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.

scholarly journals Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change

2007 ◽  
Vol 7 (16) ◽  
pp. 4187-4201 ◽  
Author(s):  
I. J. George ◽  
A. Vlasenko ◽  
J. G. Slowik ◽  
K. Broekhuizen ◽  
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=1.3 (±0.4), 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.

scholarly journals Controlled nitric oxide production via O(<sup>1</sup>D)+N<sub>2</sub>O reactions for use in oxidation flow reactor studies

2017 ◽  
Author(s):  
Andrew Lambe ◽  
Paola Massoli ◽  
Xuan Zhang ◽  
Manjula Canagaratna ◽  
John Nowak ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Flow Reactor ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Flow Reactors ◽  
Oxidative Aging ◽  
Gas Phase Oxidation

Abstract. Oxidation flow reactors that use low-pressure mercury lamps to produce hydroxyl (OH) radicals are an emerging technique for studying the oxidative aging of organic aerosols. Here, ozone (O3) is photolyzed at 254 nm to produce O(1D) radicals, which react with water vapor to produce OH. However, the need to use parts-per-million levels of O3 hinders the ability of oxidation flow reactors to simulate NOx-dependent SOA formation pathways. Simple addition of nitric oxide (NO) results in fast conversion of NOx (NO + NO2) to nitric acid (HNO3), making it impossible to sustain NO at levels that are sufficient to compete with hydroperoxy (HO2) radicals as a sink for organic peroxy (RO2) radicals. We developed a new method that is well suited to the characterization of NOx-dependent SOA formation pathways in oxidation flow reactors. NO and NO2 are produced via the reaction O(1D) + N2O→ 2NO, followed by the reaction NO + O3 → NO2+ O2. Laboratory measurements coupled with photochemical model simulations suggest that O(1D) + N2O reactions can be used to systematically vary the relative branching ratio of RO2 + NO reactions relative to RO2 + HO2 and/or RO2 + RO2 reactions over a range of conditions relevant to atmospheric SOA formation. We demonstrate proof of concept using high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) measurements with nitrate (NO3−) reagent ion to detect gas-phase oxidation products of isoprene and α-pinene previously observed in NOx-influenced environments and in laboratory chamber experiments.

scholarly journals Studying volatility from composition, dilution, and heating measurements of secondary organic aerosols formed during <i>α</i>-pinene ozonolysis

2018 ◽  
Vol 18 (8) ◽  
pp. 5455-5466 ◽  
Author(s):  
Kei Sato ◽  
Yuji Fujitani ◽  
Satoshi Inomata ◽  
Yu Morino ◽  
Kiyoshi Tanabe ◽  
...  
Keyword(s):  
Secondary Organic Aerosols ◽  
Yield Curve ◽  
Volume Fraction ◽  
Organic Aerosols ◽  
Accommodation Coefficient ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Mass Accommodation Coefficient ◽  
Kinetic Inhibition ◽  
Photochemical Aging

Abstract. Traditional yield curve analysis shows that semi-volatile organic compounds are a major component of secondary organic aerosols (SOAs). We investigated the volatility distribution of SOAs from α-pinene ozonolysis using positive electrospray ionization mass analysis and dilution- and heat-induced evaporation measurements. Laboratory chamber experiments were conducted on α-pinene ozonolysis, in the presence and absence of OH scavengers. Among these, we identified not only semi-volatile products, but also less volatile highly oxygenated molecules (HOMs) and dimers. Ozonolysis products were further exposed to OH radicals to check the effects of photochemical aging. HOMs were also formed during OH-initiated photochemical aging. Most HOMs that formed from ozonolysis and photochemical aging had 10 or fewer carbons. SOA particle evaporation after instantaneous dilution was measured at  < 1 and  ∼ 40 % relative humidity. The volume fraction remaining of SOAs decreased with time and the equilibration timescale was determined to be 24–46 min for SOA evaporation. The experimental results of the equilibration timescale can be explained when the mass accommodation coefficient is assumed to be 0.1, suggesting that the existence of low-volatility materials in SOAs, kinetic inhibition, or some combined effect may affect the equilibration timescale measured in this study.

scholarly journals Photo-oxidation of pinonaldehyde at low NO<sub>x</sub>: from chemistry to organic aerosol formation

2013 ◽  
Vol 13 (6) ◽  
pp. 3227-3236 ◽  
Author(s):  
H. J. Chacon-Madrid ◽  
K. M. Henry ◽  
N. M. Donahue
Keyword(s):  
First Generation ◽  
Single Species ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Photochemical Oxidation ◽  
Oh Radicals ◽  
General Tendency ◽  
Aerosol Formation ◽  
Uv Illumination ◽  
Terpene Oxidation

Abstract. Pinonaldehyde oxidation by OH radicals under low-NOx conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination, mass yields are lower than high-NOx yields published earlier by our group. However, when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NOx. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals, its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NOx products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.

