Organic trace analysis using high resolution mass spectrometry for the characterization of ancient, present and simulated atmospheric systems

Atmospheric aerosol particles are strongly affecting air quality, climate, and human health. Particularly, atmospheric aerosols can have major effects on the formation, properties and lifetime of clouds and significantly affect the human respiratory and cardiovascular system. Despite extensive research over the last decades, large uncertainties still remain regarding the organic fraction of such airborne particles, which is often accounting for the majority of the particulate mass. Providing high sensitivity and selectivity towards single molecules, mass spectrometry (MS) is a well-suited technique for the chemical analysis of atmospheric aerosol particles. Although MS has been proven to be a versatile and powerful tool in the field of aerosol research, the identification and trace analysis of single organic molecules still demands improvements due to insufficient mass resolution. The aim of this work was to develop analytical methods for the analysis of single organic compounds in highly-complex atmospheric matrices and to establish ultra-high-resolution mass spectrometry (UHRMS) as a versatile tool in atmospheric aerosol research. In particular, ultra-high-performance liquid chromatography (UHPLC) coupled to electrospray ionization ultra-high-resolution mass spectrometry (ESI-UHRMS) was used for the quantification of tracer molecules in ice cores and molecular characterization of laboratory generated aerosols. Furthermore, an atmospheric pressure chemical ionization Orbitrap mass spectrometry (APCI-Orbitrap-MS) technique was applied for the real-time determination of single molecules in ambient air using negative and positive ionization mode. The first part of this study is focused on the development of a single, comprehensive trace analytical method for the sensitive quantification of new and more appropriate low-volatile marker compounds in snow and ice samples. Solid phase extraction (SPE) using anion exchange functionalities was used for extraction and enrichment of the compounds from the molten sample matrix. As a proof-of-principle, the optimized method was applied for the analysis of ice core samples from the Belukha glacier in the Altai mountain range. Several organic trace components were determined for the first time in an ice core from the Belukha glacier and quantified in the low ng/g-range within a single analytical method. In the second part, UHPLC coupled to UHRMS was applied for the comprehensive molecular characterization of submicron-particles generated in the Cosmics Leaving Outdoor Droplets (CLOUD) laboratory chamber at the European Organization for Nuclear Research (CERN), Geneva. Besides attributing the identified molecules to certain molecular classes, a special focus was on the identification of highly oxidized multifunctional organic compounds (HOMs). It was shown that, varying mixing-ratios of SO2 led to a different distribution of organic mono-/di-nitrates, indicating an SO2-dependant formation pathway. In conclusion, a unique compound-list of identified SOA molecules including the exact molecular mass and the retention time of detected isomers was obtained. Finally, inspired by the participation in the CLOUD 10 campaign at CERN, the need for real-time ultra-high-resolution mass spectrometry was noticed and led to the development and characterization of APCI-Orbitrap-MS for the real-time measurement of atmospheric aerosol particles. Optimization and characterization of the APCI-Orbitrap-MS was performed by laboratory-generated model aerosol exhibiting a high time resolution, a linear response over three orders of magnitude for sub 100 nm particles and detection limits in the low ng/m³ range. As a proof of principle, the ambient aerosol composition was analyzed by sampling PM2.5 particles from the outside of the laboratory building in alternating ionization mode. Due to the soft ionization procedure, molecular ions are preserved and the deprotonated or protonated ions represent the main signal. A subsequent non-target screening, as well as single organic compound detection and quantification in aerosols, was