scholarly journals Importance of SOA formation of α-pinene, limonene and <i>m</i>-cresol comparing day-and night-time radical chemistry

2020 ◽  
Author(s):  
Anke Mutzel ◽  
Yanli Zhang ◽  
Olaf Böge ◽  
Maria Rodigast ◽  
Agata Kolodziejczyk ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Radical Reaction ◽  
Water Soluble ◽  
Oh Radicals ◽  
Oh Radical ◽  
Night Time ◽  
Formation Potential ◽  
Phase Constituent ◽  
Dry Conditions ◽  
The One

Abstract. The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate α-pinene, limonene and m-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NO3 radicals) and day-time conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NO3 significantly exceeds the one of the OH radical reaction, with SOA yields of 15–30 % and 10–21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. On the contrary, the SOA formation potential of α-pinene with NO3 slightly exceeds that of the OH radical reaction, independent from RH. In average, α-pinene yielded SOA with about 6–7 % from NO3 radicals and 3–4 % from OH radical reaction. Surprisingly, unexpected high SOA yields were found for m-cresol oxidation with OH radicals (3–9 %) with the highest yield under elevated RH (9 %) which is most likely attributed to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While α-pinene and m-cresol SOA was found to be mainly composed of water-soluble compounds, 50–68 % of nocturnal SOA and 22–39 % of daytime limonene SOA is water-insoluble. The fraction of SOA-bound peroxides which originated from α-pinene varied between 2–80 % as a function of RH. Furthermore, SOA from α-pinene revealed pinonic acid as the most important particle-phase constituent under day- and night-time conditions with fraction of 1–4 %. Further compounds detected are norpinonic acid (0.05–1.1 % mass fraction), terpenylic acid (0.1–1.1 % mass fraction), pinic acid (0.1–1.8 % mass fraction) and 3-methyl-1,2,3-tricarboxylic acid (0.05–0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and almost no RH effect when formed during night.

scholarly journals Importance of secondary organic aerosol formation of <i>α</i>-pinene, limonene, and <i>m</i>-cresol comparing day- and nighttime radical chemistry

2021 ◽  
Vol 21 (11) ◽  
pp. 8479-8498
Author(s):  
Anke Mutzel ◽  
Yanli Zhang ◽  
Olaf Böge ◽  
Maria Rodigast ◽  
Agata Kolodziejczyk ◽  
...  
Keyword(s):  
Mass Fraction ◽  
Secondary Organic Aerosol ◽  
Radical Reaction ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Oh Radicals ◽  
Oh Radical ◽  
Aerosol Formation ◽  
Formation Potential ◽  
Dry Conditions

Abstract. The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate α-pinene, limonene, and m-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NO3 radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NO3 under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15–30 % and 10–21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of α-pinene with NO3 slightly exceeds that of the OH-radical reaction, independent from RH. On average, α-pinene yielded SOA with about 6–7 % from NO3 radicals and 3–4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for m-cresol oxidation with OH radicals (3–9 %), with the highest yield under elevated RH (9 %), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While α-pinene and m-cresol SOA was found to be mainly composed of water-soluble compounds, 50–68 % of nocturnal SOA and 22–39 % of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from α-pinene varied between 2 and 80 % as a function of RH. Furthermore, SOA from α-pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1–4 %. Other compounds detected are norpinonic acid (0.05–1.1 % mass fraction), terpenylic acid (0.1–1.1 % mass fraction), pinic acid (0.1–1.8 % mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05–0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night.

Reaction kinetics of OH radicals with glutaric acid and adipic acid in the aqueous phase

2021 ◽  
Author(s):  
Liang Wen ◽  
Thomas Schaefer ◽  
Hartmut Herrmann
Keyword(s):  
Aqueous Phase ◽  
Adipic Acid ◽  
Rate Constants ◽  
Density Functional ◽  
Glutaric Acid ◽  
Radical Reaction ◽  
Basis Set ◽  
Oh Radicals ◽  
Oh Radical ◽  
Energy Barriers

