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  • 1. Bianchi, Federico
    et al.
    Kurtén, Theo
    Riva, Matthieu
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rissanen, Matti P.
    Roldin, Pontus
    Berndt, Torsten
    Crounse, John D.
    Wennberg, Paul O.
    Mentel, Thomas F.
    Wildt, Jürgen
    Junninen, Heikki
    Jokinen, Tuija
    Kulmala, Markku
    Worsnop, Douglas R.
    Thornton, Joel A.
    Donahue, Neil
    Kjaergaard, Henrik G.
    Ehn, Mikael
    Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol2019In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 119, no 6, p. 3472-3509Article, review/survey (Refereed)
    Abstract [en]

    Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earths radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.

  • 2. Buchholz, Angela
    et al.
    Lambe, Andrew T.
    Ylisirniö, Arttu
    Li, Zijun
    Tikkanen, Olli-Pekka
    Faiola, Celia
    Kari, Eetu
    Hao, Liqing
    Luoma, Olli
    Huang, Wei
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Karlsruhe Institute of Technology, Germany.
    Worsnop, Douglas R.
    Nizkorodov, Sergey A.
    Yli-Juuti, Taina
    Schobesberger, Siegfried
    Virtanen, Annele
    Insights into the O: C-dependent mechanisms controlling the evaporation of alpha-pinene secondary organic aerosol particles2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 6, p. 4061-4073Article in journal (Refereed)
    Abstract [en]

    The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced alpha-pinene SOA with three different oxidation levels (characterized by average oxygen-to-carbon ratio; (O:C) over bar = 0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH < 2 %, 40 %, and 80 %) and used a filter-based thermal desorption method to gain volatility and chemical composition information. We observed reduced particle evaporation for particles with increasing <(O:C )over bar> ratio, indicating that particles become more resilient to evaporation with oxidative aging. Particle evaporation was increased in the presence of water vapour and presumably particulate water; at the same time the resistance of the residual particles to thermal desorption was increased as well. For SOA with (O:C ) over bar = 0.96, the unexpectedly large increase in mean thermal desorption temperature and changes in the thermogram shapes under wet conditions (80 % RH) were an indication of aqueous phase chemistry. For the lower (O:C ) over bar cases, some water-induced composition changes were observed. However, the enhanced evaporation under wet conditions could be explained by the reduction in particle viscosity from the semi-solid to liquid-like range, and the observed higher desorption temperature of the residual particles is a direct consequence of the increased removal of high-volatility and the continued presence of low-volatility compounds.

  • 3. D'Ambro, Emma L.
    et al.
    Schobesberger, Siegfried
    Zaveri, Rahul A.
    Shilling, John E.
    Lee, Ben Hwan
    Lopez-Hilfiker, Felipe D.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Washington, United States.
    Thornton, Joel A.
    Isothermal Evaporation of alpha-Pinene Ozonolysis SOA: Volatility, Phase State, and Oligomeric Composition2018In: ACS earth and space chemistry, ISSN 2472-3452, Vol. 2, no 10, p. 1058-1067Article in journal (Refereed)
    Abstract [en]

    We present measurements of the isothermal evaporation of alpha-pinee ozonolysis secondary organic aerosol (SOA). Using a novel, filter-based method, we reproduce literature observations of the time-dependent evaporation of SOA particles. We apply two detailed physical models to interpret the evaporative behavior of both the bulk SOA and individual components. Both models find that a combination of effectively nonvolatile products, together with reversibly formed oligomers (or otherwise reactive monomers) having a decomposition lifetime of 9 to 28 h, best explains the evolution of composition and volatility as particles age in the absence of both organic vapors and oxidants, even under an assumption of relatively viscous (soft wax-like with a minimum diffusion coefficient of 1 x 10(-5) cm(2) s(-1)) particles. We find that the residence time in the SOA formation chamber and time spent undergoing isothermal evaporation, both indicative of the physical age of the aerosol, are the most important experimental parameters determining the evaporation rate. The evolution of volatility observed in these experiments is compared to field measurements in a boreal forest site. The ambient monoterpene-dominated SOA volatility is only reproduced in the laboratory after 24 h of extended aging in a dilute, dark, oxidant-free environment.

