| 1. |
- Andersson, August
(författare)
-
A Model for the Spectral Dependence of Aerosol Sunlight Absorption
- 2017
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 1:9, s. 533-539
-
Tidskriftsartikel (refereegranskat)abstract
- Sunlight-absorbing aerosols, e.g., black and brown carbon (BC and BrC), have a potentially large, but highly uncertain contribution to climate warming. The spectral dependence of the aerosol absorption in the visible and near-UV regime is almost universally well-described with a heuristic power law, where the exponent is termed the absorption Angstrom exponent. However, the 2 underlying physicochemical causes for this relation are unknown. Here, a model is presented that predicts the emergence of the power law spectral dependence and unifies the absorption behavior of BC and BrC. Building on the theory of light absorption in amorphous materials, the interaction between multiple functional groups upon absorption is predicted to be a key feature for this broad spectral dependence. This aerosol amorphous absorption model is in agreement with recent empirical findings and provides a conceptual basis for the additional research needed to better constrain the optical properties of light-absorbing aerosols and their environmental impact.
|
|
| 2. |
- Boström, M., et al.
(författare)
-
Dispersion Forces Stabilize Ice Coatings at Certain Gas Hydrate Interfaces That Prevent Water Wetting
- 2019
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society. - 2472-3452. ; 3:6, s. 1014-1022
-
Tidskriftsartikel (refereegranskat)abstract
- Gas hydrates formed in oceans and permafrost occur in vast quantities on Earth representing both a massive potential fuel source and a large threat in climate forecasts. They have been predicted to be important on other bodies in our solar systems such as Enceladus, a moon of Saturn. CO 2 -hydrates likely drive the massive gas-rich water plumes seen and sampled by the spacecraft Cassini, and the source of these hydrates is thought to be due to buoyant gas hydrate particles. Dispersion forces can in some cases cause gas hydrates at thermal equilibrium to be coated in a 3-4 nm thick film of ice, or to contact water directly, depending on which gas they contain. As an example, the results are valid at a quadruple point of the water-CO 2 gas hydrate system, where a film is formed not only for the model with pure ice but also in the presence of impurities in water or in the ice layer. These films are shown to significantly alter the properties of the gas hydrate clusters, for example, whether they float or sink. It is also expected to influence gas hydrate growth and gas leakage.
|
|
| 3. |
- Brownwood, B., et al.
(författare)
-
Gas-Particle Partitioning and SOA Yields of Organonitrate Products from NO3-Initiated Oxidation of Isoprene under Varied Chemical Regimes
- 2021
-
Ingår i: Acs Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 5:4, s. 785-800
-
Tidskriftsartikel (refereegranskat)abstract
- Alkyl nitrate (AN) and secondary organic aerosol (SOA) from the reaction of nitrate radicals (NO3) with isoprene were observed in the Simulation of Atmospheric PHotochemistry In a large Reaction (SAPHIR) chamber during the NO(3)Isop campaign in August 2018. Based on 15 day-long experiments under various reaction conditions, we conclude that the reaction has a nominally unity molar AN yield (observed range 90 +/- 40%) and an SOA mass yield of OA + organic nitrate aerosol of 13-15% (with similar to 50 mu g m(-3) inorganic seed aerosol and 2-5 mu g m-3 total organic aerosol). Isoprene (5-25 ppb) and oxidant (typically similar to 100 ppb O-3 and 5-25 ppb NO2) concentrations and aerosol composition (inorganic and organic coating) were varied while remaining close to ambient conditions, producing similar AN and SOA yields under all regimes. We observe the formation of dinitrates upon oxidation of the second double bond only once the isoprene precursor is fully consumed. We determine the bulk partitioning coefficient for ANs (K-p similar to 10(-3) m(3) mu g(-1)), indicating an average volatility corresponding to a C-5 hydroxy hydroperoxy nitrate.
|
|
| 4. |
- Conrad, Sarah, et al.
