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Aerosol Physics

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Aerosol Physics applies and develops methods to characterize particles of aerosols physically and investigates the partitioning of gas particles in semi-volatile organic substances.

Aerosol Physics applies and develops methods to characterize particles of aerosols physically and investigates the partitioning of gas particles in semi-volatile organic substances.

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About our research

The Aerosol Physics team drives research in air quality, combustion emissions, atmospheric aerosols, personal exposure to aerosols, occupational safety, and relevant sampling and measurement techniques. In particular, we focus on the application and development of methods for physical particle characterization and the study of gas-particle distribution of semivolatile organics. A battery of on-line instruments (e.g. for determination of particle number, size and mobility, on-line mass concentration and optical properties) is used - total organic carbon and selected gaseous components are analyzed e.g. with a flame ionization detector and on-line mass spectrometer, respectively. Sampling on impact substrates or filters and selected absorber materials enables further in-depth chemical offline analysis. In addition, sophisticated computer models have been developed and applied to study particle deposition in human lungs, animal models and in vitro incubation systems (ALI = "Air Liquid Interface").


In addition, we support the JMSC with laboratory studies using various particle generators and characterize the generated model aerosol in collaboration with the Aerosol Chemistry group. In several extended off-site measurement campaigns (e.g., at the University of Eastern Finland or at the Faculty of Technology, University of Rostock), aerosol dilution and distribution sampling trains have been set up for ALI exposure studies, adapted analyses, and in-depth characterization of aerosol from different emission sources and artificially aged aerosols.

Scientists at Aerosol Physics

Anusmita Das

PhD Student

Seongho Jeong

PhD Student

Dr. Narges Rastak

Senior Scientist

Publications

2022, Scientific Article in Toxics

Construction of an in vitro air–liquid interface exposure system to assess the toxicological impact of gas and particle phase of semi-volatile organic compounds.

Anthropogenic activities and industrialization render continuous human exposure to semi-volatile organic compounds (SVOCs) inevitable. Occupational monitoring and safety implementations consider the inhalation exposure of SVOCs as critically relevant. Due to the inherent properties of SVOCs as gas/particle mixtures, risk assessment strategies should consider particle size-segregated SVOC association and the relevance of released gas phase fractions. We constructed an in vitro air–liquid interface (ALI) exposure system to study the distinct toxic effects of the gas and particle phases of the model SVOC dibutyl phthalate (DBP) in A549 human lung epithelial cells. Cytotoxicity was evaluated and genotoxic effects were measured by the alkaline and enzyme versions of the comet assay. Deposited doses were assessed by model calculations and chemical analysis using liquid chromatography tandem mass spectrometry. The novel ALI exposure system was successfully implemented and revealed the distinct genotoxic effects of the gas and particle phases of DBP. The empirical measurements of cellular deposition and the model calculations of the DBP particle phase were concordant.The model SVOC DBP showed that inferred oxidative DNA damage may be attributed to particle-related effects. While pure gas phase exposure may follow a distinct mechanism of genotoxicity, the contribution of the gas phase to total aerosol was comparably low.

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2022, Scientific Article in Environmental Pollution

Aerosol emissions from a marine diesel engine running on different fuels and effects of exhaust gas cleaning measures.

The emissions of marine diesel engines have gained both global and regional attentions because of their impact on human health and climate change. To reduce ship emissions, the International Maritime Organization capped the fuel sulfur content of marine fuels. Consequently, either low-sulfur fuels or additional exhaust gas cleaning devices for the reduction in sulfur dioxide (SO2) emissions became mandatory. Although a wet scrubber reduces the amount of SO2 significantly, there is still a need to consider the reduction in particle emissions directly. We present data on the particle removal efficiency of a scrubber regarding particle number and mass concentration with different marine fuel types, marine gas oil, and two heavy fuel oils (HFOs). An open-loop sulfur scrubber was installed in the exhaust line of a marine diesel test engine. Fine particulate matter was comprehensively characterized in terms of its physical and chemical properties. The wet scrubber led up to a 40% reduction in particle number, whereas a reduction in particle mass emissions was not generally determined. We observed a shift in the size distribution by the scrubber to larger particle diameters when the engine was operated on conventional HFOs. The reduction in particle number concentrations and shift in particle size were caused by the coagulation of soot particles and formation/growing of sulfur-containing particles. Combining the scrubber with a wet electrostatic precipitator as an additional abatement system showed a reduction in particle number and mass emission factors by >98%. Therefore, the application of a wet scrubber for the after-treatment of marine fuel oil combustion will reduce SO2 emissions, but it does not substantially affect the number and mass concentration of respirable particulate matters. To reduce particle emission, the scrubber should be combined with additional abatement systems.

