispersive spectroscopy (EDS). The high crystallinity of Au-Cu alloy NPs was demonstrated by XRD analysis. Both XRD and SEM analyses revealed that the nanoparticles' size ranges from 15 to 25 nm. Pyrrole was polymerized into polypyrrole (PPy) over a neat and clean glassy carbon electrode (GCE) by potentiodynamic polymerization. The sensitivity of GCE was improved by modifying it into a composite electrode. The composite electrode was developed by coating GCE with an overoxidized PPy polymer followed by Au-Cu alloy NPs. The ratio of Au and Cu was carefully controlled. The composite electrode (PPyox/Au-Cu/GCE) successfully detected an environmental toxin anthracene with a detection limit of 0.15 μM, as evidenced by cyclic voltammetry (CV), square-wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS).

Tracking photodegradation products and bond-cleavage reaction pathways of triclosan using ultra-high resolution mass spectrometry and stable carbon isotope analysis

Triclosan (TCS) is an antimicrobial compound ubiquitously found in surface waters throughout the world. Although several studies have focused on the photochemical degradation of TCS, there is still limited knowledge about its environmental fate. In this study, we got molecular-level insights into the photochemical degradation of TCS. Significant stable carbon isotope fractionation was observed during photodegradation; different bond-cleavage reaction pathways under different photolytic conditions were characterized, using compound specific isotope analysis (CSIA). Photochemical modeling of TCS photodegradation showed that direct photolysis would be the main transformation pathway if pH > 7, even in presence of dissolved organic matter. Moreover, by use of ultrahigh resolution mass spectrometry, FT-ICR-MS, a broad and complex spectrum of organic by-products (some of which potentially toxic, as assessed by a quantitative structure-activity relationship approach) were identified. A detailed reaction mechanism was developed on the basis of the detected compounds. A possible sequence of steps leading to some of the detected product compounds in aqueous solution is suggested.

Photochemical reactions of 1,3-butadiene with nitrogen oxide in different matrices: Kinetic behavior, humidity effect, product and mechanisms

Understanding the photochemical reaction process between VOCs and co-pollutants in the troposphere is crucial for controlling the haze. The photochemical reactions of 1,3-butadiene (1,3-BD) with NO were carried out at 308 K for up to 96 h in clean air with various relative humidity (RH) values, and actual haze atmosphere. In the haze, the representative pseudo-first-order kinetic rate constants of the 1,3-BD-NO system was 1.53 time higher than those in dry clean air. The effect of the RH (0%-80%) on the conversion behavior of the 1,3-BD-NO system in clean air was studied, revealing that increasing RH promoted the photochemical reaction in the low range of 0%-40% but retarded it in the high range of 40%-80%. Interestingly, OH radicals were directly detected under different RH values, and the strongest OH signal was obtained at an RH of 40%. Multiple macromolecular products with carbon numbers of 10-36 were identified. Unexpectedly, richer products and extended unsaturation range were detected at an RH of 40% than 0%. The photochemical products were also analyzed using ion chromatography. A reaction mechanism was proposed from the detected NO₂, O₃, OH, HNO₂, HNO₃, organic acids and macromolecular products.

In-House Standard Method for Molecular Characterization of Dissolved Organic Matter by FT-ICR Mass Spectrometry

Electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been widely used for molecular characterization of dissolved organic matter (DOM). However, ESI FT-ICR MS generally has poor repeatability and reproducibility because of its inherent ionization mechanism and structural characteristics, which severely hindered its application in quantitative analysis of complex mixtures. In this article, we developed an in-house standard method for molecular characterization of DOM by ESI FT-ICR MS. Instead of obtaining reproducible results by determining the instrument parameters, we adopted an approach of object control on the mass spectrum to solve the problem of poor reproducibility. The mass peak shape, resolution, and relative intensity distribution of a natural organic matter standard were adjusted by optimizing the operating conditions to obtain a repeatable result. The quality control sample was run 26 times by the different operators in a 6-month-long period to evaluate the reproducibility. Results showed that the relative standard deviation (%) of repeatability and reproducibility are 1.02 and 2.35 for average H/C, respectively. The in-house standard method has been validated and successfully used for the characterization of more than 4000 DOM samples, which is transferable to other laboratories.

