Gas-to-Particle Partitioning of Products from Ozonolysis of Δ3-Carene and the Effect of Temperature and Relative Humidity.

Formation of oxidized products from Δ3-carene (C10H16) ozonolysis and their gas-to-particle partitioning at three temperatures (0, 10, and 20 °C) under dry conditions (<2% RH) and also at 10 °C under humid (78% RH) conditions were studied using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) combined with a filter inlet for gases and aerosols (FIGAERO). The Δ3-carene ozonolysis products detected by the FIGAERO-ToF-CIMS were dominated by semivolatile organic compounds (SVOCs). The main effect of increasing temperature or RH on the product distribution was an increase in fragmentation of monomer compounds (from C10 to C7 compounds), potentially via alkoxy scission losing a C3 group. The equilibrium partitioning coefficient estimated according to equilibrium partitioning theory shows that the measured SVOC products distribute more into the SOA phase as the temperature decreases from 20 to 10 and 0 °C and for most products as the RH increases from <2 to 78%. The temperature dependency of the saturation vapor pressure (above an assumed liquid state), derived from the partitioning method, also allows for a direct way to obtain enthalpy of vaporization for the detected species without accessibility of authentic standards of the pure substances. This method can provide physical properties, beneficial for, e.g., atmospheric modeling, of complex multifunctional oxidation products.

Morphology and hygroscopicity of nanoplastics in sea spray.

The role of airborne nanoparticles in atmospheric chemistry and public health is largely controlled by particle size, morphology, surface composition, and coating. Aerosol mass spectrometry provides real-time chemical characterization of submicron atmospheric particles, but analysis of nanoplastics in complex aerosol mixtures such as sea spray is severely limited by challenges associated with separation and ionization of the aerosol matrix. Here we characterize the internal and external mixing state of synthetic sea spray aerosols spiked with 150 nm nanoplastics. Aerosols generated from pneumatic atomization and from a sea spray tank are compared. A humidified tandem differential mobility analyzer is used as a size and hygroscopicity filter, resulting in separation of nanoplastics from sea spray, and an inline high-resolution time-of-flight aerosol mass spectrometer is used to characterize particle composition and ionization efficiency. The separation technique amplified the detection limit of the airborne nanoplastics. A salt coating was found on the nanoplastics with coating thickness increasing exponentially with increasing bulk solution salinity, which was varied from 0 to 40 g kg-1. Relative ionization efficiencies of polystyrene and sea salt chloride were 0.19 and 0.36, respectively. The growth-factor derived hygroscopicity of sea salt was 1.4 at 75% relative humidity. These results underscore the importance of separating airborne nanoplastics from sea salt aerosol for detailed online characterization by aerosol mass spectrometry and characterization of salt coatings as a function of water composition. The surface coating of nanoplastic aerosols by salts can profoundly impact their surface chemistry, water uptake, and humidified particle size distributions in the atmosphere.

Airway and systemic biomarkers of health effects after short-term exposure to indoor ultrafine particles from cooking and candles - A randomized controlled double-blind crossover study among mild asthmatic subjects.

