Molecular characterization of nitrogen-containing organic compounds in biomass burning aerosols using high-resolution mass spectrometry

Comparative study of atmospheric brown carbon at Shanghai and the East China Sea: Molecular characterization and optical properties

The pollution burdens and compositions of atmospheric brown carbon (BrC) that determine their impacts on climate-health-ecosystems have not been well studied, particularly in some mega-economic coastal areas. Herein, atmospheric BrC samples synchronously collected from urban Shanghai (SH) and Huaniao Island (HNI) in the East China Sea during winter were characterized through ultrahigh-performance liquid chromatography-diode array detector-high resolution mass spectrometry (UHPLC-DAD-HRMS). The three polarity-dependent BrC fractions exhibited significant differences in both light absorption and chromophore composition. The average light absorption coefficients of BrC subfractions at 365 nm in SH were 2.6-3.7 times higher than those in HNI. The water-insoluble BrC (WIS-BrC) and humic-likes BrC (HULIS-BrC) dominated the total BrC absorption in SH (45 ± 7 %) and HNI (43 ± 6 %), respectively. Compared with SH, the higher O/Cw, lower molecule conjugation degree, and reduced mass absorption efficiency at 365 nm (MAE365) in HNI imply a potential bleaching mechanism during the transportation oxidation process. Thousands of BrC chromophores were detected at both sites. >20 major chromophores with strong absorption were unambiguously identified in HULIS-BrC and accounted for ∼40 % of the HULIS light absorption at 365 nm at both sites. These chromophores in SH HULIS-BrC featured oxygenated aromatics and nitroaromatics, while alkyl benzenesulfonic acids with emissions from cargo ships were found in HNI HULIS-BrC. Moreover, 22 major chromophores identified in WIS-BrC included alkaloids, polyaromatic hydrocarbons (PAHs), and carbonyl oxygenated PAHs, contributing 39 % and 49 % of the WIS-BrC light absorption at 365 nm in SH and HNI, respectively. Ascertaining the molecular-specific optical properties of BrC chromophores over the mega-economic coastal area is helpful for the predictive understanding of the sources and evolution of BrC, as well as its atmospheric behavior from land to sea.

Accessing the Low-Polar Molecular Composition of Boreal and Arctic Peat-Burning Organic Aerosol via Thermal Analysis and Ultrahigh-Resolution Mass Spectrometry: Structural Motifs and Their Formation

Peatland fires emit organic carbon-rich particulate matter into the atmosphere. Boreal and Arctic peatlands are becoming more vulnerable to wildfires, resulting in a need for better understanding of the emissions of these special fires. Extractable, nonpolar, and low-polar organic aerosol species emitted from laboratory-based boreal and Arctic peat-burning experiments are analyzed by direct-infusion atmospheric pressure photoionization (APPI) ultrahigh-resolution mass spectrometry (UHRMS) and compared to time-resolved APPI UHRMS evolved gas analysis from the thermal analysis of peat under inert nitrogen (pyrolysis) and oxidative atmosphere. The chemical composition is characterized on a molecular level, revealing abundant aromatic compounds that partially contain oxygen, nitrogen, or sulfur and are formed at characteristic temperatures. Two main structural motifs are identified, single core and multicore, and their temperature-dependent formation is assigned to the thermal degradation of the lignocellulose building blocks and other parts of peat.

Peatland Wildfires Enhance Nitrogen-Containing Organic Compounds in Marine Aerosols over the Western Pacific

Peatland wildfires contribute significantly to the atmospheric release of light-absorbing organic carbon, often referred to as brown carbon. In this study, we examine the presence of nitrogen-containing organic compounds (NOCs) within marine aerosols across the Western Pacific Ocean, which are influenced by peatland fires from Southeast Asia. Employing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in electrospray ionization (ESI) positive mode, we discovered that NOCs are predominantly composed of reduced nitrogenous bases, including CHN+ and CHON+ groups. Notably, the count of NOC formulas experiences a marked increase within plumes from peatland wildfires compared to those found in typical marine air masses. These NOCs, often identified as N-heterocyclic alkaloids, serve as potential light-absorbing chromophores. Furthermore, many NOCs demonstrate pyrolytic stability, engage in a variety of substitution reactions, and display enhanced hydrophilic properties, attributed to chemical processes such as methoxylation, hydroxylation, methylation, and hydrogenation that occur during emission and subsequent atmospheric aging. During the daytime atmospheric transport, aging of aromatic N-heterocyclic compounds, particularly in aliphatic amines prone to oxidation and reactions with amine, was observed. The findings underscore the critical role of peatland wildfires in augmenting nitrogen-containing organics in marine aerosols, underscoring the need for in-depth research into their effects on marine ecosystems and regional climatic conditions.

Kinetic nitrogen isotope effects of 18 amino acids degradation during burning processes

Understanding the nitrogen isotopic variations of individual amino acids (AAs) is essential for utilizing the nitrogen isotope values of individual amino acids (δ15N-AA) as source indicators to identify proteinaceous matter originating from biomass combustion processes. However, the nitrogen isotope effects (ε) associated with the degradation of individual amino acids during combustion processes have not been previously explored. In this study, we measured the nitrogen isotope values of residual free amino acids -following a series of controlled combustion experiments at temperatures of 160-240 °C and durations of 2 min to 8 h, as described in Part 1. δ15N values of proline, aspartate, alanine, valine, glycine, leucine, and isoleucine are more positive than their initial δ15N values after prolonged combustion. Variations in δ15N values of the most AAs conform to the Rayleigh fractionation during combustion and their nitrogen isotope effects (ε) are greatly impacted by their respective combustion degradation pathways. This is the first time the ε values associated with the degradation pathways of AAs during combustion have been characterized. Only the ε values associated with Pathway 1 (dehydration to form dipeptide) and 2 (simultaneous deamination and decarboxylation) are found to be significant and temperature-dependent, ranging from + 2.9 to 6.4‰ and + 0.9‰ to + 3.8‰, respectively. Conversely, ε values associated with other pathways are minor. This improves the current understanding on the degradation mechanisms of protein nitrogen during biomass burning.

Effects of photochemical aging on the molecular composition of organic aerosols derived from agricultural biomass burning in whole combustion process

Biomass burning organic aerosols (BBOA) are key components of atmospheric particulate matter, yet the effects of aging process on their chemical composition and related properties remain poorly understood. In this study, fresh smoke emissions from the combustion of three types of agricultural biomass residues (rice, maize, and wheat straws) were photochemically aged in an oxidation flow reactor. The changes in BBOA composition were characterized by offline analysis using ultrahigh performance liquid chromatography coupled with Orbitrap mass spectrometry. The BBOA molecular composition varied dramatically with biomass type and aging process. Fresh and aged BBOA were predominated by CHO and nitrogen-containing CHON, CHN, and CHONS species, while with very few CHOS and other non‑oxygen species. The signal peak area variations revealed that individual molecular species underwent dynamic changes, with 77-81 % of fresh species decreased or even disappeared and 33-46 % of aged species being newly formed. A notable increase was observed in the number and peak area of CxHyO≥6 compounds in aged BBOA, suggesting that photochemical process served as an important source of highly oxygenated species. Heterocyclic CxHyN2 compounds mostly dominated in fresh CHN species, whereas CxHyN1 were more abundant in aged ones. Fragmentation and homologs oxidation by addition of oxygen-containing functional groups were important pathways for the BBOA aging. The changes in BBOA composition with aging would have large impacts on particle optical properties and toxicity. This study highlights the significance of photochemical aging process in altering chemical composition and related properties of BBOA.

Appearance of Recalcitrant Dissolved Black Carbon and Dissolved Organic Sulfur in River Waters Following Wildfire Events

Increasing wildfire frequency, a consequence of global climate change, releases incomplete combustion byproducts such as aquatic pyrogenic dissolved organic matter (DOM) and black carbon (DBC) into waters, posing a threat to water security. In August 2022, a series of severe wildfires occurred in Chongqing, China. Samples from seven locations along the Yangtze and Jialing Rivers revealed DBC, quantified by the benzene poly(carboxylic acid) (BPCA) method, comprising 9.5-19.2% of dissolved organic carbon (DOC). High concentrations of BPCA-DBC with significant polycondensation were detected near wildfire areas, likely due to atmospheric deposition driven by wind. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) revealed that wildfires were associated with an increase in condensed aromatics, proteins, and unsaturated hydrocarbons, along with a decrease in lignins. The condensed aromatics primarily consisted of dissolved black nitrogen (DBN), contributing to abundant high-nitrogen-containing compounds in locations highly affected by wildfires. Meanwhile, wildfires potentially induced the input of recalcitrant sulfur-containing protein-like compounds, characterized by high oxidation, aliphatic nature, saturation, and low aromaticity. Overall, this study revealed the appearance of recalcitrant DBC and dissolved organic sulfur in river waters following wildfire events, offering novel insights into the potential impacts of wildfires on water quality and environmental biogeochemistry.