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2022, Scientific Article in ACS Earth and Space Chemistry

On the complementarity and informative value of different electron ionization mass spectrometric techniques for the chemical analysis of secondary Organic aerosols.

The atmospheric aging of volatile organic compounds leads to the formation of complex mixtures of highly oxidized secondary organic aerosols (SOAs). State-of-the-art mass spectrometry (MS) has become a pivotal tool for their chemical characterization. In this study, we characterized the chemical complexity of naphthalene-derived SOA by three different time-of-flight (TOF) mass spectrometric techniques applying electron ionization: high-resolution-TOF-aerosol MS (AMS), direct inlet probe (DIP)-high-resolution TOFMS, and thermal desorption-comprehensive two-dimensional gas chromatography-TOFMS (GC × GC). We discuss AMS as an online, DIP as an atline, and GC × GC as an offline technique to compare their informative value for studying the oxidation state, volatility, and molecular composition of laboratory-generated SOA. For GC × GC, the accessible organic content was limited to (semi-)volatile compounds and supported a reliable assignment of the molecular composition. DIP and AMS were used to derive secondary parameters such as O/C and H/C ratios, the general functionality of the compound classes and their abundance upon photochemical aging. Thereby, while the induced pyrolysis in the AMS extended the accessibility range to polar, high-molecular-weight compounds, thermal fragmentation also led to limited molecular information. For DIP, low-volatility compounds could be volatilized and the high mass resolution was useful to resolve isobaric mass fragments and assign reliable sum formulas of fragments and molecular ions. Although no single technique can provide information to describe the full chemical complexity of the SOA, AMS, DIP, and GC × GC in their complementarity are well suited to investigate the impact of SOA on health and environment.

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2022, Scientific Article in Environment International

Exposure to naphthalene and β-pinene-derived secondary organic aerosol induced divergent changes in transcript levels of BEAS-2B cells.

The health effects of exposure to secondary organic aerosols (SOAs) are still limited. Here, we investigated and compared the toxicities of soot particles (SP) coated with β-pinene SOA (SOAβPin-SP) and SP coated with naphthalene SOA (SOANap-SP) in a human bronchial epithelial cell line (BEAS-2B) residing at the air-liquid interface. SOAβPin-SP mostly contained oxygenated aliphatic compounds from β-pinene photooxidation, whereas SOANap-SP contained a significant fraction of oxygenated aromatic products under similar conditions. Following exposure, genome-wide transcriptome responses showed an Nrf2 oxidative stress response, particularly for SOANap-SP. Other signaling pathways, such as redox signaling, inflammatory signaling, and the involvement of matrix metalloproteinase, were identified to have a stronger impact following exposure to SOANap-SP. SOANap-SP also induced a stronger genotoxicity response than that of SOAβPin-SP. This study elucidated the mechanisms that govern SOA toxicity and showed that, compared to SOAs derived from a typical biogenic precursor, SOAs from a typical anthropogenic precursor have higher toxicological potency, which was accompanied with the activation of varied cellular mechanisms, such as aryl hydrocarbon receptor. This can be attributed to the difference in chemical composition; specifically, the aromatic compounds in the naphthalene-derived SOA had higher cytotoxic potential than that of the β-pinene-derived SOA.

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2022, Scientific Article in Environmental Health Perspectives

Effect of atmospheric aging on soot particle toxicity in lung cell models at the air-liquid interface: Differential toxicological impacts of biogenic and anthropogenic Secondary Organic Aerosols (SOAs).

BACKGROUND: Secondary organic aerosols (SOAs) formed from anthropogenic or biogenic gaseous precursors in the atmosphere substantially contribute to the ambient fine particulate matter [PM ≤2.5μm in aerodynamic diameter (PM2.5)] burden, which has been associated with adverse human health effects. However, there is only limited evidence on their differential toxicological impact. OBJECTIVES: We aimed to discriminate toxicological effects of aerosols generated by atmospheric aging on combustion soot particles (SPs) of gaseous biogenic (β-pinene) or anthropogenic (naphthalene) precursors in two different lung cell models exposed at the air-liquid interface (ALI). METHODS: Mono- or cocultures of lung epithelial cells (A549) and endothelial cells (EA.hy926) were exposed at the ALI for 4 h to different aerosol concentrations of a photochemically aged mixture of primary combustion SP and β-pinene (SOAβPIN-SP) or naphthalene (SOANAP-SP). The internally mixed soot/SOA particles were comprehensively characterized in terms of their physical and chemical properties. We conducted toxicity tests to determine cytotoxicity, intracellular oxidative stress, primary and secondary genotoxicity, as well as inflammatory and angiogenic effects. RESULTS: We observed considerable toxicity-related outcomes in cells treated with either SOA type. Greater adverse effects were measured for SOANAP-SP compared with SOAβPIN-SP in both cell models, whereas the nano-sized soot cores alone showed only minor effects. At the functional level, we found that SOANAP-SP augmented the secretion of malondialdehyde and interleukin-8 and may have induced the activation of endothelial cells in the coculture system. This activation was confirmed by comet assay, suggesting secondary genotoxicity and greater angiogenic potential. Chemical characterization of PM revealed distinct qualitative differences in the composition of the two secondary aerosol types. DISCUSSION: In this study using A549 and EA.hy926 cells exposed at ALI, SOA compounds had greater toxicity than primary SPs. Photochemical aging of naphthalene was associated with the formation of more oxidized, more aromatic SOAs with a higher oxidative potential and toxicity compared with β-pinene. Thus, we conclude that the influence of atmospheric chemistry on the chemical PM composition plays a crucial role for the adverse health outcome of emissions. https://doi.org/10.1289/EHP9413.