BACKGROUND: There is insufficient knowledge about the systemic health effects of exposure to fine (PM2.5) and ultrafine particles emitted from typical indoor sources, including cooking and candlelight burning. We examined whether short-term exposure to emissions from cooking and burning candles cause inflammatory changes in young individuals with mild asthma. Thirty-six non-smoking asthmatics participated in a randomized controlled double-blind crossover study attending three exposure sessions (mean PM2.5 µg/m3; polycyclic aromatic hydrocarbons ng/m3): (a) air mixed with emissions from cooking (96.1; 1.1), (b) air mixed with emissions from candles (89.8; 10), and (c) clean filtered air (5.8; 1.0). Emissions were generated in an adjacent chamber and let into a full-scale exposure chamber where participants were exposed for five hours. Several biomarkers were assessed in relation to airway and systemic inflammatory changes; the primary outcomes of interest were surfactant Protein-A (SP-A) and albumin in droplets in exhaled air - novel biomarkers for changes in the surfactant composition of small airways. Secondary outcomes included cytokines in nasal lavage, cytokines, C-reactive protein (CRP), epithelial progenitor cells (EPCs), genotoxicity, gene expression related to DNA-repair, oxidative stress, and inflammation, as well as metabolites in blood. Samples were collected before exposure start, right after exposure and the next morning. RESULTS: SP-A in droplets in exhaled air showed stable concentrations following candle exposure, while concentrations decreased following cooking and clean air exposure. Albumin in droplets in exhaled air increased following exposure to cooking and candles compared to clean air exposure, although not significant. Oxidatively damaged DNA and concentrations of some lipids and lipoproteins in the blood increased significantly following exposure to cooking. We found no or weak associations between cooking and candle exposure and systemic inflammation biomarkers including cytokines, CRP, and EPCs. CONCLUSIONS: Cooking and candle emissions induced effects on some of the examined health-related biomarkers, while no effect was observed in others; Oxidatively damaged DNA and concentrations of lipids and lipoproteins were increased in blood after exposure to cooking, while both cooking and candle emissions slightly affected the small airways including the primary outcomes SP-A and albumin. We found only weak associations between the exposures and systemic inflammatory biomarkers. Together, the results show the existence of mild inflammation following cooking and candle exposure.

Ozonolysis of α-Pinene and Δ3-Carene Mixtures: Formation of Dimers with Two Precursors.

The formation of secondary organic aerosol (SOA) from the structurally similar monoterpenes, α-pinene and Δ3-carene, differs substantially. The aerosol phase is already complex for a single precursor, and when mixtures are oxidized, products, e.g., dimers, may form between different volatile organic compounds (VOCs). This work investigates whether differences in SOA formation and properties from the oxidation of individual monoterpenes persist when a mixture of the monoterpenes is oxidized. Ozonolysis of α-pinene, Δ3-carene, and a 1:1 mixture of them was performed in the Aarhus University Research on Aerosol (AURA) atmospheric simulation chamber. Here, ∼100 ppb of monoterpene was oxidized by 200 ppb O3 under dark conditions at 20 °C. The particle number concentration and particle mass concentration for ozonolysis of α-pinene exceed those from ozonolysis of Δ3-carene alone, while their mixture results in concentrations similar to α-pinene ozonolysis. Detailed offline analysis reveals evidence of VOC-cross-product dimers in SOA from ozonolysis of the monoterpene mixture: a VOC-cross-product dimer likely composed of the monomeric units cis-caric acid and 10-hydroxy-pinonic acid and a VOC-cross-product dimer ester likely from the monomeric units caronaldehyde and terpenylic acid were tentatively identified by liquid chromatography-mass spectrometry. To improve the understanding of chemical mechanisms determining SOA, it is relevant to identify VOC-cross-products.

Acute health effects from exposure to indoor ultrafine particles-A randomized controlled crossover study among young mild asthmatics.

Particulate matter is linked to adverse health effects, however, little is known about health effects of particles emitted from typical indoor sources. We examined acute health effects of short-term exposure to emissions from cooking and candles among asthmatics. In a randomized controlled double-blinded crossover study, 36 young non-smoking asthmatics attended three exposure sessions lasting 5 h: (a) air mixed with emissions from cooking (fine particle mass concentration): (PM2.5 : 96.1 µg/m3 ), (b) air mixed with emissions from candles (PM2.5 : 89.8 µg/m3 ), and c) clean filtered air (PM2.5 : 5.8 µg/m3 ). Health effects (spirometry, fractional exhaled Nitric Oxide [FeNO], nasal volume and self-reported symptoms) were evaluated before exposure start, then 5 and 24 h after. During exposures volatile organic compounds (VOCs), particle size distributions, number concentrations and optical properties were measured. Generally, no statistically significant changes were observed in spirometry, FeNO, or nasal volume comparing cooking and candle exposures to clean air. In males, nasal volume and FeNO decreased after exposure to cooking and candles, respectively. Participants reported additional and more pronounced symptoms during exposure to cooking and candles compared to clean air. The results indicate that emissions from cooking and candles exert mild inflammation in asthmatic males and decrease comfort among asthmatic males and females.

