| 1. |
- Bannan, T. J., et al.
(författare)
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A method for extracting calibrated volatility information from the FIGAERO-HR-ToF-CIMS and its experimental application
- 2019
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 12:3, s. 1429-1439
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Tidskriftsartikel (refereegranskat)abstract
- The Filter Inlet for Gases and AEROsols (FIGAERO) is an inlet specifically designed to be coupled with the Aerodyne High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS). The FIGAERO-HR-ToF-CIMS provides simultaneous molecular information relating to both the gas- and particle-phase samples and has been used to extract vapour pressures (VPs) of the compounds desorbing from the filter whilst giving quantitative concentrations in the particle phase. However, such extraction of vapour pressures of the measured particle-phase components requires use of appropriate, well-defined, reference compounds. Vapour pressures for the homologous series of polyethylene glycols (PEG) ((H-(O-CH 2 CH 2 ) n -OH) for n = 3 to n = 8), covering a range of vapour pressures (VP) (10 -1 to 10 -7 Pa) that are atmospherically relevant, have been shown to be reproduced well by a range of different techniques, including Knudsen Effusion Mass Spectrometry (KEMS). This is the first homologous series of compounds for which a number of vapour pressure measurement techniques have been found to be in agreement, indicating the utility as a calibration standard, providing an ideal set of benchmark compounds for accurate characterization of the FIGAERO for extracting vapour pressure of measured compounds in chambers and the real atmosphere. To demonstrate this, single-component and mixture vapour pressure measurements are made using two FIGAERO-HR-ToF-CIMS instruments based on a new calibration determined from the PEG series. VP values extracted from both instruments agree well with those measured by KEMS and reported values from literature, validating this approach for extracting VP data from the FIGAERO. This method is then applied to chamber measurements, and the vapour pressures of known products are estimated. © 2019 Author(s).
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| 2. |
- Faxon, Cameron, et al.
(författare)
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Characterization of organic nitrate constituents of secondary organic aerosol (SOA) from nitrate-radical-initiated oxidation of limonene using high-resolution chemical ionization mass spectrometry
- 2018
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18, s. 5467-5481
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Tidskriftsartikel (refereegranskat)abstract
- The gas-phase nitrate radical (NO 3 • ) initiated oxidation of limonene can produce organic nitrate species with varying physical properties. Low-volatility products can contribute to secondary organic aerosol (SOA) formation and organic nitrates may serve as a NO x reservoir, which could be especially important in regions with high biogenic emissions. This work presents the measurement results from flow reactor studies on the reaction of NO 3 • with limonene using a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO). Major condensed-phase species were compared to those in the Master Chemical Mechanism (MCM) limonene mechanism, and many non-listed species were identified. The volatility properties of the most prevalent organic nitrates in the produced SOA were determined. Analysis of multiple experiments resulted in the identification of several dominant species (including C 10 H 15 NO 6 , C 10 H 17 NO 6 , C 8 H 11 NO 6 , C 10 H 17 NO 7 , and C 9 H 13 NO 7 ) that occurred in the SOA under all conditions considered. Additionally, the formation of dimers was consistently observed and these species resided almost completely in the particle phase. The identities of these species are discussed, and formation mechanisms are proposed. Cluster analysis of the desorption temperatures corresponding to the analyzed particle-phase species yielded at least five distinct groupings based on a combination of molecular weight and desorption profile. Overall, the results indicate that the oxidation of limonene by NO 3 • produces a complex mixture of highly oxygenated monomer and dimer products that contribute to SOA formation.
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| 3. |
- Gallego-Urrea, Julian A., 1977, et al.
(författare)
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Coagulation and sedimentation of gold nanoparticles and illite in model natural waters: Influence of initial particle concentration
- 2016
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Ingår i: NanoImpact. - : Elsevier BV. - 2452-0748. ; 3-4, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- Gold nanoparticles (AuNP) possess unique characteristics that render them adequate for applications and also to be used as a model NP to evaluate the fate and behavior at low NP concentrations due to the ease of detection by modern analytical techniques. Moreover, AuNP may result in some negative effects in the environment and there is a necessity to predict their aquatic environmental concentrations by parameterizing the underlying transport and transformation processes. This study investigated the coagulation and sedimentation of 30 nm citrate-coated AuNP under enviro-mimicking conditions, i.e. model natural freshwaters (MNW) covering the range of European water chemistries relevant for colloids and NP (major ions, pH and dissolved organic matter) and artificial seawater (ASW). Firstly, the coagulation rates of AuNP at mg/L concentrations were evaluated using time-resolved dynamic light scattering which showed a decreased rate upon addition of Suwannee river natural organic matter (SRNOM) at low ionic strength (IS) but remained relatively high at high IS. Contrastingly, AuNP approaching environmental realistic concentrations (80 μg/L) in quiescent microcosms showed slow decline rates in all MNW and ASW regardless of the presence of SRNOM, as measured by nanoparticle tracking analysis and elemental Au spectrometry. When illite was added as model natural colloid the rates of decline of AuNP remained low as well. This is owing to limited collisions at low particle number concentrations. The results show that besides IS, pH, NOM concentration and type and the intrinsic surface charge of the particles, the particle number concentration and size distribution of both AuNP and natural colloids determine the extent of the large-scale fate of NP in aquatic environments.
