scholarly journals A new source of methylglyoxal in the aqueous phase

2016 ◽  
Vol 16 (4) ◽  
pp. 2689-2702 ◽  
Author(s):  
Maria Rodigast ◽  
Anke Mutzel ◽  
Janine Schindelka ◽  
Hartmut Herrmann
Keyword(s):  
Aqueous Phase ◽  
Rate Constants ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Multiphase System ◽  
Oh Radicals ◽  
Water Ice ◽  
Model Study ◽  
Phase Chemistry ◽  
First Time

Abstract. Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid-phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methylglyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methylglyoxal. Since methylglyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methylglyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp  =  5  ×  10−5 s−1), 2,3-butanedione (kp  =  9  ×  10−6 s−1), methylglyoxal (kp  =  3  ×  10−5 s−1), and hydroxyacetone (kp  =  2  ×  10−5 s−1). From the model predictions, a branching ratio of 60 /40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methylglyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methylglyoxal precursor compound for the first time.

scholarly journals A new source of methyl glyoxal in the aqueous phase

2015 ◽  
Vol 15 (21) ◽  
pp. 31891-31924
Author(s):  
M. Rodigast ◽  
A. Mutzel ◽  
J. Schindelka ◽  
H. Herrmann
Keyword(s):  
Aqueous Phase ◽  
Rate Constants ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Multiphase System ◽  
Oh Radicals ◽  
Methyl Glyoxal ◽  
Water Ice ◽  
Model Study ◽  
Phase Chemistry

Abstract. Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methyl glyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methyl glyoxal. Since methyl glyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methyl glyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp = 5 × 10−5 s−1), 2,3-butanedione (kp = 9 × 10−6 s−1), methyl glyoxal (kp = 3 × 10−5 s−1), and hydroxyacetone (kp = 2 × 10−5 s−1). From the model predictions, a branching ratio of 60/40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methyl glyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methyl glyoxal precursor compound for the first time.

scholarly journals Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone

2019 ◽  
Author(s):  
Bénédicte Picquet-Varrault ◽  
Ricardo Suarez-Bertoa ◽  
Marius Duncianu ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
...  
Keyword(s):  
Cross Sections ◽  
Rate Constants ◽  
Branching Ratio ◽  
Quantum Yields ◽  
Organic Nitrates ◽  
Oh Radicals ◽  
Important Species ◽  
Photolysis Rates ◽  
Photolysis Frequencies ◽  
First Time

Abstract. Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in NOx rich atmospheres by the degradation of VOCs. These compounds have been shown to play a key role in the transport of reactive nitrogen and consequently in the ozone budget, but also to be important components of the total organic aerosol. However, very little is known about their reactivity in both gas and condensed phases. Following a previous study we published on the gas-phase reactivity of β-nitrooxy ketones, the photolysis and the reaction with OH radicals of 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively a β-nitrooxy ketone and a γ-nitrooxy ketone, were investigated for the first time in simulation chambers. Ambient photolysis frequencies calculated for 40° latitude North were found to be (4.2 ± 0.6) × 10−5 s−1 and (2.2 ± 0.7) × 10−5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively. These results demonstrate that photolysis is a very efficient sink for these compounds with atmospheric lifetimes of few hours. It was also concluded that, similarly to α-nitrooxy ketones, β-nitrooxy ketones have enhanced UV absorption cross sections and quantum yields equal or close to unity. γ-nitrooxy ketones have been shown to have lower enhancement of cross sections which can easily be explained by the increasing distance between the two chromophore groups. Thanks to a products study, branching ratio between the two possible photodissociation pathways are also proposed. Rate constants for the reaction with OH radicals were found to be (2.9 ± 1.0) × 10−12 cm3 molecule−1 s−1 and (3.3 ± 0.9) × 10−12 cm3 molecule−1 s−1, respectively. These experimental data are in good agreement with rate constants estimated by the SAR of Kwok and Atkinson (1995) when using the parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl nitrates. Comparison with photolysis rates suggests that OH-initiated oxidation of carbonyl nitrates is a less efficient sink that photodissociation but is not negligible in polluted area.