Unveiling the Molecular Characteristics, Origins, and Formation Mechanism of Reduced Nitrogen Organic Compounds in the Urban Atmosphere of Shanghai Using a Versatile Aerosol Concentration Enrichment System

Reduced nitrogen-containing organic compounds (NOCs) in aerosols play a crucial role in altering their light-absorption properties, thereby impacting regional haze and climate. Due to the low concentration levels of individual NOCs in the air, the utilization of accurate detection and quantification technologies becomes essential. For the first time, this study investigated the diurnal variation, chemical characteristics, and potential formation pathways of NOCs in urban ambient aerosols in Shanghai using a versatile aerosol concentration enrichment system (VACES) coupled with HPLC-Q-TOF-MS. The results showed that NOCs accounted over 60% of identified components of urban organic aerosols, with O/N < 3 compounds being the major contributors (>70%). The predominance of the positive ionization mode suggested the prevalence of reduced NOCs. Higher relative intensities and number fractions of NOCs were observed during nighttime, while CHO compounds showed an opposite trend. Notably, a positive correlation between the intensity of NOCs and ammonium during the nighttime was observed, suggesting that the reaction of ammonium to form imines may be a potential pathway for the formation of reduced NOCs during the nighttime. Seven prevalent types of reduced NOCs in autumn and winter were identified and characterized by an enrichment of CH2 long-chain homologues. These NOCs included alkyl, cyclic, and aromatic amides in CHON compounds, as well as heterocyclic or cyclic amines and aniline homologue series in CHN compounds, which were associated with anthropogenic activities and may be capable of forming light-absorbing chromophores or posing harm to human health. The findings highlight the significant contributions of both primary emissions and ammonium chemistry, particularly amination processes, to the pollution of reduced NOCs in Shanghai's atmosphere.

Chemical Fingerprinting of Biomass Burning Organic Aerosols from Sugar Cane Combustion: Complementary Findings from Field and Laboratory Studies

Agricultural fires are a major source of biomass-burning organic aerosols (BBOAs) with impacts on health, the environment, and climate. In this study, globally relevant BBOA emissions from the combustion of sugar cane in both field and laboratory experiments were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. The derived chemical fingerprints of fresh emissions were evaluated using targeted and nontargeted evaluation approaches. The open-field sugar cane burning experiments revealed the high chemical complexity of combustion emissions, including compounds derived from the pyrolysis of (hemi)cellulose, lignin, and further biomass, such as pyridine and oxime derivatives, methoxyphenols, and methoxybenzenes, as well as triterpenoids. In comparison, laboratory experiments could only partially model the complexity of real combustion events. Our results showed high variability between the conducted field and laboratory experiments, which we, among others, discuss in terms of differences in combustion conditions, fuel composition, and atmospheric processing. We conclude that both field and laboratory studies have their merits and should be applied complementarily. While field studies under real-world conditions are essential to assess the general impact on air quality, climate, and environment, laboratory studies are better suited to investigate specific emissions of different biomass types under controlled conditions.

Aerosolomics based approach to discover source molecular markers: A case study for discriminating residential wood heating vs garden green waste burning emission sources

Biomass burning is a significant source of particulate matter (PM) in ambient air and its accurate source apportionment is a major concern for air quality. The discrimination between residential wood heating (RWH) and garden green waste burning (GWB) particulate matter (PM) is rarely achieved. The objective of this work was to evaluate the potential of non-targeted screening (NTS) analyses using HRMS (high resolution mass spectrometry) data to reveal discriminating potential molecular markers of both sources. Two residential wood combustion appliances (wood log stove and fireplace) were tested under different output conditions and wood moisture content. GWB experiments were carried out using two burning materials (fallen leaves and hedge trimming). PM samples were characterized using NTS approaches with both LC- and GC-HRMS (liquid and gas chromatography-HRMS). The analytical procedures were optimized to detect as many species as possible. Chemical fingerprints obtained were compared combining several multivariate statistical analyses (PCA, HCA and PLS-DA). Results showed a strong impact of the fuel nature and the combustion quality on the chemical fingerprints. 31 and 4 possible markers were discovered as characteristic of GWB and RWH, respectively. Complementary work was attempted to identify potential molecular formulas of the different potential marker candidates. The combination of HRMS NTS chemical characterization with multivariate statistical analyses shows promise for uncovering organic aerosol fingerprinting and discovering potential PM source markers.

Identification of sources of coarse mode aerosol particles (PM10) using ATR-FTIR and SEM-EDX spectroscopy over the Himalayan Region of India

This study attempts to examine the morphological, elemental and physical characteristics of PM10 over the Indian Himalayan Region (IHR) using FTIR and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis. The study aimed at source identification of PM10 by exploring the inorganic ions, organic functional groups, morphology and elemental characteristics. The pollution load of PM10 was estimated as 63 ± 22 μg m-3; 53 ± 16 μg m-3; 67 ± 26 μg m-3 and 55 ± 11 μg m-3 over Mohal-Kullu, Almora, Nainital and Darjeeling, respectively. ATR-FTIR spectrum analysis revealed the existence of inorganic ions (SiO44-, TiO2, SO42-, SO3-, NO3-, NO2-, CO32-, HCO3-, NH4+) and organic functional groups (C-C, C-H, C=C, C≡C, C=O, N-H, C≡N, C=N, O-H, cyclic rings, aromatic compounds and some heterogeneous groups) in PM10 which may arise from geogenic, biogenic and anthropogenic sources. The morphological and elemental characterization was performed by SEM-EDX, inferring for geogenic origin (Al, Na, K, Ca, Mg and Fe) due to the presence of different morphologies (irregular, spherical, cluster, sheet-like solid deposition and columnar). In contrast, particles having biogenic and anthropogenic origins (K, S and Ba) have primarily spherical with few irregular particles at all the study sites. Also, the statistical analysis ANOVA depicts that among all the detected elements, Na, Al, Si, S and K are site-specific in nature as their mean of aw% significantly varied for all the sites. The trajectory analysis revealed that the Uttarakhand, Jammu and Kashmir, the Thar Desert, Himachal Pradesh, Pakistan, Afghanistan, Nepal, Sikkim, the Indo-Gangetic Plain (IGP) and the Bay of Bengal (BoB) contribute to the increased loading of atmospheric pollutants in various locations within the IHR.

Iron content in aerosol particles and its impact on atmospheric chemistry

Atmospheric aerosol effects on ecological and human health remain uncertain due to their highly complex and evolving nature when suspended in air. Atmospheric chemistry, global climate/oceanic and health exposure models need to incorporate more realistic representations of aerosol particles, especially their bulk and surface chemistry, to account for the evolution in aerosol physicochemical properties with time. (Photo)chemistry driven by iron (Fe) in atmospheric aerosol particles from natural and anthropogenic sources remains limited in these models, particularly under aerosol liquid water conditions. In this feature article, recent advances from our work on Fe (photo)reactivity in multicomponent aerosol systems are highlighted. More specifically, reactions of soluble Fe with aqueous extracts of biomass burning organic aerosols and proxies of humic like substances leading to brown carbon formation are presented. Some of these reactions produced nitrogen-containing gaseous and condensed phase products. For comparison, results from these bulk aqueous phase chemical studies were compared to those from heterogeneous reactions simulating atmospheric aging of Fe-containing reference materials. These materials include Arizona test dust (AZTD) and combustion fly ash particles. Also, dissolution of Fe and other trace elements is presented from simulated human exposure experiments to highlight the impact of aerosol aging on levels of trace metals. The impacts of these chemical reactions on aerosol optical, hygroscopic and morphological properties are also emphasized in light of their importance to aerosol-radiation and aerosol-cloud interactions, in addition to biogeochemical processes at the sea/ocean surface microlayer upon deposition. Future directions for laboratory studies on Fe-driven multiphase chemistry are proposed to advance knowledge and encourage collaborations for efficient utilization of expertise and resources among climate, ocean and health scientific communities.

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.