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| 4. |
- Gallego-Urrea, Julian A., 1977, et al.
(författare)
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Multimethod 3D characterization of natural plate-like nanoparticles: shape effects on equivalent size measurements
- 2014
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Ingår i: Journal of nanoparticle research. - : Springer Science and Business Media LLC. - 1388-0764 .- 1572-896X. ; 16:5
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Tidskriftsartikel (refereegranskat)abstract
- The fundamental properties and processes that govern nanoparticle behavior in colloidal dispersions are critical to predict their performance in applications and also their environmental and health implications. Illite is a platy clay mineral that is present in large amounts in aquatic environments and can be used as a model natural particle for environmental risk assessment. However, the high-aspect ratio of illite makes conventional analysis, usually assuming a spherical size, insufficient for the assessment of shape-dependent properties. In the current paper, a multimethod characterization of a suspension of illite particles was done using atomic force microscopy, scanning electron microscopy, dynamic light scattering (DLS), nanoparticle tracking analysis, differential centrifugal sedimentation, and centrifugal- field flow fractionation coupled to multiangle light scattering and DLS. The relation between the different measurands was investigated, and the effect of the shape on the equivalent particle size was reported. While some of the used techniques are capable of assessing the aspect ratio of illite, the results confirm the need for multiple techniques and analysis of different types of measurands especially for high-aspect-ratio particles.
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| 5. |
- Gonçalves, Sandra F., et al.
(författare)
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Effects of silver nanoparticles to the freshwater snail Physa acuta: The role of test media and snails' life cycle stage
- 2017
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Ingår i: Environmental Toxicology and Chemistry. - : Wiley. - 0730-7268 .- 1552-8618. ; 36:1, s. 243-253
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Tidskriftsartikel (refereegranskat)abstract
- Silver nanoparticles (AgNP) are highly used worldwide, which will most likely lead to their release to the environment and subsequently increase environmental concentrations. Therefore studying AgNPs' deleterious effects to organisms is crucial to understand their environmental impacts. The freshwater snail Physa acuta was chosen to evaluate the potential deleterious effects of AgNP and counterpart AgNO3, through water only exposures. AgNPs' toxicity is greatly influenced by medium composition. Thus, two test media were tested: Artificial Pond Water (APW) and modified APW (modified by removing calcium chloride from medium). Acute tests (96h) were performed with juvenile and adult snails, in both media, to assess lethality, and egg mass chronic tests, with APW medium only, to assess embryo viability and mortality, carried out until reaching 90% hatching success in the control. Acute toxicity increased with decreasing shell length for both silver forms (ion and nanoparticle), i.e. juveniles where more sensitive than adults. Different test media led to dissimilar LC50 values, with chloride playing an important role in toxicity, most probably by complexation with silver ions and thus reducing silver's bioavailability, uptake and toxicity. Chronic tests showed that hatching success was more sensitive to silver in the ionic form than in the particulate form. Different forms of silver, exposure media and life cycle stages led to different patterns of toxicity, highlighting an impairment in the snails' life cycle.
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| 6. |
- Hammes, Julia
(författare)
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Atmospheric Chemistry of Volatile Organic Compounds: Oxidation Products, Mechanisms and Secondary Organic Aerosol Formation
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The results from this work are a piece in understanding the complex puzzle of atmospheric aerosol formation. Secondary organic aerosol (SOA) formed by the oxidation of volatile organic compounds (VOC) in the atmosphere is a key component of air pollution with a strong negative impact on human health and influence on climate, but its formation is poorly understood. Because air pollution and climate change are major challenges facing modern societies, there is a clear need to better understand atmospheric SOA formation. SOA formation can be estimated from distributions of potential oxidation products, but such estimates are only as useful as the underlying chemical mechanisms and physical properties on which they are based. The work presented in this thesis was conducted to better characterize VOC oxidation products and the chemical mechanisms governing their formation. The SOA precursor compounds a-pinene and limonene (representing biogenic VOC) and 1,3,5- trimethylbenzene (TMB) (an anthropogenic VOC) were studied in the G-FROST and Go:PAM flow reactors to characterize their oxidation and the subsequent SOA-forming processes. Previously unknown compounds including dimer esters, carboxylic acids, nitrates and highly oxygenated molecules were identified using state-of-the-art mass spectrometric methods. These oxidation products were shown to be important SOA contributors and explicit mechanisms for their formation were proposed. Some of the identified compounds were suggested to be of extremely low volatility and thus important for new particle formation. Oxidation of TMB under conditions representative of urban environments reduced particle formation potential; this effect was attributed to the disruption of RO2 auto-oxidation cycles by NOx and subsequent nitrate formation at the expense of highly oxygenated molecules. During the course of this work, an automated algorithm was developed to extract compound-specific volatility data from FIGAERO thermograms. The scientific understanding of SOA formation would be greatly improved by a detailed knowledge of the products of VOC oxidation, the mechanisms by which they are formed, and their vapour pressures, all of which this work aims to contribute to.