Spectroscopic and molecular-level characteristics of dissolved organic matter in the Pearl River Estuary, South China

Coastal populations are expanding globally, resulting in great anthropogenic impacts on the organic matter in estuaries and regional carbon cycles. However, the molecular-level characteristics of dissolved organic matter (DOM) within highly disturbed estuaries are still not well understood. Here, water samples collected during two seasons (wet and dry) from the subtropical Pearl River Estuary of China were analyzed using absorption and fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to determine the spatiotemporal variations in the DOM characteristics. In the seaward direction, the abundances of chromophoric and fluorescent DOM decreased by greater percentages than the bulk dissolved organic carbon concentration. The spectroscopy and FT-ICR MS analyses collectively indicated seaward declines in the aromaticity of DOM and terrestrial DOM contributions from natural terrestrial markers and anthropogenic synthetic surfactants. In particular, the S content in DOM was much higher here than in previously reported estuaries, suggesting a strong anthropogenic impact on the estuarine DOM. Greater terrestrial and anthropogenic signatures in DOM were observed in the wet season than in the dry season. Importantly, this study implies that the terrestrial and anthropogenic contributions to DOM were strongly driven by season in the anthropogenically disturbed subtropical estuary.

The Key Role of Sulfate in the Photochemical Renoxification on Real PM2.5

The active nitrogen species (HONO, NO, and NO₂) have important impacts on the atmospheric oxidative capacity and the transformation of many atmospheric species. In this study, a fast photochemical renoxification rate of adsorbed HNO₃/NO₃^- to active nitrogen species (HONO, NO, and NO₂) was detected on real urban PM_2.5, and sulfate was found to play a key role in this process. Different from the reported direct photolysis pathway, the photochemical reaction of HNO₃/NO₃^- on PM_2.5 is dominated by a photosensitizing mechanism. Acidic protons are proved to be essential for this pathway. The role of sulfate, because of the nonvolatility of its conjugated acid, is to conserve the necessary acidic protons when interacting with HNO₃ and thus maintain its photoreactivity. This work implies that sulfate will have important implications in atmospheric nitrogen cycling by accelerating the release of nitrogen oxides from photochemical renoxification of HNO₃/NO₃^- adsorbed on ambient particulates and thus can cause major environmental problems.

Molecular traits of phenolic moieties in dissolved organic matter: Linkages with membrane fouling development

Phenolic moieties are important constituents in dissolved organic matter (DOM) in natural and engineered systems. However, their roles in membrane fouling mechanism during drinking water treatment by ultrafiltration (UF) have remained elusive. Herein, by using water insoluble polyvinylpolypyrrolidone (PVPP) resins, we sequestered the phenolic moieties from a model DOM (Suwannee River DOM, SRDOM) and characterized their molecular profiles using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Subsequently, their roles in UF membrane fouling propensity were investigated using reconstituted DOM solutions with various concentrations of phenolic moieties. The results showed that the phenolic moieties were of higher molecular weight and rich in unsaturation cyclic structures and oxygen-rich groups. Van Krevelen diagrams revealed that the sequestered sample was rich in aromatics structures and tannins-like compounds while contained less alicyclic organic acids in comparison with the original SRDOM, which was consistent with the aromaticity index (AI) analysis. UF experiments showed that the more phenolic moieties in DOM solution, the severer decline of flux was observed. The phenolic moieties played a significant role in membrane irremovable fouling due to the hydrophobic interactions and their higher molecular weight as evidenced by membrane cleaning tests. By surface characterization, the SRDOM fouled membrane was identified to have a higher water contact angle value and abundant C-O groups, likely due to the adsorption of more hydrophobic phenolic moieties. Overall, these findings highlighted links between phenolic moieties and membrane fouling development, and implied that membrane performance could be improved by pre-removal of phenolic moieties in DOM.

