| 1. |
- Elm, Jonas, et al.
(författare)
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Formation of atmospheric molecular clusters consisting of sulfuric acid and C8H12O6 tricarboxylic acid
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:6, s. 4877-4886
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Tidskriftsartikel (refereegranskat)abstract
- Using computational methods, we investigate the formation of atmospheric clusters consisting of sulfuric acid (SA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), identified from a-pinene oxidation. The molecular structure of the clusters is obtained using three different DFT functionals (PW91, M06-2X and oB97X-D) with the 6-31++ G(d, p) basis set and the binding energies are calculated using a high level DLPNO-CCSD(T)/ Def2-QZVPP method. The stability of the clusters is evaluated based on the calculated formation free energies. The interaction between MBTCA and sulfuric acid is found to be thermodynamically favourable and clusters consisting of 2-3 MBTCA and 2-3 SA molecules are found to be particularly stable. There is a large stabilization of the cluster when the amount of sulfuric acid-carboxylic acid hydrogen bonded interactions is maximized. The reaction free energies for forming the (MBTCA) 2-3(SA) 2-3 clusters are found to be similar in magnitude to those of the formation of the sulfuric acid-dimethylamine cluster. Using cluster kinetics calculations we identify that the growth of the clusters is essentially limited by a weak formation of the largest clusters studied, implying that other stabilizing vapours are required for stable cluster formation and growth.
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| 2. |
- Krieger, Ulrich K., et al.
(författare)
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A reference data set for validating vapor pressure measurement techniques : homologous series of polyethylene glycols
- 2018
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 11:1, s. 49-63
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Tidskriftsartikel (refereegranskat)abstract
- To predict atmospheric partitioning of organic compounds between gas and aerosol particle phase based on explicit models for gas phase chemistry, saturation vapor pressures of the compounds need to be estimated. Estimation methods based on functional group contributions require training sets of compounds with well-established saturation vapor pressures. However, vapor pressures of semivolatile and low-volatility organic molecules at atmospheric temperatures reported in the literature often differ by several orders of magnitude between measurement techniques. These discrepancies exceed the stated uncertainty of each technique which is generally reported to be smaller than a factor of 2. At present, there is no general reference technique for measuring saturation vapor pressures of atmospherically relevant compounds with low vapor pressures at atmospheric temperatures. To address this problem, we measured vapor pressures with different techniques over a wide temperature range for intercomparison and to establish a reliable training set. We determined saturation vapor pressures for the homologous series of polyethylene glycols (H-(O-CH2-CH2)(n)-OH) for n = 3 to n = 8 ranging in vapor pressure at 298 K from 10(-7) to 5 x 10(-2) Pa and compare them with quantum chemistry calculations. Such a homologous series provides a reference set that covers several orders of magnitude in saturation vapor pressure, allowing a critical assessment of the lower limits of detection of vapor pressures for the different techniques as well as permitting the identification of potential sources of systematic error. Also, internal consistency within the series allows outlying data to be rejected more easily. Most of the measured vapor pressures agreed within the stated uncertainty range. Deviations mostly occurred for vapor pressure values approaching the lower detection limit of a technique. The good agreement between the measurement techniques (some of which are sensitive to the mass accommodation coefficient and some not) suggests that the mass accommodation coefficients of the studied compounds are close to unity. The quantum chemistry calculations were about 1 order of magnitude higher than the measurements. We find that extrapolation of vapor pressures from elevated to atmospheric temperatures is permissible over a range of about 100 K for these compounds, suggesting that measurements should be performed best at temperatures yielding the highest-accuracy data, allowing subsequent extrapolation to atmospheric temperatures.
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| 3. |
- Myllys, Nanna, et al.