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| 7. |
- Hammes, Julia, et al.
(författare)
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Carboxylic acids from limonene oxidation by ozone and hydroxyl radicals: insights into mechanisms derived using a FIGAERO-CIMS
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:20, s. 13037-13052
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Tidskriftsartikel (refereegranskat)abstract
- This work presents the results from a flow reactor study on the formation of carboxylic acids from limonene oxidation in the presence of ozone under NOx-free conditions in the dark. A High-Resolution Time-of-Flight acetate Chemical Ionisation Mass Spectrometer (HR-ToF-CIMS) was used in combination with a Filter Inlet for Gases and AEROsols (FIGAERO) to measure the carboxylic acids in the gas and particle phases. The results revealed that limonene oxidation produced large amounts of carboxylic acids which are important contributors to secondary organic aerosol (SOA) formation. The highest 10 acids contributed 56 %-91 % to the total gas-phase signal, and the dominant gas-phase species in most experiments were C8H12O4, C9H14O4, C7H10O4 and C10H16O3. The particle-phase composition was generally more complex than the gas-phase composition, and the highest 10 acids contributed 47 %-92 % to the total signal. The dominant species in the particle phase were C8H12O5, C9H14O5, C9H12O5 and C10H16O4. The measured concentration of dimers bearing at least one carboxylic acid function in the particle phase was very low, indicating that acidic dimers play a minor role in SOA formation via ozone (O-3)/hydroxyl (OH) oxidation of limonene. Based on the various experimental conditions, the acidic compositions for all experiments were modelled using descriptions from the Master Chemical Mechanism (MCM). The experiment and model provided a yield of large (C-7-C-10) carboxylic acid of the order of 10 % (2 %-23 % and 10 %-15 %, respectively). Significant concentrations of 11 acids, from a total of 16 acids, included in the MCM were measured with the CIMS. However, the model predictions were, in some cases, inconsistent with the measurement results, especially regarding the OH dependence. Reaction mechanisms are suggested to fill-in the knowledge gaps. Using the additional mechanisms proposed in this work, nearly 75 % of the observed gas-phase signal in our lowest concentration experiment (8.4 ppb converted, ca. 23 % acid yield) carried out under humid conditions can be understood.
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| 8. |
- Hammes, Julia, et al.
(författare)
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Geographically distributed classification of surface water chemical parameters influencing fate and behavior of nanoparticles and colloid facilitated contaminant transport.
- 2013
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354. ; 47:14, s. 5350-5361
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Tidskriftsartikel (refereegranskat)abstract
- The current production and use of nanomaterials in consumer products have increased the concern about the possibility that these enter the rivers during their entire life cycle. Further, many aquatic contaminants undergo partitioning to the ubiquitous aquatic colloids. Here is presented the development of a set of European water types for environmental risk assessment of chemicals transported as nanovectors as is the case of environmental fate of manufactured nanoparticles and colloid-bound contaminants. A compilation of river quality geochemical data with information about multi-element composition for near 800 rivers in Europe was used to perform a principal component analysis (PCA) and define 6 contrasting water classes. With the aid of geographical information system algorithms, it was possible to analyse how the different sampling locations were predominantly represented within each European water framework directive drainage basin. These water classes and their associated Debye–Hückel parameter are determining factors to evaluate the large scale fate and behaviour of nanomaterials and other colloid-transported pollutants in the European aquatic environment.
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| 9. |
- Kristensen, Kasper, et al.
(författare)
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High-Molecular Weight Dimer Esters Are Major Products in Aerosols from α-Pinene Ozonolysis and the Boreal Forest
- 2016
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 3:8, s. 280-285
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the contribution of high-molecular weight dimer esters to laboratory-generated α-pinene gas- and particle-phase secondary organic aerosol (SOA) and particulate matter (PM) collected at the Nordic boreal forest site of Hyytiälä, Finland. Laboratory flow reactor experiments (25 °C) show that dimer esters from ozonolysis of α-pinene contribute between 5 and 16% of the freshly formed α-pinene particle-phase SOA mass. An increased level of formation is observed at a higher relative humidity of ∼40%, and the presence of a hydroxyl radical (OH) scavenger is shown to affect the formation of dimer esters. Of the 28 dimer esters identified in laboratory α-pinene SOA, 15 are also observed in ambient PM samples, contributing between 0.5 and 1.6% of the total PM1. The observed esters show good correlation with known α-pinene SOA tracers in collected PM samples. This work reveals an, until now, unrecognized contribution of dimer esters from α-pinene oxidation to boreal forest PM.
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| 10. |
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