  • 4. Huang, Wei
    et al.
    Saathoff, Harald
    Pajunoja, Aki
    Shen, Xiaoli
    Naumann, Karl-Heinz
    Wagner, Robert
    Virtanen, Annele
    Leisner, Thomas
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Karlsruhe Institute of Technology, Germany.
    alpha-Pinene secondary organic aerosol at low temperature: chemical composition and implications for particle viscosity2018In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 4, p. 2883-2898Article in journal (Refereed)
    Abstract [en]

    Chemical composition, size distributions, and degree of oligomerization of secondary organic aerosol (SOA) from alpha-pinene (C10H16) ozonolysis were investigated for low-temperature conditions (223 K). Two types of experiments were performed using two simulation chambers at the Karlsruhe Institute of Technology: the Aerosol Preparation and Characterization (APC) chamber, and the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber. Experiment type 1 simulated SOA formation at upper tropospheric conditions: SOA was generated in the AIDA chamber directly at 223K at 61% relative humidity (RH; experiment termed cold humid, CH) and for comparison at 6% RH (experiment termed cold dry, CD) conditions. Experiment type 2 simulated SOA uplifting: SOA was formed in the APC chamber at room temperature (296 K) and < 1% RH (experiment termed warm dry, WD) or 21% RH (experiment termed warm humid, WH) conditions, and then partially transferred to the AIDA chamber kept at 223 K, and 61% RH (WDtoCH) or 30% RH (WHtoCH), respectively. Precursor concentrations varied between 0.7 and 2.2 ppm alpha-pinene, and between 2.3 and 1.8 ppm ozone for type 1 and type 2 experiments, respectively. Among other instrumentation, a chemical ionization mass spectrometer (CIMS) coupled to a filter inlet for gases and aerosols (FIGAERO), deploying I as reagent ion, was used for SOA chemical composition analysis.

    For type 1 experiments with lower alpha-pinene concentrations and cold SOA formation temperature (223 K), smaller particles of 100-300 nm vacuum aerodynamic diameter (d(va)/and higher mass fractions (> 40 %) of adducts (molecules with more than 10 carbon atoms) of alpha-pinene oxidation products were observed. For type 2 experiments with higher alpha-pinene concentrations and warm SOA formation temperature (296 K), larger particles (similar to 500 nm d(va)/with smaller mass fractions of adducts (< 35 %) were produced.

    We also observed differences (up to 20 degrees C) in maximum desorption temperature (T-max/of individual compounds desorbing from the particles deposited on the FIGAERO Teflon filter for different experiments, indicating that T-max is not purely a function of a compound's vapor pressure or volatility, but is also influenced by diffusion limitations within the particles (particle viscosity), interactions between particles deposited on the filter (particle matrix), and/or particle mass on the filter. Highest T max were observed for SOA under dry conditions and with higher adduct mass fraction; lowest T-max were observed for SOA under humid conditions and with lower adduct mass fraction. The observations indicate that particle viscosity may be influenced by intra-and inter-molecular hydrogen bonding between oligomers, and particle water uptake, even under such low-temperature conditions.

    Our results suggest that particle physicochemical properties such as viscosity and oligomer content mutually influence each other, and that variation in T-max of particle desorptions may have implications for particle viscosity and particle matrix effects. The differences in particle physicochemical properties observed between our different experiments demonstrate the importance of taking experimental conditions into consideration when interpreting data from laboratory studies or using them as input in climate models.