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2022, Scientific Article in Atmospheric Chemistry and Physics

Single-particle characterization of polycyclic aromatic hydrocarbons in background air in northern Europe.

We investigated the distribution of polycyclic aromatic hydrocarbons (PAHs) on individual ambient aerosol particles at the Swedish western coast in a pristine environment for 10 d in October 2019. The measurements were carried out using new technology with single-particle mass spectrometry (SPMS) that reveals both the inorganic particle composition as well as the particle-bound PAHs (Schade et al., 2019). More than 290 000 particles were characterized; 4412 of them reveal PAH signatures. Most of the PAH-containing particles were internal mixtures of carbonaceous material, secondary nitrate and metals from distant sources in central and eastern Europe. We characterize the aerosol with respect to the inorganic composition, comparable to conventional SPMS, before we discuss the distribution of PAHs within this particle ensemble. Vice versa, we analyze the single-particle PAH spectra for characteristic patterns and discuss the inorganic composition, origin and atmospheric processing of the respective particles. The study period comprised different meteorological situations: clean air conditions with winds from the North Sea/Kattegat and little terrestrial air pollution, long-range transport from eastern Europe and southern Sweden, and transport of aerosols from central Europe over the sea. For all meteorological conditions, PAHs were detected in particles whose inorganic content indicates traffic emissions, such as combinations of soot, iron and calcium as well as in particles with biomass-burning signatures. However, there were variations in their amounts, dependent on the geographic origin. Because of strong mixing, rapid degradation and speciation limits, e.g., for PAHs of the same nominal mass, the application of diagnostic ratios for source apportionment is limited under the conditions of our study. Nevertheless, the combination with the inorganic content and meteorological data provides unique insights into the particles' origin, aging and mixing state. We exemplarily show how the observation of PAH profiles and inorganic secondary components on a single-particle level can open a new door to investigate aerosol aging processes. To our best knowledge, we herewith present the first comprehensive study on the single-particle distribution of PAHs in ambient air as well as the first set of combined data on PAHs and inorganic composition on a single-particle level.

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2022, Scientific Article in Atmospheric Chemistry and Physics

Are reactive oxygen species (ROS) a suitable metric to predict toxicity of carbonaceous aerosol particles?

It is being suggested that particle-bound or particle-induced reactive oxygen species (ROS), which significantly contribute to the oxidative potential (OP) of aerosol particles, are a promising metric linking aerosol compositions to toxicity and adverse health effects. However, accurate ROS quantification remains challenging due to the reactive and short-lived nature of many ROS components and the lack of appropriate analytical methods for a reliable quantification. Consequently, it remains difficult to gauge their impact on human health, especially to identify how aerosol particle sources and atmospheric processes drive particle-bound ROS formation in a real-world urban environment. In this study, using a novel online particle-bound ROS instrument (OPROSI), we comprehensively characterized and compared the formation of ROS in secondary organic aerosols (SOAs) generated from organic compounds that represent anthropogenic (naphthalene, SOANAP) and biogenic (β-pinene, SOAβPIN) precursors. The SOA mass was condensed onto soot particles (SP) under varied atmospherically relevant conditions (photochemical aging and humidity) to mimic the SOA formation from a mixing of traffic-related carbonaceous primary aerosols and volatile organic compounds (VOCs). We systematically analyzed the ability of the aqueous extracts of the two aerosol types (SOANAP-SP and SOAβPIN-SP) to induce ROS production and OP. We further investigated cytotoxicity and cellular ROS production after exposing human lung epithelial cell cultures (A549) to extracts of the two aerosols. A significant finding of this study is that more than 90% of all ROS components in both SOA types have a short lifetime, highlighting the need to develop online instruments for a meaningful quantification of ROS. Our results also show that photochemical aging promotes particle-bound ROS production and enhances the OP of the aerosols. Compared to SOAβPIN-SP, SOANAP-SP elicited a higher acellular and cellular ROS production, a higher OP, and a lower cell viability. These consistent results between chemical-based and biological-based analyses indicate that particle-bound ROS quantification could be a feasible metric to predict aerosol particle toxicity and adverse human effects. Moreover, the cellular ROS production caused by SOA exposure not only depends on aerosol type but is also affected by exposure dose, highlighting a need to mimic the process of particle deposition onto lung cells and their interactions as realistically as possible to avoid unknown biases.

