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Δ3 -carene is a prominent monoterpene in the atmosphere, contributing significantly to secondary organic aerosol (SOA) formation. However, knowledge about Δ3 -carene oxidation pathways, particularly regarding their ability to form highly oxygenated organic molecules (HOMs), is still limited. In this study, we present HOM measurements during Δ3 -carene ozonolysis under various conditions in two simulation chambers. We identified numerous HOMs (monomers: C 7-10 H 10-18 O 6-14 ; dimers: C 17-20 H 24-34 O 6-18) using a chemical ionization mass spectrometer (CIMS). Δ3 -carene ozonolysis yielded higher HOM concentrations than α -pinene, with a distinct distribution, indicating differences in formation pathways. All HOM signals decreased considerably at lower temperatures, reducing the estimated molar HOM yield from ∼ 3 % at 20 °C to ∼ 0.5 % at 0 °C. Interestingly, the temperature change altered the HOM distribution, increasing the observed dimer-to-monomer ratios from roughly 0.8 at 20 °C to 1.5 at 0 °C. HOM monomers with six or seven O atoms condensed more efficiently onto particles at colder temperatures, while monomers with nine or more O atoms and all dimers condensed irreversibly even at 20 °C. Using the gas- and particle-phase chemistry kinetic multilayer model ADCHAM, we were also able to reproduce the experimentally observed HOM composition, yields, and temperature dependence. [ABSTRACT FROM AUTHOR]

We describe a new experimental system for direct measurements of the absolute saturation vapor pressures of liquid or solid samples. The setup allows the isolation of the sample under steady conditions in an ultra-high vacuum chamber, where the measurement of the sample's vapor pressure as a function of its temperature can be performed in a range around room temperature and in a pressure range defined only by the applied absolute pressure sensor. We characterize the setup and illustrate its capability to measure saturation vapor pressures as well as enthalpies of evaporation around room temperature with explicit measurements on four liquid compounds (diethyl phthalate, 1-decanol, 1-heptanol, and 1-hexanol) for which accurate vapor pressures have previously been reported. [ABSTRACT FROM AUTHOR]

Δ3-carene is a prominent monoterpene in the atmosphere, contributing significantly to secondary organic aerosol (SOA) formation. However, knowledge about Δ3-carene oxidation pathways, particularly regarding its ability to form highly oxygenated organic molecules (HOM), is still limited. In this study, we present HOM measurements during Δ3-carene ozonolysis under various conditions in two simulation chambers. We identified numerous HOM (monomers: C7-10H10-18O6-14, dimers: C17-20H24-34O6-18) using a chemical ionization mass spectrometer (CIMS). Δ3-carene ozonolysis yielded higher HOM concentrations than a-pinene, with a distinct distribution, indicating differences in formation pathways. All HOM signals decreased considerably at lower temperatures, reducing the estimated molar HOM yield from ~3 % at 20 °C to ~0.5 % at 0 °C. Interestingly, temperature change altered the HOM distribution, increasing the observed dimer-to-monomer ratios from roughly 0.8 at 20 °C to 1.5 at 0 °C. HOM monomers with 6 or 7 O-atoms condensed more efficiently onto particles at colder temperatures, while monomers with nine or more O-atoms and all dimers condensed irreversibly even at 20 °C. Using the gas and particle-phase chemistry kinetic multilayer model ADCHAM, we were also able to reproduce the experimentally observed HOM composition, yields and temperature dependence. [ABSTRACT FROM AUTHOR]

Time-resolved action spectroscopy together with a fs-pump probe scheme is used in an electrostatic ion-storage ring to address lifetimes of specific vibrational levels in electronically excited states. Here we specifically consider the excited-state lifetime of cryogenically cooled green fluorescent protein (GFP) chromophore anions which is systematically measured across the S0–S1 spectral region (450–482 nm). A long lifetime of 5.2 ± 0.3 ns is measured at the S0–S1 band origin. When exciting higher vibrational levels in S1, the lifetime changes dramatically. It decreases by more than two orders of magnitude in a narrow energy region ∼250 cm−1 (31 meV) above the 0–0 transition. This is attributed to the opening of internal conversion over an excited-state energy barrier. The applied experimental technique provides a new way to uncover even small energy barriers, which are crucial for excited-state dynamics. [ABSTRACT FROM AUTHOR]