  • 5. Huang, Wei
    et al.
    Saathoff, Harald
    Shen, Xiaoli
    Ramisetty, Ramakrishna
    Leisner, Thomas
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Chemical Characterization of Highly Functionalized Organonitrates Contributing to Night-Time Organic Aerosol Mass Loadings and Particle Growth2019In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 53, no 3, p. 1165-1174Article in journal (Refereed)
    Abstract [en]

    Reactions of volatile organic compounds (VOC) with NO3 radicals and of reactive intermediates of oxidized VOC with NO can lead to the formation of highly functionalized organonitrates (ON). We present quantitative and chemical information on ON contributing to high nighttime organic aerosol (OA) mass concentrations measured during July-August 2016 in a rural area in southwest Germany. A filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS) was used to analyze the molecular composition of ON in both the gas and particle phase. We find larger contributions of ON to OA mass during the night. Identified ON are highly functionalized, with 4 to 12 oxygen atoms. The diel patterns of ON compounds with 5, 7, 10, or 15 carbon atoms per molecule vary, indicating a corresponding behavior of their potential precursor VOC. The temporal behavior of ON after sunset correlates with that of the number concentration of ultrafine particles, indicating a potential role of ON in night-time new particle formation (NPF) regularly observed at this location. We estimate an ON contribution of 18-25% to the mass increase of newly formed particles after sunset. Our study provides insights into the chemical composition of highly functionalized ON in the rural atmosphere and the role of anthropogenic emissions for night-time SOA formation in an area where biogenic VOC emissions dominate.

  • 6. Huang, Wei
    et al.
    Saathoff, Harald
    Shen, Xiaoli
    Ramisetty, Ramakrishna
    Leisner, Thomas
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Seasonal characteristics of organic aerosol chemical composition and volatility in Stuttgart, Germany2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 18, p. 11687-11700Article in journal (Refereed)
    Abstract [en]

    The chemical composition and volatility of organic aerosol (OA) particles were investigated during July-August 2017 and February-March 2018 in the city of Stuttgart, one of the most polluted cities in Germany. Total non-refractory particle mass was measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS; hereafter AMS). Aerosol particles were collected on filters and analyzed in the laboratory with a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS; hereafter CIMS), yielding the molecular composition of oxygenated OA (OOA) compounds. While the average organic mass loadings are lower in the summer period (5.1 +/- 3.2 mu g m(-3)) than in the winter period (8.4 +/- 5.6 mu g m(-3)), we find relatively larger mass contributions of organics measured by AMS in summer (68.8 +/- 13.4 %) compared to winter (34.8 +/- 9.5 %). CIMS mass spectra show OOA compounds in summer have O : C of 0.82 +/- 0.02 and are more influenced by biogenic emissions, while OOA compounds in winter have O : C of 0.89 +/- 0.06 and are more influenced by biomass burning emissions. Volatility parametrization analysis shows that OOA in winter is less volatile with higher contributions of low-volatility organic compounds (LVOCs) and extremely low-volatility organic compounds (ELVOCs). We partially explain this by the higher contributions of compounds with shorter carbon chain lengths and a higher number of oxygen atoms, i.e., higher O : C in winter. Organic compounds desorbing from the particles deposited on the filter samples also exhibit a shift of signal to higher desorption temperatures (i.e., lower apparent volatility) in winter. This is consistent with the relatively higher O : C in winter but may also be related to higher particle viscosity due to the higher contributions of larger-molecular-weight LVOCs and ELVOCs, interactions between different species and/or particles (particle matrix), and/or thermal decomposition of larger molecules. The results suggest that whereas lower temperature in winter may lead to increased partitioning of semi-volatile organic compounds (SVOCs) into the particle phase, this does not result in a higher overall volatility of OOA in winter and that the difference in sources and/or chemistry between the seasons plays a more important role. Our study provides insights into the seasonal variation of the molecular composition and volatility of ambient OA particles and into their potential sources.

  • 7. Lopez-Hilfiker, Felipe D.
    et al.
    Pospisilova, Veronika
    Huang, Wei
    Kalberer, Markus
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Stefenelli, Giulia
    Thornton, Joel A.
    Baltensperger, Urs
    Prevot, Andre S. H.
    Slowik, Jay G.
    An extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for online measurement of atmospheric aerosol particles2019In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 12, no 9, p. 4867-4886Article in journal (Refereed)
    Abstract [en]

