Heterogeneous oxidation of folpet and dimethomorph by OH radicals: A kinetic and mechanistic study

2014 ◽  
Vol 82 ◽  
pp. 164-171 ◽  
Author(s):  
M. Al Rashidi ◽  
A. Chakir ◽  
E. Roth
Keyword(s):  
Mechanistic Study ◽  
Oh Radicals ◽  
Heterogeneous Oxidation

scholarly journals Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: Uptake kinetics and condensed-phase products

2007 ◽  
Vol 7 (3) ◽  
pp. 6803-6842 ◽  
Author(s):  
I. J. George ◽  
A. Vlasenko ◽  
J. G. Slowik ◽  
J. P. D. Abbatt
Keyword(s):  
Hydroxyl Radicals ◽  
Particle Density ◽  
Organic Aerosols ◽  
Oxidation Products ◽  
Photochemical Oxidation ◽  
Mass Spectrometry Analysis ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Phase Reaction ◽  
Heterogeneous Oxidation

Abstract. The kinetics and reaction mechanism for the heterogeneous oxidation of saturated organic aerosols by gas-phase OH radicals were investigated under NOx-free conditions. The reaction of 150 nm diameter Bis(2-ethylhexyl) sebacate (BES) particles with OH was studied as a proxy for chemical aging of atmospheric aerosols containing saturated organic matter. An aerosol reactor flow tube combined with an Aerodyne time-of-flight aerosol mass spectrometer (ToF-AMS) and scanning mobility particle sizer (SMPS) was used to study this system. Hydroxyl radicals were produced by 254 nm photolysis of O3 in the presence of water vapour. The kinetics of the heterogeneous oxidation of the BES particles was studied by monitoring the loss of a mass fragment of BES with the ToF-AMS as a function of OH exposure. We measured an initial OH uptake coefficient of γ0 = 1.26 (±0.04), confirming that this reaction is highly efficient. The density of BES particles increased by up to 20% of the original BES particle density at the highest OH exposure studied, consistent with the particle becoming more oxidized. Electrospray ionization mass spectrometry analysis showed that the major particle-phase reaction products are multifunctional carbonyls and alcohols with higher molecular weights than the starting material. Volatilization of oxidation products accounted for a maximum of 17% decrease of the particle volume at the highest OH exposure studied. Tropospheric organic aerosols will become more oxidized from heterogeneous photochemical oxidation, which may affect not only their physical and chemical properties, but also their hygroscopicity and cloud nucleation activity.

Atmospheric Degradation of CH2═C(CH3)C(O)OCH3 Initiated by OH Radicals: Mechanistic Study and Quantification of CH3C(O)C(O)OCH3 in NOx Free Air

2015 ◽  
Vol 119 (33) ◽  
pp. 8775-8783 ◽  
Author(s):  
Rodrigo G. Gibilisco ◽  
Jorge G. Uranga ◽  
Ana N. Santiago ◽  
Mariano A. Teruel
Keyword(s):  
Mechanistic Study ◽  
Oh Radicals ◽  
Free Air ◽  
Atmospheric Degradation

Evolution in the Reactivity of Citric Acid toward Heterogeneous Oxidation by Gas-Phase OH Radicals

2018 ◽  
Vol 2 (12) ◽  
pp. 1323-1329 ◽  
Author(s):  
Man Mei Chim ◽  
Christopher Y. Lim ◽  
Jesse H. Kroll ◽  
Man Nin Chan
Keyword(s):  
Citric Acid ◽  
Gas Phase ◽  
Oh Radicals ◽  
Heterogeneous Oxidation

scholarly journals Influence of relative humidity on the heterogeneous oxidation of secondary organic aerosol

2018 ◽  
Vol 18 (19) ◽  
pp. 14585-14608 ◽  
Author(s):  
Ziyue Li ◽  
Katherine A. Smith ◽  
Christopher D. Cappa
Keyword(s):  
Relative Humidity ◽  
Mass Loss ◽  
Mass Spectra ◽  
Secondary Organic Aerosol ◽  
Complex Mixture ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Heterogeneous Oxidation ◽  
Substantial Impact ◽  
The Difference

