Modeling the formation and growth of atmospheric molecular clusters : A review

Molecular clusters are ubiquitous constituents of the ambient atmosphere, that can grow into larger sizes forming new aerosol particles. The formation and growth of small clusters into aerosol particles remain one of the largest uncertainties in global climate predictions. This has made the modeling of atmospheric molecular clustering into an active field of research, yielding direct molecular level information about the formation mechanism. We review the present state of-the-art quantum chemical methods and cluster distribution dynamics models that are applied to study the formation and growth of atmospheric molecular clusters. We outline the current challenges in applying theoretical methods and the future directions to move the field forward.Peer reviewe

Psoriasis Carries an Increased Risk of Venous Thromboembolism: A Danish Nationwide Cohort Study

Psoriasis is an immunoinflammatory disease associated with cardiovascular risk factors, atherothrombotic events, and hypercoagulability. Venous thromboembolism (VTE) is potentially lethal and shares risk factors with psoriasis, but the risk of VTE associated with psoriasis is unknown. The present study investigated the potential association between psoriasis and VTE.Information from nationwide prospectively recorded registers of hospitalization, drug dispensing from pharmacies, socio-economic data, and causes of death was linked on an individual level. In an unselected nationwide cohort, we used multivariate Poisson regression models controlling for age, gender, comorbidity, concomitant medication, socio-economic data, and calendar year, to assess the risk of VTE associated with psoriasis. A total of 35,138 patients with mild and 3,526 patients with severe psoriasis were identified and compared with 4,126,075 controls. Patients with psoriasis had higher incidence rates per 1000 person-years of VTE than controls (1.29, 1.92, and 3.20 for controls, mild psoriasis, and severe psoriasis, respectively). The rate ratio (RR) of VTE was elevated in all patients with psoriasis with RR 1.35 (95% confidence interval [CI] 1.21–1.49) and RR 2.06 (CI 1.63–2.61) for mild and severe psoriasis, respectively. Exclusion of patients with malignancies, and censoring of patients undergoing surgery did not alter the results.This nationwide cohort study indicates that patients with psoriasis are at increased risk of VTE. The risk was highest in young patients with severe psoriasis. Physicians should be aware that patients with psoriasis may be at increased risk of both venous and arterial thromboembolic events

Strong Even/Odd Pattern in the Computed Gas-Phase Stability of Dicarboxylic Acid Dimers : Implications for Condensation Thermodynamics

The physical properties of small straight-chain dicarboxylic acids are well known to exhibit even/odd alternations with respect to the carbon chain length. For example, odd numbered diacids have lower melting points and higher saturation vapor pressures than adjacent even numbered diacids. This alternation has previously been explained in terms of solid-state properties, such as higher torsional strain of odd number diacids. Using quantum chemical methods, we demonstrate an additional contribution to this alternation in properties resulting from gas-phase dimer formation. Due to a combination of hydrogen bond strength and torsional strain, dimer formation in the gas phase occurs efficiently for glutaric acid (CS) and pimelic acid (C7) but is unfavorable for succinic acid (C4) and adipic acid (C6). Our results indicate that a significant fraction of the total atmospheric gas-phase concentration of glutaric and pimelic acid may consist of dimers.Peer reviewe

Strong even/odd pattern in the computed gas-phase stability of dicarboxylic acid dimers:implications for condensation thermodynamics

Abstract The physical properties of small straight-chain dicarboxylic acids are well known to exhibit even/odd alternations with respect to the carbon chain length. For example, odd numbered diacids have lower melting points and higher saturation vapor pressures than adjacent even numbered diacids. This alternation has previously been explained in terms of solid-state properties, such as higher torsional strain of odd number diacids. Using quantum chemical methods, we demonstrate an additional contribution to this alternation in properties resulting from gas-phase dimer formation. Due to a combination of hydrogen bond strength and torsional strain, dimer formation in the gas phase occurs efficiently for glutaric acid (C5) and pimelic acid (C7) but is unfavorable for succinic acid (C4) and adipic acid (C6). Our results indicate that a significant fraction of the total atmospheric gas-phase concentration of glutaric and pimelic acid may consist of dimers

The Aarhus Chamber Campaign on Highly Oxygenated Organic Molecules and Aerosols (ACCHA) : particle formation, organic acids, and dimer esters from alpha-pinene ozonolysis at different temperatures