Emissions of soot, PAHs, ultrafine particles, NOx, and other health relevant compounds from stressed burning of candles in indoor air.

Burning candles release a variety of pollutants to indoor air, some of which are of concern for human health. We studied emissions of particles and gases from the stressed burning of five types of pillar candles with different wax and wick compositions. The stressed burning was introduced by controlled fluctuating air velocities in a 21.6 m3 laboratory chamber. The aerosol physicochemical properties were measured both in well-mixed chamber air and directly above the candle flame with online and offline techniques. All candles showed different emission profiles over time with high repeatability among replicates. The particle mass emissions from stressed burning for all candle types were dominated by soot (black carbon; BC). The wax and wick composition strongly influenced emissions of BC, PM2.5 , and particle-phase polycyclic aromatic hydrocarbons (PAHs), and to lower degree ultrafine particles, inorganic and organic carbon fraction of PM, but did not influence NOx , formaldehyde, and gas-phase PAHs. Measurements directly above the flame showed empirical evidence of short-lived strong emission peaks of soot particles. The results show the importance of including the entire burn time of candles in exposure assessments, as their emissions can vary strongly over time. Preventing stressed burning of candles can reduce exposure to pollutants in indoor air.

Emissions of ultrafine particles from five types of candles during steady burn conditions.

Emissions from candles are of concern for indoor air quality. In this work, five different types of pillar candles were burned under steady burn conditions in a new laboratory scale system for repeatable and controlled comparison of candle emissions (temperature ~25°C, relative humidity ~13%, O2 >18%, air exchange rate 1.9 h-1 ). Burn rate, particle number concentrations, mass concentrations, and mode diameters varied between candle types. Based on the results, the burning period was divided in two phases: initial (0-1 h) and stable (1-6 h). Burn rates were in the range 4.4-7.3 and 4.7-7.1 g/h during initial and stable phase, respectively. Relative particle number emissions, mode diameters, and mass concentrations were higher during the initial phase compared to the stable phase for a majority of the candles. We hypothesize that this is due to elevated emissions of wick additives upon ignition of the candle together with a slightly higher burn rate in the initial phase. Experiments at higher relative humidity (~40%) gave similar results with a tendency toward larger particle sizes at the higher relative humidity. Chemical composition with respect to inorganic salts was similar in the emitted particles (dry conditions) compared to the candlewicks, but with variations between different candles.

The reaction of isotope-substituted hydrated iodide I(HO)- with ozone: the reactive influence of the solvent water molecule.

We report an investigation of the reaction of isotope-substituted hydrated iodide I(HO)- with ozone 16O3 to examine the involvement of the water molecules in the oxidation reactions that terminate with the formation of IO3-. Experimentally, we studied the reaction in the gas phase as elementary reactions using a radio-frequency (RF) ion-trap combined with a quadrupole mass spectrometer (QMS). In approximately 1.2% of the reactions of I(HO)- and 16O3, the 18O atom is found to appear in iodine oxide anions, thus giving evidence for a close involvement of the water molecule in a non-negligible number of the reactions towards IO3-. As a part of the experimental investigation, the reaction rate constant for the exchange reaction I(HO)- + HO → I(HO)- + HO at 300 K was found to be (1.3 ± 0.1) × 10-8 cm3 s-1. Quantum chemical calculations are exploited to establish the energetic difference between I(HO)- and I(HO)-.

Hydration of Atmospheric Molecular Clusters III: Procedure for Efficient Free Energy Surface Exploration of Large Hydrated Clusters.