Abundance and sources of organic nitrogen in fine (PM2.5) and coarse (PM2.5-10) particulate matter in urban Hong Kong

Organic nitrogen (ON) in atmospheric particles is much less monitored compared to inorganic nitrogen (IN), despite its significant contribution to atmospheric N deposition budget. In this study, we expanded a newly developed instrumental method for IN and ON in PM2.5 samples to PM10 samples. We determined the quantities of ON and IN for paired PM2.5 and PM10 samples collected at an urban coastal site in Hong Kong, southern China over a year. These measurements also allowed the determination of IN and ON abundance in the coarse PM (i.e., PM2.5-10) by taking the difference between PM10 and PM2.5. The measurement results show that ON accounted for 27.6 % and 21.1 % of total N in fine and coarse particles, respectively, and was mainly (87.7 %) distributed in the fine mode at the site. The seasonal variation of ON/total N was relatively small in PM2.5 (23.6-30.4 %) while considerably larger in coarse PM (4.3-42.1 %). Analysis aided by concurrently measured source indicators revealed that sea spray, biological particle emissions, and dust mixed with anthropogenic pollutants are potentially significant sources of ON in coarse particles. Positive matrix factorization (PMF) source apportionment further revealed that industrial emissions/coal combustion (43.6 %), soil dust emission (16.3 %), fresh sea salt emission (15.2 %), and aged sea salt (24.9 %) are major sources of PMcoarse-bound ON at the site. The contributions of industrial emissions/coal combustion and soil dust emission to ON were significantly higher in autumn and winter. Fresh sea salt emissions contributed greater proportions to ON in spring and summer, while ON associated with the aged sea salt source was higher in spring and autumn. These findings have advanced our quantitative understanding of the sources of PMcoarse-bound ON, which was scarcely determined in the past. Furthermore, the ON measurement data in fine and coarse particles helps estimate ON deposition, which has been previously under-evaluated.

Aqueous-Phase Reactions of Anthropogenic Emissions Lead to the High Chemodiversity of Atmospheric Nitrogen-Containing Compounds during the Haze Event

Nitrogen-containing organic compounds (NOCs), a type of important reactive-nitrogen species, are abundant in organic aerosols in haze events observed in Northern China. However, due to the complex nature of NOCs, the sources, formation, and influencing factors are still ambiguous. Here, the molecular composition of organic matters (OMs) in hourly PM2.5 samples collected during a haze event in Northern China was characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We found that CHON compounds (formulas containing C, H, O, and N atoms) dominated the OM fractions during the haze and showed high chemodiversity and transformability. Relying on the newly developed revised-workflow and oxidation-hydrolyzation knowledge for CHON compounds, 64% of the major aromatic CHON compounds (>80%) could be derived from the oxidization or hydrolyzation processes. Results from FT-ICR MS data analysis further showed that the aerosol liquid water (ALW)-involved aqueous-phase reactions are important for the molecular distribution of aromatic-CHON compounds besides the coal combustion, and the ALW-involved aromatic-CHON compound formation during daytime and nighttime was different. Our results improve the understanding of molecular composition, sources, and potential formation of CHON compounds, which can help to advance the understanding for the formation, evolution, and control of haze.

Formation of nitrogen-containing gas phase products from the heterogeneous (photo)reaction of NO2 with gallic acid

Heterogeneous reaction of gas phase NO2 with atmospheric humic-like substances (HULIS) is potentially an important source of volatile organic compounds (VOCs) including nitrogen (N)-containing compounds, a class of brown carbon of emerging importance. However, the role of ubiquitous water-soluble aerosol components in this multiphase chemistry, namely nitrate and iron ions, remains largely unexplored. Here, we used secondary electrospray ionization ultrahigh-resolution mass spectrometry for real-time measurements of VOCs formed during the heterogeneous reaction of gas phase NO2 with a solution containing gallic acid (GA) as a proxy of HULIS at pH 5 relevant for moderately acidic aerosol particles. Results showed that the number of detected N-containing organic compounds largely increased from 4 during the NO2 reaction with GA in the absence of nitrate and iron ions to 55 in the presence of nitrate and iron ions. The N-containing compounds have reduced nitrogen functional groups, namely amines, imines and imides. These results suggest that the number of N-containing compounds is significantly higher in deliquescent aerosol particles due to the influence of relatively higher ionic strength from nitrate ions and complexation/redox reactivity of iron cations compared to that in the dilute aqueous phase representative of cloud, fog, and rain water.

Hygroscopicity of nitrogen-containing organic carbon compounds: o-aminophenol and p-aminophenol

Nitrogen-containing Organic Carbon (NOC) is a major constituent of atmospheric aerosols and they have received significant attention in the atmospheric science community. While extensive research and advancements have been made regarding their emission sources, concentrations, and their secondary formation in the atmosphere, little is known about their water uptake efficiencies and their subsequent role in climate, air quality, and visibility. In this study, we investigated the water uptake of two sparingly soluble aromatic NOCs: o-aminophenol (oAP) and p-aminophenol (pAP) under subsaturated and supersaturated conditions using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Cloud Condensation Nuclei Counter (CCNC), respectively. Our results show that oAP and pAP are slightly hygroscopic with comparable hygroscopicities to various studied organic aerosols. The supersaturated single hygroscopicity parameter (κ_CCN) was measured and reported to be 0.18 ± 0.05 for oAP and 0.04 ± 0.02 for pAP, indicating that oAP is more hygroscopic than pAP despite them having the same molecular formulae. The observed disparity in hygroscopicity is attributed to the difference in functional group locations, interactions with gas phase water molecules, and the reported bulk water solubilities of the NOC. Under subsaturated conditions, both oAP and pAP aerosols showed size dependent water uptake. Both species demonstrated growth at smaller dry particle sizes, and shrinkage at larger dry particle sizes. The measured growth factor (G_f) range, at RH = 85%, for oAP was 1.60-0.74 and for pAP was 1.53-0.74 with increasing particle size. The growth and shrinkage dichotomy is attributed to morphological particle differences verified by TEM images of small and large particles. Subsequently, aerosol physicochemical properties must be considered to properly predict the droplet growth of NOC aerosols in the atmosphere.

Real-time measurements of product compounds formed through the reaction of ozone with breath exhaled VOCs

Human presence can affect indoor air quality because of secondary organic compounds formed upon reactions between gaseous oxidant species, e.g., ozone (O₃), hydroxyl radicals (OH), and chemical compounds from skin, exhaled breath, hair and clothes. We assess the gas-phase product compounds generated by reactions of gaseous O₃ with volatile organic compounds (VOCs) from exhaled human breath by real time analysis using a high-resolution quadrupole-orbitrap mass spectrometer (HRMS) coupled to a secondary electrospray ionization (SESI) source. Based on the product compounds identified we propose a reaction mechanism initiated by O₃ oxidation of the most common breath constituents, isoprene, α-terpinene and ammonia (NH₃). The reaction of O₃ with isoprene and α-terpinene generates ketones and aldehydes such as 3,4-dihydroxy-2-butanone, methyl vinyl ketone, 3-carbonyl butyraldehyde, formaldehyde and toxic compounds such as 3-methyl furan. Formation of compounds with reduced nitrogen containing functional groups such as amines, imines and imides is highly plausible through NH₃ initiated cleavage of the C-O bond. The detected gas-phase product compounds suggest that human breath can additionally affect indoor air quality through the formation of harmful secondary products and future epidemiological studies should evaluate the potential health effects of these compounds.

Inter-Comparisons of Major Ions and Organic Matter Using Aerodyne Aerosol Mass Spectrometer, Ion Chromatography and Sunset Lab Carbon Analyzer in Aged Aerosols from Okinawa in the Western North Pacific Rim

Inorganic components were measured in the aged ambient aerosols from Cape Hedo, Okinawa, an outflow region of East Asia, using online quadrupole Aerodyne aerosol mass spectrometer (Q-AMS) and offline ion chromatography (IC) and Sunset Lab carbon analyzer. Here, we performed an inter-comparison study on nitrate (NO3−), ammonium (NH4+) and sulfate (SO42−) that were measured by IC and AMS. Sulfate and ammonium showed a good agreement between two instruments. However, abundances of NO3− by AMS are on average twice overestimated compared to nitrate obtained by IC. We also found that a significant amount of organic nitrogen (ON) was detected in the filter samples from Okinawa. The online measurement (Q-AMS) data and offline filter based-NO3− data need to be carefully evaluated when ON is abundantly present in aerosols. The OM/OC ratios derived from AMS are consistent with the bulk OMAMS/OCSunset ratios (2.1). This study demonstrates that the OM/OC of 2.1 is the reasonable criteria for more aged aerosols.

Molecular Characterization of Organophosphorus Compounds in Wildfire Smoke Using 21-T Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

We present a detailed molecular characterization of organophosphorus compounds in ambient organic aerosol influenced by wildfire smoke. Biomass burning organic aerosol (BBOA) is an important source of phosphorus (P) to surface waters, where even a small imbalance in the P flux can lead to substantial effects on water quality, such as eutrophication, algal blooms, and oxygen depletion. We aimed to exploit the ultrahigh resolving power, mass accuracy, and sensitivity of Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular composition of an ambient BBOA sample collected downwind of Pacific Northwest wildfires. The 21-T FT-ICR MS yielded 10 533 distinct formulae, which included molecular species comprising C, H, O, and P with or without N, i.e., organophosphorus compounds that have long been quantified in wildfire smoke but have not yet been characterized at the molecular level. The lack of detailed molecular characterization of organophosphorus compounds in BBOA is primarily due to their inherently low concentrations in aerosols and poor ionization efficiency in complex mixtures. We demonstrate that the exceptional sensitivity of the 21-T FT-ICR MS allows qualitative analysis of a previously uncharacterized fraction of BBOA without its selective concentration from the organic matrix, exemplifying the need for ultrahigh-resolution tools for a more detailed and accurate molecular depiction of such complex mixtures.