Little is known about the effects of subzero temperatures on the formation of secondary organic aerosol (SOA) from alpha-pinene. In the current work, ozone-initiated oxidation of alpha-pinene at initial concentrations of 10 and 50 ppb, respectively, is performed at temperatures of 20, 0, and -15 degrees C in the Aarhus University Research on Aerosol (AURA) smog chamber during the Aarhus Chamber Campaign on Highly Oxygenated Organic Molecules and Aerosols (ACCHA). Herein, we show how temperature influences the formation and chemical composition of alpha-pinene-derived SOA with a specific focus on the formation of organic acids and dimer esters. With respect to particle formation, the results show significant increase in particle-formation rates, particle number concentrations, and particle mass concentrations at low temperatures. In particular, the number concentrations of sub-10 nm particles were significantly increased at the lower 0 and -15 degrees C temperatures. Temperature also affects the chemical composition of formed SOA. Here, detailed offline chemical analyses show that organic acids contribute from 15 % to 30 % by mass, with highest contributions observed at the lowest temperatures, indicative of enhanced condensation of these semivolatile species. In comparison, a total of 30 identified dimer esters were seen to contribute between 4 % and 11 % to the total SOA mass. No significant differences in the chemical composition (i.e. organic acids and dimer esters) of the alpha-pinene-derived SOA particles are observed between experiments performed at 10 and 50 ppb initial alpha-pinene concentrations, thus suggesting a higher influence of reaction temperature compared to that of alpha-pinene loading on the SOA chemical composition. Interestingly, the effect of temperature on the formation of dimer esters differs between the individual species. The formation of less oxidized dimer esters - with oxygento-carbon ratio (O : C) 0.4) is suppressed, consequently resulting in temperature-modulated composition of the a -pinene-derived SOA. Temperature ramping experiments exposing alpha-pinenederived SOA to changing temperatures (heating and cooling) reveal that the chemical composition of the SOA with respect to dimer esters is governed almost solely by the temperature at which oxidization started and is insusceptible to subsequent changes in temperature Similarly, the resulting SOA mass concentrations were found to be more influenced by the initial alpha-pinene oxidation temperatures, thus suggesting that the formation conditions to a large extent govern the type of SOA formed, rather than the conditions to which the SOA is later exposed. For the first time, we discuss the relation between the identified dimer ester and the highly oxygenated organic molecules (HOMs) measured by chemical ionization-atmospheric pressure interface-time-of-flight mass spectrometer (CI-APi-ToF) during the ACCHA experiments. We propose that, although very different in chemical structures and O : C ratios, many dimer esters and HOMs may be linked through similar RO2 reaction pathways and that dimer esters and HOMs merely represent two different fates of the RO2 radicals.Peer reviewe

Technical note:estimating aqueous solubilities and activity coefficients of mono- and α,ω-dicarboxylic acids using COSMOtherm

Abstract We have used the COSMOtherm program to estimate activity coefficients and solubilities of mono- and α,ω-dicarboxylic acids and water in binary acid–water systems. The deviation from ideality was found to be larger in the systems containing larger acids than in the systems containing smaller acids. COnductor-like Screening MOdel for Real Solvents (COSMO-RS) underestimates experimental monocarboxylic acid activity coefficients by less than a factor of 2, but experimental water activity coefficients are underestimated more especially at high acid mole fractions. We found a better agreement between COSMOtherm-estimated and experimental activity coefficients of monocarboxylic acids when the water clustering with a carboxylic acid and itself was taken into account using the dimerization, aggregation, and reaction extension (COSMO-RS-DARE) of COSMOtherm. COSMO-RS-DARE is not fully predictive, but fit parameters found here for water–water and acid–water clustering interactions can be used to estimate thermodynamic properties of monocarboxylic acids in other aqueous solvents, such as salt solutions. For the dicarboxylic acids, COSMO-RS is sufficient for predicting aqueous solubility and activity coefficients, and no fitting to experimental values is needed. This is highly beneficial for applications to atmospheric systems, as these data are typically not available for a wide range of mixing states realized in the atmosphere, due to a lack of either feasibility of the experiments or sample availability. Based on effective equilibrium constants of different clustering reactions in the binary solutions, acid dimer formation is more dominant in systems containing larger dicarboxylic acids (C₅–C₈), while for monocarboxylic acids (C₁–C₆) and smaller dicarboxylic acids (C₂–C₄), hydrate formation is more favorable, especially in dilute solutions

