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

On the temperature of large biomolecules in ion-storage rings

A method to determine the temperature of molecular ions in an ion-storage ring is presented. Molecular ions were repeatedly irradiated by laser pulses over several hundred milliseconds, and the rate of fragmentation was used to determine the temperature of the photoexcited ions. The initial temperature of the ions before photoabsorption was in turn found from the microcanonical caloric curve for the molecule of interest. The temperature evolution of the protonated GFP chromophore in the ELISA storage ring was found for different starting conditions by this method. We find that the initial temperature of the ions when entering the ring depends on the ion-trap temperature and the amount of buffer gas used in the trap. In particular, collisional heating during acceleration after the ion trap can be significant. Protonated GFP chromophores, produced under different conditions, were used to determine temperature effects on the gas-phase absorption spectra

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

Effect of temperature on the formation of highly oxygenated organic molecules (HOMs) from alpha-pinene ozonolysis

Highly oxygenated organic molecules (HOMs) are important contributors to secondary organic aerosol (SOA) and new-particle formation (NPF) in the boreal atmosphere. This newly discovered class of molecules is efficiently formed from atmospheric oxidation of biogenic volatile organic compounds (VOCs), such as monoterpenes, through a process called autoxidation. This process, in which peroxy-radical intermediates isomerize to allow addition of molecular oxygen, is expected to be highly temperature-dependent. Here, we studied the dynamics of HOM formation during a -pinene ozonolysis experiments performed at three different temperatures, 20, 0 and - 15 degrees C, in the Aarhus University Research on Aerosol (AURA) chamber. We found that the HOM formation, under our experimental conditions (50 ppb alpha-pinene and 100 ppb ozone), decreased considerably at lower temperature, with molar yields dropping by around a factor of 50 when experiments were performed at 0 degrees C, compared to 20 degrees C. At -15 degrees C, the HOM signals were already close to the detection limit of the nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer used for measuring gas-phase HOMs. Surprisingly, comparing spectra measured at 0 and 20 degrees C, ratios between HOMs of different oxidation levels, e.g., the typical HOM products C10H14O7, C10H14O9, and C10H14O11, changed considerably less than the total HOM yields. More oxidized species have undergone more isomerization steps; yet, at lower temperature, they did not decrease more than the less oxidized species. One possible explanation is that the primary rate-limiting steps forming these HOMs occur before the products become oxygenated enough to be detected by our CI-APi-TOF (i.e., typically seven or more oxygen atoms). The strong temperature dependence of HOM formation was observed under temperatures highly relevant to the boreal forest, but the exact magnitude of this effect in the atmosphere will be much more complex: the fate of peroxy radicals is a competition between autoxidation (influenced by temperature and VOC type) and bimolecular termination pathways (influenced mainly by concentration of reaction partners). While the temperature influence is likely smaller in the boreal atmosphere than in our chamber, both the magnitude and complexity of this effect clearly deserve more consideration in future studies in order to estimate the ultimate role of HOMs on SOA and NPF under different atmospheric conditions.Peer reviewe