    Real-time, online measurements of atmospheric organic aerosol (OA) composition are an essential tool for determining the emissions sources and physicochemical processes governing aerosol effects on climate and health. However, the reliance of current techniques on thermal desorption, hard ionization, and/or separated collection/analysis stages introduces significant uncertainties into OA composition measurements, hindering progress towards these goals. To address this gap, we present a novel, field-deployable extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF), which provides online, near-molecular (i.e., molecular formula) OA measurements at atmospherically relevant concentrations without analyte fragmentation or decomposition. Aerosol particles are continuously sampled into the EESI-TOF, where they intersect a spray of charged droplets generated by a conventional electrospray probe. Soluble components are extracted and then ionized as the droplets are evaporated. The EESI-TOF achieves a linear response to mass, with detection limits on the order of 1 to 10 ng m(-3) in 5 s for typical atmospherically relevant compounds. In contrast to conventional electrospray systems, the EESI-TOF response is not significantly affected by a changing OA matrix for the systems investigated. A slight decrease in sensitivity in response to increasing absolute humidity is observed for some ions. Although the relative sensitivities to a variety of commercially available organic standards vary by more than a factor of 30, the bulk sensitivity to secondary organic aerosol generated from individual precursor gases varies by only a factor of 15. Further, the ratio of compound-by-compound sensitivities between the EESI-TOF and an iodide adduct FIGAERO-I-CIMS varies by only +/- 50%, suggesting that EESI-TOF mass spectra indeed reflect the actual distribution of detectable compounds in the particle phase. Successful deployments of the EESI-TOF for laboratory environmental chamber measurements, ground-based ambient sampling, and proof-of-concept measurements aboard a research aircraft highlight the versatility and potential of the EESI-TOF system.

  • 8. Lutz, Anna
    et al.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Le Breton, Michael
    Lopez-Hilfiker, Felipe D.
    Priestley, Michael
    Thornton, Joel A.
    Hallquist, Mattias
    Gas to Particle Partitioning of Organic Acids in the Boreal Atmosphere2019In: Acs Earth and Space Chemistry, ISSN 2472-3452, Vol. 3, no 7, p. 1279-1287Article in journal (Refereed)
    Abstract [en]

    Gas to particle partitioning of carboxylic acids was investigated using a high-resolution chemical ionization time-of-flight mass spectrometer (HR-CI-ToF-MS) with the filter inlet for gases and aerosol (FIGAERO). Specifically, the partitioning coefficients of 640 components with unique molecular composition were calculated from an assumed linear relationship between [particle]/[gas] versus the mass of the organic fraction (M-org) according to Raoult's law, i.e., equilibrium phase partitioning. We demonstrate that, using the full data set, most of the compounds do not follow a linear relationship. This is especially the case for low- and high-molecular-weight species. Using a subset of the data, with concurrent low sulfate ambient observations ([SO42- < 0.4 mu g m(-3)), the relationship improved significantly and K-i could be derived from the slope of a linear regression to the data. The 100 species with the highest R-2 (>= 0.7) of this regression are presented. The restrictions during high sulfate conditions can be explained by changes in either the equilibrium conditions (e.g., the activity coeffient, gamma(i)) or uptake kinetics (mass transfer limitation). This study demonstrates that partitioning of compounds in the complex ambient atmosphere follows ideal Raoult's law for some limited conditions and stresses the need for studies also in more polluted environments.

  • 9.
    Mohr, Claudia
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Thornton, Joel A.
    Heitto, Arto
    Lopez-Hilfiker, Felipe D.
    Lutz, Anna
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hong, Juan
    Donahue, Neil M.
    Hallquist, Mattias
    Petaja, Tuukka
    Kulmala, Markku
    Yli-Juuti, Taina
    Molecular identification of organic vapors driving atmospheric nanoparticle growth2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 4442Article in journal (Refereed)
    Abstract [en]

    Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50 nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.