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2021, Scientific Article in Environmental and Molecular Mutagenesis

In vitro genotoxicity of dibutyl phthalate on A549 lung cells at air-liquid interface in exposure concentrations relevant at workplaces.

The ubiquitous use of phthalates in various materials and the knowledge about their potential adverse effects is of great concern for human health. Several studies have uncovered their role in carcinogenic events and suggest various phthalate-associated adverse health effects that include pulmonary diseases. However, only limited information on pulmonary toxicity is available considering inhalation of phthalates as the route of exposure. While in vitro studies are often based on submerged exposures, this study aimed to expose A549 alveolar epithelial cells at the air-liquid interface (ALI) to unravel the genotoxic and oxidative stress-inducing potential of dibutyl phthalate (DBP) with concentrations relevant at occupational settings. Within this scope, a computer modeling approach calculating alveolar deposition of DBP particles in the human lung was used to define in vitro ALI exposure conditions comparable to potential occupational DBP exposures. The deposited mass of DBP ranged from 0.03 to 20 ng/cm2 , which was comparable to results of a human lung particle deposition model using an 8 h workplace threshold limit value of 580 μg/m3 proposed by the Scientific Committee on Occupational Exposure Limits for the European Union. Comet and Micronucleus assay revealed that DBP induced genotoxicity at DNA and chromosome level in sub-cytotoxic conditions. Since genomic instability was accompanied by increased generation of the lipid peroxidation marker malondialdehyde, oxidative stress might play an important role in phthalate-induced genotoxicity. The results highlight the importance of adapting in vitro studies to exposure scenarios relevant at occupational settings and reconsidering occupational exposure limits for DBP.

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2021, Scientific Article in Energy & Fuels

Emissions of gases and volatile organic compounds from residential heating: A comparison of brown coal briquettes and logwood combustion.

Coal continues to be a major source of energy for residential heating in some parts of the world due to its low price and good availability. However, only little information on emissions for coal combustion in small-scale appliances, in particular manually-operated stoves, is available. This study investigates the emissions of gases and volatile organic compounds (VOCs) from brown coal briquettes (BCBs) burned in a typical Central European wood stove and compares them to emissions from spruce wood logs. Special emphasis was placed on the evolution of emissions over consecutive batches. In comparison to wood, BCBs made from Lusatian lignite showed higher emissions of compounds that were attributed to the decomposition of lignin, while emissions that were attributed to having originated from pyrosynthesis did not show significant differences between both fuels. Furthermore, a 20-fold higher emission factor for SO2 was obtained from BCB combustion, which is known for its deleterious effect. In addition to a reduction in the carbon footprint, replacing BCBs with logwood as a fuel for residential heating might be beneficial for human health due to vast differences in SO2 emissions, whereas a potential effect from the reduction of organic emissions is questionable due to the rather small differences in organic emissions.

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2021, Scientific Article in Analytical Chemistry

Atmospheric pressure single photon laser ionization (APSPLI) mass spectrometry using a 157 nm fluorine excimer laser for sensitive and selective detection of non- to semipolar hydrocarbons.

Atmospheric pressure single photon ionization (APSPLI) mass spectrometry utilizing a fluorine excimer laser (157 nm, 7.9 eV) is presented for the first time. For evaluation and optimization, polycyclic aromatic hydrocarbon (PAH) standard mixtures were used. The presented technique allowed for the selective ionization of semi- to nonpolar compounds in a single photon ionization process using VUV photons. Molecular radical cations were found as a base peak, whereas protonated species were almost absent. Although the ionization chamber is flushed by pure nitrogen, remaining oxygen and water traces caused unwanted oxidized ionization artifacts. Installation of water and oxygen filter cartridges significantly reduced the abundance of artifacts. For evaluating complex mixture analysis, APSPLI was applied to characterize a light crude oil. In addition to aromatic hydrocarbons, APSPLI allowed for the sensitive ionization of sulfur-containing aromatic constituents (PASH). A comparison of APSPLI to atmospheric pressure laser ionization (266 nm, 4.7 eV) revealed the additional compositional space accessible by the single photon process. APLI, conducted with UV radiation, is mainly restricted to PAH analysis. APSPLI overcomes this limitation, and PAH and PASH, which often occur simultaneously in complex mixtures, can be detected. This novel ionization concept is envisioned to have a high analytical potential further explored in the future.