The document is an erratum for a scientific paper on measuring absolute saturation vapor pressures. It corrects errors in equations (2), (24), and (25) where a logarithmic function was mistakenly written instead of an exponential function. The correction does not impact the results or modeling presented in the paper. The corrected equations are provided in the erratum. [Extracted from the article]

This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentrations on the chemical composition of particles formed in the dark ozonolysis of α -pinene. All experiments were conducted in a 5 m 3 Teflon chamber at an initial ozone concentration of 100 ppb and initial α -pinene concentrations of 10 and 50 ppb, respectively; at constant temperatures of 20, 0, or - 15 ∘ C; and at changing temperatures (ramps) from - 15 to 20 and from 20 to - 15 ∘ C. The chemical composition of the particles was probed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). A four-factor solution of a positive matrix factorization (PMF) analysis of the combined HR-ToF-AMS data is presented. The PMF analysis and the elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α -pinene concentration (10 ppb) and at the highest temperature (20 ∘ C). A higher initial α -pinene concentration (50 ppb) and/or lower temperature (0 or - 15 ∘ C) results in a lower oxidation level of the molecules contained in the particles. With respect to the carbon oxidation state, particles formed at 0 ∘ C are more comparable to particles formed at - 15 ∘ C than to those formed at 20 ∘ C. A remarkable observation is that changes in temperature during particle formation result in only minor changes in the elemental composition of the particles. Thus, the temperature at which aerosol particle formation is induced seems to be a critical parameter for the particle elemental composition. Comparison of the HR-ToF-AMS-derived estimates of the content of organic acids in the particles based on m/z 44 in the mass spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. Higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), while the organic acid functionalities account for an increasing fraction of the measured particle mass. [ABSTRACT FROM AUTHOR]

Little is known about the effects of subzero temperatures on the formation of secondary organic aerosol (SOA) from α -pinene. In the current work, ozone-initiated oxidation of α -pinene at initial concentrations of 10 and 50 ppb, respectively, is performed at temperatures of 20, 0, and -15 ∘ 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 α -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 ∘ 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 α -pinene-derived SOA particles are observed between experiments performed at 10 and 50 ppb initial α -pinene concentrations, thus suggesting a higher influence of reaction temperature compared to that of α -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 oxygen-to-carbon ratio (O:C)<0.4 – is shown to increase at low temperatures, while the formation of the more oxidized species (O:C>0.4) is suppressed, consequently resulting in temperature-modulated composition of the α -pinene-derived SOA. Temperature ramping experiments exposing α -pinene-derived 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 α -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. [ABSTRACT FROM AUTHOR]

We report an investigation of the reaction of isotope-substituted hydrated iodide I(H 182 O)− 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(H 182 O)− 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(H 182 O)− + H 162 O → I(H 162 O)− + H 182 O 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(H 182 O)− and I(H 162 O)−. [ABSTRACT FROM AUTHOR]

This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentration on the chemical composition of particles formed in the dark ozonolysis of α-pinene. All experiments were conducted in a 5 m³ Teflon chamber at an initial ozone concentration of 100 ppb and α-pinene concentrations of 10 ppb and 50 ppb, respectively, at constant temperatures of 20 °C, 0 °C, or −15 °C, and at changing temperatures (ramps) from −15 °C to 20 °C and from 20 °C to −15 °C. The chemical composition of the particles was probed using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). A four-factor solution of a Positive Matrix Factorization (PMF) analysis of combined HR-ToF-AMS data from experiments conducted under different conditions is presented. The PMF analysis as well as elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α-pinene concentration (10 ppb) and at the highest temperature (20 °C). Higher initial α-pinene concentration (50 ppb) and/or lower temperature (0 °C or −15 °C) result in lower oxidation level of the molecules contained in the particles. With respect to carbon oxidation state, particles formed at 0 °C are more comparable to particles formed at −15 °C than to those formed at 20 °C. A remarkable observation is that changes in temperature during or after particle formation result in only minor changes in the elemental composition of the particles. The temperature at which aerosol particle formation is initiated thus seems to be a critical parameter for the particle elemental composition. Comparison of the AMS derived estimates of the content of organic acids in the particles based on m/z 44 in the spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. While higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), the organic acid functionalities account for an increasing fraction of the measured SOA mass at higher temperatures. [ABSTRACT FROM AUTHOR]