&lt;p&gt;Dicarboxylic acids (DCAs) are widely distributed in atmospheric aerosols and cloud droplets and are mainly formed by the oxidation of volatile organic compounds (VOCs). For example, glutaric acid and adipic acid are two kinds of the DCAs that can be oxidized by hydroxyl radical (&amp;#8231;OH) reactions in the aqueous phase of aerosols and droplets. In the present study, the temperature- and pH-dependent rate constants of the aqueous OH radical reactions of the two DCAs were investigated by a laser flash photolysis-long path absorption setup using the competition kinetics method. Based on speciation calculations, the OH radical reaction rate constants of the fully protonated (H&lt;sub&gt;2&lt;/sub&gt;A), deprotonated (HA&lt;sup&gt;-&lt;/sup&gt;) and fully deprotonated (A&lt;sup&gt;2-&lt;/sup&gt;) forms of the two DCAs were determined. The following Arrhenius expressions for the T-dependency of the OH radical reaction of glutaric acid, k(T, H&lt;sub&gt;2&lt;/sub&gt;A) = (3.9 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1270 &amp;#177; 200 K)/T], k(T, HA&lt;sup&gt;-&lt;/sup&gt;) = (2.3 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;11&lt;/sup&gt; &amp;#215; exp[(-1660 &amp;#177; 190 K)/T], k(T, A&lt;sup&gt;2-&lt;/sup&gt;) = (1.4 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;11&lt;/sup&gt; &amp;#215; exp[(-1400 &amp;#177; 170 K)/T] and adipic acid, k(T, H&lt;sub&gt;2&lt;/sub&gt;A) = (7.5 &amp;#177; 0.2) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1210 &amp;#177; 170 K)/T], k(T, HA&lt;sup&gt;-&lt;/sup&gt;) = (9.5 &amp;#177; 0.3) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1200 &amp;#177; 200 K)/T], k(T, A&lt;sup&gt;2-&lt;/sup&gt;) = (8.7 &amp;#177; 0.2) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1100 &amp;#177; 170 K)/T] (in unit of L mol&lt;sup&gt;-1&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;) were derived.&lt;/p&gt;&lt;p&gt;The energy barriers of the H-atom abstractions were simulated by the Density Functional Theory calculations run with the GAUSSIAN package using the M06-2X method and the basis set m062x/6-311++g(3df,2p). The results showed that the energy barriers were lower at the C&lt;sub&gt;&amp;#946;&lt;/sub&gt;-atoms and are higher at the C&lt;sub&gt;&amp;#945;&lt;/sub&gt;-atoms of the two DCAs, clearly suggesting that the H-atom abstractions occurred predominately at the C&lt;sub&gt;&amp;#946;&lt;/sub&gt;-atoms. In addition, the ionizations can enhance the electrostatic effects of the carboxyl groups, significantly reducing the energy barriers, leading to the order of OH radical reactivity as &amp;#160;&lt; &amp;#160;&lt; . This study intends to better characterize the losing processes of glutaric acid and adipic acid in atmospheres.&lt;/p&gt;

scholarly journals Influence of relative humidity and temperature on the production of pinonaldehyde and OH radicals from the ozonolysis of α-pinene

2010 ◽  
Vol 10 (15) ◽  
pp. 7057-7072 ◽  
Author(s):  
R. Tillmann ◽  
M. Hallquist ◽  
Å. M. Jonsson ◽  
A. Kiendler-Scharr ◽  
H. Saathoff ◽  
...  
Keyword(s):  
Gas Phase ◽  
Degradation Mechanism ◽  
Product Distribution ◽  
Major Product ◽  
Radical Formation ◽  
Oh Radicals ◽  
Oh Radical ◽  
Significant Difference ◽  
Dry Conditions

Abstract. The ozonolysis of α-pinene has been investigated under dry and humid conditions in the temperature range of 243–303 K. The results provided new insight into the role of water and temperature in the degradation mechanism of α-pinene and in the formation of secondary organic aerosols (SOA). The SOA yields were higher at humid conditions than at dry conditions. The water induced gain was largest for the lowest temperatures investigated (243 and 253 K). The increase in the SOA yields was dominated by water (and temperature) effects on the organic product distribution, whilst physical uptake of water was negligible. This will be demonstrated for the example of pinonaldehyde (PA) which was formed as a major product in the humid experiments with total molar yields of 0.30±0.06 at 303 K and 0.15±0.03 at 243 K. In the dry experiments the molar yields of PA were only 0.07±0.02 at 303 K and 0.02±0.02 at 253 K. The observed partitioning of PA as a function of the SOA mass present at 303 K limited the effective vapour pressure of pure PA pPA0 to the range of 0.01–0.001 Pa, 3–4 orders of magnitude lower than literature values. The corresponding mass partitioning coefficient was determined to KPA=0.005±0.004 m3 μg−1 and the total mass yield αPAtotal=0.37±0.08. At 303 K PA preferably stayed in the gas-phase, whereas at 253 K and 243 K it exclusively partitioned into the particulate phase. PA could thus account at least for half of the water induced gain in SOA mass at 253 K. The corresponding effect was negligible at 303 K because the PA preferably remained in the gas-phase. The yield of OH radicals, which were produced in the ozonolysis, was indirectly determined by means of the yield of cyclohexanone formed in the reaction of OH radicals with cyclohexane. OH yields of the α-pinene ozonolysis were determined to 0.67±0.17 for humid and 0.54±0.13 for dry conditions at 303 K, indicating a water dependent path of OH radical formation. For 253 and 243 K OH yields could be estimated to 0.5 with no significant difference between the dry and humid experiments. This is the first clear indication for OH radical formation by α-pinene ozonolysis at such low temperatures.