performed under ambient atmospheric conditions without preconcentration or filter sampling steps. Particularly, in the non-target screening, the molecular composition of ambient organic aerosol during night- and daytime was examined both in negative and positive ionization mode. With the presented mass spectrometric system it was possible to detect highly oxidized organic nitrates, organic di-nitrates and nitrooxy organosulfates with a high time resolution in the ambient particle phase. In conclusion, it has been shown that the Orbitrap technique can be used as a versatile tool offering a number of advantages for the analysis of organic aerosols in offline as well as online mode, which will help to shed light on the atmospheric aerosol composition and formation mechanisms.Atmosphärische Aerosolpartikel haben einen großen Einfluss auf Luftqualität, Klima und die menschliche Gesundheit. Insbesondere die Bildung, Eigenschaften und Lebensdauer von Wolken, aber auch das menschliche Atmungs- und Herz-Kreislaufsystem werden durch atmosphärische Aerosole maßgeblich beeinflusst. Trotz umfangreicher Forschungen in den letzten Jahrzehnten bestehen noch große Unsicherheiten hinsichtlich des organischen Anteils solcher luftgetragenen Partikel, die meist zum Großteil der Partikelmasse beitragen. Diese organischen Aerosole (OA) bestehen aus einer hochkomplexen Mischung, die kontinuierlich atmosphärischen Umwandlungen unterliegt und deren Messung geeignete Instrumente erfordert, um die zugrundeliegenden Prozesse aufzuklären. Die Massenspektrometrie (MS) bietet eine hohe Empfindlichkeit und Selektivität gegenüber einzelnen Molekülen und eignet sich daher besonders gut für die chemische Analyse atmosphärischer Aerosolpartikel. Obwohl sich die Massenspektrometrie bereits als ein vielseitiges und leistungsfähiges Werkzeug auf dem Gebiet der Aerosolforschung erwiesen hat, erfordert die Identifizierung und Spurenanalyse einzelner organischer Moleküle weiterhin Verbesserungen aufgrund oft unzureichender Massenauflösung. Insbesondere ultrahochauflösende, massenspektrometrische Konzepte nach aktuellem Stand der Technik, wie die Orbitrap, als jüngste Entwicklung der Massenspektrometer, sind in diesem Forschungsgebiet noch wenig etabliert. Ziel dieser Arbeit war es, analytische Methoden zur Analyse einzelner organischer Verbindungen in hochkomplexen atmosphärischen Matrizes zu entwickeln und die ultrahochauflösende Massen-spektrometrie als ein vielseitiges Werkzeug in der atmosphärischen Aerosolforschung zu etablieren. Insbesondere wurde die Ultrahochleistungs-Flüssigkeitschromatographie (ultra-high-performance liquid chromatography, UHPLC) in Kopplung mit Elektrospray-Ionisation und ultrahochauflösender Massenspektrometrie (electrospray ionization ultra-high-resolution mass spectrometry, ESI-UHRMS) zur Quantifizierung von Marker-Molekülen in Eisbohrkernen, sowie zur molekularen Charakterisierung von im Labor erzeugten Aerosolen eingesetzt. Darüber hinaus wurde die Technik der chemischen Ionisierung bei Atmosphärendruck in Verbindung mit Orbitrap-Massenspektrometrie (atmospheric pressure chemical ionization Orbitrap mass spectrometry, APCI-Orbitrap-MS) verwendet, um einzelne Moleküle mit positiver und negativer Ionisierung in Echtzeit in der Umgebungsluft zu bestimmen. Der Schwerpunkt des ersten Teils dieser Arbeit lag auf der Entwicklung einer umfassenden spurenanalytischen Methode zur sensitiven Quantifizierung von neuen und besser geeigneten, schwerflüchtigen atmosphärischen Markern in Schnee- und Eisproben. Die analysierten Moleküle umfassten eine Reihe von atmosphärischen Marker-Molekülen bestehend aus Levoglucosan, Lignin-stämmigen Waldbrandmarkern, Markern für sekundäres organisches Aerosol (SOA) aus Isopren, Monoterpenen und Sesquiterpenen sowie Fettsäuren. Zur Extraktion und Anreicherung der Verbindungen aus der geschmolzenen Probenmatrix wurde die Festphasenextraktion (solid phase extraction, SPE) mit Anionenaustauscher-Funktion verwendet. Eine Erhöhung der Signalintensitäten der Analyten im Ionisierungsprozess wurde durch Einleiten einer Ammoniaklösung in Methanol nach der Trennsäule erreicht. Im Fokus der Methodenentwicklung standen die Anpassung der Konzentrationen und Flussraten der Ammoniaklösung