The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

Abstract. Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR), methyl vinyl ketone (MVK), methyl glyoxal (MG), and glyoxal (GL). We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous and gas phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 1.2 ± 0.4) × 1010 M−1 s−1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (24.1 ± 0.8 %) to MACR (10.9 ± 1.1%) in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH = CH2) produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3 % and 3.8 ± 0.1 %, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0.8 % at 6 h. The observed carbon balance accounted for ~50 % of the consumed isoprene. The presence of high-molecular-weight compounds may have accounted for a large portion of the missing carbons, but they were not quantified in this study. In summary, our work has provided experimental evidence that the availably abundant water could affect the distribution of oxygenated organic compounds produced in the oxidation of volatile organic compounds.

Download Full-text

The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxy radical

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-8515-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 8515-8551

Author(s):

D. Huang ◽

X. Zhang ◽

Z. M. Chen ◽

Y. Zhao ◽

X. L. Shen

Keyword(s):

Volatile Organic Compounds ◽

Oxalic Acid ◽

Gas Phase ◽

Organic Compounds ◽

Aqueous Phase ◽

Laboratory Simulation ◽

Oh Radical ◽

Volatile Organic ◽

Isoprene Oxidation ◽

Aqueous Oxidation

Abstract. Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous oxidation of isoprene in clouds and its reaction products, including carbonyl compounds and organic acids. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR), methyl vinyl ketone (MVK), methyl glyoxal (MG), and glyoxal (GL). We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous- and gas-phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 3.50 (± 0.98) × 109 M−1 s−1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (18.9 ± 0.8%) to MACR (9.0 ± 1.1%) in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH = CH2) produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3% and 3.8 ± 0.1%, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0.8% at 6 h. The observed carbon balance accounted for ~50% of the consumed isoprene. The presence of high-molecular-weight compounds may have accounted for a large portion of the missing carbons, but they were not quantified in this study. In summary, our work has provided experimental evidence that condensed water could affect the distribution of oxygenated organic compounds produced in the oxidation of volatile organic compounds. If volatile organic compounds like isoprene and terpenes undergo aqueous oxidation to a larger extent than considered previously, the contribution of their atmospheric aqueous oxidation should be considered when constructing future models of the global SOA budget.

Download Full-text

OH radical-initiated gas-phase reaction products of phenanthrene

The Science of The Total Environment ◽

10.1016/0048-9697(94)90368-9 ◽

1994 ◽

Vol 148 (1) ◽

pp. 11-21 ◽

Cited By ~ 30

Author(s):

Detlev Helmig ◽

William P. Harger

Keyword(s):

Gas Phase ◽

Phase Reaction ◽

Oh Radical ◽

Reaction Products ◽

Gas Phase Reaction

Download Full-text

Explicit modeling of volatile organic compounds partitioning in the atmospheric aqueous phase

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-1023-2013 ◽

2013 ◽

Vol 13 (2) ◽

pp. 1023-1037 ◽

Cited By ~ 30

Author(s):

C. Mouchel-Vallon ◽

P. Bräuer ◽

M. Camredon ◽

R. Valorso ◽

S. Madronich ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Water Content ◽

Gas Phase ◽

Aqueous Phase ◽

Water Soluble ◽

Chemical Mechanism ◽

Organic Species ◽

Cloud Water Content ◽

Isoprene Oxidation

Abstract. The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and α-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (yield less than 2% on carbon atom basis) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for α-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.