Dwindling aromatic compounds in fine aerosols from chunk coal to honeycomb briquette combustion

With the implementation of clean coal policy in China, the chunk coal has been gradually replaced by honeycomb briquette in domestic energies. In this study, the molecular composition of fine particles (PM_2.5) from chunk coal and honeycomb briquette combustion is characterized using the Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). More than 6000 molecular formulae were detected in each PM_2.5 sample. A remarkable decrease in unsaturation and aromatic compounds was found from chunk coal to honeycomb briquette derived aerosols. Around 73.6% of the unique CHON compounds in chunk coal are considered to have aromatic structures, while it decreased to 7.3% in honeycomb briquette. Most of these nitroaromatics detected only in chunk coal are highly carcinogenic and mutagenic with 4-6 rings. Moreover, the aromatic compounds in sulfur-containing compounds also showed a significant decrease. Meanwhile, because of the perforated shape and the additives added during the production of honeycomb briquettes, there are more heteroatoms-containing molecules released from honeycomb briquette combustion, which are highly functional compounds with high molecular weight, high degree of oxidation, and low volatility. Our results provide molecular level evidence that the transformation from chunk coal to honeycomb briquette can effectively reduce the emission of aromatic compounds, which is beneficial to assessing and reducing the impacts to climate change as well as human health.

Molecular characterization of nitrogen-containing organic compounds in the winter North China Plain

The molecular characteristics of organic aerosols (OAs) in heavily polluted areas affected by coal combustion (CC) were investigated. In terms of relative abundance, the total nitrogen-containing organic compounds (NOC) accounted for about 61%-68% of all molecules detected in methanol-soluble organic carbon (MSOC) by LC - Q-TOF - MS. More than 85% of the CHON- formulas are nitro-aromatic compounds, which are generally considered to be secondary organic compounds, as evidenced by the lower degree of overlap of these substances in the atmospheric samples and CC samples. Some polycyclic aromatic compounds with 4 N and 1-2O and very low H/C and O/C ratio produced by CC are unstable and easily react to form compounds with higher degrees of saturation. Almost all of the CHON+ homologues detected in the CC samples were also found in the atmospheric samples, indicating that the large amount of CHON+ compounds produced by CC are stable during atmospheric processes. The CHN+ compounds produced by CC contain a certain amount of highly unsaturated compounds, among which 1 N-containing polycyclic aromatic hydrocarbons (1 N-PAHs) is stable in atmosphere and can serve as markers of CC.

Physical and chemical characterization of urban grime: An impact on the NO2 uptake coefficients and N-containing product compounds

Urban grime represents an important environmental surface for heterogeneous reactions in urban environment. Here, we assess the physical and chemical properties of urban grime collected during six consecutive months in downtown of Guangzhou, China. There is a significant variation of the uptake coefficients of NO₂ on the urban grime as a function of the relative humidity (RH). In absence of water molecules (0% RH), the light-induced uptake coefficients of NO₂ on urban grime samples collected during six months are very similar in order of ≈10^-6. At 80% RH, depending on the sampling month the light-induced uptake coefficient of NO₂ can reach one order of magnitude higher values (1.5 × 10^-5, at 80% RH) compared to those uptakes at 0% RH. In presence of 80% RH, there are strong correlations between the measured NO₂ uptakes and the concentrations of the water soluble carbon, soluble anions, polycyclic aromatic hydrocarbons and n-alkanes depicted in the urban grime. These correlations, demonstrate that surface adsorbed water on urban grime play an important role for the uptakes of NO₂. The heterogeneous conversion of NO₂ on two-month old urban grime under sunlight irradiation (68 W m^-2, 300 nm < λ < 400 nm) at 60% RH leads to the formation of unprecedented HONO surface flux of 4.7 × 10¹⁰ molecules cm^-2 s^-1 which is higher than all previously observed HONO fluxes, thereby affecting the oxidation capacity of the urban atmosphere. During the heterogeneous chemistry of NO₂ with urban grime, the unsaturated and N-containing organic compounds are released in the gas phase which can affect the air quality in the urban environment.

Molecular characterization of nitrogen-containing organic compounds in fractionated atmospheric humic-like substances (HULIS) and its relationship with optical properties

Diverse nitrogen-containing organics are important components of humic-like substances (HULIS) in the atmosphere. In this study, organic components in particulate matter (PM) samples representing multiple sources were separated by successive solvent fractionation, which were then analyzed by mass spectrometric and optical instruments. The CHON compounds were eluted and clustered into the Low-polar, Medium-polar, and High-polar fractions, and discrepancies of the polar-fractions were particularly reflected by molecular descriptors such as aromaticity, oxygen content and molecular weight. In addition, the results from the light-absorbing parameters (i.e., MAE₃₆₅ and SUVA₂₅₄) underscored the importance of the Low-polar and High-polar fractions on optical absorption properties. The Low-polar fraction accounted for 40% of the cumulative SUVA₂₅₄ values, suggesting significant content of ultraviolet-absorbing organics. The High-polar fraction contributed 52% of the cumulative MAE₃₆₅ values, indicating abundant light absorption capacity and efficiency. Significant improvements were made on statistical analysis of multidimensional data by a combination of the molecular descriptors and optical parameters. Molecular structures, including condensed aromatic, lignin-like, and aliphatic compounds observed in distinct electrospray ionization modes, were found as main contributors to the light absorption capacity and the abundances of fluorophores in individual polar-fractions. Differential contributions of molecular characteristics on types and abundances of fluorophores were further found among the samples of multiple sources. Conclusions obtained from this successive solvent fractionation experiment could promote development of the pretreatment method for exploring the potential light-absorbing organics, which also provide insights into the emission sources of organics that are related to specific light absorption and fluorescence properties.

Chemical characteristics and sources of nitrogen-containing organic compounds at a regional site in the North China Plain during the transition period of autumn and winter

Organic nitrogen constitutes a significant fraction of the nitrogen budget in particulate matter (PM). However, the composition and sources of nitrogen-containing organic compounds (NOCs) in PM remain unclear currently in North China Plain (NCP), China. Rare local or regional studies on NOCs were conducted. In this study, ambient fine particles (PM_2.5) were collected in Xianghe, a regional background site in NCP, from 26 October to 26 December 2017. The insights from this study include NOC molecule identification, concentration level, and NOC sources and origins. Specifically, we have identified and quantified >90 NOC species, with urea being the most abundant, accounting for 39.7 ± 4.7% of the total NOC followed by free amino acids (FAAs; 21.9 ± 1.5%), cyclic NOCs (15.3 ± 4.5%), amines (14.8 ± 1.5%), alkyl amides (5.8 ± 0.5%), isocyanates (1.7 ± 0.2%), and nitriles (1.1 ± 0.2%). The time series of FAAs was well correlated (r = 0.51-0.68, p < 0.01) with the organic marker of levoglucosan and was moderately correlated with O_x (r = 0.29-0.41, p < 0.01), suggesting biomass burning and secondary formation were important FAAs sources. We also show that amines can be oxidized and/or reacted by aqueous-phase processing to form secondary aerosols, which are further enhanced by the involvement of iron in the catalytic process. Using the receptor model of positive matrix factorization (PMF), six factors were identified including coal combustion, crustal sources, biomass burning, industry-related sources, traffic emissions, and secondary aerosols. Source apportionment of NOC shows biomass burning was the dominant factor, accounting for 31.8% of the total NOCs. This study provides a unique dataset of NOCs at this regional background site in the NCP, with the insights of NOC chemical composition and sources gained in this study being important for future NOC modeling as well as NOC health effects studies.

Gridded distribution of total suspended particulate matter (TSP) and their chemical characterization over Delhi during winter

In the present study, total suspended particulate matter (TSP) samples were collected at 47 different sites (47 grids of 5 × 5 km² area) of Delhi during winter (January-February 2019) in campaign mode. To understand the spatial variation of sources, TSP samples were analyzed for chemical compositions including carbonaceous species [organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC)], water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), polycyclic aromatic hydrocarbons (16 PAHs), water-soluble inorganic species (WSIS) (F^-, Cl^-, SO₄^2-, NO₂^-, NO₃^-, PO₄^3-, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, and K⁺), and major and minor trace elements (B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Fe, Zn, Cr, Mn, Cu, As, Pd, F, and Ag). During the campaign, the maximum concentration of several components of TSP (996 μg/m³) was recorded at the Rana Pratap Bagh area, representing a pollution hotspot of Delhi. The maximum concentrations of PAHs were recorded at Udhyog Nagar, a region close to heavily loaded diesel vehicles, small rubber factories, and waste burning areas. Higher content of Cl^- and Cl^-/Na⁺ ratio (>1.7) suggests the presence of nonmarine anthropogenic sources of Cl^- over Delhi. Minimum concentrations of OC, EC, WSOC, PAHs, and WSIS in TSP were observed at Kalkaji, representing the least polluted area in Delhi. Enrichment factor <5.0 at several locations and a significant correlation of Al with Mg, Fe, Ti, and Ca and C/N ratio indicated the abundance of mineral/crustal dust in TSP over Delhi. Principal component analysis (PCA) was also performed for the source apportionment of TSP, and extracted soil dust was found to be the major contributor to TSP, followed by biomass burning, open waste burning, secondary aerosol, and vehicular emissions.