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2020, Scientific Article in Atmospheric Chemistry and Physics

Resonance-enhanced detection of metals in aerosols using single-particle mass spectrometry.

We describe resonance effects in laser desorption-ionization (LDI) of particles that substantially increase the sensitivity and selectivity to metals in single-particle mass spectrometry (SPMS). Within the proposed scenario, resonant light absorption by ablated metal atoms increases their ionization rate within a single laser pulse. By choosing the appropriate laser wavelength, the key micronutrients Fe, Zn and Mn can be detected on individual aerosol particles with considerably improved efficiency. These ionization enhancements for metals apply to natural dust and anthropogenic aerosols, both important sources of bioavailable metals to marine environments. Transferring the results into applications, we show that the spectrum of our KrF-excimer laser is in resonance with a major absorption line of iron atoms. To estimate the impact of resonant LDI on the metal detection efficiency in SPMS applications, we performed a field experiment on ambient air with two alternately firing excimer lasers of different wavelengths. Herein, resonant LDI with the KrF-excimer laser (248.3 nm) revealed iron signatures for many more particles of the same aerosol ensemble compared to the more common ArF-excimer laser line of 193.3 nm (nonresonant LDI of iron). Many of the particles that showed iron contents upon resonant LDI were mixtures of sea salt and organic carbon. For nonresonant ionization, iron was exclusively detected in particles with a soot contribution. This suggests that resonant LDI allows a more universal and secure metal detection in SPMS. Moreover, our field study indicates relevant atmospheric iron transport by mixed organic particles, a pathway that might be underestimated in SPMS measurements based on nonresonant LDI. Our findings show a way to improve the detection and source attribution capabilities of SPMS for particle-bound metals, a health-relevant aerosol component and an important source of micronutrients to the surface oceans affecting marine primary productivity.

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2020, Scientific Article in Particle and Fibre Toxicology

Influence of wood species on toxicity of log-wood stove combustion aerosols: A parallel animal and air-liquid interface cell exposure study on spruce and pine smoke.

Background Wood combustion emissions have been studied previously either by in vitro or in vivo models using collected particles, yet most studies have neglected gaseous compounds. Furthermore, a more accurate and holistic view of the toxicity of aerosols can be gained with parallel in vitro and in vivo studies using direct exposure methods. Moreover, modern exposure techniques such as air-liquid interface (ALI) exposures enable better assessment of the toxicity of the applied aerosols than, for example, the previous state-of-the-art submerged cell exposure techniques. Methods We used three different ALI exposure systems in parallel to study the toxicological effects of spruce and pine combustion emissions in human alveolar epithelial (A549) and murine macrophage (RAW264.7) cell lines. A whole-body mouse inhalation system was also used to expose C57BL/6 J mice to aerosol emissions. Moreover, gaseous and particulate fractions were studied separately in one of the cell exposure systems. After exposure, the cells and animals were measured for various parameters of cytotoxicity, inflammation, genotoxicity, transcriptome and proteome. Results We found that diluted (1:15) exposure pine combustion emissions (PM(1)mass 7.7 +/- 6.5 mg m(- 3), 41 mg MJ(- 1)) contained, on average, more PM and polycyclic aromatic hydrocarbons (PAHs) than spruce (PM(1)mass 4.3 +/- 5.1 mg m(- 3), 26 mg MJ(- 1)) emissions, which instead showed a higher concentration of inorganic metals in the emission aerosol. Both A549 cells and mice exposed to these emissions showed low levels of inflammation but significantly increased genotoxicity. Gaseous emission compounds produced similar genotoxicity and a higher inflammatory response than the corresponding complete combustion emission in A549 cells. Systems biology approaches supported the findings, but we detected differing responses between in vivo and in vitro experiments. Conclusions Comprehensive in vitro and in vivo exposure studies with emission characterization and systems biology approaches revealed further information on the effects of combustion aerosol toxicity than could be achieved with either method alone. Interestingly, in vitro and in vivo exposures showed the opposite order of the highest DNA damage. In vitro measurements also indicated that the gaseous fraction of emission aerosols may be more important in causing adverse toxicological effects. Combustion aerosols of different wood species result in mild but aerosol specific in vitro and in vivo effects.

