Multi-generation OH oxidation as a source for highly oxygenated organic molecules from aromatics

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(1), P. 515 - 537

Published: Jan. 15, 2020

Abstract. Recent studies have recognised highly oxygenated organic molecules (HOMs) in the atmosphere as important formation of secondary aerosol (SOA). A large number focused on HOM from oxidation biogenically emitted monoterpenes. However, anthropogenic vapours has so far received much less attention. Previous identified importance aromatic volatile compounds (VOCs) for SOA formation. In this study, we investigated several compounds, benzene (C6H6), toluene (C7H8), and naphthalene (C10H8), their potential to form HOMs upon reaction with hydroxyl radicals (OH). We performed flow tube experiments all three VOCs detail Jülich Plant Atmosphere Chamber (JPAC). JPAC, also response NOx seed aerosol. Using a nitrate-based chemical ionisation mass spectrometer (CI-APi-TOF), observed reactor first OH attack. naphthalene, which were injected at lower concentrations, multi-generation seemed impact composition. tested more system allowed studying longer residence times. The results showed that apparent molar yield under our experimental conditions varied 4.1 % 14.0 %, strong dependence concentration, indicating majority formed through multiple OH-oxidation steps. composition spectrum supported hypothesis. By injecting only phenol into chamber, found cannot be solely responsible experiments. When was added changed many nitrogen-containing products CI-APi-TOF. Upon injection, loss rate higher than predicted by irreversible condensation, suggesting some undetected intermediates condensed onto aerosol, is line hypothesis oxidation. Based results, conclude systems strongly depend VOC concentration are needed fully understand effect and, consequently, SOA. suggest chamber may explain part variability yields reported literature advise monitoring future studies.

Language: Английский

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Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO<sub><i>x</i></sub> in Beijing

Atmospheric chemistry and physics, Journal Year: 2021, Volume and Issue: 21(3), P. 2125 - 2147

Published: Feb. 12, 2021

Abstract. Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) total radicals taken during the integrated Study AIR Pollution PROcesses in Beijing (AIRPRO) campaign central summer 2017, alongside observations OH reactivity, are presented. The concentrations were elevated, with reaching up to 2.8×107moleculecm-3, HO2 peaking at 1×109moleculecm-3 concentration 5.5×109moleculecm-3. reactivity (k(OH)) peaked 89 s−1 night, a minimum afternoon ≈22s-1 on average. An experimental budget analysis, which rates production destruction compared, highlighted that although sources sinks balanced under high NO concentrations, exceeded known (by 15 ppbv h−1) very low conditions (<0.5 ppbv) experienced afternoons, demonstrating missing source consistent previous studies volatile organic compound (VOC) emissions loadings. Under highest mixing ratios (104 ppbv), rate by ≈50ppbvh-1, whilst same rate, indicating net propagation may be substantially slower than assumed. If just 10 % propagate upon reaction NO, budgets could closed but this lower revealed sink was similar magnitude source. A detailed box model incorporated latest Master Chemical Mechanism (MCM3.3.1) reproduced observed well over-predicted (<1 under-predicted (both fraction other types we classify as simple most significantly concentrations. also k(OH) consistently ≈10s-1 across all NOx levels, highlighting good agreement for fortuitous due cancellation terms its budget. Including heterogeneous loss aerosol surfaces did reduce modelled line only <0.3 ppbv. inclusion Cl atoms, formed from photolysis nitryl chloride, enhanced several mornings when atom calculated exceed 1×104atomscm-3 reconcile measured these times. However, mornings, lower, large under-predictions remained. Furthermore, chemistry not enhance beyond first few hours after sunrise so unable resolve under-prediction times day. Model scenarios, VOC included an additional converted RO2, sensitive choice product. level simple) improved if larger species able undergo followed isomerisation reactions reforming species, before eventually generating HO2. In work α-pinene-derived used example. simulation, underestimated uncertainty, regards present they form (HO2 directly or another species), leads over order less O3 predicted peroxy This demonstrates indeed needs understood accurately simulate ozone environments such Beijing, where multifunctional VOCs likely present.

Language: Английский

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Organic Peroxides in Aerosol: Key Reactive Intermediates for Multiphase Processes in the Atmosphere

Chemical Reviews, Journal Year: 2023, Volume and Issue: 123(4), P. 1635 - 1679

Published: Jan. 11, 2023

Organic peroxides (POs) are organic molecules with one or more peroxide (−O–O−) functional groups. POs commonly regarded as chemically labile termination products from gas-phase radical chemistry and therefore serve temporary reservoirs for oxidative radicals (HOx ROx) in the atmosphere. Owing to their ubiquity, active gas-particle partitioning behavior, reactivity, key reactive intermediates atmospheric multiphase processes determining life cycle (formation, growth, aging), climate, health impacts of aerosol. However, there remain substantial gaps origin, molecular diversity, fate due complex nature dynamic behavior. Here, we summarize current understanding on POs, a focus identification quantification, state-of-the-art analytical developments, molecular-level formation mechanisms, chemical transformation pathways, well environmental impacts. We find that interactions SO2 transition metal ions generally fast PO pathways liquid water, lifetimes estimated be minutes hours, while hydrolysis is particularly important α-substituted hydroperoxides. Meanwhile, photolysis thermolysis likely minor sinks POs. These distinctly different fates, such reaction OH radicals, which highlights need understand By summarizing advances remaining challenges investigation propose future research priorities regarding fate,

