Estimation of rate coefficients and branching ratios for reactions of
organic peroxy radicals for use in automated mechanism
construction

Jenkin, Michael E.; Valorso, Richard; Aumont, Bernard; Rickard, Andrew R.

doi:10.5194/acp-2019-44

Cited by 15 publications

(21 citation statements)

References 102 publications

(187 reference statements)

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“…The reaction rate coefficient between RO 2 radicals can range from 10 −17 to 10 −11 cm 3 molecule −1 s −1 60 , with recent studies reporting values on the order of 10 −10 cm 3 molecule −1 s −1 for selected HOM-RO 2 21 , 61 . While kinetic studies show that the RO 2 + RO 2 → ROOR + O 2 reaction rate coefficients generally increase with the RO 2 oxygen content 62 , further enhanced by intramolecular hydrogen bonds that may help with transition state stabilization 28 , the contribution of different RO 2 radicals to dimer formation remains unknown. Online MS/MS analysis provides insights into the dimer structure and formation, as shown for C 20 H 30 O 12 NO 3 – ( m/z 524.1608) and C 20 H 30 O 14 NO 3 – ( m/z 556.1520) in Fig.…”

Section: Resultsmentioning

confidence: 99%

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

et al. 2021

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Organic peroxy radicals (RO2) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO2 radicals produces highly oxygenated organic molecules (HOMs), including low-volatility ROOR dimers formed by bimolecular RO2 + RO2 reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles. As a result, HOMs have far-reaching health and climate implications. Nevertheless, the structures and formation mechanism of RO2 radicals and HOMs remain elusive. Here, we present the in-situ characterization of RO2 and dimer structure in the gas-phase, using online tandem mass spectrometry analyses. In this study, we constrain the structures and formation pathway of several HOM-RO2 radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.

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Section: Resultsmentioning

confidence: 99%

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

et al. 2021

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“…This new peroxy radical can then react with NO, HO 2 , and RO 2 or undergo another internal H-shift reaction. Repetitive sequential H-shift reactions followed by O 2 addition lead to highly oxidized RO 2 radicals which produce highly oxidized molecules (HOMs) by radical termination reactions (e.g., Ehn et al, 2014Ehn et al, , 2017Jokinen et al, 2014). Due to their low vapor pressure, HOMs are efficient precursors for organic particles, which are produced from the original VOCs with yields in the low percent range (e.g., Ehn et al, 2014;Jokinen et al, 2015).…”

Section: Oh Regeneration Mechanismsmentioning

confidence: 99%

Experimental budgets of OH, HO2, and RO2 radicals and implications for ozone formation in the Pearl River Delta in China 2014

Tan

Hofzumahaus³

et al. 2019

Atmos. Chem. Phys.

122

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Abstract. Hydroxyl (OH) and peroxy radicals (HO2 and RO2) were measured in the Pearl River Delta, which is one of the most polluted areas in China, in autumn 2014. The radical observations were complemented by measurements of OH reactivity (inverse OH lifetime) and a comprehensive set of trace gases including carbon monoxide (CO), nitrogen oxides (NOx=NO, NO2) and volatile organic compounds (VOCs). OH reactivity was in the range from 15 to 80 s−1, of which about 50 % was unexplained by the measured OH reactants. In the 3 weeks of the campaign, maximum median radical concentrations were 4.5×106 cm−3 for OH at noon and 3×108 and 2.0×108 cm−3 for HO2 and RO2, respectively, in the early afternoon. The completeness of the daytime radical measurements made it possible to carry out experimental budget analyses for all radicals (OH, HO2, and RO2) and their sum (ROx). The maximum loss rates for OH, HO2, and RO2 reached values between 10 and 15 ppbv h−1 during the daytime. The largest fraction of this can be attributed to radical interconversion reactions while the real loss rate of ROx remained below 3 ppbv h−1. Within experimental uncertainties, the destruction rates of HO2 and the sum of OH, HO2, and RO2 are balanced by their respective production rates. In case of RO2, the budget could be closed by attributing the missing OH reactivity to unmeasured VOCs. Thus, the presumption of the existence of unmeasured VOCs is supported by RO2 measurements. Although the closure of the RO2 budget is greatly improved by the additional unmeasured VOCs, a significant imbalance in the afternoon remains, indicating a missing RO2 sink. In case of OH, the destruction in the morning is compensated by the quantified OH sources from photolysis (HONO and O3), ozonolysis of alkenes, and OH recycling (HO2+NO). In the afternoon, however, the OH budget indicates a missing OH source of 4 to 6 ppbv h−1. The diurnal variation of the missing OH source shows a similar pattern to that of the missing RO2 sink so that both largely compensate each other in the ROx budget. These observations suggest the existence of a chemical mechanism that converts RO2 to OH without the involvement of NO, increasing the RO2 loss rate during the daytime from 5.3 to 7.4 ppbv h−1 on average. The photochemical net ozone production rate calculated from the reaction of HO2 and RO2 with NO yields a daily integrated amount of 102 ppbv ozone, with daily integrated ROx primary sources being 22 ppbv in this campaign. The produced ozone can be attributed to the oxidation of measured (18 %) and unmeasured (60 %) hydrocarbons, formaldehyde (14 %), and CO (8 %). An even larger integrated net ozone production of 140 ppbv would be calculated from the oxidation rate of VOCs with OH if HO2 and all RO2 radicals react with NO. However, the unknown RO2 loss (evident in the RO2 budget) causes 30 ppbv less ozone production than would be expected from the VOC oxidation rate.