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2020, Scientific Article in Waste management

Real time monitoring of slow pyrolysis of polyethylene terephthalate (PET) by different mass spectrometric techniques.

In the context of waste upgrading of polyethylene terephthalate (PET) by pyrolysis, this study presents three on-line mass spectrometric techniques with soft ionization for monitoring the emitted decomposition products and their thermal dependent evolution profiles. Pyrolysis experiments were performed using a thermogravimetric analyzer (TGA) under nitrogen atmosphere with a heating rate of 5 degrees C/min from 30 degrees C to 600 degrees C. Single-photon ionization (SPI at 118 nm/10.5 eV) and resonance enhanced multiple photon ionization (REMPI at 266 nm) were used with time-of-flight mass spectrometry (TOF-MS) for evolved gas analysis (TGA-SPI/REMPI-TOFMS). Additionally, the chemical signature of the pyrolysis products was investigated by atmospheric pressure chemical ionization (APCI) ultra high resolution Fourier Transform ion cyclotron resonance mass spectrometry (FT-ICR MS) which enables assignment of molecular sum formulas (TGA-APCI FT-ICR MS). Despite the soft ionization by SPI, the fragmentation of some compounds with the loss of the [O-CH = CH2] fragment is observed. The major compounds were acetaldehyde (m/z 44), benzoic acid (m/z 122) and a fragment of m/z 149. Using REMPI, aromatic species were selectively detected. Several series of pyrolysis products were observed in different temperature intervals, showing the presence of polycyclic aromatic hydrocarbons (PAHs), especially at high temperatures. FT-ICR MS data showed, that the CHO4 class was the most abundant compound class with a relative abundance of 45.5%. The major compounds detected with this technique corresponded to m/z 193.0495 (C10H9O4+) and 149.0233 (C8H5O3+). Based on detailed chemical information, bulk reaction pathways are proposed, showing the formation of both cyclic monomer/dimer and linear structures.

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2019, Scientific Article in Analytical Chemistry

Spatially shaped laser pulses for the simultaneous detection of polycyclic aromatic hydrocarbons as well as positive and negative inorganic ions in single particle mass spectrometry.

Polycyclic aromatic hydrocarbons (PAHs) are toxic organic trace components in atmospheric aerosols that have impacts on climate and human health. They are bound to airborne particles and transported over long distances. Observations of their distribution, transport pathways, and degradation are crucial for risk assessment and mitigation. Such estimates would benefit from online detection of PAHs along with analysis of the carrying particles to identify the source. Typically, laser desorption/ionization (LDI) in a bipolar mass spectrometer reveals the inorganic constituents and provides limited molecular information. In contrast, two-step ionization approaches produce detailed PAH mass spectra from individual particles but without the source-specific inorganic composition. Here we report a new technique that yields the single-particle PAH composition along with both positive and negative inorganic ions via LDI. Thus, the complete particle characterization and source apportionment from conventional bipolar LDI-analysis becomes possible, combined with a detailed PAH spectrum for the same particle. The key idea of the method is spatiotemporal matching of the ionization laser pulse to the transient component distribution in the particle plume after laser desorption. The technique is robust and field-deployable with only slightly higher costs and complexity compared to two-step approaches. We demonstrate its capability to reveal the PAH-distribution on different particle types in combustion aerosols and ambient air.

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2019, Scientific Article in Aerosol Science and Technology

A novel high-volume Photochemical Emission Aging flow tube Reactor (PEAR).

Aerosols emitted from various anthropogenic and natural sources undergo constant physicochemical transformations in the atmosphere, altering their impacts on health and climate. This article presents the design and characteristics of a novel Photochemical Emission Aging flow tube Reactor (PEAR). The PEAR was designed to provide sufficient aerosol mass and flow for simultaneous measurement of the physicochemical properties of aged aerosols and emission exposure studies (in vivo and in vitro). The performance of the PEAR was evaluated by using common precursors of secondary aerosols as well as combustion emissions from a wood stove and a gasoline engine. The PEAR was found to provide a near laminar flow profile, negligible particle losses for particle sizes above 40 nm, and a narrow residence time distribution. These characteristics enable resolution of temporal emission patterns from dynamic emission sources such as small-scale wood combustion. The formation of secondary organic aerosols (SOA) in the PEAR was found to be similar to SOA formation in a smog chamber when toluene and logwood combustion emissions were used as aerosol sources. The aerosol mass spectra obtained from the PEAR and smog-chamber were highly similar when wood combustion was used as the emission source. In conclusion, the PEAR was found to plausibly simulate the photochemical aging of organic aerosols with high flow rates, needed for studies to investigate the effects of aged aerosols on human health. The method also enables to study the aging of different emission phases in high time resolution, and with different OH-radical exposures up to conditions representing long-range transported aerosols. Copyright (c) 2019 American Association for Aerosol Research

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2019, Scientific Article in Fuel

Composition of carbonaceous fine particulate emissions of a flexible fuel DISI engine under high velocity and municipal conditions.