Language: Английский

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

Atmospheric chemistry and physics, Journal Year: 2019, Volume and Issue: 19(11), P. 7691 - 7717

Published: June 7, 2019

Abstract. Organic peroxy radicals (RO2), formed from the degradation of hydrocarbons and other volatile organic compounds (VOCs), play a key role in tropospheric oxidation mechanisms. Several competing reactions may be available for given RO2 radical, relative rates which depend on both structure ambient conditions. Published kinetics branching ratio data are reviewed bimolecular with NO, NO2, NO3, OH HO2; their self-reactions cross-reactions radicals. This information is used to define generic rate coefficients structure–activity relationship (SAR) methods that can applied series important classes hydrocarbon oxygenated Information selected unimolecular isomerization (i.e. H-atom shift ring-closure reactions) also summarized discussed. The presented here intended guide representation radical chemistry next generation explicit detailed chemical

Language: Английский

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Molecular understanding of new-particle formation from α-pinene between −50 and +25 °C

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(15), P. 9183 - 9207

Published: Aug. 3, 2020

Abstract. Highly oxygenated organic molecules (HOMs) contribute substantially to the formation and growth of atmospheric aerosol particles, which affect air quality, human health Earth's climate. HOMs are formed by rapid, gas-phase autoxidation volatile compounds (VOCs) such as α-pinene, most abundant monoterpene in atmosphere. Due their abundance low volatility, can play an important role new-particle (NPF) early aerosols, even without any further assistance other low-volatility sulfuric acid. Both reaction forming NPF rates expected be strongly dependent on temperature. However, experimental data both effects limited. Dedicated experiments were performed at CLOUD (Cosmics Leaving OUtdoor Droplets) chamber CERN address this question. In study, we show that a decrease temperature (from +25 −50 ∘C) results reduced HOM yield oxidation state products, whereas (J1.7 nm) increase substantially. Measurements with two different chemical ionization mass spectrometers (using nitrate protonated water reagent ion, respectively) provide molecular composition gaseous two-dimensional volatility basis set (2D VBS) model provides distribution. The decreases from 6.2 % 25 ∘C 0.7 ∘C. there is strong reduction saturation vapor pressure each reduced. Overall, leads nucleation up 3 orders magnitude compared addition, enhancement ions decreasing temperature, since neutral clusters have increased stability against evaporation. resulting quantify how interplay between temperature-dependent pathways associated pressures biogenic level. Our measurements, therefore, improve our understanding pure for wide range tropospheric temperatures precursor concentrations.

Language: Английский

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Formation of Highly Oxygenated Organic Molecules from α-Pinene Ozonolysis: Chemical Characteristics, Mechanism, and Kinetic Model Development

ACS Earth and Space Chemistry, Journal Year: 2019, Volume and Issue: 3(5), P. 873 - 883

Published: April 3, 2019

Terpenes are emitted by vegetation, and their oxidation in the atmosphere is an important source of secondary organic aerosol (SOA). A part this can proceed through autoxidation process, yielding highly oxygenated molecules (HOMs) with low saturation vapor pressure. They therefore contribute, even absence sulfuric acid, to new particle formation (NPF). The understanding mechanism its kinetics still far from complete. Here, we present a mechanistic kinetic analysis mass spectrometry data α-pinene (AP) ozonolysis experiments performed during CLOUD 8 campaign at CERN. We grouped HOMs classes according identified chemical composition investigated relative changes these groups components as function reagent concentration. determined reaction rate constants for different HOM peroxy radical pathways. accretion between radicals was found be extremely fast. developed pseudo-mechanism added it AP scheme Master Chemical Mechanism (MCM). With extended model, observed concentrations trends were successfully simulated.

Language: Английский

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Molecular understanding of the suppression of new-particle formation by isoprene

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(20), P. 11809 - 11821

Published: Oct. 20, 2020

Abstract. Nucleation of atmospheric vapours produces more than half global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together isoprene (C5H8), which the highest emission all organic vapours. Previous have shown suppresses new-particle formation from monoterpenes, but cause this suppression is under debate. Here, in experiments performed conditions CERN CLOUD chamber, we reduces yield dimers 19 20 carbon atoms – drive particle nucleation early growth while increasing production 14 15 atoms. The (termed C20 C15, respectively) produced termination reactions between pairs peroxy radicals (RO2⚫) arising monoterpenes isoprene. Compared pure conditions, rates at 1.7 nm (depending ∕ ratio) approximately halves 1.3 3.2 nm. However, above nm, C15 contribute to secondary aerosol, unaffected We further increased hydroxyl radical (OH⚫) our chemical system rather enhances it as previously proposed, since increases isoprene-derived RO2⚫ reduce formation. emerges critical step determines molecule (HOM) distribution corresponding capability. Species yield, such NO, HO2 isoprene, thus effectively biogenic growth. Therefore rate aerosol a particular region atmosphere study will vary according precise ambient conditions.