Download Full-text

Gas-phase reaction products and yields of terpinolene with ozone and nitric oxide using a new derivatization agent

Atmospheric Environment ◽

10.1016/j.atmosenv.2015.10.015 ◽

2015 ◽

Vol 122 ◽

pp. 513-520 ◽

Cited By ~ 7

Author(s):

Jason E. Ham ◽

Stephen R. Jackson ◽

Joel C. Harrison ◽

J.R. Wells

Keyword(s):

Nitric Oxide ◽

Gas Phase ◽

Phase Reaction ◽

Reaction Products ◽

Gas Phase Reaction

Download Full-text

ChemInform Abstract: Products of the Gas-Phase Reaction of Methyl tert-Butyl Ether with the OH Radical in the Presence of NOx

ChemInform ◽

10.1002/chin.199205096 ◽

2010 ◽

Vol 23 (5) ◽

pp. no-no

Author(s):

E. C. TUAZON ◽

W. P. L. CARTER ◽

S. M. ASCHMANN ◽

R. ATKINSON

Keyword(s):

Gas Phase ◽

Methyl Tert Butyl Ether ◽

Phase Reaction ◽

Oh Radical ◽

Butyl Ether ◽

Gas Phase Reaction ◽

Tert Butyl

Download Full-text

Aircraft observations of water-soluble dicarboxylic acids in the aerosols over China

10.5194/acp-2016-5 ◽

2016 ◽

Author(s):

Yan-Lin Zhang ◽

Kimitaka Kawamura ◽

Ping Qing Fu ◽

Suresh K. R. Boreddy ◽

Tomomi Watanabe ◽

...

Keyword(s):

Oxalic Acid ◽

Organic Compounds ◽

Aqueous Phase ◽

Dicarboxylic Acids ◽

Liquid Water Content ◽

Water Soluble ◽

Aircraft Observations ◽

Volatile Organic ◽

Intercontinental Transport ◽

Surface Measurements

Abstract. Vertical profiles of low molecular weight dicarboxylic acids, related organic compounds and SOA tracer compounds in particle phase have not yet been simultaneously explored in East Asia, although there is growing evidence that aqueous phase oxidation of volatile organic compounds may be responsible for the elevated organic aerosols (OA) in the free troposphere. Here, we found consistently good correlation of oxalic acid, the most abundant organics globally, with its precursors as well as biogenic-derived secondary OA (SOA) compounds in Chinese tropospheric aerosols by aircraft measurements. Anthropogenically derived dicarboxylic acids (i.e., C5 and C6 diacids) at high altitudes were 4–20 times higher than those from surface measurements and even occasionally dominant over oxalic acid at altitude higher than 2 km, which is in contrast to the predominance of oxalic acid previously reported globally including the tropospheric and surface aerosols. This indicates an enhancement of tropospheric SOA formation from anthropogenic precursors. Furthermore, oxalic acid-tosulfate ratio maximized at altitude of ~2 km, explaining aqueous-phase SOA production that was supported by good correlations with predicted liquid water content, organic carbon and biogenic SOA tracers. These results demonstrate that elevated oxalic acid and related SOA compounds from both the anthropogenic and biogenic sources may substantially contribute to tropospheric OA burden over polluted regions of China, implying aerosol-associated climate effects and intercontinental transport.

Download Full-text

A gas chromatographic detector based on the quenching of luminescence from a P4/O2 cold flame

Canadian Journal of Chemistry ◽

10.1139/v79-202 ◽

1979 ◽

Vol 57 (10) ◽

pp. 1238-1243 ◽

Cited By ~ 2

Author(s):

Walter A. Aue ◽

Zbigniew M. Mielniczuk

Keyword(s):

Oxygen Atom ◽

Gas Phase ◽

Organic Compounds ◽

Linear Response ◽

Phase Reaction ◽

Quenching Effect ◽

Gas Phase Reaction ◽

Cold Flame ◽

Branched Chain ◽

Considerable Range

Gas chromatographic effluents were detected by their quenching effect on the luminescence of a steady 'cold flame', as provided by the gas-phase reaction of phosphorus vapor and oxygen. The response of organic compounds correlated with their 'ease of oxidation' in accordance with the literature, suggesting that such compounds act as oxygen atom scavengers in the branched-chain P4/O2 reaction.Most substances showed linear response over one to two orders of magnitude, and minimum detectable amounts ranged from 2 × 10−9g (benzaldehyde) to 2 × 10−4g (dichloromethane). The detector temperature could be varied to (a) alter response ratios, i.e. selectivity, among some types of compounds; and (b) produce easily-obtained Arrhenius plots. However, the response (luminescence quenching) of most compounds was independent of temperature over a considerable range.