Sampling the shallow free energy surface of hydrated atmospheric molecular clusters is a significant challenge. Using computational methods, we present an efficient approach to obtain minimum free energy structures for large hydrated clusters of atmospheric relevance. We study clusters consisting of two to four sulfuric acid (sa) molecules and hydrate them with up to five water (w) molecules. The structures of the "dry" clusters are obtained using the ABCluster program to yield a large pool of low-lying conformer minima with respect to free energy. The conformers (up to ten) lowest in free energy are then hydrated using our recently developed systematic hydrate sampling technique. Using this approach, we identify a total of 1145 unique (sa)2-4(w)1-5 cluster structures. The cluster geometries and thermochemical parameters are calculated at the ωB97X-D/6-31++G(d,p) level of theory, at 298.15 K and 1 atm. The single-point energy of the most stable clusters is calculated using a high-level DLPNO-CCSD(T0)/aug-cc-pVTZ method. Using the thermochemical data, we calculate the equilibrium hydrate distribution of the clusters under atmospheric conditions and find that the larger (sa)3 and (sa)4 clusters are significantly more hydrated than the smaller (sa)2 cluster or the sulfuric acid (sa)1 molecule. These findings indicate that more than five water molecules might be required to fully saturate the sulfuric acid clusters with water under atmospheric conditions. The presented methodology gives modelers a tool to take the effect of water explicitly into account in atmospheric particle formation models based on quantum chemistry.

Sea Spray Aerosol Formation: Laboratory Results on the Role of Air Entrainment, Water Temperature, and Phytoplankton Biomass.

Sea spray aerosol (SSA) emission is a complex process affected by various controlling factors. This work seeks to deconvolute some of this complexity in a controlled laboratory setting using a plunging jet by varying three key parameters, one at a time: (1) air entrainment rate, (2) seawater temperature, and (3) biomass of phytoplankton. The production of SSA is found to vary linearly with air entrainment rate. By normalizing the production flux to air entrainment rate, we observe nonlinear variation of the production efficiency of SSA with seawater temperature with a minimum around 6-10 °C. For comparison, SSA was also generated by detraining air into artificial seawater using a diffuser demonstrating that the production efficiency of SSA generated using a diffuser decreases almost linearly with increasing seawater temperature, and the production efficiency is significantly higher than that for SSA generated using a plunging jet. Finally, by varying the amount of phytoplankton biomass we demonstrate that SSA particle production varies nonlinearly with the amount of biomass in seawater.

Molecular Characterization and Source Identification of Atmospheric Particulate Organosulfates Using Ultrahigh Resolution Mass Spectrometry.

Organosulfates (OSs) have been observed as substantial constituents of atmospheric organic aerosol (OA) in a wide range of environments; however, the chemical composition, sources, and formation mechanism of OSs are still not well understood. In this study, we first created an "OS precursor map" based on the elemental composition of previous OS chamber experiments. Then, according to this "OS precursor map", we estimated the possible sources and molecular structures of OSs in atmospheric PM2.5 (particles with aerodynamic diameter ≤ 2.5 µm) samples, which were collected in urban areas of Beijing (China) and Mainz (Germany) and analyzed by ultrahigh-performance liquid chromatography (UHPLC) coupled with an Orbitrap mass spectrometer. On the basis of the "OS precursor map", together with the polarity information provided by UHPLC, OSs in Mainz samples are suggested to be mainly derived from isoprene/glyoxal or other unknown small polar organic compounds, while OSs in Beijing samples were generated from both isoprene/glyoxal and anthropogenic sources (e.g., long-chain alkanes and aromatics). The nitrooxy-OSs in the clean aerosol samples were mainly derived from monoterpenes, while much fewer monoterpene-derived nitrooxy-OSs were obtained in the polluted aerosol samples, showing that nitrooxy-OS formation is affected by different precursors in clean and polluted air conditions.

Reply to the 'Comment on "Atmospheric chemistry of iodine anions: elementary reactions of I-, IO-, and IO with ozone studied in the gas-phase at 300 K using an ion trap"' by D. Britz, Phys. Chem. Chem. Phys., 2019, 21, C9CP03851E.

We reply to the comment by Dieter Britz on two recent papers in Physical Chemistry Chemical Physics. The comment presents a valuable, however, less flexible, alternative to the analysis performed in these papers and as such has no impact on any of the scientific results reported in the two publications.

