Evolution of volatility and composition in sesquiterpene-mixed and <i>α</i>-pinene secondary organic aerosol particles during isothermal evaporation

Efforts have been spent on investigating the isothermal evaporation of α-pinene secondary organic aerosol (SOA) particles at ranges of conditions and decoupling the impacts of viscosity and volatility on evaporation. However, little is known about the evaporation behavior of SOA particles from biogenic organic compounds other than α-pinene. In this study, we investigated the isothermal evaporation behavior of the α-pinene and sesquiterpene mixture (SQTmix) SOA particles under a series of relative humidity (RH) conditions. With a set of in situ instruments, we monitored the evolution of particle size, volatility, and composition during evaporation. Our finding demonstrates that the SQTmix SOA particles evaporated slower than the α-pinene ones at any set of RH (expressed with the volume fraction remaining, VFR), which is primarily due to their lower volatility and possibly aided by higher viscosity under dry conditions. We further applied positive matrix factorization (PMF) to the thermal desorption data containing volatility and composition information. Analyzing the net change ratios (NCRs) of each PMF-resolved factor, we can quantitatively compare how each sample factor evolves with increasing evaporation time or RH. When sufficient particulate water content was present in either SOA system, the most volatile sample factor was primarily lost via evaporation, and changes in the other sample factors were mainly governed by aqueous-phase processes. The evolution of each sample factor of the SQTmix SOA particles was controlled by a single type of process, whereas for the α-pinene SOA particles it was regulated by multiple processes. As indicated by the coevolution of VFR and NCR, the effect of aqueous-phase processes could vary from one to another according to particle type, sample factors, and evaporation timescale.

The Crystal Structures of Two Hydro-closo-Borates with Divalent Tin in Comparison: Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O

Single crystals of Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O are easily accessible by reactions of aqueous solutions of the acids (H3O)2[B10H10] and (H3O)2[B12H12] with an excess of tin metal powder after isothermal evaporation of the clear brines. Both compounds crystallize with similar structures in the triclinic system with space group P$$\bar{1 }$$ 1 ¯ and Z = 2. The crystallographic main features are electroneutral $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B10H10]3/3} and $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B12H12]3/3} double chains running along the a-axes. Each Sn2+ cation is coordinated by three water molecules of hydration (d(Sn–O) = 221–225 pm for the B10 and d(Sn–O) = 222–227 pm for the B12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters (d(Sn–H) = 281–322 pm for the B10 and d(Sn–H) = 278–291 pm for the B12 compound), which complete the coordination sphere. Between these tin(II)-bonded water and the three or four interstitial crystal water molecules, classical bridging hydrogen bonds are found, connecting the double chains to each other. Furthermore, there is also non-classical hydrogen bonding between the anionic [BnHn]2− (n = 10 and 12) clusters and the crystal water molecules pursuant to B–Hδ−$$\cdots$$ ⋯ δ+H–O interactions often called dihydrogen bonds.

Evolution of volatility and composition in sesquiterpene-mixed and α-pinene secondary organic aerosol particles during isothermal evaporation

Efforts have been spent on investigating the isothermal evaporation of α-pinene SOA particles at ranges of conditions and decoupling the impacts of viscosity and volatility on evaporation. However, little is known about the evaporation behavior of SOA particles from biogenic organic compounds other than α-pinene. In this study, we investigated the isothermal evaporation behaviors of α-pinene (αpin) and sesquiterpene mixture (SQTmix) SOA particles under a series of relative humidity (RH) conditions. With a set of in-situ instruments, we monitored the evolution of particle size, volatility, and composition during evaporation. Our finding demonstrates that the SQTmix SOA particles evaporated slower than the αpin ones at any set of RH (expressed with the volume fraction remaining (VFR)), which is primarily due to their lower volatility and possibly aided by higher viscosity under dry conditions. We further applied positive matrix factorization (PMF) to thermal desorption data containing volatility and composition information. Analyzing the net change ratios (NCRs) of each PMF-resolved factor, we can quantitatively compare how each sample factor evolves with increasing evaporation time/RH. When sufficient particulate water content was present in either SOA system, the most volatile sample factor was primarily lost via evaporation and changes in other sample factors were mainly governed by aqueous-phase processes. The evolution of each sample factor of SQTmix SOA particles was controlled by a single type of process, whereas for αpin SOA particles it was regulated by multiple processes. As indicated by the coevolution of VFR and NCR, the effect of aqueous-phase processes could vary from one to another according to particle type, sample factors and evaporation timescale.

Successive Crystallization of Organically Templated Uranyl Sulfates: Synthesis and Crystal Structures of [pyH](H3O)[(UO2)3(SO4)4(H2O)2], [pyH]2[(UO2)6(SO4)7(H2O)], and [pyH]2[(UO2)2(SO4)3]