(författare)
-
Seasonal Variations of Redox State in Hemiboreal Soils Indicated by Changes of δ56Fe, Sulfate, and Nitrate in Headwater Streams
- 2019
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 3:12, s. 2816-2823
-
Tidskriftsartikel (refereegranskat)abstract
- During recent decades, much focus has been put on the iron (Fe) isotope ratios in soils, rivers, and oceans, while studies on the variation in headwater streams are scarce. Here we assess seasonal water chemical data from 104 hemiboreal headwater streams. Between summer and late autumn, decreasing Fe concentrations and simultaneously increasing sulfate and nitrate concentrations suggest a shift from reduced to oxidized conditions in the soils along the main groundwater flow paths. Fe isotope data, obtained from a subpopulation of 16 streams, show low δ56Fe ratios during summer drought, indicating an important influx of reduced groundwater to the streams with primarily Fe(II) as an important Fe source. In total, the δ56Fe data ranged between −0.8 ± 0.1 and 1.8 ± 0.1‰ with the lowest values in summer and maximum δ56Fe ratios in late autumn or spring, indicating an influx of more oxidized, less Fe(II) rich groundwater during those seasons. Local differences in δ56Fe ratios between the headwater streams, seemed to be driven by the different soil redox status of the catchments. The streams with the lowest δ56Fe ratios during summer are characterized by a small share (4.4 ± 6.6%) of wetlands, indicating discharge of reduced groundwater from mainly anoxic, moist, organic-rich mineral soils during drought. Relatively high total organic carbon (TOC) concentrations (2.4 ± 1.1 mM) and low pH (5.2 ± 0.8) may have restricted efficient Fe(II) oxidation in streamwater especially during the late autumn survey. Our results from hemiboreal headwater streams reveal the importance of climatic, pedogenic, and land cover-derived controls on the provenance of stream Fe loads that is likely broadly applicable to similar streams elsewhere.
|
|
| 5. |
- D'Ambro, Emma L., et al.
(författare)
-
Isothermal Evaporation of alpha-Pinene Ozonolysis SOA : Volatility, Phase State, and Oligomeric Composition
- 2018
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 2:10, s. 1058-1067
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Falcinelli, Stefano, et al.
(författare)
-
The Fragmentation Dynamics of Simple Organic Molecules of Astrochemical Interest Interacting with VUV Photons
- 2019
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 3:9, s. 1862-1872
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation on the fragmentation dynamics following the double photoionization of simple organic molecules of astrochemical interest, propylene oxide and N-methylformamide molecules, induced by VUV photons has been reported. Experiments used linearly polarized light in the 18–37 eV (propylene oxide) and 26–45 eV (N-methylformamide) photon energy range at the ELETTRA Synchrotron Facility of Trieste (Italy), coupling ion imaging and electron–ion–ion coincidence techniques with time-of-flight mass spectrometry. In the case of propylene oxide, six different two-body fragmentation processes have been recorded with the formation of CH2+/C2H4O+, CH3+/C2H3O+, O+/C3H6+, OH+/C3H5+, C2H3+/CH3O+, C2H4+/CH2O+ ion pairs. On the other hand, the double photoionization of N-methylformamide occurs producing two main fragmentation reactions, forming CH3+ + CH2NO+ and H+ + C2H4NO+. The relative cross sections and the threshold energies for all fragmentation channels are recorded as a function of the photon energy. Furthermore, in the case of the double photoionization of propylene oxide, the measure of the kinetic energy released distribution for the CH3+/C2H3O+ final ions with their angular distributions allowed the identification of a bimodal behavior indicating the possible formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. The obtained results are important to clarify the physical chemistry of the elementary processes induced by the interaction of ionizing radiations with simple organic molecules of astrochemical interest: propylene oxide and N-methylformamide.
|
|
| 7. |
|
|
| 8. |
- Graeffe, Frans, et al.
(författare)
-
Detecting and Characterizing Particulate Organic Nitrates with an Aerodyne Long-ToF Aerosol Mass Spectrometer
- 2023
-
Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 7:1, s. 230-242
-
Tidskriftsartikel (refereegranskat)abstract
- Particulate organic nitrate (pON) can be a major part of secondary organic aerosol (SOA) and is commonly quantified by indirect means from aerosol mass spectrometer (AMS) data. However, pON quantification remains challenging. Here, we set out to quantify and characterize pON in the boreal forest, through direct field observations at Station for Measuring Ecosystem Atmosphere Relationships (SMEAR) II in Hyytiälä, Finland, and targeted single-precursor laboratory studies. We utilized a long time-of-flight AMS (LToF-AMS) for aerosol chemical characterization, with a particular focus to identify CxHyOzN+ (“CHON+”) fragments. We estimate that during springtime at SMEAR II, pON (including both the organic and nitrate part) accounts for ∼10% of the particle mass concentration (calculated by the NO+/NO2+ method) and originates mainly from the NO3 radical oxidation of biogenic volatile organic compounds. The majority of the background nitrate aerosol measured is organic. The CHON+ fragment analysis was largely unsuccessful at SMEAR II, mainly due to low concentrations of the few detected fragments. However, our findings may be useful at other sites as we identified 80 unique CHON+ fragments from the laboratory measurements of SOA formed from NO3 radical oxidation of three pON precursors (β-pinene, limonene, and guaiacol). Finally, we noted a significant effect on ion identification during the LToF-AMS high-resolution data processing, resulting in too many ions being fit, depending on whether tungsten ions (W+) were used in the peak width determination. Although this phenomenon may be instrument-specific, we encourage all (LTOF-) AMS users to investigate this effect on their instrument to reduce the possibility of incorrect identifications.
