scholarly journals Stochastic methods for aerosol chemistry: a compact molecular description of functionalization and fragmentation in the heterogeneous oxidation of squalane aerosol by OH radicals

2015 ◽  
Vol 17 (6) ◽  
pp. 4398-4411 ◽  
Author(s):  
A. A. Wiegel ◽  
K. R. Wilson ◽  
W. D. Hinsberg ◽  
F. A. Houle
Keyword(s):  
Chemical Reactions ◽  
Organic Aerosol ◽  
Ageing Process ◽  
Stochastic Methods ◽  
Oh Radicals ◽  
Aerosol Chemistry ◽  
Heterogeneous Oxidation ◽  
Specific Chemical ◽  
Specific Chemical Reactions ◽  
Molecular Description

A compact, experimentally validated model of organic aerosol oxidation enables the ageing process to be connected to specific chemical reactions.

Topological Indices of Molecular Graphs Under Specific Chemical Reactions

2013 ◽  
Vol 2 (1) ◽  
pp. 68-74 ◽  
Author(s):  
Ramakrishnan S ◽  
◽  
Senbagamalar J ◽  
Baskar Babujee J ◽  
◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Topological Indices ◽  
Specific Chemical ◽  
Molecular Graphs ◽  
Specific Chemical Reactions

scholarly journals Formation of hydroxyl radicals from photolysis of secondary organic aerosol material

2015 ◽  
Vol 15 (4) ◽  
pp. 4117-4143 ◽  
Author(s):  
K. M. Badali ◽  
S. Zhou ◽  
D. Aljawhary ◽  
M. Antiñolo ◽  
W. J. Chen ◽  
...  
Keyword(s):  
Hydroxyl Radicals ◽  
Secondary Organic Aerosol ◽  
Formation Rate ◽  
Cumene Hydroperoxide ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Aerosol Chemistry ◽  
Peroxide Content ◽  
Radical Trap ◽  
Organic Hydroperoxides

Abstract. This paper demonstrates that OH radicals are formed by photolysis of secondary organic aerosol (SOA) material formed by terpene ozonolysis. The SOA aerosol is collected on filters, dissolved in water containing a radical trap (benzoic acid), and then exposed to ultraviolet light in a photochemical reactor. The OH formation rates, which are similar for both α-pinene and limonene SOA, are measured from the formation rate of p-hydroxybenzoic acid as measured using offline HPLC analysis. To evaluate whether the OH is formed by photolysis of H2O2 or organic hydroperoxides (ROOH), the peroxide content of the SOA was measured using the horseradish peroxidase-dichlorofluorescein (HRP-DCF) assay, which was calibrated using H2O2. The OH formation rates from SOA are five times faster than from the photolysis of H2O2 solutions whose concentrations correspond to the peroxide content of the SOA solutions assuming that the HRP-DCF signal arises from H2O2 alone. The higher rates of OH formation from SOA are likely due to ROOH photolysis. This result is substantiated by photolysis experiments conducted with t-butyl hydroperoxide and cumene hydroperoxide which produce over three times more OH than photolysis of equivalent concentrations of H2O2. Relative to the peroxide level in the SOA, the quantum yield for OH generation from α-pinene SOA is 0.8 ± 0.4. This is the first demonstration of an efficient photolytic source of OH in SOA, one that may affect both cloudwater and aerosol chemistry.

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.

Organic chemistry students' ideas about nucleophiles and electrophiles: the role of charges and mechanisms

2015 ◽  
Vol 16 (4) ◽  
pp. 797-810 ◽  
Author(s):  
Mary E. Anzovino ◽  
Stacey Lowery Bretz
Keyword(s):  
Organic Chemistry ◽  
Chemical Reactions ◽  
Reaction Mechanisms ◽  
Learning Mechanisms ◽  
Specific Chemical ◽  
Chemistry Students ◽  
Specific Chemical Reactions

Organic chemistry students struggle with reaction mechanisms and the electron-pushing formalism (EPF) used by practicing organic chemists. Faculty have identified an understanding of nucleophiles and electrophiles as one conceptual prerequisite to mastery of the EPF, but little is known about organic chemistry students' knowledge of nucleophiles and electrophiles. This research explored the ideas held by second-semester organic chemistry students about nucleophiles and electrophiles, finding that these students prioritize structure over function, relying primarily on charges to define and identify such species, both in general and in the context of specific chemical reactions. Contrary to faculty who view knowledge of nucleophiles and electrophiles as prerequisite to learning mechanisms and EPF, students demonstrated that they needed to know the mechanism of a reaction before they were able to assess whether the reaction involved nucleophiles and electrophiles or not.

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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