Download Full-text

Modelling the photochemical formation of high H2O2 concentrations and secondary sulfate observed during winter haze periods in the NCP

10.5194/egusphere-egu2020-9793 ◽

2020 ◽

Author(s):

Andreas Tilgner ◽

Erik Hans Hoffmann ◽

Lin He ◽

Bernd Heinold ◽

Can Ye ◽

...

Keyword(s):

Air Pollution ◽

Gas Phase ◽

Aqueous Phase ◽

Photochemical Reactions ◽

Data Availability ◽

Phase Reaction ◽

Aerosol Composition ◽

Chemistry Research ◽

The Impact

During winter, the North China Plain (NCP) is frequently characterized by severe haze conditions connected with extremely high PM2.5 and NOx concentrations, i.e. strong air pollution. The NCP is one of the most populated regions worldwide where haze periods have direct health effects. Tropospheric haze particles are a complex multiphase and multi-component environment, in which multiphase chemical processes are able to alter the chemical aerosol composition and deduced physical aerosol properties and can strongly contribute to air pollution. Despite many past investigations, the chemical haze processing is still uncertain and represents a challenge to atmospheric chemistry research. Recent NCP studies during autumn/winter 2017 haze periods have revealed unexpected high H2O2 concentrations of about 1&#160;ppb suggesting H2O2 as a potential contributor to secondary PM2.5 mass, e.g., due to sulfur(IV) oxidation. However, the multiphase H2O2 formation under such NOx concentrations is still unclear. Therefore, the present study aimed at the examination of potential multiphase H2O2 formation pathways, and the feedback on sulfur oxidation.Multiphase chemistry simulations of a measurement campaign in the NCP are performed with the box model SPACCIM. The multiphase chemistry model within SPACCIM contains the gas-phase mechanism MCMv3.2 and the aqueous-phase mechanism CAPRAM4.0 together with both its aromatics module CAPRAM-AM1.0 and its halogen module CAPRAM-HM2.1. Furthermore, based on available literature data, the multiphase chemistry mechanism is extended considering further multiphase formation pathways of HONO and an advanced HOx mechanism scheme enabling higher in-situ H2O2 formations in haze particles. The simulations have been performed for three periods characterized by high H2O2 concentrations, high RH and PM2.5 conditions and high measurement data availability. Several sensitivity runs have been performed examining the impact of the soluble transition metal ion (TMI) content on the predicted H2O2 formation.Simulations with the improved multiphase chemistry mechanism shows a good agreement of the modelled H2O2 concentrations with field data. The modelled H2O2 concentration shows a substantial dependency on the soluble TMI content. Higher soluble TMI contents result in higher H2O2 concentrations demonstrating the strong influence of TMI chemistry in haze particles on H2O2 formation. The analysis of the chemical production and sink fluxes reveals that a huge fraction of the multiphase HO2 radicals and nearly all of the subsequently formed reaction product H2O2 is produced in-situ within the haze particles and does not origin from the gas phase. Further chemical analyses show that, during the morning hours, the aqueous-phase reaction of H2O2 with S(IV) contributes considerably to S(VI) formation beside the HONO related formation of sulfuric acid by OH in the gas-phase.Finally, a parameterization was developed to study the particle-phase H2O2 formations as potential source with the global model ECHAM-HAMMOZ. The performed global modelling identifies an increase of gas-phase H2O2 by a factor of 2.8 through the newly identified particle chemistry. Overall, the study demonstrated that photochemical reactions of HULIS and TMIs in particles are an important H2O2 source leading to increased particle sulfate formation.

Download Full-text