Kinetic study on the linalool ozonolysis reaction in the atmosphere

2012 ◽  
Vol 90 (4) ◽  
pp. 353-361 ◽  
Author(s):  
Xiaomin Sun ◽  
Chenxi Zhang ◽  
Yuyang Zhao ◽  
Jing Bai ◽  
Maoxia He
Keyword(s):  
Rate Constants ◽  
Transition State Theory ◽  
State Theory ◽  
Oxidation Products ◽  
Tunneling Effect ◽  
Total Rate ◽  
Variational Transition State Theory ◽  
Atmospheric Lifetime ◽  
Ozone Addition ◽  
First Time

In the atmosphere, linalool ozonolysis will generate a series of oxidation products and then form particles through nucleation. In this study, the linalool ozonolysis mechanisms were studied and some of the main products detected from experiment are verified. The Rice–Ramsperger–Kassel–Marcus (RRKM) theory and the canonical variational transition state theory (CVT) with small curvature tunneling effect (SCT) are used to calculate rate constants over the temperature range of 200∼800 K. The total rate constant for the reaction of ozone with linalool is 4.50 × 10−16 cm3 molecule–l s–l, and the addition of ozone to (CH3)2C=CH– is the main ozone addition position. Furthermore, the Arrhenius formulas are fitted and the lifetimes of reaction species in the troposphere are discussed for the first time. The total atmospheric lifetime of linalool relative to O3 is 2.30 h. The O3-initiated atmospheric lifetimes of P1, P3, and P6 are 2.64 months, 16.67 days, and 15.5 h, respectively.

scholarly journals Structure–activity relationship for the estimation of OH-oxidation rate constants of carbonyl compounds in the aqueous phase

2013 ◽  
Vol 13 (23) ◽  
pp. 11625-11641 ◽  
Author(s):  
J.-F. Doussin ◽  
A. Monod
Keyword(s):  
Aqueous Phase ◽  
Rate Constants ◽  
Oxidation Rate ◽  
Carbonyl Compounds ◽  
Estimation Method ◽  
Structure Activity Relationship ◽  
Activity Relationship ◽  
Oh Radicals ◽  
Structure Activity ◽  
Polyfunctional Compounds

Abstract. In the atmosphere, one important class of reactions occurs in the aqueous phase in which organic compounds are known to undergo oxidation towards a number of radicals, among which OH radicals are the most reactive oxidants. In 2008, Monod and Doussin have proposed a new structure–activity relationship (SAR) to calculate OH-oxidation rate constants in the aqueous phase. This estimation method is based on the group-additivity principle and was until now limited to alkanes, alcohols, acids, bases and related polyfunctional compounds. In this work, the initial SAR is extended to carbonyl compounds, including aldehydes, ketones, dicarbonyls, hydroxy carbonyls, acidic carbonyls, their conjugated bases, and the hydrated form of all these compounds. To do so, only five descriptors have been added and none of the previously attributed descriptors were modified. This extension leads now to a SAR which is based on a database of 102 distinct compounds for which 252 experimental kinetic rate constants have been gathered and reviewed. The efficiency of this updated SAR is such that 58% of the rate constants could be calculated within ±20% of the experimental data and 76% within ±40% (respectively 41 and 72% for the carbonyl compounds alone).

An experimental and theoretical study of the kinetics of the reaction between 3-hydroxy-3-methyl-2-butanone and OH radicals

RSC Advances ◽  
2015 ◽  
Vol 5 (34) ◽  
pp. 26559-26568 ◽  
Author(s):  
Angappan Mano Priya ◽  
Gisèle El Dib ◽  
Lakshmipathi Senthilkumar ◽  
Chantal Sleiman ◽  
Alexandre Tomas ◽  
...  
Keyword(s):  
Rate Constants ◽  
Theoretical Study ◽  
Oh Radicals ◽  
First Time ◽  
Kinetics Of

Absolute experimental and theoretical rate constants are determined for the first time for the reaction of 3-hydroxy-3-methyl-2-butanone with OH as a function of temperature. The atmospheric implications are discussed.

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.