Analytical dataset on the molecular compositional changes of dissolved organic matter during hyperthermophilic composting

The aim of this research work was to determine the molecular compositional changes of dissolved organic matter (DOM) taken from different phases of the hyperthermophilic composting (HTC) process. The DOM samples were extracted by the standard protocol of C18 extraction methodology, and then analyzed by electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The profiles of negative ion mass spectrum and DOM molecular formulas of four compost samples were reported. Data related to the molecular compositional changes of DOM during HTC were also presented. Further interpretation and discussion on these datasets can be found in the related article entitled “Molecular insights into the transformation of dissolved organic matter during hyperthermophilic composting using ESI FT-ICR MS” [1].

Profiling Murchison Soluble Organic Matter for New Organic Compounds with APPI- and ESI-FT-ICR MS

The investigation of the abundant organic matter in primitive meteorite such as carbonaceous chondrites is of major interest in the field of origin of life. In this study, the soluble organic fraction of the Murchison meteorite was analyzed by atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), in both detection modes. Such an approach ensured that we obtained an extensive description of the organic matter of the CM2 meteorite. Indeed, while in total close to 16,000 unique features were assigned, only 4% are common to all analyses, illustrating the complementarity of both the detection modes and the ionization sources. ESI FT-ICR MS analysis, in negative-ion mode, ensured to observe specifically CHOS and CHNOS species, whereas the positive-ion mode is more dedicated to the detection of CHNO and CHN species. Moreover, new organomagnesium components were observed in (+) ESI. Eventually, (+) APPI FT-ICR MS analysis was a preferred method for the detection of less polar or nonpolar species such as polycyclic aromatic hydrocarbons but also heteroatom aromatic species composing the organic matter of Murchison.

Size-Segregated Chemical Compositions of HULISs in Ambient Aerosols Collected during the Winter Season in Songdo, South Korea

The primary objective of this study was to investigate the molecular compositions of humic-like substances (HULISs) in size-resolved ambient aerosols, which were collected using an Anderson-type air sampler (eight size cuts between 0.43 and 11 μm) during the winter season (i.e., the heating period of 8–12 January 2018) in Songdo, South Korea. The aerosol samples collected during the pre- (preheating, 27 November–1 December 2017) and post-winter (postheating, 12–16 March 2018) periods were used as controls for the winter season samples. According to the concentrations of the chromophoric organics determined at an ultraviolet (UV) wavelength of 305 nm, most of the HULIS compounds were found to be predominantly enriched in particles less than 2.1 μm regardless of the sampling period, which shows that particulate matter (diameter less than 2.5 μm; PM2.5) aerosols were the dominant carriers of airborne organics. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (UHR FT–ICR MS) analysis of the aerosol-carried organic substances revealed that as the aerosol size increased the proportions of CHO and nitrogen-containing CHO (CHON) compounds decreased, while the proportion of sulfur-containing CHO (CHOS) species increased. In particular, the ambient aerosols during the heating period seemed to present more CHO and CHON and less CHOS molecules compared to aerosols collected during the pre- and postheating periods. The aerosols collected during the heating period also exhibited more aromatic nitrogen-containing compounds, which may have originated from primary combustion processes. Overall, the particle size distribution was likely influenced by source origins; smaller particles are likely from local sources, such as traffic and industries, and larger particles (i.e., aged particles) are likely derived from long-range transport generating secondary organic aerosols (SOAs) in the atmosphere. The results of the size-segregated particles can be utilized to understand particle formation mechanisms and shed light on their toxicity to human health.

PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) in Beijing: Seasonal variations, sources, and risk assessment

Polycyclic aromatic hydrocarbons (PAHs) have been of health concern due to its carcinogenesis and mutagenesis. In this study, we aimed to assess the variations, sources, and lifetime excessive cancer risk (ECR) attributable to PAHs bound to ambient particulate matters with aerodynamic diameter less than 2.5μm (PM_2.5) in metropolitan Beijing, China. We collected 24-hour integrated PM_2.5 samples on daily basis between November 2014 and June 2015 across both central heating (cold months) and non-heating (warm months) seasons, and further analyzed the PAH components in these daily PM_2.5 samples. Our results showed that total concentrations of PM_2.5-bound PAHs varied between (88.6±75.4)ng/m³ in the cold months and (11.0±5.9)ng/m³ in the warm months. Benzo[a]pyrene (BaP), the carcinogenic marker of PAHs, averaged at 5.7 and 0.4ng/m³ in the cold and warm months, respectively. Source apportionment analyses illustrated that gasoline, biomass burning, diesel, coal combustion and cooking were the major contributors, accounting for 12.9%, 17.8%, 24.7%, 24.3% and 6.4% of PM_2.5-bound PAHs, respectively. The BaP equivalent lifetime ECR from inhalation of PM_2.5-bound PAHs was 16.2 cases per million habitants. Our results suggested that ambient particulate reduction from energy reconstruction and adaption of clean fuels would result in reductions PM_2.5-bound PAHs and its associated cancer risks. However, as only particulate phased PAHs was analyzed in the present study, the concentration of ambient PAHs could be underestimated.

Photochemical conversion of toluene in simulated atmospheric matrix and characterization of large molecular weight products by +APPI FT-ICR MS

The lack of kinetic parameters of VOC photochemical conversion especially in the presence of NO and O₃, and product information, will result in the incomplete understanding for the occurrence of haze. In the present study, the photochemical conversion of toluene, one of most significant hydrocarbons of VOCs, in toluene, toluene/NO, toluene/O₃ and reaction systems was assessed for up to 4 days in a smog chamber at 278 K and 308 K. The results indicated that the addition of NO and O₃ promoted the conversion of toluene. The first-order kinetic rate constants of toluene assessed in the toluene reaction system at 278 K and 308 K were 0.12 and 0.19 day^-1, respectively. The second-order kinetic rate constants of toluene assessed in the toluene/NO were 0.1 × 10^-13 cm³ molecule^-1 day^-1 (at 278 K) and 0.9 × 10^-13 cm³ molecule^-1 day^-1 (at 308 K), and those in the toluene/O₃ reaction systems were 0.06 × 10^-12 cm³ molecule^-1 day^-1 (at 278 K) and 0.11 × 10^-12 cm³ molecule^-1 day^-1 (at 308 K). The small difference of second-order kinetic rate constants between 278 K and 308 K obtained for the toluene/O₃ system when compared with the toluene/NO system indicated the reduced reaction sensitivity of O₃ to the temperature. Several dozens of large molecule products containing up to O₆ heteroatoms were identified by positive ion atmospheric pressure photoionization (+APPI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), with double bond equivalents up to 18, and carbon numbers ranging within 12-38, respectively. The findings presented herein may provide a new train of thought for the photochemical reaction process of toluene and its conversion in ambient air.

Pyrene-based MOFs as fluorescent sensors for PAHs: an energetic pathway of the backbone structure effect on response

The sensing performance of metal-organic frameworks (MOFs), a novel kind of crystalline fluorescent sensing materials, would be profoundly affected by their backbone structures. The current understanding about the backbone effect is limited to the modulation of analyte accommodation through pore structures. Herein, three topologically different pyrene-based MOFs, including NU-1000, NU-901 and ROD-7, were investigated as potential fluorescent sensors for polycyclic aromatic hydrocarbons (PAHs). Although these MOFs are constructed by the same photoactive component, they exhibited distinct sensing behaviors. NU-1000 gave different forms of fluorescent response to acenaphthylene, pyrene and fluoranthene with detection limits at the ng L-1 level. In contrast, NU-901 and ROD-7 were unresponsive to all tested PAHs. Experimental and computational investigations illustrate that this distinction is due to the variance in the excited state energy. The strong inter-ligand interaction in NU-901 and ROD-7 lowers their excited state energy and thus thermodynamically inhibits the photo-induced electron transfer and excimer/exciplex formation, which works in the NU-1000 system. This work proves for the first time that the topological structure of MOFs could affect their sensing performance in an energetic way.