  • 10. Pospisilova, V.
    et al.
    Lopez-Hilfiker, F. D.
    Bell, D. M.
    El Haddad, I
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Huang, W.
    Heikkinen, L.
    Xiao, M.
    Dommen, J.
    Prevot, A. S. H.
    Baltensperger, U.
    Slowik, J. G.
    On the fate of oxygenated organic molecules in atmospheric aerosol particles2020In: Science Advances, E-ISSN 2375-2548, Vol. 6, no 11, article id eaax8922Article in journal (Refereed)
    Abstract [en]

    Highly oxygenated organic molecules (HOMs) are formed from the oxidation of biogenic and anthropogenic gases and affect Earth's climate and air quality by their key role in particle formation and growth. While the formation of these molecules in the gas phase has been extensively studied, the complexity of organic aerosol (OA) and lack of suitable measurement techniques have hindered the investigation of their fate post-condensation, although further reactions have been proposed. We report here novel real-time measurements of these species in the particle phase, achieved using our recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF). Our results reveal that condensed-phase reactions rapidly alter OA composition and the contribution of HOMs to the particle mass. In consequence, the atmospheric fate of HOMs cannot be described solely in terms of volatility, but particle-phase reactions must be considered to describe HOM effects on the overall particle life cycle and global carbon budget.

  • 11. Ramisetty, Ramakrishna
    et al.
    Abdelmonem, Ahmed
    Shen, Xiaoli
    Saathoff, Harald
    Leisner, Thomas
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Karlsruhe Institute of Technology, Germany.
    Exploring femtosecond laser ablation in single-particle aerosol mass spectrometry2018In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 11, no 7, p. 4345-4360Article in journal (Refereed)
    Abstract [en]

    Size, composition, and mixing state of individual aerosol particles can be analysed in real time using single-article mass spectrometry (SPMS). In SPMS, laser ablation is the most widely used method for desorption and ionization of particle components, often realizing both in one single step. Excimer lasers are well suited for this task due to their relatively high power density (10(7)-10(10)Wcm(-2)) in nanosecond (ns) pulses at ultraviolet (UV) wavelengths and short triggering times. However, varying particle optical properties and matrix effects make a quantitative interpretation of this analytical approach challenging. In atmospheric SPMS applications, this influences both the mass fraction of an individual particle that is ablated, as well as the resulting mass spectral fragmentation pattern of the ablated material. The present study explores the use of shorter (femtosecond, fs) laser pulses for atmospheric SPMS. Its objective is to assess whether the higher laser power density of the fs laser leads to a more complete ionization of the entire particle and higher ion signal and thus improvement in the quantitative abilities of SPMS. We systematically investigate the influence of power density and pulse duration on airborne particle (polystyrene latex, SiO2, NH4NO3, NaCl, and custom-made core-shell particles) ablation and reproducibility of mass spectral signatures. We used a laser ablation aerosol time-of-flight single-particle mass spectrometer (LAAPTOF, AeroMegt GmbH), originally equipped with an excimer laser (wavelength 193 nm, pulse width 8 ns, pulse energy 4 mJ), and coupled it to an fs laser (Spectra Physics Solstice-100F ultrafast laser) with similar pulse energy but longer wavelengths (266 nm with 100 fs and 0.2 mJ, 800 nm with 100 fs and 3.2 mJ). We successfully coupled the free-firing fs laser with the single-particle mass spectrometer employing the fs laser light scattered by the particle to trigger mass spectra acquisition. Generally, mass spectra exhibit an increase in ion intensities (factor 1 to 5) with increasing laser power density (similar to 10(9) to similar to 10(13)Wcm(-2)/from ns to fs laser. At the same time, fs-laser ablation produces spectra with larger ion fragments and ion clusters as well as clusters with oxygen, which does not render spectra interpretation more simple compared to ns-laser ablation. The idea that the higher power density of the fs laser leads to a more complete particle ablation and ionization could not be substantiated in this study. Quantification of ablated material remains difficult due to incomplete ionization of the particle. Furthermore, the fs-laser application still suffers from limitations in triggering it in a useful time frame. Further studies are needed to test potential advantages of fs-over ns-laser ablation in SPMS.