Insights into high concentrations of particle-bound imidazoles in the background atmosphere of southern China: Potential sources and influencing factors

Imidazoles are important constituents in atmospheric brown carbon and have gained increasing attention in the past decade. Although imidazoles have been studied widely in laboratories, the sparse field observations severely limit the understanding of imidazole's abundance and sources in the atmosphere. In this study, we measured particle-bound imidazoles and their precursors at a background forest site in the Nanling Mountains of southern China. The average concentration of imidazoles (4.17 ± 3.76 ng/m³) was found to be significantly higher than other background sites worldwide. Further analyses revealed that a majority of imidazoles (59.1%) at the site originated from secondary formation through reactions of dicarbonyls (e.g., glyoxal and methylglyoxal) and reduced nitrogen species, with relatively minor contributions from regional transport (32.8%) and biomass burning (8.1%). In addition, the key factors influencing secondary formation of imidazoles, such as relative humidity, water-soluble inorganic ions, and pH, were analyzed. Our results indicated that the secondary formation of imidazoles can be greatly enhanced under high humidity conditions, particularly during fog events. Overall, this study offers valuable insights into potential sources and influencing factors of ambient imidazoles in background atmospheres.

Molecular Characterization of Nitrogen-Containing Compounds in Humic-like Substances Emitted from Biomass Burning and Coal Combustion

N-containing organic compounds (NOCs) in humic-like substances (HULIS) emitted from biomass burning (BB) and coal combustion (CC) were characterized by ultrahigh-resolution mass spectrometry in the positive electrospray ionization mode. Our results indicate that NOCs include CHON+ and CHN+ groups, which are detected as a substantial fraction in both BB- and CC-derived HULIS, and suggest that not only BB but also CC is the potential important source of NOCs in the atmosphere. The CHON+ compounds mainly consist of reduced nitrogen compounds with other oxygenated functional groups, and straw- and coal-smoke HULIS exhibit a lower degree of oxidation than pine-smoke HULIS. In addition, the NOCs with higher N atoms (N₂ and/or N₃) generally bear higher modified aromaticity index (AI_mod) values and are mainly contained in BB HULIS, especially in straw-smoke HULIS, whereas the NOCs with a lower N atom (N₁) always have relatively lower AI_mod values and are the dominant NOCs in CC HULIS. These findings imply that the primary emission from CC may be a significant source of N₁ compounds, whereas high N number (e.g., N_2-3) compounds could be associated with burning of biomass materials. Further study is warranted to distinguish the NOCs from more sources.

Diurnal variability in the spectral characteristics and sources of water-soluble brown carbon aerosols over Delhi

It is well established that light-absorbing organic aerosols (commonly known as brown carbon, BrC) impact climate. However, uncertainties remain as their contributions to absorption at different wavelengths are often ignored in climate models. Further, BrC exhibits differences in absorption at different wavelengths due to the variable composition including varying sources and meteorological conditions. However, diurnal variability in the spectral characteristics of water-soluble BrC (hereafter BrC) is not yet reported. This study presents unique measurement hitherto lacking in the literature. Online measurements of BrC were performed using an assembled system including a particle-into-liquid sampler, portable UV-Visible spectrophotometer with liquid waveguid capillary cell, and total carbon analyzer (PILS-LWCC-TOC). This system measured the absorption of ambient aerosol extracts at the wavelengths ranging from 300 to 600 nm with 2 min integration time and water-soluble organic carbon (WSOC) with 4 min integration time over a polluted megacity, New Delhi. Black carbon, carbon monoxide (CO), nitrogen oxides (NOx), and the chemical composition of non-refractory submicron aerosols were also measured in parallel. Diurnal variability in absorption coefficient (0.05 to 65 Mm^-1), mass absorption efficiency (0.01 to 3.4 m^-2 gC^-1) at 365 nm, and absorption angstrom exponent (AAE) of BrC for different wavelength range (AAE_300-400: 4.2-5.8; AAE_400-600: 5.5-8.0; and AAE_300-600: 5.3-7.3) is discussed. BrC chromophores absorbing at any wavelength showed minimum absorption during afternoon hours, suggesting the effects of boundary layer expansion and their photo-sensitive/volatile nature. On certain days, a considerable presence of BrC absorbing at 490 nm was observed during nighttime that disappears during the daytime. It appeared to be associated with secondary BrC. Observations also infer that BrC species emitted from the biomass and coal burning are more absorbing among all sources. A fraction of BrC is likely associated with trash burning, as inferred from the spectral characteristics of Factor-3 from the PMF analysis of BrC spectra. Such studies are essential in understanding the BrC characteristics and their further utilization in climate models.

Screening of imidazoles in atmospheric aerosol particles using a hybrid targeted and untargeted method based on ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry

The method for identification and quantification of imidazoles in atmospheric aerosol particles with an aerodynamic diameter up to 2.5 μm (PM_2.5) is scarce, and the existing method focus on only a few imidazoles. With the goal of measuring more imidazoles, especially some previously unidentified ones, we developed a screening workflow based on data-dependent acquisition (DDA) auto MS/MS with a preferred targeted list containing 421 imidazoles using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). To enable our method to effectively and accurately detect as many imidazoles as possible, we optimized and validated the method based on specificity, limit of detection (LOD), limit of quantification (LOQ), linearity, accuracy, precision and matrix effects using 20 imidazole standards with different functional groups. The method exhibited excellent performance with LOD and LOQ of 0.5-2 ng/mL and 1.5-6 ng/mL, respectively, and spiked recoveries ranging from 64.7 to 98.7% with standard deviations less than 16.0%, and with relatively shorter analytical time. The established method was then used to screen imidazoles in 37 ambient PM_2.5 samples. Ten targeted imidazoles were identified and quantified using imidazole standards, while five suspected imidazoles were identified without standards, and three imidazoles have not been reported before. Concentrations of the 10 targeted imidazoles ranged from 0.13 to 0.42 ng/m³. The established method enabled us to identify a wide range of imidazoles in ambient aerosol particles with and without using standards.

Role of phytoconstituents in the management of COVID-19

BACKGROUND

COVID-19, a severe global pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has emerged as one of the most threatening transmissible disease. As a great threat to global public health, the development of treatment options has become vital, and a rush to find a cure has mobilized researchers globally from all areas.

SCOPE AND APPROACH

This review focuses on deciphering the potential of different secondary metabolites from medicinal plants as therapeutic options either as inhibitors of therapeutic targets of SARS-CoV-2 or as blockers of viral particles entry through host cell receptors. The use of medicinal plants containing specific phytomoieties could be seen in providing a safer and long-term solution for the population with lesser side effects. Key Findings and Conclusions: Considering the high cost and time-consuming drug discovery process, therapeutic repositioning of existing drugs was explored as treatment option in COVID-19, however several molecules have been retracted as therapeutics either due to no positive outcomes or the severe side effects. These effects call for exploring the alternate treatment options which are therapeutically effective as well as safe. Keeping this in mind, phytopharmaceuticals derived from medicinal plants could be explored as important resources in the development of COVID-19 treatment, as their role in the past for treatment of viral diseases like HIV, MERS-CoV, and influenza has been well reported. Considering this fact, different phytoconstituents such as flavonoids, alkaloids, tannins and glycosides etc. Possessing antiviral properties against coronaviruses and possessing potential against SARS-CoV-2 have been reviewed in the present work.

The decomposition process and nutrient release of invasive plant litter regulated by nutrient enrichment and water level change

Wetlands are vulnerable to plant invasions and the decomposition of invasive plant litter could make impacts on the ecosystem services of wetlands including nutrient cycle and carbon sequestration. However, few studies have explored the effects of nutrient enrichment and water level change on the decomposition of invasive plant litter. In this study, we conducted a control experiment using the litterbag method to compare the decomposition rates and nutrient release in the litter of an invasive plant Alternanthera philoxeroides in three water levels and two nutrient enrichment treatments. This study found that the water level change and nutrient enrichment showed significant effects on the litter decomposition and nutrient dynamic of A. philoxeroides. The increase of water level significantly reduced the decomposition rate and nutrient release of litter in the nutrient control treatment, whereas no clear relationship was observed in the nutrient enrichment treatment, indicating that the effect of water level change on litter decomposition might be affected by nutrient enrichment. At the late stage of decomposition, the increase of phosphorus (P) concentration and the decrease of the ratio of carbon to P suggested that the decomposition of invasive plant litter was limited by P. Our results suggest that controlling P enrichment in water bodies is essential for the management of invasive plant and carbon sequestration of wetlands. In addition, the new index we proposed could provide a basis for quantifying the impact of invasive plant litter decomposition on carbon cycle in wetlands.