Reaction of OH radicals with 5-hydroxy-2-pentanone: formation yield of 4-oxopentanal and its OH radical reaction rate constant

2013 ◽  
Vol 10 (3) ◽  
pp. 145 ◽  
Author(s):  
Sara M. Aschmann ◽  
Janet Arey ◽  
Roger Atkinson
Keyword(s):  
Gas Phase ◽  
Rate Constant ◽  
First Generation ◽  
Solid Phase ◽  
Radical Reaction ◽  
Oh Radicals ◽  
Oh Radical ◽  
Aerosol Formation ◽  
Gas Phase Reactions ◽  
Concentration Data

Environmental context Alkanes, major constituents of vehicle exhausts, are emitted to the atmosphere where they react, chiefly by gas-phase reactions with the hydroxyl radical, to form products which can also react further. In laboratory experiments, we studied the further reactions of a model first-generation alkane reaction product. Understanding alkane reaction chains is important because the toxicity, secondary aerosol formation and other properties of vehicle emissions can change as new compounds are formed. Abstract 1,4-Hydroxycarbonyls are major products of the gas-phase reactions of alkanes with OH radicals, and in the atmosphere they will react with OH radicals or undergo acid-catalysed cyclisation with subsequent dehydration to form highly reactive dihydrofurans. 3-Oxobutanal (CH3C(O)CH2CHO) and 4-oxopentanal (CH3C(O)CH2CH2CHO) are first-generation products of the OH radical-initiated reaction of 5-hydroxy-2-pentanone (CH3C(O)CH2CH2CH2OH). The behaviours of 3-oxobutanal and 4-oxopentanal have been monitored during OH+5-hydroxy-2-pentanone reactions carried out in the presence of NO, using solid phase microextraction fibres coated with O-(2,3,4,5,6,-pentafluorobenzyl)hydroxyl amine (PFBHA) for on-fibre derivatisation of carbonyl compounds and an annular denuder coated with XAD resin and further coated with PFBHA. The time-concentration data for 4-oxopentanal during OH+5-hydroxy-2-pentanone reactions were independent of relative humidity (0–50%), and were consistent with a rate constant for OH+4-oxopentanal of (1.2±0.5)×10–11cm3 molecule–1s–1 at 296±2K, a factor of 2 lower than both literature rate constants for other aldehydes and that estimated using a structure-reactivity approach. The molar formation yield for 4-oxopentanal from OH+5-hydroxy-2-pentanone in the presence of NO was determined to be 17±5%, consistent with predictions based on a structure-reactivity relationship and current knowledge of the subsequent reaction mechanisms.

scholarly journals Molecular composition of fresh and aged secondary organic aerosol from a mixture of biogenic volatile compounds: a high-resolution mass spectrometry study

2015 ◽  
Vol 15 (10) ◽  
pp. 5683-5695 ◽  
Author(s):  
I. Kourtchev ◽  
J.-F. Doussin ◽  
C. Giorio ◽  
B. Mahon ◽  
E. M. Wilson ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
High Resolution ◽  
High Resolution Mass Spectrometry ◽  
Radical Reaction ◽  
Organic Aerosol ◽  
Molecular Composition ◽  
Oh Radicals ◽  
Oh Radical ◽  
High Resolution Mass ◽  
Resolution Mass