Three new uranyl sulfates, [pyH](H3O)[(UO2)3(SO4)4(H2O)2] (1), [pyH]2[(UO2)6(SO4)7(H2O)] (2), and [pyH]2[(UO2)2(SO4)3] (3), were produced upon hydrothermal treatment and successive isothermal evaporation. 1 is monoclinic, P21/c, a = 14.3640(13), b = 10.0910(9), c = 18.8690(17) Å, β = 107.795(2), V = 2604.2(4) Å3, R1 = 0.038; 2 is orthorhombic, C2221, a = 10.1992(8), b = 18.5215(14), c = 22.7187(17) Å, V = 4291.7(6) Å3, R1 = 0.030; 3 is orthorhombic, Pccn, a = 9.7998(8), b = 10.0768(8), c = 20.947(2) Å, V = 2068.5(3) Å3, R1 = 0.055. In the structures of 1 and 2, the uranium polyhedra and SO4 tetrahedra share vertices to form ∞3[(UO2)3(SO4)4(H2O)2]2− and ∞3[(UO2)6(SO4)7(H2O)]2− frameworks featuring channels (12.2 × 6.7 Å in 1 and 12.9 × 6.5 Å in 2), which are occupied by pyridinium cations. The structure of 3 is comprised of ∞2[(UO2)2(SO4)3]2− layers linked by hydrogen bonds donated by pyridinium cations. The compounds 1–3 are formed during recrystallization processes, in which the evaporation of mother liquor leads to a stepwise loss of hydration water.

Deconvolution of FIGAERO–CIMS thermal desorption profiles using positive matrix factorisation to identify chemical and physical processes during particle evaporation

The measurements of aerosol particles with a filter inlet for gases and aerosols (FIGAERO) together with a chemical ionisation mass spectrometer (CIMS) yield the overall chemical composition of the particle phase. In addition, the thermal desorption profiles obtained for each detected ion composition contain information about the volatility of the detected compounds, which is an important property for understanding many physical properties like gas–particle partitioning. We coupled this thermal desorption method with isothermal evaporation prior to the sample collection to investigate the chemical composition changes during isothermal particle evaporation and particulate-water-driven chemical reactions in α-pinene secondary organic aerosol (SOA) of three different oxidative states. The thermal desorption profiles of all detected elemental compositions were then analysed with positive matrix factorisation (PMF) to identify the drivers of the chemical composition changes observed during isothermal evaporation. The keys to this analysis were to use the error matrix as a tool to weight the parts of the data carrying most information (i.e. the peak area of each thermogram) and to run PMF on a combined data set of multiple thermograms from different experiments to enable a direct comparison of the individual factors between separate measurements. The PMF was able to identify instrument background factors and separate them from the part of the data containing particle desorption information. Additionally, PMF allowed us to separate the direct desorption of compounds detected at a specific elemental composition from other signals with the same composition that stem from the thermal decomposition of thermally instable compounds with lower volatility. For each SOA type, 7–9 factors were needed to explain the observed thermogram behaviour. The contribution of the factors depended on the prior isothermal evaporation. Decreased contributions from the factors with the lowest desorption temperatures were observed with increasing isothermal evaporation time. Thus, the factors identified by PMF could be interpreted as volatility classes. The composition changes in the particles due to isothermal evaporation could be attributed to the removal of volatile factors with very little change in the desorption profiles of the individual factors (i.e. in the respective temperatures of peak desorption, Tmax). When aqueous-phase reactions took place, PMF was able to identify a new factor that directly identified the ions affected by the chemical processes. We conducted a PMF analysis of the FIGAERO–CIMS thermal desorption data for the first time using laboratory-generated SOA particles. But this method can be applied to, for example, ambient FIGAERO–CIMS measurements as well. There, the PMF analysis of the thermal desorption data identifies organic aerosol (OA) sources (such as biomass burning or oxidation of different precursors) and types, e.g. hydrocarbon-like (HOA) or oxygenated organic aerosol (OOA). This information could also be obtained with the traditional approach, namely the PMF analysis of the mass spectra data integrated for each thermogram. But only our method can also obtain the volatility information for each OA source and type. Additionally, we can identify the contribution of thermal decomposition to the overall signal.

Topological analysis of the layered uranyl compounds bearing slabs with UO2:TO4 ratio of 2:3

Nine new templated uranyl sulfates and selenates, [(H9O4)2(H2O)][(UO2)2(SO4)3(H2O)2] (H9US), [(C5H7 NO)2(H2O)][(UO2)2(SeO4)3(H2O)2](H2O) (OUSe), [C6H6N3][H5O2] [(UO2)2(SeO4)3(H2O)] (BH5USe), [C6H6N3][H7O3][(UO2)2(SO4)3 (H2O)](H2O) (BH7US), [C6H16N][H5O2][(UO2)2(SeO4)3(H2O)] (TeH5USe), [C6H18N2][(UO2)2(SO4)3(H2O)] (TmUS), [H5O2]2 [(UO2)2(SeO4)3(H2O)](H2O) (H5USe-1), [H5O2]2[(UO2)2(SeO4)3 (H2O)2](H2O)9 (H5USe-2), and [C4H14N2][(UO2)2(SeO4)3(H2O)](H2O) (DmUSe) have been prepared by isothermal evaporation of aqueous solutions containing extra sulfuric or selenic acid. Their crystal structures can be considered as organo-inorganic hybrids constructed of alternating [(UO2)2 (TO4)3(H2O)n]2− slabs (T = Se6+, S6+, n = 1, 2) and layers containing templating organic moieties and/or hydronium ions and water molecules. The organic and inorganic parts of the structures are linked by multiple hydrogen bonds. Besides structure description, we offer topological analysis of the inorganic fragments with UO2:TO4 ratio of 2:3 as modular units resulting from self-assembly of fundamental chains formed by [(UO2)2(TO4)2] tetramers and TO4 tetrahedra.