Chemical Characteristics and Sources of Water-Soluble Organic Nitrogen Species in PM2.5 in Nanjing, China

Water-soluble organic nitrogen (WSON) is an important component of PM2.5 which may affect air quality, climate and human health. Herein, one-year field samples of atmospheric PM2.5 (June 2017–May 2018) were collected in northern Nanjing. Chemical characterization of PM2.5 major components as well as WSON were conducted, and WSON composition and sources were further investigated via measurements by a Aerodyne soot particle aerosol mass spectrometer (SP-AMS) as well as positive matrix factorization (PMF). Inorganic ions, mainly consisting of ammonium, sulfate, and nitrate, were found to dominate PM2.5 mass (58.7%), followed by organic matter (OM) (22.6%), and elemental carbon (EC) (2.1%). Water-soluble OM dominated OM (65.1%), and its temporal variation was closely correlated with that of secondary organic matter, while time series of water-insoluble OM concentrations correlated tightly with that of primary organic matter. Average WSON concentration was 2.15 μg/m3, which was highest in winter and lowest in summer. Correlation analysis of WSON with PM2.5 components also indicated that WSON was mainly from secondary sources. SP-AMS revealed that WSON mass spectrum was composed of CxHyNp+ (91.2%) and CxHyOzNp+ (8.8%), indicating dominance of amines and other oxygenated ON compounds. PMF analysis resolved two primary sources (traffic, biomass burning) and two secondary sources (less-oxidized and more-oxidized factors) of WSOM and WSON, and the secondary source dominated both WSOM and WSON. Contribution of the more-oxidized ON factor was very high in winter, and the less-oxidized factor was significant in summer, indicating a likely important role of aqueous-phase processing in winter as well as photochemical oxidation in summer to WSON.

Source identification of particulate phosphorus in the atmosphere in Beijing

We tracked atmospheric phosphorus (P) in suspended particulate matter (PM) from a site in Beijing, China over a three-year period and found a new relationship between plants and atmospheric P. Concentrations of total phosphorus (TP) in the atmosphere during plant growing seasons were 2.5 times those observed in other months and levels of organic phosphorus (OP) were 3.9 times as high. TP and OP increases during growing seasons were much more significant in PM with diameters of over 2.5 μm (PM_>2.5). PM collected during growing seasons included high levels of P but less nitrogen than that in primary biogenic aerosol particles (PBAPs) and differed from other emission sources such as combustion emissions and dust. A time series of OP concentrations in the atmosphere shows a time lag relative to Normalized Difference Vegetation Index (NDVI) data with high levels found during early growing periods and much lower levels found during flourishing periods. Thus, we find that plants contribute to atmospheric P and especially to OP rather than to PBAP levels.

Characteristics and sources of water-soluble organic aerosol in a heavily polluted environment in Northern China

Water-soluble organic aerosol (WSOA) in fine particles (PM_2.5) collected during wintertime in a polluted city (Handan) in Northern China was characterized using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS). Through comparing with real-time measurements from a collocated Aerosol Chemical Speciation Monitor (ACSM), we determined that WSOA on average accounts for 29% of total organic aerosol (OA) mass and correlates tightly with secondary organic aerosol (SOA; Pearson's r = 0.95). The mass spectra of WSOA closely resemble those of ambient SOA, but also show obvious influences from coal combustion and biomass burning. Positive matrix factorization (PMF) analysis of the WSOA mass spectra resolved a water-soluble coal combustion OA (WS-CCOA; O/C = 0.17), a water-soluble biomass burning OA (WS-BBOA; O/C = 0.32), and a water-soluble oxygenated OA (WS-OOA; O/C = 0.89), which account for 10.3%, 29.3% and 60.4% of the total WSOA mass, respectively. The water-solubility of the OA factors was estimated by comparing the offline AMS analysis results with the ambient ACSM measurements. OOA has the highest water-solubility of 49%, consistent with increased hygroscopicity of oxidized organics induced by atmospheric aging processes. In contrast, CCOA is the least water soluble, containing 17% WS-CCOA. The distinct characteristics of WSOA from different sources extend our knowledge of the complex aerosol chemistry in the polluted atmosphere of Northern China and the water-solubility analysis may help us to understand better aerosol hygroscopicity and its effects on radiative forcing in this region.

Using highly time-resolved online mass spectrometry to examine biogenic and anthropogenic contributions to organic aerosol in Beijing

Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C₅-C₉ and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, α-pinene and sesquiterpenes.

Comparison of molecular transformation of dissolved organic matter in vermicomposting and thermophilic composting by ESI-FT-ICR-MS

The aim of this study was to investigate the effects of vermicomposting (VC) and thermophilic composting (TC) on the molecular transformation of dissolved organic matter (DOM). Here, the DOM after VC and TC (DOM_v and DOM_t, respectively) was characterized using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). The results indicated that VC could improve the preservation of nitrogen and the humification of DOM compared with TC. Concurrently, VC facilitated the formation of highly oxidized molecules (O/C = 0.4-0.9) by enhancing the oxidation. The aromatized molecules in each component were more easily generated during VC, especially N-containing aromatized molecules (39.4-58.0%), thereby improving the quality of compost products. Furthermore, this study found that VC could reduce the anaerobic microsites in pile, thus increasing nominal oxidation state of carbon (NOSC) of organic matter and promoting the decomposition of high-energy substrates (mainly lipids, NOSC = - 1.7~- 1.3). These findings provided new molecular insights that VC can significantly improve the oxidation of organic matter and the preservation of nitrogen. Graphical abstract.

Biomass burning organic aerosols significantly influence the light absorption properties of polarity-dependent organic compounds in the Pearl River Delta Region, China

Atmospheric brown carbon (BrC) is an important constituent of light-absorbing organic aerosols with many unclear issues. Here, the light-absorption properties of BrC with different polarity characteristics at a regional site of Pearl River Delta Region during 2016-2017, influenced by sources and molecular compositions, were revealed using radiocarbon analysis and Fourier transform ion cyclotron resonance mass spectrometry. Humic-like substance (HULIS), middle polar (MP), and low polar (LP) carbon fractions constitute 46 ± 17%, 30 ± 7%, and 7 ± 3% of total absorption coefficient from bulk extracts, respectively. Our results show that the absorption proportions of HULIS and MP to the total BrC absorption are higher than their mass proportions to organic carbon mass, indicating that HULIS and MP are the main light-absorbing components in water-soluble and water-insoluble organic carbon fractions, respectively. With decreases in non-fossil HULIS, MP, and LP carbon fractions (66 ± 2%, 52 ± 2%, and 36 ± 3%, respectively), the abundances of unsaturated compounds and mass absorption efficiency at 365 nm of three fractions decreased synchronously. Increases in both non-fossil carbon and levoglucosan in winter imply that the enhanced light-absorption could be attributed to elevated levels of biomass burning organic aerosols (BBOA), which increases the number of light-absorbing nitrogen-containing compounds. Moreover, the major type of potential BrC in HULIS and MP carbon fractions are oxidized BBOA, but the potential BrC chromophores in LP are mainly associated with primary BBOA. This study reveals that biomass burning has adverse effects on radiative forcing and air quality, and probably indicates the significant influences of atmospheric oxidation reactions on the forms of chromophores.

Peat burning - An important source of pyridines in the earth atmosphere

Studies of the chemical composition of atmospheric aerosols, rain water and snow in various regions of the globe quite often show the presence of pyridine and a number of its low mass derivatives. Nevertheless, the sources of those compounds in the environment have not yet been established and definitely require elucidation, supported by reliable experimental results. In the present work the chemical composition of peat combustion products as one of the important sources of atmospheric aerosol emission is studied by two-dimensional gas chromatography - high-resolution mass spectrometry with a focus on the detection of pyridine derivatives. Twenty-five compounds of this class were reliably identified and quantified in laboratory experiments on peat burning. Among them 3-hydroxypyridine predominates, while the rest analytes are mostly represented by alkyl derivatives: pyridine, 2-methylpyridine, 3-methylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine, 2-ethylpyridine, lutidines (in order of decreasing concentration). The distribution of these combustion products coincides with that obtained earlier in environmental studies carried out in Arctic, Central Russia and France. The experiments on peat thermal decomposition by pyrolysis GC-MS demonstrated that the maximum concentrations as well as the number of detected analytes were found under conditions of oxygen lack and a temperature of about 500 °C, i.e. characteristic conditions of peat wildfires. The observed levels of pyridines' emission recalculated on the peat dry weight exceeded 200 mg kg^-1. Considering hundreds of millions tons of peat burning in megafires over 20,000 tons of pyridines penetrate the Earth atmosphere annually. The obtained results allow concluding that peat burning may be the major and still underestimated source of pyridine and lower alkylpyridines in the Earth atmosphere.