Abstract. Field observations over the past decade indicate that a significant fraction of organic aerosol in remote areas may contain highly oxidized molecules. Aerosol processing or further oxidation (aging) of organic aerosol has been suggested to be responsible for their formation through heterogeneous reaction with oxidants and multigenerational oxidation of vapours by OH radicals. In this study we investigated the influence of several aging processes on the molecular composition of secondary organic aerosols (SOA) using direct infusion and liquid chromatography high-resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, Δ3-carene and isoprene. The SOA was subsequently aged under three different sets of conditions: in the dark in the presence of residual ozone, with UV irradiation and OH radicals, and using UV light only. Among all studied conditions, only OH radical-initiated aging was found to influence the molecular composition of the aerosol and showed an increase in carbon oxidation state (OSC) and elemental O / C ratios of the SOA components. None of the aging processes produced an observable effect on the oligomers formed from ozonolysis of the BVOC mixture, which were found to be equally abundant in both "fresh" and "aged" SOA. Additional experiments using α-pinene as the sole precursor demonstrated that oligomers are an important group of compounds in SOA produced from both ozonolysis and OH radical-initiated oxidation processes; however, a completely different set of oligomers is formed under these two oxidation regimes. SOA from the OH-initiated oxidation of α-pinene had a significantly higher overall OSC and O / C compared to that from pure ozonolysis experiments confirming that the OH radical reaction is more likely to be responsible for the occurrence of highly oxidized species in ambient biogenic SOA.

scholarly journals Molecular composition of aged secondary organic aerosol generated from a mixture of biogenic volatile compounds using ultrahigh resolution mass spectrometry

2015 ◽  
Vol 15 (4) ◽  
pp. 5359-5389 ◽  
Author(s):  
I. Kourtchev ◽  
J.-F. Doussin ◽  
C. Giorio ◽  
B. Mahon ◽  
E. M. Wilson ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Uv Light ◽  
Radical Reaction ◽  
Organic Aerosol ◽  
Molecular Composition ◽  
Oh Radicals ◽  
Oh Radical ◽  
Ultrahigh Resolution ◽  
Ageing Processes ◽  
Resolution Mass

Abstract. Field observations over the past decade indicate that a significant fraction of organic aerosol in remote areas may contain highly oxidised molecules. Aerosol processing or further oxidation (ageing) of organic aerosol has been suggested to be responsible for their formation through heterogeneous uptake of oxidants and multigenerational oxidation of vapours by OH radicals. In this study we investigated the influence of several ageing processes on the molecular composition of secondary organic aerosols (SOA) using direct infusion and liquid chromatography ultrahigh resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, Δ3-carene and isoprene. The SOA was subsequently aged under three different sets of conditions: in the dark in the presence of residual ozone, with UV irradiation and OH radicals, and using UV light only. Among all studied conditions, only OH radical-initiated ageing was found to influence the molecular composition of the aerosol and showed an increase in carbon oxidation state (OSC) and elemental O/C ratios of the SOA components. None of the ageing processes produced an observable effect on the oligomers formed from ozonolysis of the BVOC mixture, which were found to be equally abundant in both "fresh" and "aged" SOA. Additional experiments using α-pinene as the sole precursor demonstrated that oligomers are an important group of compounds in SOA produced from both ozonolysis and OH radical-initiated oxidation processes; however, a completely different set of oligomers is formed under these two oxidation regimes. SOA from the OH radical-initiated α-pinene oxidation had a significantly higher overall OSC and O/C compared to that from pure ozonolysis experiments confirming that the OH radical reaction is more likely to be responsible for the occurrence of highly oxidised species in ambient biogenic SOA.

scholarly journals Influence of relative humidity and temperature on the production of pinonaldehyde and OH radicals from the ozonolysis of α-pinene

2010 ◽  
Vol 10 (2) ◽  
pp. 3129-3172 ◽  
Author(s):  
R. Tillmann ◽  
M. Hallquist ◽  
Å. M. Jonsson ◽  
A. Kiendler-Scharr ◽  
H. Saathoff ◽  
...  
Keyword(s):  
Gas Phase ◽  
Degradation Mechanism ◽  
Product Distribution ◽  
Major Product ◽  
Radical Formation ◽  
Oh Radicals ◽  
Oh Radical ◽  
Significant Difference ◽  
Dry Conditions