Review of recent developments in GC-MS approaches to metabolomics-based research

BACKGROUND

Metabolomics aims to identify the changes in endogenous metabolites of biological systems in response to intrinsic and extrinsic factors. This is accomplished through untargeted, semi-targeted and targeted based approaches. Untargeted and semi-targeted methods are typically applied in hypothesis-generating investigations (aimed at measuring as many metabolites as possible), while targeted approaches analyze a relatively smaller subset of biochemically important and relevant metabolites. Regardless of approach, it is well recognized amongst the metabolomics community that gas chromatography-mass spectrometry (GC-MS) is one of the most efficient, reproducible and well used analytical platforms for metabolomics research. This is due to the robust, reproducible and selective nature of the technique, as well as the large number of well-established libraries of both commercial and 'in house' metabolite databases available.

AIM OF REVIEW

This review provides an overview of developments in GC-MS based metabolomics applications, with a focus on sample preparation and preservation techniques. A number of chemical derivatization (in-time, in-liner, offline and microwave assisted) techniques are also discussed. Electron impact ionization and a summary of alternate mass analyzers are highlighted, along with a number of recently reported new GC columns suited for metabolomics. Lastly, multidimensional GC-MS and its application in environmental and biomedical research is presented, along with the importance of bioinformatics.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The purpose of this review is to both highlight and provide an update on GC-MS analytical techniques that are common in metabolomics studies. Specific emphasis is given to the key steps within the GC-MS workflow that those new to this field need to be aware of and the common pitfalls that should be looked out for when starting in this area.

Ionic-Strength Effects on the Reactive Uptake of Ozone on Aqueous Pyruvic Acid: Implications for Air-Sea Ozone Deposition

A vertical wetted-wall flow-tube technique was used to explore the ionic strength effects at the air-water interface in mediating the sea-surface reaction between ozone (O₃) and pyruvic acid (PA). The uptake coefficients of ozone on aqueous PA increase substantially with the concentrations of bromide (Br^-) ions, clearly indicating that the dry deposition of ozone could be significantly enhanced due to the presence of carbonyl compounds such as PA at the bromide-rich sea surface. Based on the observed uptake coefficients, the estimated deposition velocity of ozone (100 ppb) for a nanomolar range of PA concentrations is ∼1 × 10^-3 m s^-1, which represents a significant contribution to the known deposition velocity of ozone at the sea surface. The analysis of reaction products by ultra-high-resolution Fourier transform-ion cyclotron resonance mass spectrometry suggests the formation of oligomers during both the dark and light-induced heterogeneous reactions between gaseous O₃ and PA occurring at the surface of a dilute aqueous phase (representative of cloud droplets). The detected high-molecular-weight compounds are much more complex than the oligomeric species identified during the photolytic degradation of bulk aqueous PA alone.

Comprehensive Molecular Characterization of Atmospheric Brown Carbon by High Resolution Mass Spectrometry with Electrospray and Atmospheric Pressure Photoionization

Light-absorbing components of atmospheric organic aerosols, which are collectively termed "brown carbon" (BrC), are ubiquitous in the atmosphere. They affect absorption of solar radiation by aerosols in the atmosphere and human health as some of them have been identified as potential toxins. Understanding the sources, formation, atmospheric evolution, and environmental effects of BrC requires molecular identification and characterization of light-absorption properties of BrC chromophores. Identification of BrC components is challenging due to the complexity of atmospheric aerosols. In this study, we employ two complementary ionization techniques, atmospheric pressure photo ionization (APPI) and electrospray ionization (ESI), to obtain broad coverage of both polar and nonpolar BrC components using high-resolution mass spectrometry (HRMS). These techniques are combined with chromatographic separation of BrC compounds with high performance liquid chromatography (HPLC), characterization of their light absorption with a photodiode array (PDA) detector, and chemical composition with HRMS. We demonstrate that this approach enables more comprehensive characterization of BrC in biomass burning organic aerosols (BBOAs) emitted from test burns of sage brush biofuel. In particular, we found that nonpolar BrC chromophores such as PAHs are only detected using positive mode APPI. Meanwhile, negative mode ESI results in detection of polar compounds such as nitroaromatics, aromatic acids, and phenols. For the BrC material examined in this study, over 40% of the solvent-extractable BrC light absorption is attributed to water insoluble, nonpolar to semipolar compounds such as PAHs and their derivatives, which require APPI for their identification. In contrast, the polar, water-soluble BrC compounds, which are detected in ESI, account for less than 30% of light absorption by BrC.