  • 12. Schobesberger, Siegfried
    et al.
    D'Ambro, Emma L.
    Lopez-Hilfiker, Felipe D.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Washington, USA.
    Thornton, Joel A.
    A model framework to retrieve thermodynamic and kinetic properties of organic aerosol from composition-resolved thermal desorption measurements2018In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 20, p. 14757-14785Article in journal (Refereed)
    Abstract [en]

    Chemical ionization mass spectrometer (CIMS) techniques have been developed that allow for quantitative and composition-resolved measurements of organic compounds as they desorb from secondary organic aerosol (SOA) particles, in particular during their heat-induced evaporation. One such technique employs the Filter Inlet for Gases and AEROsol (FIGAERO). Here, we present a newly developed model framework with the main aim of reproducing FIGAERO-CIMS thermograms: signal vs. ramped desorption temperature. The model simulates the desorption of organic compounds during controlled heating of filter-sampled SOA particles, plus the subsequent transport of these compounds through the FIGAERO manifold into an iodide-CIMS. Desorption is described by a modified Hertz-Knudsen equation and controlled chiefly by the temperature-dependent saturation concentration C*, mass accommodation (evaporation) coefficient, and particle surface area. Subsequent transport is governed by interactions with filter and manifold surfaces. Reversible accretion reactions (oligomer formation and decomposition) and thermal decomposition are formally described following the Arrhenius relation. We use calibration experiments to tune instrument-specific parameters and then apply the model to a test case: measurements of SOA generated from dark ozonolysis of alpha-pinene. We then discuss the ability of the model to describe thermograms from simple calibration experiments and from complex SOA, and the associated implications for the chemical and physical properties of the SOA. For major individual compositions observed in our SOA test case (#C = 8 to 10), the thermogram peaks can typically be described by assigning C*(25 degrees C) values in the range 0.05 to 5 mu g m(-3), leaving the larger, high-temperature fractions (> 50 %) of the thermograms to be described by thermal decomposition, with dissociation rates on the order of similar to 1 h 1 at 25 degrees C. We conclude with specific experimental designs to better constrain instrumental model parameters and to aid in resolving remaining ambiguities in the interpretation of more complex SOA thermogram behaviors. The model allows retrieval of quantitative volatility and mass transport information from FIGAERO thermograms, and for examining the effects of various environmental or chemical conditions on such properties.

  • 13. Shen, Xiaoli
    et al.
    Saathoff, Harald
    Huang, Wei
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Karlsruhe Institute of Technology, Germany.
    Ramisetty, Ramakrishna
    Leisner, Thomas
    Understanding atmospheric aerosol particles with improved particle identification and quantification by single-particle mass spectrometry2019In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 12, no 4, p. 2219-2240Article in journal (Refereed)
    Abstract [en]

    Single-particle mass spectrometry (SPMS) is a widely used tool to determine chemical composition and mixing state of aerosol particles in the atmosphere. During a 6-week field campaign in summer 2016 at a rural site in the upper Rhine valley, near the city of Karlsruhe in southwest Germany, similar to 3.7 x 10(5) single particles were analysed using a laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). Combining fuzzy classification, marker peaks, typical peak ratios, and laboratory-based reference spectra, seven major particle classes were identified. With the precise particle identification and well-characterized laboratory-derived overall detection efficiency (ODE) for this instrument, particle similarity can be transferred into corrected number and mass fractions without the need of a reference instrument in the field. Considering the entire measurement period, aged-biomass-burning and soil-dust-like particles dominated the particle number (45.0% number fraction) and mass (31.8% mass fraction); sodium-salt-like particles were the second lowest in number (3.4 %) but the second dominating class in terms of particle mass (30.1 %). This difference demonstrates the crucial role of particle number counts' correction for mass quantification using SPMS data. Using corrections for size-resolved and chemically resolved ODE, the total mass of the particles measured by LAAPTOF accounts for 23 %-68% of the total mass measured by an aerosol mass spectrometer (AMS) depending on the measurement periods. These two mass spectrometers show a good correlation (Pearson's correlation coefficient gamma > 0.6) regarding total mass for more than 85% of the measurement time, indicating non-refractory species measured by AMS may originate from particles consisting of internally mixed non-refractory and refractory components. In addition, specific relationships of LAAPTOF ion intensities and AMS mass concentrations for non-refractory compounds were found for specific measurement periods, especially for the fraction of org / (org + nitrate). Furthermore, our approach allows the non-refractory compounds measured by AMS to be assigned to different particle classes. Overall AMS nitrate mainly arose from sodium-salt-like particles, while aged-biomass-burning particles were dominant during events with high organic aerosol particle concentrations.