Abstract. The ozonolysis of α-pinene has been investigated under dry and humid conditions in the temperature range of 243–303 K. The results provided new insight into the role of water and temperature in the degradation mechanism of α-pinene and in the formation of secondary organic aerosols (SOA). The SOA yields were higher at humid conditions than at dry conditions. The water induced gain was largest for the lowest temperatures investigated (243 and 253 K). The increase in the SOA yields was dominated by water (and temperature) effects on the organic product distribution, whilst physical uptake of water was negligible. This will be demonstrated for the example of pinonaldehyde (PA) which was formed as a~major product in the humid experiments with total molar yields of 0.30±0.06 at 303 K and 0.15±0.03 at 243 K. In the dry experiments the molar yields of PA were only 0.07±0.02 at 303 K and 0.02±0.02 at 253 K. The observed partitioning of PA as a function of the SOA mass present at 303 K limited the effective vapour pressure of pure PA pPA0 to the range of 0.01–0.001 Pa, 3–4 orders of magnitude lower than literature values. The corresponding mass partitioning coefficient was determined to KPA=0.005±0.004 m3/μg and the total mass yield αPA.total=0.37±0.08. At 303 K PA preferably stayed in the gas-phase, whereas at 253 K and 243 K it exclusively partitioned into the particulate phase. PA could thus account at least for half of the water induced gain in SOA mass at 253 K. The corresponding effect was negligible at 303 K because the PA preferably remained in the gas-phase. The yield of OH radicals, which were produced in the ozonolysis, was indirectly determined by means of the yield of cyclohexanone formed in the reaction of OH radicals with cyclohexane. OH yields of the α-pinene ozonolysis were determined to 0.67±0.17 for humid and 0.54±0.13 for dry conditions at 303 K, indicating a water dependent path of OH radical formation. For 253 and 243 K OH yields could be estimated to 0.5 with no significant difference between the dry and humid experiments. This is the first clear indication for OH radical formation by α-pinene ozonolysis at such low temperatures.

Glyoxal secondary organic aerosol chemistry: effects of dilute nitrate and ammonium and support for organic radical–radical oligomer formation

2013 ◽  
Vol 10 (3) ◽  
pp. 158 ◽  
Author(s):  
Jeffrey R. Kirkland ◽  
Yong B. Lim ◽  
Yi Tan ◽  
Katye E. Altieri ◽  
Barbara J. Turpin
Keyword(s):  
Secondary Organic Aerosol ◽  
Inorganic Nitrogen ◽  
Radical Reaction ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Organic Radical ◽  
Oh Radical ◽  
Radical Oxidation ◽  
Oligomer Formation ◽  
First Time

Environmental context Atmospheric waters (clouds, fogs and wet aerosols) are media in which gases can be converted into particulate matter. This work explores aqueous transformations of glyoxal, a water-soluble gas with anthropogenic and biogenic sources. Results provide new evidence in support of previously proposed chemical mechanisms. These mechanisms are beginning to be incorporated into transport models that link emissions to air pollution concentrations and behaviour. Abstract Glyoxal (GLY) is ubiquitous in the atmosphere and an important aqueous secondary organic aerosol (SOA) precursor. At dilute (cloud-relevant) organic concentrations, OH• radical oxidation of GLY has been shown to produce oxalate. GLY has also been used as a surrogate species to gain insight into radical and non-radical reactions in wet aerosols, where organic and inorganic concentrations are very high (in the molar region). The work herein demonstrates, for the first time, that tartarate forms from GLY+OH•. Tartarate is a key product in a previously proposed organic radical–radical reaction mechanism for oligomer formation from GLY oxidation. Previously published model predictions that include this GLY oxidation pathway suggest that oligomers are major products of OH• radical oxidation at the high organic concentrations found in wet aerosols. The tartarate measurements herein provide support for this proposed oligomer formation mechanism. This paper also demonstrates, for the first time, that dilute (cloud or fog-relevant) concentrations of inorganic nitrogen (i.e. ammonium and nitrate) have little effect on the GLY+OH• chemistry leading to oxalate formation in clouds. This, and results from previous experiments conducted with acidic sulfate, increase confidence that the currently understood dilute GLY+OH• chemistry can be used to predict GLY SOA formation in clouds and fogs. It should be recognised that organic–inorganic interactions can play an important role in droplet evaporation chemistry and in wet aerosols. The chemistry leading to SOA formation in these environments is complex and remains poorly understood.