|
|
| 9. |
- Gramlich, Yvette, 1993-, et al.
(författare)
-
Impact of Biomass Burning on Arctic Aerosol Composition
- 2024
-
Ingår i: ACS Earth and Space Chemistry. - 2472-3452.
-
Tidskriftsartikel (refereegranskat)abstract
- Emissions from biomass burning (BB) occurring at midlatitudes can reach the Arctic, where they influence the remote aerosol population. By using measurements of levoglucosan and black carbon, we identify seven BB events reaching Svalbard in 2020. We find that most of the BB events are significantly different to the rest of the year (nonevents) for most of the chemical and physical properties. Aerosol mass and number concentrations are enhanced by up to 1 order of magnitude during the BB events. During BB events, the submicrometer aerosol bulk composition changes from an organic- and sulfate-dominated regime to a clearly organic-dominated regime. This results in a significantly lower hygroscopicity parameter κ for BB aerosol (0.4 ± 0.2) compared to nonevents (0.5 ± 0.2), calculated from the nonrefractory aerosol composition. The organic fraction in the BB aerosol showed no significant difference for the O:C ratios (0.9 ± 0.3) compared to the year (0.9 ± 0.6). Accumulation mode particles were present during all BB events, while in the summer an additional Aitken mode was observed, indicating a mixture of the advected air mass with locally produced particles. BB tracers (vanillic, homovanillic, and hydroxybenzoic acid, nitrophenol, methylnitrophenol, and nitrocatechol) were significantly higher when air mass back trajectories passed over active fire regions in Eastern Europe, indicating agricultural and wildfires as sources. Our results suggest that the impact of BB on the Arctic aerosol depends on the season in which they occur, and agricultural and wildfires from Eastern Europe have the potential to disturb the background conditions the most.
|
|
| 10. |
- Gustafsson, Jon-Petter
(författare)
-
Competitive Arsenate and Phosphate Adsorption on Ferrihydrite as Described by the CD-MUSIC Model
- 2022
-
Ingår i: ACS Earth and space chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 6, s. 1397-1406
-
Tidskriftsartikel (refereegranskat)abstract
- The solubility and bioavailability of arsenic in the environment are to a large extent governed by adsorption reactionswith iron (hydr)oxides, the extent of which is affected by competitive interactions with other ions, for example, phosphate. Here,batch experiments were performed with ferrihydrite suspensions to determine the adsorption of arsenate [As(V)] and phosphate(PO4)atdifferent As(V)-PO4ratios. A surface complexation model based on the Charge Distribution MUltisite Ion Complexation(CD-MUSIC) concept (the"Ferrihydrite CD-MUSIC model") was developed to describe these interactions in a way consistent withresults from spectroscopic studies. For this purpose, several previously published data sets on As(V) and PO4adsorption inferrihydrite suspensions were reviewed, including a number of systems containing other major ions (CO32-and Ca2+), and newsurface complexation constants were derived. During model development, it was found that the inclusion of ternary complexes wasnot needed to describe the observed Ca2+-PO4interactions. For both As(V) and PO4, the resulting model predicts the presence ofcorner-sharing bidentate complexes as well as monodentate complexes, with the latter being important particularly at low pH. Theexperimental results showed that As(V) and PO4displayed similar adsorption patterns in the single-ion systems studied, which wereconducted using a constant anion-to-Fe ratio of 0.2. Even so, As(V) was preferentially adsorbed over PO4in competitive systems,particularly at low As(V)-to-PO4ratios when theKdvalues for As(V) were up to 2.1 times as high as those for PO4. The model,which described these patterns very well, suggests that adsorbed As(V) consists of a larger fraction of bidentate complexes than inthe case of PO4. This causes aflatter adsorption isotherm for As(V), which leads to a stronger As(V) adsorption as the As(V)-to-Feratio decreases, compared to that for PO4
|
|