Photochemical aging of organic aerosols at temperatures between 213 K and 293 K

2020 ◽  
Author(s):  
Magdalena Vallon ◽  
Linyu Gao ◽  
Junwei Song ◽  
Feng Jiang ◽  
Harald Saathoff
Keyword(s):  
Mass Spectrometer ◽  
Time Of Flight ◽  
Organic Aerosols ◽  
Photochemical Reactions ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Particle Phase ◽  
Resolution Time ◽  
Institute Of Technology ◽  
Photochemical Aging

&lt;p&gt;The chemical composition of aerosols, in both gas and particle phase, is an important factor regarding their properties influencing weather, climate and human health. Organic compounds are a major fraction of atmospheric aerosols and their composition depends on chemical processing by atmospheric oxidants and photochemical reactions. These processes are complex due to the abundance of possible reactions and reaction partners and rarely studied over a wider range of atmospheric temperatures. To get a better understanding of photochemical processes in the atmosphere we studied different organic test aerosols from simple to more complex systems between 213 K and 293 K in the AIDA simulation chamber at the Karlsruhe Institute of Technology.&amp;#160; Photochemical reactions were studied using a new LED light-source simulating solar radiation in the UV and visible. The organic aerosols were either generated in situ by oxidation of VOC with ozone, OH radicals and NO&lt;sub&gt;3&lt;/sub&gt; radicals or by nebulizing aqueous solutions containing the aerosol components. &amp;#160;The aerosols were analysed by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a high&amp;#8211;resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS). &amp;#160;The latter one offers the possibility to study the composition of gas phase and particle phase separately. First results suggest that secondary organic aerosols from single precursors like toluene or &amp;#945;-pinene show no or only very small changes related to photochemistry even when formed in presence of high NOx concentrations. In contrast, aerosol particles containing molecules with larger mesomeric systems or atmospherically relevant photosensitizers show significant changes upon irradiation.&lt;/p&gt;&lt;p&gt;In this presentation, we will discuss the changes that organic aerosols undergo in gas and particle phase, during photochemical aging at temperatures between 213 and 293 K.&lt;/p&gt;

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.

scholarly journals SO<sub>2</sub> oxidation products other than H<sub>2</sub>SO<sub>4</sub> as a trigger of new particle formation. Part 1: Laboratory investigations

2008 ◽  
Vol 8 (21) ◽  
pp. 6365-6374 ◽  
Author(s):  
T. Berndt ◽  
F. Stratmann ◽  
S. Bräsel ◽  
J. Heintzenberg ◽  
A. Laaksonen ◽  
...  
Keyword(s):  
Gas Phase ◽  
Particle Formation ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Phase Reaction ◽  
Peroxy Radicals ◽  
New Particle Formation ◽  
Reaction Conditions ◽  
Laboratory Investigations ◽  
Particle Formation And Growth

Abstract. Mechanistic investigations of atmospheric H2SO4 particle formation have been performed in a laboratory study taking either H2SO4 from a liquid reservoir or using the gas-phase reaction of OH radicals with SO2. Applying both approaches for H2SO4 generation simultaneously it was found that H2SO4 evaporated from the liquid reservoir acts considerably less effective for the process of particle formation and growth than the products originating from the reaction of OH radicals with SO2. Furthermore, for NOx concentrations >5×1011 molecule cm−3 the formation of new particles from the reaction of OH radicals with SO2 is inhibited. This suggests that substances other than H2SO4 (potentially products from sulphur-containing peroxy radicals) trigger lower tropospheric new particle formation and growth. The currently accepted mechanism for SO2 gas-phase oxidation does not consider the formation of such substances. The analysis of new particle formation for different reaction conditions in our experiment suggests that a contribution of impurities to the nucleation process is unlikely.

scholarly journals Photo-oxidation of pinonaldehyde at low NO<sub>x</sub>: from chemistry to organic aerosol formation

2012 ◽  
Vol 12 (3) ◽  
pp. 7727-7752 ◽  
Author(s):  
H. J. Chacon-Madrid ◽  
K. M. Henry ◽  
N. M. Donahue
Keyword(s):  
First Generation ◽  
Single Species ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Photochemical Oxidation ◽  
Oh Radicals ◽  
General Tendency ◽  
Aerosol Formation ◽  
Uv Illumination ◽  
Terpene Oxidation

Abstract. Pinonaldehyde oxidation by OH radicals under low-NOx conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination, mass yields are lower than high-NOx yields published earlier by our group. However, when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NOx. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals, its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NOx products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.

scholarly journals Lower than expected volatility of secondary organic aerosols formed during α-pinene ozonolysis

2017 ◽  
Author(s):  
Kei Sato ◽  
Yuji Fujitani ◽  
Satoshi Inomata ◽  
Yu Morino ◽  
Kiyoshi Tanabe ◽  
...  
Keyword(s):  
Secondary Organic Aerosols ◽  
Yield Curve ◽  
Organic Aerosols ◽  
Curve Analysis ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Mass Analysis ◽  
Volatile Products ◽  
Volatile Organic ◽  
Photochemical Aging

Abstract. Traditional yield curve analysis shows that semi-volatile organic compounds are a major component of secondary organic aerosols (SOAs). We investigated the volatility distribution of SOAs from α-pinene ozonolysis using positive electrospray ionization mass analysis and dilution- and heat-induced evaporation measurements. Laboratory chamber experiments were conducted on α-pinene ozonolysis, in the presence and absence of OH scavengers. Among these, we identified not only semi-volatile products, but also less volatile highly oxygenated molecules (HOMs) and dimers. Ozonolysis products were further exposed to OH radicals to check the effects of photochemical aging. HOMs were also formed during OH-initiated photochemical aging. Most HOMs that formed from ozonolysis and photochemical aging had ten or less carbons. SOA particle evaporation after instantaneous dilution was measured at

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