Collision cross section (CCS) measurement by ion cyclotron resonance mass spectrometry with short-time Fourier transform

RATIONALE

The collision cross section (CCS) is an important shape parameter which is often used in molecular structure investigation. In Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), the CCS affects the ion signal damping shape due to the effect of ion-neutral collisions. It is potential to obtain ion CCS values from FTICR-MS with the help of a proper ion-collision model.

METHODS

We have developed a rapid method to obtain the ion damping profile and CCS for mixtures by only one FTICR-MS measurement. The method utilizes short-time Fourier transform (STFT) to process FTICR-MS time domain signals. The STFT-processed result is a three-dimensional (3D) spectrum which has an additional time axis in addition to the conventional mass-to-charge ratio and intensity domains. The damping profile of each ion can be recognized from the 3D spectrum.

RESULTS

After extracting the decay profile of a specified ion, all the three ion-neutral collision models were tested in curve fitting. The hard-sphere model was proven to be suitable for our experimental setup. A linear relationship was observed between the CCS value and hard-sphere model parameters. Therefore, the CCS values of all the peaks were obtained through the addition of internal model compounds and linear calibration.

CONCLUSIONS

The proposed method was successfully applied to determine the CCSs of fatty acids and polyalanines in a petroleum gas oil matrix. This technique can be used for simultaneous measurement of cross sections for many ions in congested spectra.

Molecular Characterization of Water-Soluble Humic like Substances in Smoke Particles Emitted from Combustion of Biomass Materials and Coal Using Ultrahigh-Resolution Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Water-soluble humic like substances (HULIS) in smoke particles emitted from combustion of biomass materials and coal were characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. The formulas identified were classified into four main groups: CHO, CHON, CHOS, and CHONS. The average H/C and O/C ratios are 1.13-1.33, 1.01-1.13, 1.26-1.48, 1.09-1.24 and 0.21-0.41, 0.27-0.45, 0.41-0.46, 0.44-0.61 for the CHO, CHON, CHOS, and CHONS groups, respectively. The CHO compound was the predominant component (43%-72%) of the smoke HULIS from biomass burning (BB) and coal combustion, followed by the CHON group for BB-smoke HULIS and the S-containing groups (i.e., CHOS and CHONS) for coal-smoke HULIS. These results indicate that the primary HULIS emitted from biomass burning contain a high abundance of CHON species, which appear to be made up mainly of oxidized nitrogen functional groups such as nitro compounds and/or organonitrates. The coal-smoke HULIS contained more compounds with relatively low molecular weight and high aromaticity index (AI_mod). They were significantly enriched in S-containing compounds with high double bond equivalent (≥4), and O/S ratios suggest that they are most likely made up of aromatic organosulfates and nitrooxy organosulfates that are usually found in polluted atmospheres. These findings imply that the primary emissions from combustion of biomass and coal fuels are potential sources of water-soluble HULIS in an atmospheric matrix and that coal combustion is an especially important source of sulfate compounds.

Development and Application of a Novel Bioassay System for Dioxin Determination and Aryl Hydrocarbon Receptor Activation Evaluation in Ambient-Air Samples