sowie die Optimierung der chromatographischen Trennung und die massenspektrometrische Detektion im Tandem MS Modus (MS²) unter Berücksichtigung der hohen Anzahl an unterschiedlichen Markerverbindungen. In einer Machbarkeits-Studie wurde die optimierte Methode zur Analyse von Eisbohrkern-Proben aus dem Belukha-Gletscher im Altai-Gebirge eingesetzt. Mehrere organische Spurenanalyten wurden erstmals in einem Eisbohrkern des Belukha-Gletschers nachgewiesen und mit einer einzigen analytischen Methode im niedrigen ng/g-Bereich quantifiziert. Weiterhin zeigte eine Hauptkomponentenanalyse (principal components analysis, PCA), dass Biomasseverbrennung und biogenes SOA, Pflanzenwachse, sowie Sesquiterpen-Oxidationsprodukte und kurzkettige Fettsäuren die Hauptfaktoren sind, welche die Probenahmestätte beeinflussten. Im zweiten Teil wurde die Kopplung aus UHPLC und UHRMS für eine umfassende molekulare Charakterisierung von Submikrometerpartikeln genutzt, welche in der CLOUD-Kammer (Cosimcs Leaving Outdoor Droplets, CLOUD) bei der Europäischen Organisation für Kernforschung (European Organization for Nuclear Research, CERN) in Genf generiert wurden. Im Rahmen der CLOUD 10-Kampage wurde insbesondere die Partikelneubildung aus den flüchtigen organischen Substanzen (volatile organic compounds, VOCs) α-Pinen und Δ-3-Caren in Anwesenheit von SO2 und NOX untersucht. Die gesammelten Filterproben wurden mit Hilfe eines Wasser/Acetonitril-Gemischs mehrfach extrahiert und anschließend mit dem Ansatz eines Non-Target-Screenings analysiert. Neben einer Zuordnung der identifizierten Moleküle zu bestimmten Molekülklassen lag ein besonderer Fokus auf der Identifizierung von hochoxidierten multifunktionellen organischen Verbindungen (highly oxidized molecules, HOMs). Darüber hinaus wurden dimere Strukturen von Organonitraten und Nitrooxy-Organosulfaten durch MS²-Studien aufgedeckt. Es wurde zudem gezeigt, dass unterschiedliche Konzentrationen an SO2 zu unterschiedlichen Anteilen an Mono- und Di-Organonitraten geführt haben, was auf einen SO2-abhängigen Bildungsweg hinweist. Zusammenfassend wurde eine einzigartige Liste an identifizierten SOA-Verbindungen erhalten, einschließlich der exakten Molekülmasse und Retentionszeit nachgewiesener Isomere. Schließlich wurde, inspiriert durch die Teilnahme an der CLOUD 10-Kampagne am CERN, der Bedarf nach hochauflösender Massenspektrometrie in Echtzeit festgestellt, was zu der Entwicklung und Charakterisierung der APCI-Orbitrap-MS für die Echtzeit-Messung von Aerosolpartikeln geführt hat. Die Optimierung und Charakterisierung der APCI-Orbitrap-MS erfolgte durch im Labor erzeugtes Modellaerosol und wies eine hohe Zeitauflösung, eine lineare Abhängigkeit für Partikel kleiner als 100 nm über drei Größenordnungen und Nachweisgrenzen im unteren ng/m³-Bereich auf. In einer ersten Anwendbarkeitsstudie wurde die Zusammensetzung des Aerosols in der Umgebungsluft analysiert, indem Partikel der Größe PM2.5 (Particulate Matter < 2,5 µm) in der Umgebungsluft außerhalb des Laborgebäudes in abwechselnden Ionisationsmodi beprobt wurden. Aufgrund des sanften Ionisierungsprozesses blieben die Molekülionen erhalten und die Signale der deprotonierten oder protonierten Moleküle stellten jeweils das Hauptsignal dar. Ein anschließendes Non-Target-Screening sowie der Nachweis und die Quantifizierung einzelner organischer Verbindungen in Aerosolen wurden unter atmosphärischen Bedingungen, ohne jegliche Anreicherung oder Filterprobenahme, durchgeführt. Insbesondere wurde die molekulare Zusammensetzung des organischen Aerosols in der Außenluft zu Tages- und Nachtzeit im negativen und positiven Ionisierungsmodus untersucht. Mit dem hier vorgestellten massenspektrometrischen System konnten weiterhin hochoxidierte Mono- und Di-Organonitrate und Nitrooxy-Organosulfate mit sehr hoher Zeitauflösung in der Partikelphase der Umgebungsluft nachgewiesen werden. Zusammenfassend konnte gezeigt werden, dass die Orbitrap-Technik als ein vielseitiges Werkzeug eingesetzt werden kann, welche eine Reihe von Vorteilen für die Analyse von organischen Aerosolen sowohl im offline- als auch im online-Modus bietet, um die atmosphärische Zusammensetzung und Bildungsmechanismen von Aerosolen aufzuklären.iv, 153 Seite