The reaction of hydrated iodide I(H2O)- with ozone: a new route to IO2- products.

We report on an experimental characterization of the isolated reaction of hydrated iodide I(H2O)- with ozone O3 at room temperature performed using a radio-frequency ion trap combined with a quadrupole mass spectrometer. Contrary to the oxidation reaction of the bare I- ion, the hydrated iodide I(H2O)- primarily reacts to form I- and IO2- with significant absolute reaction rate constants of 2.0 ± 0.3 × 10-10 cm3 molecule-1 s-1 and 2.5 ± 0.3 × 10-10 cm3 molecule-1 s-1 while direct pathways to IO- and IO3- are much weaker. Quantum chemical calculations indicate that in aqueous phase and for atmospherically relevant temperatures, the presence of hydrated iodides are favored over bare I- ions, thus suggesting that the chemistry of the hydrated ions is relevant for understanding and modeling atmospheric processes at the air-water interface.

Atmospheric chemistry of iodine anions: elementary reactions of I-, IO-, and IO2- with ozone studied in the gas-phase at 300 K using an ion trap.

Using a radio-frequency ion trap to study ion-molecule reactions under isolated conditions, we report a direct experimental determination of reaction rate constants for the sequential oxidation of iodine anions by ozone at room temperature (300 K). The results are R1: I- + O3 → IO- + O2, k1 = (7 ± 2) × 10-12 cm3 s-1; R2: IO- + O3 → IO2- + O2, k2 = (10 ± 2) × 10-9 cm3 s-1; R3: IO2- + O3 → IO3- + O2, k3 = (16 ± 2) × 10-9 cm3 s-1. More oxidized forms such as IO4- and IO5- were not observed. Additionally, we performed quantum chemical calculations to elucidate the energetics of these oxidation reactions.

Hydration of Atmospheric Molecular Clusters II: Organic Acid-Water Clusters.

Using computational methods, we study the gas phase hydration of three different atmospherically relevant organic acids with up to 10 water molecules. We study a dicarboxylic acid (pinic acid) and a tricarboxylic acid (3-methyl-1,2,3-butanetricarboxylic acid (mbtca)) that are both identified as products from α-pinene oxidation reactions. We also study a 2-oxohexanediperoxy acid (ohdpa) that has been identified as a product from cyclohexene autoxidation. To sample the cluster structures, we employ our recently developed systematic hydrate sampling technique and identify a total of 551 hydrate clusters. The cluster structures and thermochemical parameters (at 298.15 K and 1 atm) are obtained at the ωB97X-D/6-31++G(d,p) level of theory, and the single point energy of the clusters have been refined using a high level DLPNO-CCSD(T)/aug-cc-pVTZ calculation. We find that all three tested organic acids interact significantly more weakly with water compared to the primary nucleation precursor sulfuric acid. Even at 100% relative humidity (298.15 K and 1 atm), we find that ohdpa remains unhydrated and only the monohydrate of pinic acid and mbtca are slightly populated (4% and 2%, respectively). From the obtained molecular structures, potential implications for the ice nucleating ability of aerosol particles is discussed.

Hydration of Atmospheric Molecular Clusters: A New Method for Systematic Configurational Sampling.

We present a new systematic configurational sampling algorithm for investigating the potential energy surface of hydrated atmospheric molecular clusters. The algorithm is based on creating a Fibonacci sphere around each atom in the cluster and adding water molecules to each point in nine different orientations. For the sampling of water molecules to existing hydrogen bonds, the cluster is displaced along the hydrogen bond, and a water molecule is placed in between in three different orientations. Generated redundant structures are eliminated based on minimizing the root-mean-square distance of different conformers. Initially, the clusters are sampled using the semiempirical PM6 method and subsequently using density functional theory (M06-2X and ωB97X-D) with the 6-31++G(d,p) basis set. Applying the developed algorithm, we study the hydration of sulfuric acid with up to 15 water molecules. We find that the addition of the first four water molecules "saturate" the sulfuric acid molecule and that they are more thermodynamically favorable than the addition of water molecules 5-15. Using the large generated set of conformers, we assess the performance of approximate methods (ωB97X-D, M06-2X, PW91, and PW6B95-D3) in calculating the binding energies and assigning the global minimum conformation compared to high level CCSD(T)-F12a/VDZ-F12 reference calculations. The tested DFT functionals systematically overestimate the binding energies compared to coupled cluster calculations, and we find that this deficiency can be corrected by a simple scaling factor.