  • 14. Shen, Xiaoli
    et al.
    Vogel, Heike
    Vogel, Bernhard
    Huang, Wei
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ramisetty, Ramakrishna
    Leisner, Thomas
    Prévôt, André S. H.
    Saathoff, Harald
    Composition and origin of PM2.5 aerosol particles in the upper Rhine valley in summer2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 20, p. 13189-13208Article in journal (Refereed)
    Abstract [en]

    We conducted a 6-week measurement campaign in summer 2016 at a rural site about 11 km north of the city of Karlsruhe in southwest Germany in order to study the chemical composition and origin of aerosols in the upper Rhine valley. In particular, we deployed a single-particle mass spectrometer (LAAPTOF) and an aerosol mass spectrometer (AMS) to provide complementary chemical information on aerosol particles smaller than 2.5 mu m. For the entire measurement period, the total aerosol particle mass was dominated by sodium salts, contributing on average (36 +/- 27) % to the total single particles measured by the LAAPTOF. The total particulate organic compounds, sulfate, nitrate, and ammonium contributed on average (58 +/- 12) %, (22 +/- 7) %, (10 +/- 1) %, and (9 +/- 3) % to the total non-refractory particle mass measured by the AMS. Positive matrix factorization (PMF) analysis for the AMS data suggests that the total organic aerosol (OA) consisted of five components, including (9 +/- 7) % hydrocarbon-like OA (HOA), (16 +/- 11) % semi-volatile oxygenated OA (SV-OOA), and (75 +/- 15) % low-volatility oxygenated OA (LV-OOA). The regional transport model COSMO-ART was applied for source apportionment and to achieve a better understanding of the impact of complex transport patterns on the field observations. Combining field observations and model simulations, we attributed high particle numbers and SO2 concentrations observed at this rural site to industrial emissions from power plants and a refinery in Karlsruhe. In addition, two characteristic episodes with aerosol particle mass dominated by sodium salts particles comprising (70 +/- 24) % of the total single particles and organic compounds accounting for (77 +/- 6) % of total non-refractory species, respectively, were investigated in detail. For the first episode, we identified relatively fresh and aged sea salt particles originating from the Atlantic Ocean more than 800 km away. These particles showed markers like m/z 129 C5H7NO3+, indicating the influence of anthropogenic emissions modifying their composition, e.g. from chloride to nitrate salts during the long-range transport. For a 3 d episode including high organic mass concentrations, model simulations show that on average (74 +/- 7) % of the particulate organics at this site were of biogenic origin. Detailed model analysis allowed us to find out that three subsequent peaks of high organic mass concentrations originated from different sources, including local emissions from the city and industrial area of Karlsruhe, regional transport from the city of Stuttgart (similar to 64 km away), and potential local night-time formation and growth. Biogenic (forest) and anthropogenic (urban) emissions were mixed during transport and contributed to the formation of organic particles. In addition, topography, temperature inversion, and stagnant meteorological conditions also played a role in the build-up of higher organic particle mass concentrations. Furthermore, the model was evaluated using field observations and corresponding sensitivity tests. The model results show good agreement with trends and concentrations observed for several trace gases (e.g. O-3, NO2, and SO2) and aerosol particle compounds (e.g. ammonium and nitrate). However, the model underestimates the number of particles by an order of magnitude and underestimates the mass of organic particles by a factor of 2.3. The discrepancy was expected for particle number since the model does not include all nucleation processes. The missing organic mass indicates either an underestimated regional background or missing sources and/or mechanisms in the model, like night-time chemistry. This study demonstrates the potential of combining comprehensive field observations with dedicated transport modelling to understand the chemical composition and complex origin of aerosols.

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