Interfacial photochemistry of biogenic surfactants: a major source of abiotic volatile organic compounds

International audience15 Films of biogenic compounds exposed to the atmosphere are ubiquitously found on surfaces of cloud droplets, aerosol particles, buildings, plants, soils, and the ocean. These air/water interfaces host countless amphiphilic compounds concentrated there with respect to bulk water, leading to a unique chemical environment. Here, photochemical processes at the air/water interface of biofilm-containing solutions were studied, demonstrating abiotic VOC production from authentic biogenic 20 surfactants under ambient conditions. Using a combination of online-APCI-HRMS and PTR-ToF-MS, unsaturated and functionalized VOCs were identified and quantified, giving emission fluxes comparable to previous field and laboratory observations. Interestingly, VOC fluxes increased with the decay of microbial cells in the samples, indicating that cell lysis due to cell death was the main source for surfactants, and VOC production. In particular, irradiation of samples containing solely 25 biofilm cells without matrix components exhibited the strongest VOC production upon irradiation. In agreement with previous studies, LC-MS measurements of the liquid phase suggested the presence of fatty acids and known photosensitizers, possibly inducing the observed VOC production via peroxy-radical chemistry. Up to now such VOC emissions were directly accounted to high biological activity in surface waters. However, the obtained results suggest that abiotic photochemistry can 30 lead to similar emissions into the atmosphere, especially in less biologically-active regions. Furthermore, chamber experiments suggested that oxidation (O 3 /OH-radicals) of the photochemically-produced VOCs leads to aerosol formation and growth, possibly affectin

Aerosol Chemistry Resolved by Mass Spectrometry: Linking Field Measurements of Cloud Condensation Nuclei Activity to Organic Aerosol Composition

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science & Technology, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.est.6b01675Aerosol hygroscopic properties were linked to its chemical composition by using complementary online mass spectrometric techniques in a comprehensive chemical characterization study at a rural mountaintop station in central Germany in August 2012. In particular, atmospheric pressure chemical ionization mass spectrometry ((−)APCI-MS) provided measurements of organic acids, organosulfates, and nitrooxy-organosulfates in the particle phase at 1 min time resolution. Offline analysis of filter samples enabled us to determine the molecular composition of signals appearing in the online (−)APCI-MS spectra. Aerosol mass spectrometry (AMS) provided quantitative measurements of total submicrometer organics, nitrate, sulfate, and ammonium. Inorganic sulfate measurements were achieved by semionline ion chromatography and were compared to the AMS total sulfate mass. We found that up to 40% of the total sulfate mass fraction can be covalently bonded to organic molecules. This finding is supported by both on- and offline soft ionization techniques, which confirmed the presence of several organosulfates and nitrooxy-organosulfates in the particle phase. The chemical composition analysis was compared to hygroscopicity measurements derived from a cloud condensation nuclei counter. We observed that the hygroscopicity parameter (κ) that is derived from organic mass fractions determined by AMS measurements may overestimate the observed κ up to 0.2 if a high fraction of sulfate is bonded to organic molecules and little photochemical aging is exhibited

Interfacial photochemistry of biogenic surfactants: a major source of abiotic volatile organic compounds?