Abstract. Secondary organic aerosol (SOA) is a complex mixture of hundreds of semi-volatile to extremely low-volatility organic compounds that are chemically processed in the atmosphere, including via heterogeneous oxidation by gas-phase radicals. Relative humidity (RH) has a substantial impact on particle phase, which can affect how SOA evolves in the atmosphere. In this study, SOA from dark α-pinene ozonolysis is heterogeneously aged by OH radicals in a flow tube at low and high RH. At high RH (RH =89 %) there is substantial loss of particle volume (∼60 %) at an equivalent atmospheric OH exposure of 3 weeks. In contrast, at low RH (RH =25 %) there is little mass loss (<20 %) at the same OH exposure. Mass spectra of the SOA particles were measured as a function of OH exposure using a vacuum ultraviolet aerosol mass spectrometer (VUV-AMS). The mass spectra observed at low RH overall exhibit minor changes with oxidation and negligible further changes above an OH exposure =2×1012 molecule cm−3 s suggesting limited impact of oxidation on the particle composition. In contrast, the mass spectra observed at high RH exhibit substantial and continuous changes as a function of OH exposure. Further, at high RH clusters of peaks in the mass spectra exhibit unique decay patterns, suggesting different responses of various species to oxidation. A model of heterogeneous oxidation has been developed to understand the origin of the difference in aging between the low- and high-RH experiments. Differences in diffusivity of the SOA between the low- and high-RH experiments alone can explain the difference in compositional change but cannot explain the difference in mass loss. Instead, the difference in mass loss is attributable to RH-dependent differences in the OH uptake coefficient and/or the net probability of fragmentation, with either or both larger at high RH compared to low RH. These results illustrate the important impact of relative humidity on the fate of SOA in the atmosphere.

A Kinetic and Mechanistic Study of the Reactions of OH Radicals and Cl Atoms with 3,3,3-Trifluoropropanol under Atmospheric Conditions

2005 ◽  
Vol 109 (2) ◽  
pp. 347-355 ◽  
Author(s):  
Tanya Kelly ◽  
Valérie Bossoutrot ◽  
Isabelle Magneron ◽  
Klaus Wirtz ◽  
Jack Treacy ◽  
...  
Keyword(s):  
Mechanistic Study ◽  
Oh Radicals ◽  
Atmospheric Conditions ◽  
Cl Atoms

scholarly journals Chemical evolution of secondary organic aerosol from OH-initiated heterogeneous oxidation

2010 ◽  
Vol 10 (2) ◽  
pp. 3265-3300 ◽  
Author(s):  
I. J. George ◽  
J. P. D. Abbatt
Keyword(s):  
Mass Spectra ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Heterogeneous Oxidation ◽  
Atmospheric Aging ◽  
Aerosol Mass ◽  
Degree Of Oxidation ◽  
Aerosol Aging

Abstract. The heterogeneous oxidation of laboratory Secondary Organic Aerosol (SOA) particles by OH radicals was investigated. SOA particles, produced by reaction of α-pinene and O3, were exposed to OH radicals in a flow tube, and particle chemical composition, size, and hygroscopicity were measured to assess modifications due to oxidative aging. Aerosol Mass Spectrometer (AMS) mass spectra indicated that the degree of oxidation of SOA particles was significantly enhanced due to OH-initiated oxidation. Particle O/C ratios calculated from m/z 44 fraction from organic mass spectra rose by a maximum of ~0.04 units under equivalent atmospheric aging timescales of 2 weeks assuming a 24-h average OH concentration of 106 cm−3. Particle densities also increased with heterogeneous oxidation, consistent with the observed increase in the degree of oxidation. Minor reductions in particle size, with volume losses of up to 10%, were observed due to volatilization of oxidation products. The SOA particles became slightly more CCN active with an increase in the κ hygroscopicity parameter of up to a factor of two for the equivalent of 2 weeks of OH atmospheric exposure. These results indicate that OH heterogeneous oxidation of typical SOA proceeds sufficiently rapidly to be an atmospherically important organic aerosol aging mechanism.

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