Airborne persistent toxic substances are associated with health impacts resulting from air pollution, for example, dioxins, dioxin-like polychlorinated biphenyls, and certain polycyclic aromatic hydrocarbons (PAHs), which activate aryl hydrocarbon receptors (AhR) and thereby produce adverse outcomes. Thus, a bioassay for evaluating AhR activation is required for risk assessment of ambient-air samples, and for this purpose, we developed a new and sensitive recombinant mouse hepatoma cell line, CBG2.8D, in which a novel luciferase-reporter plasmid containing two copies of a newly designed dioxin-responsive domain and a minimal promoter derived from a native gene were integrated. The minimal detection limit for 2,3,7,8-tetrachlorodibenzo- p-dioxin with this assay system was 0.1 pM. We used CBG2.8D to determine dioxin levels in 45 ambient-air samples collected in Beijing. The measured bioanalytical equivalent (BEQ) values were closely correlated with the toxic equivalent values obtained from chemical analysis. In haze ambient-air samples, the total activation of aryl hydrocarbon receptors (TAA) was considerably higher than the BEQ of dioxin-rich fractions, according to the results of the cell-based bioassay. Notably, the haze samples contained abundant amounts of PAHs, whose relative toxicity equivalent was correlated with the TAA; this finding suggests that PAHs critically contribute to the AhR-related biological impacts of haze ambient-air samples.

Assessing on toxic potency of PM2.5-bound polycyclic aromatic hydrocarbons at a national atmospheric background site in North China

A total of 76PM_2.5 samples collected at Tuoji Island from November 2011 to January 2013 were used to analyze 15 congeners of polycyclic aromatic hydrocarbons (∑₁₅PAHs) and assess their toxic potency. The average ∑₁₅PAHs was 15.34±8.87ngm^-3, ranging from 4.24 to 40.62ngm^-3 over the sampling period. BkF, BbF, Phe and BaP were dominant PAH congeners, contributing together 60.64% of the ∑₁₅PAH concentration. The highest monthly ∑₁₅PAHs concentration was in January 2012, followed by the next January, which was closely four times greater than the lowest level occurred in July 2012. Wheat straw burning was responsible for the high PAH concentrations in June 2012. The averaged BaP toxicity equivalent (TEQ-BaP) concentration was 2.70±1.88ngm^-3 over the sampling period. BaP and DaA were the largest contributors, which contributed 58.5% and 14.7% of totals, respectively. The high TEQ-BaP and TEQ-BaP value per unit of ∑₁₅PAHs concentration (TEQ-BaP(U)) values occurred in the cold season and the low levels presented in the warm period. The heaviest monthly TEQ-BaP was 5.28±2.84ngm^-3, which appeared in January 2012; the lowest value was 0.86±0.33ngm^-3, which occurred in July 2012. The potential source contribution function (PSCF) showed the occurrence of the high health risk associated with PAHs in the middle of Liaoning and the south of Shandong Peninsula.

In-depth compositional analysis of water-soluble and -insoluble organic substances in fine (PM2.5) airborne particles using ultra-high-resolution 15T FT-ICR MS and GC×GC-TOFMS

Airborne particulate matter consisting of ionic species, salts, heavy metals and carbonaceous material is one of the most serious environmental pollutants owing to its impacts on the environment and human health. Although elemental and organic carbon compounds are known to be major components of aerosols, information on the elemental composition of particulate matter remains limited because of the broad range of compounds involved and the limits of analytical instruments. In this study, we investigated water-soluble and -insoluble organic compounds in fine (PM_2.5) airborne particles collected during winter in Korea to better understand the elemental compositions and distributions of these compounds. To collect ultra-high-resolution mass profiles, we analyzed water-soluble and -insoluble organic compounds, extracted with water and dichloromethane, respectively, using an ultra-high-resolution 15 T Fourier transform ion cyclotron resonance (15T FT-ICR) mass spectrometer in positive ion mode (via both electrospray ionization [ESI] and atmospheric pressure photoionization [APPI] for water-extracts and via APPI for dichloromethane-extracts). In conjunction with the FT-ICR mass spectrometry (MS) data, subsequent two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) data were used to identify potentially hazardous organic components, such as polycyclic aromatic hydrocarbons. This analysis provided information on the sources of ambient particles collected during winter season and partial evidence of contributions to the acidity of organic content in PM_2.5 particles. The compositional and structural features of water-soluble and -insoluble organic compounds from PM_2.5 particles are important for understanding the potential impacts of aerosol-carried organic substances on human health and global ecosystems in future toxicological studies.