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 Development of a protocol for the auto-generation of explicit aqueous-phase oxidation schemes of organic compounds

2019 ◽  
Vol 19 (14) ◽  
pp. 9209-9239 ◽  
Author(s):  
Peter Bräuer ◽  
Camille Mouchel-Vallon ◽  
Andreas Tilgner ◽  
Anke Mutzel ◽  
Olaf Böge ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Aqueous Phase ◽  
Rate Constants ◽  
Particle Growth ◽  
Chemical Mechanism ◽  
Estimation Methods ◽  
Radical Reactivity ◽  
Chemical Complexity ◽  
Model Studies ◽  
Phase Chemistry

Abstract. This paper presents a new CAPRAM–GECKO-A protocol for mechanism auto-generation of aqueous-phase organic processes. For the development, kinetic data in the literature were reviewed and a database with 464 aqueous-phase reactions of the hydroxyl radical with organic compounds and 130 nitrate radical reactions with organic compounds has been compiled and evaluated. Five different methods to predict aqueous-phase rate constants have been evaluated with the help of the kinetics database: gas–aqueous phase correlations, homologous series of various compound classes, radical reactivity comparisons, Evans–Polanyi-type correlations, and structure–activity relationships (SARs). The quality of these prediction methods was tested as well as their suitability for automated mechanism construction. Based on this evaluation, SARs form the basis of the new CAPRAM–GECKO-A protocol. Evans–Polanyi-type correlations have been advanced to consider all available H atoms in a molecule besides the H atoms with only the weakest bond dissociation enthalpies (BDEs). The improved Evans–Polanyi-type correlations are used to predict rate constants for aqueous-phase NO3 and organic compounds reactions. Extensive tests have been performed on essential parameters and on highly uncertain parameters with limited experimental data. These sensitivity studies led to further improvements in the new CAPRAM–GECKO-A protocol but also showed current limitations. Biggest uncertainties were observed in uptake processes and the estimation of Henry's law coefficients as well as radical chemistry, in particular the degradation of alkoxy radicals. Previous estimation methods showed several deficits, which impacted particle growth. For further evaluation, a 1,3,5-trimethylbenzene oxidation experiment has been performed in the aerosol chamber “Leipziger Aerosolkammer” (LEAK) at high relative humidity conditions and compared to a multiphase mechanism using the Master Chemical Mechanism (MCMv3.2) in the gas phase and using a methylglyoxal oxidation scheme of about 600 reactions generated with the new CAPRAM–GECKO-A protocol in the aqueous phase. While it was difficult to evaluate single particle constituents due to concentrations close to the detection limits of the instruments applied, the model studies showed the importance of aqueous-phase chemistry in respect to secondary organic aerosol (SOA) formation and particle growth. The new protocol forms the basis for further CAPRAM mechanism development towards a new version 4.0. Moreover, it can be used as a supplementary tool for aerosol chambers to design and analyse experiments of chemical complexity and help to understand them on a molecular level.

scholarly journals Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: rate constants and product yields

2021 ◽  
Vol 21 (16) ◽  
pp. 12665-12685
Author(s):  
Luisa Hantschke ◽  
Anna Novelli ◽  
Birger Bohn ◽  
Changmin Cho ◽  
David Reimer ◽  
...  
Keyword(s):  
Rate Constants ◽  
Oxidation Products ◽  
Organic Nitrate ◽  
Effective Quantum Yield ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Mixing Ratios ◽  
Photolysis Frequency ◽  
First Time ◽  
Good Agreement

Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)×10-11 cm3 s−1 at 304 K, (4.4±0.2)×10-17 cm3 s−1 at 300 K and (4.6±1.6)×10-11 cm3 s−1 at 300 K, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the chamber experiments. In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

scholarly journals Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: Rate constants and product yields

2021 ◽  
Author(s):  
Luisa Lamberta Hantschke ◽  
Anna Novelli ◽  
Birger Bohn ◽  
Changmin Cho ◽  
David Reimer ◽  
...  
Keyword(s):  
Rate Constants ◽  
Reactive Nitrogen Species ◽  
Oxidation Products ◽  
Organic Nitrate ◽  
Effective Quantum Yield ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Mixing Ratios ◽  
Photolysis Frequency ◽  
First Time

Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3, and of the reaction of caronaldehyde with OH were determined to be (8.0 ± 0.5) × 10−11 cm3 s−1 at 304 K, (4.4 ± 0.2) × 10−17 cm3 s−1 at 300 K and (4.6 ± 1.6) × 10−11 cm3 s−1 at 300 K, respectively, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be (0.30 ± 0.05) and (0.06 ± 0.02), respectively. Both values are in reasonably well agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of (0.25 ± 0.04) was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be (0.10 ± 0.02). The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of (0.65 ± 0.10) was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx = OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the the chamber experiments. In an OH free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar acintic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

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