A study about the chemical composition of carbonaceous fine particulate emissions of flexible fuel direct injection spark ignition engine under high velocity and municipal conditions was conducted with two different gasoline-ethanol blended fuels (E10 and E85). A self-designed engine test cycle simulating high vehicle velocity conditions of up to of 180 km/h was introduced (high velocity driving cycle, HVDC), simulating a possible motorway scenario without speed legislations as allowed in Germany, and compared to a municipal driving cycle (MDC), which is derived from the New European Driving Cycle (NEDC). The fingerprint of polycyclic aromatic hydrocarbons (PAHs) and their alkylated and oxygenated derivatives as well as the concentrations for PM2.5, elemental carbon (EC), organic carbon (OC) and also for the three most abundant PAHs were determined using a modified thermal optical carbon analyser (TOCA) hyphenated to soft resonance-enhanced multi-photon ionisation mass spectrometry (REMPI-TOFMS). Driving under high velocity conditions resulted in a significant increase of concentrations for PM, EC, OC, methyl-phenanthrenes and pyrene. Engine operation on E85 led to a strong decrease for all concentrations for both cycles. A good correlation was found between concentrations obtained by REMPI-TOFMS and TD-GC/MS. Most prominent PAHs were the alkylated series of phenanthrene, pyrene and naphthalene, whereby the abundances decrease with increasing degree of alkylation. The organic composition between HVDC and MDC mainly differed in quantity and to a lower extent in the aromatic pattern. Nevertheless, methyl-phenanthrenes, pyrene and methyl-pyrenes as well as 4H-cyclopenta[def] phenanthrene and benzo[b]naphtho[1,2-d]furan/benzo[b]naphtho[2,3-d] furan and it alkylated series showed a higher abundance in the pattern under high velocity conditions, where alkylated naphthalenes were enhanced in the MDC mode.

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2017, Scientific Article in Energy & Fuels

Thermal analysis coupled to ultrahigh resolution mass spectrometry with collision induced dissociation for complex petroleum samples: Heavy oil composition and asphaltene precipitation effects.

Thermal desorption and pyrolysis of various heavy oils and asphaltenes (precipitated with different paraffinic solvents) were studied. For this purpose evolved gas analysis was realized by hyphenation of a thermobalance to ultrahigh-resolution mass spectrometry (FT-ICR MS). The chemical pattern was preserved by applying soft atmospheric pressure chemical ionization (APCI). Collision induced dissociation (CID) was performed for deeper structural insights. Viscous or solid petroleum samples and fractions can be easily measured by the setup. The SARA fractions (maltenes, C7-asphaltenes, aromatics, saturated, and resins), deployed for evaluation purposes, revealed a very complex molecular pattern, and fractionation drastically increased the number of assigned elemental compositions. Species from m/z 150 to m/z 700 and two main phases (desorption and pyrolysis), which transits at roughly 300-350 °C, are observed. Both phases overlap partially but can be separated by applying matrix factorization. The heavy oil and asphaltene mass spectra are dominated by CH-, CHS-, and CHN-class compounds, whereas for the CID spectra a lower abundance of oxygenated species was found. Furthermore, physicochemical properties and the molecular response were correlated for the heavy oils and asphaltene samples, finding a strong correlation between sulfur content and abundance of CHS x -class compounds as well as between double bond equivalent (DBE) and API gravity. As the CID leads mainly to dealkylation, the length of alkylated side chains of components evolved thermally or by pyrolytic processes can be traced during the temperature ramp. In general, an increase of dealkylation in the desorption phase, followed by a decrease during the transition to pyrolysis and an increase reaching a stable plateau for stable pyrolysis, was detected. This behavior was found to be similar for all asphaltenes and for the mean DBE progression. Deploying a lighter paraffinic solvent for asphaltene precipitation causes a higher abundance of species emitted in the desorption phase. They belong mainly to CHO x -class compounds from the maltene fraction occluded and coprecipitated with the asphaltenes. Besides this, no significant effect of the precipitation solvent on the asphaltenic core structures and molecular pattern in the pyrolysis phase was observed. The DBE distribution sug gests the presence of the archipelago asphaltene molecular architecture.

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2017, Scientific Article in Analytical Chemistry

Direct infusion resonance-enhanced multiphoton ionization mass spectrometry of liquid samples under vacuum conditions.