Optical properties of aerosol brown carbon (BrC) in the eastern Indo-Gangetic Plain

We report here measurements of aerosol black carbon (BC) and aqueous and methanol-extractable brown carbon (BrC_aq and BrC_me) from a receptor location in the eastern Indo-Gangetic Plain (IGP) under two aerosol regimes: the photochemistry-dominated summer and biomass burning (BB) dominated post-monsoon. We couple time-resolved measurements of BC and aerosol light absorption coefficients (b_abs) with time-integrated analysis of BrC UV-Vis and fluorescence characteristics, along with measurements of total and water-soluble organic carbon (OC and WSOC), and ionic species (NH₄⁺, K⁺, NO₃^-). In the BB regime, BC and its BB-derived fraction (BC_BB) increased by factors of 3-4 over summertime values. In comparison, b_{abs_365_aq} and b_{abs_365_me} (absorption coefficients of BrC_aq and BrC_me at 365 nm) increased by a factor of 5 (9.7 ± 7.8 vs 2.1 ± 1.4 Mm^-1) and 2.5 (17.2 ± 9.0 vs 6.9 ± 2.9 Mm^-1), respectively, in the BB period over summer, and were highly correlated (r = 0.82-0.87; p < 0.01) with the BB-tracer nssK⁺. The wavelength dependence of b_{abs_BrC} (Ångstrom exponent: 5.9-6.2) and the presence of characteristic fluorescence peaks at 420-430 nm suggested presence of humic-like substances (HULIS) in the aged BB aerosol, while significant association between BrC_aq and NO₃^- (r = 0.73; p < 0.01) possibly indicated formation of water-soluble nitroaromatic compounds. BrC_aq contributed 55% to total BrC absorption at 300-400 nm while that for the water-insoluble component (WI-BrC) increased from 41% at 340 nm to ~60% at 550 nm, suggesting formation of water-insoluble polycyclic aromatic hydrocarbons (PAHs) and/or N-PAHs. Mass absorption efficiencies at 365 nm (MAE₃₆₅) of BrC_aq and BrC_me in the BB regime (0.95 ± 0.45 and 1.17 ± 0.78 m² g^-1, respectively) were in line with values expected from photobleaching of BB source emissions after transport to the eastern IGP. Overall, BrC_aq and BrC_me were significant components of light absorbing aerosol in the BB regime, with contributions of 9 ± 5% and 16 ± 7%, respectively, to radiative forcing vis-à-vis BC in the 300-400 nm range.

Investigation of Primary and Secondary Particulate Brown Carbon in Two Chinese Cities of Xi'an and Hong Kong in Wintertime

Brown carbon (BrC), an aerosol carbonaceous matter component, impacts atmospheric radiation and global climate because of its absorption in the near-ultraviolet-visible region. Simultaneous air sampling was conducted in two megacities of Xi'an (northern) and Hong Kong (southern) in China in winter of 2016-2017. The aim of this study is to determine and characterize the BrC compounds in collected filter samples. Characteristic absorption peaks corresponding to aromatic C-C stretching bands, organo-nitrates, and C═O functional groups were seen in spectra of Xi'an samples, suggesting that the BrC was derived from freshly smoldering biomass and coal combustion as well as aqueous formation of anthropogenic secondary organic carbon. In Hong Kong, the light absorption of secondary BrC accounted for 76% of the total absorbances of BrC. The high abundance of strong C═O groups, biogenic volatile organic compounds (BVOCs) and atmospheric oxidants suggest secondary BrC was likely formed from photochemical oxidation of BVOCs in Hong Kong. Several representative BrC molecular markers were detected using Fourier transform ion cyclotron resonance mass spectrometry and their absorption properties were simulated by quantum chemistry. The results demonstrate that light absorption capacities of secondary anthropogenic BrC with nitro-functional groups were stronger than those of biogenic secondary BrC and anthropogenic primary BrC.

Formation of Secondary Brown Carbon in Biomass Burning Aerosol Proxies through NO3 Radical Reactions

Atmospheric brown carbon (BrC) is an important contributor to the radiative forcing of climate by organic aerosols. Because of the molecular diversity of BrC compounds and their dynamic transformations, it is challenging to predictively understand BrC optical properties. OH radical and O₃ reactions, together with photolysis, lead to diminished light absorption and lower warming effects of biomass burning BrC. The effects of night-time aging on the optical properties of BrC aerosols are less known. To address this knowledge gap, night-time NO₃ radical chemistry with tar aerosols from wood pyrolysis was investigated in a flow reactor. This study shows that the optical properties of BrC change because of transformations driven by reactions with the NO₃ radical that form new absorbing species and lead to significant absorption enhancement over the ultraviolet-visible (UV-vis) range. The overnight aging increases the mass absorption coefficients of the BrC by a factor of 1.3-3.2 between 380 nm and 650 nm. Nitrated organic compounds, particularly nitroaromatics, were identified as the main products that contribute to the enhanced light absorption in the secondary BrC. Night-time aging of BrC aerosols represents an important source of secondary BrC and can have a pronounced effect on atmospheric chemistry and air pollution.

Assessment of Interactions between Transition Metals and Atmospheric Organics: Ascorbic Acid Depletion and Hydroxyl Radical Formation in Organic-Metal Mixtures

Excessive oxidative stress has been recognized as an important cause of the adverse health effects associated with exposure to ambient particulate matter (PM). Transition metals (TMs) (e.g., iron (Fe) and copper (Cu)) are known catalysts in the formation of reactive oxygen species (ROS) in surrogate lung fluid containing antioxidants. Humic-like substances (HULIS), extracted from atmospheric aerosols, retain the compositional complexity of real-world samples. It contains mixtures of organics that chelate TMs and was used in this work to examine the roles of atmospheric organics in affecting ROS formation and antioxidant depletion by TMs. Two types of metal-binding organics known to be present in HULIS, oxygen-containing (i.e., carboxylic acids) and reduced-nitrogen-containing organics (i.e., imidazoles), were first investigated for their effects on the ascorbic acid depletion (denoted as OP_AA) and hydroxyl radical formation (denoted as OP_•OH) from both Fe(II) and Cu(II) in phosphate buffered saline (pH 7.40) containing ascorbic acid. Our results show that carboxylic acids enhance the OP_AA and OP_•OH by TMs while imidazoles suppress them. Similar experiments using three HULIS samples with distinctly different chemical compositions revealed complexity in metal-organics interactions. While ambient HULIS showed negligible impacts, two biomass burning source HULIS samples from rice straw and sugar cane leaf burning displayed unambiguous suppression or enhancement effects on OP_AA and OP_•OH by TMs. The effect was metal-specific and source HULIS-specific. The distinct behaviors of the three HULIS types can be explained by their different chemical compositions, for example, outstanding higher level of alkaloid compounds (e.g., imidazoles) in rice straw burning HULIS was consistent with the suppression effect exerted by this source of HULIS. In addition, we found OP_AA and OP_•OH are well-correlated while the proportion of OP_•OH/OP_AA by Cu is noticeably lower than that by Fe, indicating varying sensitivity of the metals to different OP end points. Our work highlights the importance and complexity of metal-organics interactions and the advantages of comeasurements of ROS generation and antioxidant depletion when assessing oxidative stress elicited by atmospheric PM.

Dissolved organic matter in the deep TALDICE ice core: A nano-UPLC-nano-ESI-HRMS method

Trace organic compounds in deep ice cores supply important paleoclimatic information. Untargeted analyses of dissolved organic matter provide an overview of molecular species in ice samples however, sample volumes usually required for these analyses are generally not available from deep ice cores. Here, we developed an analytical method using a nano-UPLC-nano-ESI-HRMS to detect major molecular species in ice cores. Samples (4 µL) from the TALos Dome Ice CorE (TALDICE), allowed investigating molecular species across a range of depths including during glacial and interglacial periods. We detected 317 chemical species that were tentatively assigned to fatty acids, hydroxy fatty acids and their degradation products (oxo-fatty acids and dicarboxylic acids), as well as oxidation byproducts of isoprene and monoterpenes. These compounds indicate that the main sources of the organic fraction are microbes as well as primary and secondary aerosols. Interglacial samples encompass a wide range of species including compounds from the oxidation of isoprene and monoterpenes as well as unsaturated fatty acids, while the glacial samples contained less diverse species. This difference may be due to decreased temperatures during the glacial period inhibiting terrestrial vegetation growth and increasing the sea ice extent, thereby weakening the emission sources.