(författare)
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Effect of Bisulfate, Ammonia, and Ammonium on the Clustering of Organic Acids and Sulfuric Acid
- 2017
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 121:25, s. 4812-4824
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of the bisulfate anion HSO4-, ammonium cation NH4+, and ammonia NH3 on the clustering of sulfuric acid and pinic acid or 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA). The systems were chosen based on their expected relevance in atmospheric new particle formation. Using quantum chemical methods together with kinetic calculations, we study the ability of these compounds to enhance cluster formation and growth. The cluster structures are obtained and frequencies are calculated using three different DFT functionals (M06-2X, PW91, and omega B97X-D) with the 6-31++G(d,p) basis set. The electronic energies are corrected using an accurate DLPNO-CCSD(T)/def2-QZVPP level of theory. The evaporation rates are evaluated based on the calculated Gibbs free energies. The interaction between the ions and sulfuric acid or carboxylic acid group is strong, and thereby small two-component ionic clusters are found to be very stable against evaporation. The presence of bisulfate stimulates the cluster formation through addition of the sulfuric acid, whereas the presence of ammonium favors the addition of organic acids. Bisulfate and ammonium enhance the first steps of cluster formation; however, at atmospheric conditions further cluster growth is limited due to the weak interaction and fast evaporation of the larger three-component clusters. On the basis of our results it is therefore unlikely that the studied organic acids and sulfuric acid, even together with bisulfate, ammonia, or ammonium can drive new-particle formation via clustering mechanisms. Other mechanisms such as chemical reactions are needed to explain observed new-particle formation events in the presence of oxidized organic compounds resembling the acids studied here.
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| 4. |
- Myllys, Nanna, et al.
(författare)
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Guanidine : A Highly Efficient Stabilizer in Atmospheric New-Particle Formation
- 2018
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:20, s. 4717-4729
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Tidskriftsartikel (refereegranskat)abstract
- The role of a strong organobase, guanidine, in sulfuric acid-driven new-particle formation is studied using state-of-the-art quantum chemical methods and molecular cluster formation simulations. Cluster formation mechanisms at the molecular level are resolved, and theoretical results on cluster stability are confirmed with mass spectrometer measurements. New-particle formation from guanidine and sulfuric acid molecules occurs without thermodynamic barriers under studied conditions, and clusters are growing close to a 1:1 composition of acid and base. Evaporation rates of the most stable clusters are extremely low, which can be explained by the proton transfers and symmetrical cluster structures. We compare the ability of guanidine and dimethylamine to enhance sulfuric acid-driven particle formation and show that more than 2000-fold concentration of dimethylamine is needed to yield as efficient particle formation as in the case of guanidine. At similar conditions, guanidine yields 8 orders of magnitude higher particle formation rates compared to dimethylamine. Highly basic compounds such as guanidine may explain experimentally observed particle formation events at low precursor vapor concentrations, whereas less basic and more abundant bases such as ammonia and amines are likely to explain measurements at high concentrations.
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| 5. |
- Myllys, Nanna, et al.
(författare)
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Molecular-Level Understanding of Synergistic Effects in Sulfuric Acid-Amine-Ammonia Mixed Clusters
- 2019
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 123:12, s. 2420-2425
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Tidskriftsartikel (refereegranskat)abstract
- The abundance and basicity of a stabilizing base have shown to be key factors in sulfuric acid driven atmospheric new-particle formation. However, since experiments indicate that a low concentration of ammonia enhances particle formation from sulfuric acid and dimethylamine, which is a stronger base, there must be additional factors affecting the particle formation efficiency. Using quantum chemistry, we provide a molecular-level explanation for the synergistic effects in sulfuric acid-dimethylamine-ammonia cluster formation. Because of the capability of ammonia to form more intermolecular interactions than dimethylamine, it can act as a bridge-former in sulfuric acid-dimethylamine clusters. In many cluster compositions, ammonia is more likely to be protonated than dimethylamine, although it is a weaker base. By nanoparticle formation rate simulations, we show that due to the synergistic effects, ammonia can increase the particle formation rate by up to 5 orders of magnitude compared to the two-component sulfuric acid-amine system.
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| 6. |
- Myllys, Nanna, et al.
(författare)
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Role of base strength, cluster structure and charge in sulfuric-acid-driven particle formation
- 2019
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:15, s. 9753-9768
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Tidskriftsartikel (refereegranskat)abstract
- In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and we systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can also stabilize small clusters for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.
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