Thermodynamic properties of isoprene- and monoterpene-derived organosulfates estimated with COSMOtherm

Abstract Organosulfates make significant contributions to atmospheric secondary organic aerosol (SOA), but little is known about the thermodynamic properties of atmospherically relevant organosulfates. We have used the COSMOtherm program to calculate both the gas- and condensed-phase properties of previously identified atmospherically relevant monoterpene- and isoprene-derived organosulfates. Properties include solubilities, activities and saturation vapor pressures, which are critical to the aerosol-phase stability and atmospheric impact of organosulfate SOA. Based on the estimated saturation vapor pressures, the organosulfates of this study can all be categorized as semi-volatile or low-volatile, with saturation vapor pressures 4 to 8 orders of magnitude lower than that of sulfuric acid. The estimated pKa values of all the organosulfates indicate a high degree of dissociation in water, leading in turn to high dissociation-corrected solubilities. In aqueous mixtures with inorganic sulfate, COSMOtherm predicts a salting-out of both the organosulfates and their sodium salts from inorganic co-solutes. The salting-out effect of ammonium sulfate (less acidic) is stronger than of ammonium bisulfate (more acidic). Finally, COSMOtherm predicts liquid–liquid-phase separation in systems containing water and monoterpene-derived organosulfates. The COSMOtherm-estimated properties support the observed stability of organosulfates as SOA constituents and their long-range transport in the atmosphere but also show significant variation between specific compounds and ambient conditions

Glyoxal and Methylglyoxal Setschenow Salting Constants in Sulfate, Nitrate, and Chloride Solutions: Measurements and Gibbs Energies

Knowledge about Setschenow salting constants, <i>K</i>_<i>S</i>, the exponential dependence of Henry’s Law coefficients on salt concentration, is of particular importance to predict secondary organic aerosol (SOA) formation from soluble species in atmospheric waters with high salt concentrations, such as aerosols. We have measured <i>K_S</i> of glyoxal and methylglyoxal for the atmospherically relevant salts (NH₄)₂SO₄, NH₄NO₃, NaNO₃, and NaCl and find that glyoxal consistently “salts-in” (<i>K_S</i> of −0.16, −0.06, −0.065, −0.1 molality^–1, respectively) while methylglyoxal “salts-out” (<i>K</i>_<i>S</i> of +0.16, +0.075, +0.02, +0.06 molality^–1). We show that <i>K</i>_<i>S</i> values for different salts are additive and present an equation for use in atmospheric models. Additionally, we have performed a series of quantum chemical calculations to determine the interactions between glyoxal/methylglyoxal monohydrate with Cl^–, NO₃^–, SO₄^2–, Na⁺, and NH₄⁺ and find Gibbs free energies of water displacement of −10.9, −22.0, −22.9, 2.09, and 1.2 kJ/mol for glyoxal monohydrate and −3.1, −10.3, −7.91, 6.11, and 1.6 kJ/mol for methylglyoxal monohydrate with uncertainties of 8 kJ/mol. The quantum chemical calculations support that SO₄^2–, NO₃^–, and Cl^– modify partitioning, while cations do not. Other factors such as ion charge or partitioning volume effects likely need to be considered to fully explain salting effects

Computational Study of the Effect of Glyoxal–Sulfate Clustering on the Henry’s Law Coefficient of Glyoxal

We have used quantum chemical methods to investigate the molecular mechanism behind the recently reported (Kampf, C. J.; Environ. Sci. Technol. 2013, 47, 4236−4244) strong dependence of the Henry’s law coefficient of glyoxal (C₂O₂H₂) on the sulfate concentration of the aqueous phase. Although the glyoxal molecule interacts only weakly with sulfate, its hydrated forms (C₂O₃H₄ and C₂O₄H₆) form strong complexes with sulfate, displacing water molecules from the solvation shell and increasing the uptake of glyoxal into sulfate-containing aqueous solutions, including sulfate-containing aerosol particles. This promotes the participation of glyoxal in reactions leading to secondary organic aerosol formation, especially in regions with high sulfate concentrations. We used our computed equilibrium constants for the complexation reactions to assess the magnitude of the Henry’s law coefficient enhancement and found it to be in reasonable agreement with experimental results. This indicates that the complexation of glyoxal hydrates with sulfate can explain the observed uptake enhancement