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“…As NO concentrations exceed 1ppb the first generation RO2 is scavenged by NO thereby reducing the concentration of organonitrate HOM (Ehn et al, 2014), possibly affecting SOA yields. The MCM contribution also decreases with increasing NO concentrations mostly due to the formation more volatile organonitrates (Jenkin et al, 2019) . concentrations.…”

Section: Nox Dependencementioning

confidence: 99%

Aerosol Mass yields of selected Biogenic Volatile Organic Compounds – a theoretical study with near explicit gas-phase chemistry

Xavier¹,

Rusanen²,

Zhou³

et al. 2019

Preprint

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Abstract. In this study we modeled secondary organic aerosols (SOA) mass loadings from the oxidation (by O3, OH and NO3) of five representative Biogenic Volatile Organic compounds (BVOCs): isoprene, endocyclic bond containing monoterpenes (&#945;-pinene and limonene), exocyclic double bond compound (&#946;-pinene) and a sesquiterpene (&#946;-caryophyllene). The simulations were designed to replicate idealized smog chamber and oxidative flow reactors (OFR). The master chemical mechanism (MCM) together with the peroxy radical autoxidation mechanism (PRAM), were used to simulate the gas-phase chemistry. The aim of this study was to compare the potency of MCM and MCM+PRAM in predicating SOA formation. SOA yields were in good agreement with experimental values for chamber simulations when MCM+PRAM mechanism was applied, while a standalone MCM under-predicted the SOA yields. Compared to experimental yields, the OFR simulations using the MCM+PRAM mechanism over-predicted SOA mass yields for BVOCs oxidized by O3 and OH, probably owing to increased seed particle surface area used in the OFR simulations. SOA yields increased with decreasing temperatures and NO concentrations and vice-versa. This highlights the limitations posed when using fixed SOA yields in a majority of global and regional models. Few compounds that play a crucial role (>&#8201;95&#8201;% of mass load) in contributing to SOA mass increase (using MCM+PRAM) are identified. The results further emphasized that incorporating PRAM in conjunction with MCM does improve SOA mass yields estimation.

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Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction

Cited by 15 publications

References 102 publications

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

Experimental budgets of OH, HO<sub>2</sub>, and RO<sub>2</sub> radicals and implications for ozone formation in the Pearl River Delta in China 2014

Aerosol Mass yields of selected Biogenic Volatile Organic Compounds – a theoretical study with near explicit gas-phase chemistry

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Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction

Cited by 15 publications

References 102 publications

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

Experimental budgets of OH, HO&lt;sub&gt;2&lt;/sub&gt;, and RO&lt;sub&gt;2&lt;/sub&gt; radicals and implications for ozone formation in the Pearl River Delta in China 2014

Aerosol Mass yields of selected Biogenic Volatile Organic Compounds – a theoretical study with near explicit gas-phase chemistry

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Experimental budgets of OH, HO<sub>2</sub>, and RO<sub>2</sub> radicals and implications for ozone formation in the Pearl River Delta in China 2014