Direct infusion resonance-enhanced multiphoton ionization (DI-REMPI) was performed on liquid samples, which were introduced to the ion source via a direct liquid interface, to enable the investigation of dissolved aromatic compounds. Desolvation and nebulization of the samples were supported by a heated repeller using flow rates in the upper nL min -1 range. The obtained mass spectra of five pure polycyclic aromatic hydrocarbons as well as complex petroleum samples revealed predominantly molecular ions without evidence of solvent or dopant effects as observed in atmospheric pressure photoionization (APPI) and laser ionization (APLI) with limits of detection in the lower pmol range. Furthermore, it is demonstrated by the analysis of different complex oil samples that DI-REMPI covers a larger m/z range than external volatilization of the sample prior to introduction to the ion source by using thermogravimetry (TG) hyphenated to REMPI time-of-flight mass spectrometry (TOFMS). Analogous to reported setups with direct liquid interface and electron ionization, direct-REMPI may be an option for soft ionization in liquid chromatography. (Figure Presented).

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2017, Scientific Article in European Journal of Mass Spectrometry

Comprehensive chemical comparison of fuel composition and aerosol particles emitted from a ship diesel engine by gas chromatography atmospheric pressure chemical ionisation ultra-high resolution mass spectrometry with improved data processing routines.

The analysis of petrochemical materials and particulate matter originating from combustion sources remains a challenging task for instrumental analytical techniques. A detailed chemical characterisation is essential for addressing health and environmental effects. Sophisticated instrumentation, such as mass spectrometry coupled with chromatographic separation, is capable of a comprehensive characterisation, but needs advanced data processing methods. In this study, we present an improved data processing routine for the mass chromatogram obtained from gas chromatography hyphenated to atmospheric pressure chemical ionisation and ultra high resolution mass spectrometry. The focus of the investigation was the primary combustion aerosol samples, i.e. particulate matter extracts, as well as the corresponding fossil fuels fed to the engine. We demonstrate that utilisation of the entire transient and chromatographic information results in advantages including minimisation of ionisation artefacts and a reliable peak assignment. A comprehensive comparison of the aerosol and the feed fuel was performed by applying intensity weighted average values, compound class distribution and principle component analysis. Certain differences between the aerosol generated with the two feed fuels, diesel fuel and heavy fuel oil, as well as between the aerosol and the feed were revealed. For the aerosol from heavy fuel oil, oxidised species from the CHN and CHS class precursors of the feed were predominant, whereas the CHOx class is predominant in the combustion aerosol from light fuel oil. Furthermore, the complexity of the aerosol increases significantly compared to the feed and incorporating a higher chemical space. Coupling of atmospheric pressure chemical ionisation to gas chromatography was found to be a useful additional approach for characterisation of a combustion aerosol, especially with an automated utilisation of the information from the ultra-high resolution mass spectrometer and the chromatographic separation.

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2017, Scientific Article in Atmospheric Environment

A chemometric investigation of aromatic emission profiles from a marine engine in comparison with residential wood combustion and road traffic: Implications for source apportionment inside and outside sulphur emission control areas.

Ship emissions are known to cause severe impacts on human health, but are less restricted than land-based emissions. A regulation to improve air quality in coastal regions and frequented waterways is the limitation of fuel sulphur content to 0.1% in sulphur emission control areas (SECAs), which has caused a switch from heavy fuel oil (HFO) towards diesel-like marine gas oil (MGO) or marine diesel oil (MDO). The fraction of aromatic organic vapours in the exhaust from a marine engine, operating on HFO and MGO, was investigated by resonance-enhanced multi-photon ionisation time-of-flight mass spectrometry (REMPI-TOFMS). MGO with fuel sulphur content (FSC) below 0.1% and HFO with an average FSC of 2.7% denote representative marine fuels inside and outside SECAs, respectively. The obtained emission spectra were combined with data of previous REMPI-TOFMS studies of combustion engines and wood combustion in statistical analyses to derive marker substances for ship emissions inside and outside SECAs. A diagnostic ratio of C2-naphthalenes to methyl-naphthalenes was found to hold for a good discriminator between ship emissions on the one hand and road traffic and wood combustion on the other hand. Furthermore, random REMPI spectra from all emission sources were mixed with different proportions in a simulation to create a model based on partial least square (PLS) regression for the prediction of ship contribution to aromatic organic vapours. We point out that in particular PAHs with higher degree of alkylation are significant markers for primary ship emissions which may support source apportionment studies inside and outside SECAs to assess the benefits of fuel sulphur content regulation on air quality.

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Head of Aerosol Physics

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Dr. Martin Sklorz

Head of Aerosol Physics

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