Phase State and Saturation Vapor Pressure of Submicron Particles of meso-Erythritol at Ambient Conditions.

meso-Erythritol is a sugar alcohol identified in atmospheric aerosol particles. In this work, evaporation of submicron-sized particles of meso-erythritol was studied in a TDMA system including a laminar flow tube under dry conditions at five temperatures (278-308 K) and ambient pressure. A complex behavior was observed and attributed to the formation of particles of three different phase states: (1) crystalline, (2) subcooled liquid or amorphous, and (3) mixed. With respect to saturation vapor pressure, the subcooled liquid and amorphous states are treated to be the same. The particle phase state was linked to initial particle size and flow tube temperature. Saturation vapor pressures of two phase states attributed to the crystalline and subcooled liquid state respectively are reported. Our results suggest a mass accommodation coefficient close to one for both states.

Aging of biogenic secondary organic aerosol via gas-phase OH radical reactions.

The Multiple Chamber Aerosol Chemical Aging Study (MUCHACHAS) tested the hypothesis that hydroxyl radical (OH) aging significantly increases the concentration of first-generation biogenic secondary organic aerosol (SOA). OH is the dominant atmospheric oxidant, and MUCHACHAS employed environmental chambers of very different designs, using multiple OH sources to explore a range of chemical conditions and potential sources of systematic error. We isolated the effect of OH aging, confirming our hypothesis while observing corresponding changes in SOA properties. The mass increases are consistent with an existing gap between global SOA sources and those predicted in models, and can be described by a mechanism suitable for implementation in those models.

Computational study of the Rayleigh light scattering properties of atmospheric pre-nucleation clusters.

The Rayleigh and hyper Rayleigh scattering properties of the binary (H2SO4)(H2O)n and ternary (H2SO4)(NH3)(H2O)n clusters are investigated using a quantum mechanical response theory approach. The molecular Rayleigh scattering intensities are expressed using the dipole polarizability α and hyperpolarizability ß tensors. Using density functional theory, we elucidate the effect of cluster morphology on the scattering properties using a combinatorial sampling approach. We find that the Rayleigh scattering intensity depends quadratically on the number of water molecules in the cluster and that a single ammonia molecule is able to induce a high anisotropy, which further increases the scattering intensity. The hyper Rayleigh scattering activities are found to be extremely low. This study presents the first attempt to map the scattering of atmospheric molecular clusters using a bottom-up approach.

Molecular interaction of pinic acid with sulfuric acid: exploring the thermodynamic landscape of cluster growth.

We investigate the molecular interactions between the semivolatile α-pinene oxidation product pinic acid and sulfuric acid using computational methods. The stepwise Gibbs free energies of formation have been calculated utilizing the M06-2X functional, and the stability of the clusters is evaluated from the corresponding ΔG values. The first two additions of sulfuric acid to pinic acid are found to be favorable with ΔG values of -9.06 and -10.41 kcal/mol. Addition of a third sulfuric acid molecule is less favorable and leads to a structural rearrangement forming a bridged sulfuric acid-pinic acid cluster. The involvement of more than one pinic acid molecule in a single cluster is observed to lead to the formation of favorable (pinic acid)2(H2SO4) and (pinic acid)2(H2SO4)2 clusters. The identified most favorable growth paths starting from a single pinic acid molecule lead to closed structures without the further possibility for attachment of either sulfuric acid or pinic acid. This suggests that pinic acid cannot be a key species in the first steps in nucleation, but the favorable interactions between sulfuric acid and pinic acid imply that pinic acid can contribute to the subsequent growth of an existing nucleus by condensation.