Films of biogenic compounds exposed to the atmosphere are ubiquitously found on surfaces of cloud droplets, aerosol particles, buildings, plants, soils, and the ocean. These air/water interfaces host 15 countless amphiphilic compounds concentrated there with respect to bulk water, leading to a unique chemical environment. Here, photochemical processes at the air/water interface of biofilm-containing solutions were studied, demonstrating abiotic VOC production from a mixture of authentic biogenic surfactants under ambient conditions. Using a combination of online-APCI-HRMS and PTR-TOF-MS, unsaturated and functionalized VOCs were identified and quantified, giving fluxes comparable to previous field and laboratory observations. Interestingly, VOC fluxes increased with less living organisms in the samples, indicating that cell lysis due to cell death was the main source for surfactants. In particular, irradiation of samples containing solely biofilm cells and no matrix components exhibited the strongest VOC production upon irradiation. In agreement with previous studies, LC-MS measurements of the liquid phase suggested the presence of fatty acids and known photosensitizers, possibly inducing the observed VOC production via peroxy-radical chemistry. Up to now such VOC emissions were directly accounted to high biological activity in surface waters. However, the obtained results suggest that abiotic photochemistry can lead to similar emissions into the atmosphere, especially in less biologically-active regions. Furthermore, chamber experiments suggested that oxidation (O3/OH-radicals) of the photochemically-produced VOCs leads to aerosol formation and growth, possibly affecting atmospheric chemistry and climate-related processes, such as cloud formation or the Earth’s radiation budget

Ultrahigh-Resolution Mass Spectrometry in Real Time: Atmospheric Pressure Chemical Ionization Orbitrap Mass Spectrometry of Atmospheric Organic Aerosol

The accurate and precise mass spectrometric measurement of organic compounds in atmospheric aerosol particles is a challenging task that requires analytical developments and adaptations of existing techniques for the atmospheric application. Here we describe the development and characterization of an atmospheric pressure chemical ionization Orbitrap mass spectrometer (APCI-Orbitrap-MS) for the measurement of organic aerosol in real time. APCI is a well-known ionization technique, featuring minimal fragmentation and matrix dependencies, and allows rapid alternation between the positive and negative ionization mode. As a proof of principle, we report ambient organic aerosol composition in real-time, with alternating ionization, high mass resolution (<i>R</i> = 140 000) and accuracy (<2 ppm). The instrument was calibrated in the negative ion mode using 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) model aerosol. We obtain a detection limit of 1.3 ng/m³. Based on the performed calibration using MBTCA particles, the ambient concentration of MBTCA in the particle phase measured in an urban area in Mainz, Germany, ranged between 10 and 80 ng/m³. For the first time, we apply a nontarget screening approach on real-time data, showing molecular variability between ambient day- and nighttime aerosol composition. The detected compounds were grouped in the night- and daytime and analyzed by ultrahigh-resolution MS (UHRMS) visualization methods. Among several prevalent biogenic secondary organic aerosol (BSOA) markers, 24 organic mononitrates and one organic dinitrate were detected. We further estimate that, on average, organic nitrates contribute to 5% and 14% of the measured particulate organic aerosol at day and night, respectively

Real-time detection of highly oxidized organosulfates and BSOA marker compounds during the F-BEACh 2014 field study

The chemical composition of ambient organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in central Europe in July 2014 (Fichtelgebirge – Biogenic Emission and Aerosol Chemistry, F-BEACh 2014). Among several common biogenic secondary organic aerosol (BSOA) marker compounds, 93 acidic oxygenated hydrocarbons were detected with elevated abundances and were thus attributed to be characteristic for the organic aerosol mass at the site. Monoterpene measurements exhibited median mixing ratios of 1.6 and 0.8 ppbV for in and above canopy levels respectively. Nonetheless, concentrations for early-generation oxidation products were rather low, e.g., pinic acid (c  =  4.7 (±2.5) ng m−3). In contrast, high concentrations were found for later-generation photooxidation products such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA, c  =  13.8 (±9.0) ng m−3) and 3-carboxyheptanedioic acid (c  =  10.2 (±6.6) ng m−3), suggesting that aged aerosol masses were present during the campaign period. In agreement, HYSPLIT trajectory calculations indicate that most of the arriving air masses traveled long distances (>  1500 km) over land with high solar radiation. In addition, around 47 % of the detected compounds from filter sample analysis contained sulfur, confirming a rather high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were tentatively identified by high-resolution mass spectrometry. Correlations among HOOS, sulfate, and highly oxidized multifunctional organic compounds (HOMs) support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Moreover, periods with high relative humidity indicate that aqueous-phase chemistry might play a major role in HOOS production. However, for dryer periods, coinciding signals for HOOS and gas-phase peroxyradicals (RO2•) were observed, suggesting RO2• to be involved in HOOS formation