Enhancement in Particulate Organic Nitrogen and Light Absorption of Humic-Like Substances over Tibetan Plateau Due to Long-Range Transported Biomass Burning Emissions

To elucidate the influence of long-range transported biomass burning organic aerosols (BBOA) on the Tibetan Plateau, the molecular compositions and light absorption of HUmic-Like Substances (HULIS), major fractions of brown carbon, were characterized during the premonsoon season. Under the significant influence of biomass burning, HULIS concentrations increased to as high as 26 times of the background levels, accounting for 54% of water-soluble organic carbon (WSOC) and 50% of organic carbon (OC). The light absorption of HULIS also enhanced up to 42 times of the background levels, contributing 61% of the WSOC absorption and 50% of OC absorption. Meanwhile, elevated nitrogen-containing compounds (NOCs) among HULIS were observed. The NOCs from fresh and aged BBOA were unambiguously identified on the molecular level, through comparing with the molecular compositions of NOCs from lab-controlled and field burning experiments. N-Heterocyclic bases represent major fractions in the reduced nitrogen compounds from fresh BBOA, and nitroaromatic compounds are important groups among the oxidized nitrogen compounds from aged BBOA. The nitrogen-containing compounds, including nitroaromatics and N-heterocyclic compounds, were also important chromophores, which contributed to the enhanced light absorption of extracted HULIS during biomass burning-influenced periods.

Molecular Characterization of Water- and Methanol-Soluble Organic Compounds Emitted from Residential Coal Combustion Using Ultrahigh-Resolution Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Water-soluble organic compounds (WSOC) and methanol-soluble organic compounds (MSOC) in smoke particles emitted from residential coal combustion were characterized by ultrahigh-resolution mass spectrometry. The results showed that the molecular compositions of WSOC and MSOC are different. S-containing compounds (CHOS and CHONS) are found to be the dominant components (65-87%) of the WSOC, whereas CHO and CHON compounds make a great contribution (79-96%) to the MSOC samples. It is worth noting that greater abundance of S-containing compounds was found in smoke produced from coal combustion compared to biomass burning and atmospheric samples. The molecular compositions of WSOC and MSOC also varied significantly depending on the maturity of the coal. The WSOC and MSOC derived from the combustion of low-maturity coal contained a higher proportion of oxidized functional groups but with a lower degree of aromaticity than the compounds derived from the combustion of high-maturity coal. Our findings suggest that organic molecules with a high modified aromaticity index, low O/C ratio, and low polarity showed stronger light absorption. This study also suggests that CHO and CHON compounds significantly contributed to the light absorption of WSOC and MSOC and that the contribution of CHON may be stronger.

Epiphytic bacterial community shift drives the nutrient cycle during Potamogeton malaianus decomposition

Epiphytic bacteria on submerged macrophytes play important roles in the nutrient cycle in freshwater ecosystems. However, little is known about the composition and role of epiphytic bacteria during the decomposition of submerged macrophytes. In this study, the alterations in epiphytic bacterial composition, abundances of nitrogen cycle-related genes and nutrient release were investigated in a 56-day decomposition process of Potamogeton malaianus. The total reduced biomass was positively related to the contents of carbon, nitrogen and phosphorus released from plant residues. Nutrient released from plant litter showed a positively effect on the concentrations of carbon, nitrogen and phosphorus in the overlying water (p < 0.01). The carbon, phosphorus and nitrogen decreased with decomposition process in both plant debris and overlying water. Humic acid-like substances were the main component of dissolved organic matter in the conditioning stage, whereas fulvic acid-like substances dominated in the fragmentation stage. Results from network analysis and canonical correspondence analysis showed dominant bacterial clades changed with decomposition process. Bacteroidetes was the most abundant phylum in the leaching stage and Spirochaetes, Chlorobi, and Bacteroidetes dominated in the conditioning stage, while Chlorobi dominated in the fragmentation stage. The highest abundance of cnorB and nosZ were detected in the leaching and fragmentation stage, respectively. Bacterial denitrification contributed to nitrogen removal and might be promoted by high ORP and DOC concentration. Our results indicate that epiphytic bacterial community shift drived the metabolism of nutrients C, N, and S during the decomposition of P. malaianus.

Separation and quantification of imidazoles in atmospheric particles using LC-Orbitrap-MS

A method using ultra-high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol particles. The aqueous particle extract was used without further enrichment or sample clean-up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25 nM) and good intraday and interday repeatability (<1.6 and <6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10 µg m^-3 . The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4-imidazolecarboxaldehyde and 4-methyl-5-imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples.

Volatile organic compound measurements point to fog-induced biomass burning feedback to air quality in the megacity of Delhi

We report the first ambient measurements of thirteen VOCs for investigations of emissions and air quality during fog and non-fog wintertime conditions at a tower site (28.57° N, 77.11° E, 220 m amsl) in the megacity of Delhi. Measurements of acetonitrile (biomass burning (BB) tracer), isoprene (biogenic emission tracer in daytime), toluene (a traffic exhaust tracer) and benzene (emitted from BB and traffic), together with soluble and reactive oxygenated VOCs such as methanol, acetone and acetaldehyde were performed during the winters of 2015-16 and 2016-17, using proton transfer reaction mass spectrometry. Remarkably, ambient VOC composition changes during fog were not governed by solubility. Acetaldehyde, toluene, sum of C8-aromatics (e.g. xylenes), sum of C9-aromatics (e.g. trimethyl benzenes) decreased by ≥30% (>95% confidence interval), whereas acetonitrile and benzene showed significant increases by 20% (>70% confidence interval), even after accounting for boundary layer dilution. During fog, the lower temperatures appeared to induce an emissions feedback from enhanced open BB within Delhi for warming, releasing both gaseous and aerosol pollutants with consequences for fog chemistry, sustenance and intensity. The potential feedback is important to consider for improving current emission parametrizations in models used for predicting air quality and fog in such atmospheric environments.

Adsorption of Formamide at the Surface of Amorphous and Crystalline Ices under Interstellar and Tropospheric Conditions. A Grand Canonical Monte Carlo Simulation Study

The adsorption of formamide is studied both at the surface of crystalline (I_h) ice at 200 K and at the surface of low density amorphous (LDA) ice in the temperature range of 50-200 K by grand canonical Monte Carlo (GCMC) simulation. These systems are characteristic of the upper troposphere and of the interstellar medium (ISM), respectively. Our results reveal that while no considerable amount of formamide is dissolved in the bulk ice phase in any case, the adsorption of formamide at the ice surface under these conditions is a very strongly preferred process, which has to be taken into account when studying the chemical reactivity in these environments. The adsorption is found to lead to the formation of multimolecular adsorption layer, the occurrence of which somewhat precedes the saturation of the first molecular layer. Due to the strong lateral interaction acting between the adsorbed formamide molecules, the adsorption isotherm does not follow the Langmuir shape. Adsorption is found to be slightly stronger on LDA than I_h ice under identical thermodynamic conditions, due to the larger surface area exposed to the adsorption. Indeed, the monomolecular adsorption capacity of the LDA and I_h ice surfaces is found to be 10.5 ± 0.7 μmol/m² and 9.4 μmol/m², respectively. The first layer formamide molecules are very strongly bound to the ice surface, forming typically four hydrogen bonds with each other and the surface water molecules. The heat of adsorption at infinitely low surface coverage is found to be -105.6 kJ/mol on I_h ice at 200 K.

Chemical Characterization of Nanoparticles and Volatiles Present in Mainstream Hookah Smoke

Waterpipe smoking is becoming more popular worldwide and there is a pressing need to better characterize the exposure of smokers to chemical compounds present in the mainstream smoke. We report real-time measurements of mainstream smoke for carbon monoxide, volatile organic compounds and nanoparticle size distribution and chemical composition using a custom dilution flow tube. A conventional tobacco mixture, a dark leaf unwashed tobacco and a nicotine-free herbal tobacco were studied. Results show that carbon monoxide is present in the mainstream smoke and originates primarily from the charcoal used to heat the tobacco. Online measurements of volatile organic compounds in mainstream smoke showed an overwhelming contribution from glycerol. Gas phase analysis also showed that very little filtration of the gas phase products is provided by the percolation of mainstream smoke through water. Waterpipe smoking generated high concentrations of 4-100 nm nanoparticles, which were mainly composed of sugar derivatives and especially abundant in the first 10 min of the smoking session. These measured emissions of volatiles and particles are compared with those from a reference cigarette (3R4F) and represent the equivalent of the emission of one or more entire cigarettes for a single puff of hookah smoke. Considerations related to the health impacts of waterpipe smoking are discussed.