A new analytical method, using the dark Fenton reaction as an OH radical source to study oxidations of unsaturated (di)aldehydes in the aqueous phase

2021 ◽  
Author(s):  
Majda Mekic ◽  
Thomas Schaefer ◽  
Hartmut Herrmann
Keyword(s):  
Organic Compounds ◽  
Aqueous Phase ◽  
Phase Transfer ◽  
Catalytic Decomposition ◽  
Water Soluble ◽  
Radical Scavenger ◽  
Oh Radicals ◽  
Oh Radical ◽  
Fenton Chemistry ◽  
Typical Experiment

&lt;p&gt;Anthropogenic and biogenic sources produce numerous primary emitted gases, organic compounds, and aerosols in the atmosphere. An important group of such compounds are &amp;#945;, &amp;#946;-unsaturated carbonyl molecules, which can be formed in the atmosphere due to their secondary origin, including oxidation of their precursors such as hydrocarbons with common atmospheric oxidants such as hydroxyl radicals (&amp;#8231;OH). Since those compounds contain at least one double bond and one carbonyl group, they are characterized as water-soluble molecules, which can diffuse on the cloud droplets&amp;#8217; surface and undergo a phase transfer from the gas phase to the atmospheric aqueous phase. In the latter, the oxidized organic compounds can contribute to aerosol mass production through in-cloud processes, yielding aqueous phase secondary organic aerosols (aqSOA). Due to their strong photochemical behavior, the development of a new analytical approach for evaluating the OH radical kinetics in the aqueous phase under dark conditions was essential. One of the most studied non-photolytic reactions is Fenton chemistry (Fe(II)/H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;), which serves as an OH radical source in the dark in the atmospheric aqueous phase after catalytic decomposition of H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; in the presence of Fe(II) at acidic pH values. In a typical experiment, temperature-dependent second-order rate constants of OH radicals with unsaturated dialdehydes, such as (1) crotonaldehyde, and (2) 1,4-butenedial, were determined in a bulk reactor by using the competition kinetics method. In the newly developed method, the role of radical scavenger was performed by isotopically labeled 2-propanol (d8), while the OH-initiated oxidation produces deuterated acetone (d6), being analyzed with GC-MS after derivatization. The findings from our research will be incorporated in the CAPRAM model to explain discrepancies between experimentally observed and predicted aqSOA properties.&lt;/p&gt;

scholarly journals Atmospheric oxidation of α,β-unsaturated ketones: kinetics and mechanism of the OH radical reaction

2021 ◽  
Author(s):  
Niklas Illmann ◽  
Rodrigo Gastón Gibilisco ◽  
Iustinian Gabriel Bejan ◽  
Iulia Patroescu-Klotz ◽  
Peter Wiesen
Keyword(s):  
Radical Reaction ◽  
Rate Coefficients ◽  
Organic Nitrates ◽  
Oh Radicals ◽  
Oh Radical ◽  
Peroxyacetyl Nitrate ◽  
Unsaturated Ketones ◽  
Product Yields ◽  
Mechanistic Investigation ◽  
Cl Atoms

Abstract. The OH radical initiated oxidation of 3-methyl-3-penten-2-one and 4-methyl-3-penten-2-one was investigated in two atmospheric simulation chambers at 298 ± 3 K and 990 ± 15 mbar using long-path FTIR spectroscopy. The rate coefficients of the reactions of 3-methyl-3-penten-2-one and 4-methyl-3-penten-2-one with OH radicals were determined to be (6.5 ± 1.2) × 10−11 cm3 molecule−1 s−1 and (8.1 ± 1.3) × 10−11 cm3 molecule−1 s−1, respectively. To enlarge the kinetics data pool the rate coefficients of the target species with Cl atoms were determined to be (2.8 ± 0.4) × 10−10 cm3 molecule−1 s−1 and (3.1 ± 0.4) × 10−10 cm3 molecule−1 s−1, respectively. The mechanistic investigation of the OH initiated oxidation focuses on the RO2 + NO reaction. The quantified products were acetoin, acetaldehyde, biacetyl, CO2 and peroxyacetyl nitrate (PAN) for the reaction of 3-methyl-3-penten-2-one with OH radicals and acetone, methyl glyoxal, 2-hydroxy-2-methylpropanal, CO2 and peroxyacetyl nitrate (PAN) for the reaction of 4-methyl-3-penten-2-one with OH, respectively. Based on the calculated product yields an upper limit of 0.15 was determined for the overall organic nitrates (RONO2) yield derived from the OH reaction of 4-methyl-3-penten-2-one. By contrast, no RONO2 formation was observed for the OH reaction of 3-methyl-3-penten-2-one. Additionally, a simple model is presented to correct product yields for secondary processes.

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