Language: Английский

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Optical Properties of Secondary Organic Aerosol Produced by Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds

Environmental Science & Technology, Journal Year: 2021, Volume and Issue: 55(5), P. 2878 - 2889

Published: Feb. 17, 2021

Nighttime oxidation of biogenic volatile organic compounds (BVOCs) by nitrate radicals (NO3·) represents one the most important interactions between anthropogenic and natural emissions, leading to substantial secondary aerosol (SOA) formation. The direct climatic effect such SOA cannot be quantified because its optical properties atmospheric fate are poorly understood. In this study, we generated from NO3· a series BVOCs including isoprene, monoterpenes, sesquiterpenes. were subjected comprehensive online offline chemical composition analysis using high-resolution mass spectrometry measurements novel broadband (315–650 nm) cavity-enhanced spectrometer, which covers wavelength range needed understand potential contribution radiative forcing. contained significant fraction oxygenated nitrates (ONs), consisting monomers oligomers that responsible for detected light absorption in 315–400 nm range. created β-pinene α-humulene was further photochemically aged an flow reactor. has photochemical bleaching lifetime >6.2 h, indicating some ONs may serve as atmosphere-stable nitrogen oxide sinks or reservoirs will absorb scatter incoming solar radiation during daytime.

Language: Английский

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Experimental investigation into the volatilities of highly oxygenated organic molecules (HOMs)

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(2), P. 649 - 669

Published: Jan. 20, 2020

Abstract. Secondary organic aerosol (SOA) forms a major part of the tropospheric submicron aerosol. Still, exact formation mechanisms SOA have remained elusive. Recently, newly discovered group oxidation products volatile compounds (VOCs), highly oxygenated molecules (HOMs), been proposed to be responsible for large fraction formation. To assess potential HOMs form and even take in new particle formation, knowledge their volatilities is essential. However, due exotic, partially unknown, structures, estimating volatility challenging. In this study, we performed set continuous flow chamber experiments, supported by box modelling, study HOMs, along with some less compounds, formed ozonolysis α-pinene, an abundant VOC emitted boreal forests. Along gaseous precursors, periodically injected inorganic seed into vary condensation sink (CS) low-volatility vapours. We monitored decrease gas phase response increasing CS, were able relate responses compounds. found that HOM monomers are mainly low volatility, small being semi-volatile. dimers all at least but probably extremely volatility; however, our method not directly distinguish between two. model terms carbon, hydrogen, oxygen nitrogen numbers. levels oxygenation correspond lower volatilities, as expected, steep than would expected based on many existing models such SIMPOL. The hydrogen number compound also predicted its independently carbon number, higher numbers corresponding volatilities. This can explained functional groups making up molecule: high associated with, e.g. hydroxy groups, which more than, carbonyls, number. presented should applicable systems other α-pinene ozonolysis, different loadings, order ranges.

Language: Английский

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Impact of NO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; on secondary organic aerosol (SOA) formation from &lt;i&gt;α&lt;/i&gt;-pinene and &lt;i&gt;β&lt;/i&gt;-pinene photooxidation: the role of highly oxygenated organic nitrates

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(17), P. 10125 - 10147

Published: Sept. 1, 2020

Abstract. The formation of organic nitrates (ONs) in the gas phase and their impact on mass secondary aerosol (SOA) was investigated a laboratory study for α-pinene β-pinene photooxidation. Focus elucidation those mechanisms that cause often observed suppression SOA by NOx, therein role highly oxygenated multifunctional molecules (HOMs). We with increasing NOx concentration (a) portion HOM (HOM-ONs) increased, (b) fraction accretion products (HOM-ACCs) decreased, (c) HOM-ACCs contained average smaller carbon numbers. Specifically, we (HOM-ONs), arising from termination reactions peroxy radicals permutation (HOM-PPs), such as ketones, alcohols, or hydroperoxides, formed other reactions. Effective uptake coefficients γeff HOMs particles were determined. more than six O atoms efficiently condensed (γeff>0.5 average), containing eight atoms, every collision led to loss. There no systematic difference HOM-ONs HOM-PPs same radicals. This similarity is attributed character HOMs: functional groups precursor radical are identical, vapor pressures should not strongly depend final group. As consequence, suppressing effect cannot be simply explained replacement terminal nitrate groups. According all will contribute bound (OrgNO3) particulate phase. However, OrgNO3 stored condensable molecular masses > 230 Da appeared substantially higher spectrometry. result suggests losses particles, probably due hydrolysis releases HNO3 into but leaves behind rest loss alone could explain particle β-pinene. Instead can attribute most reduction yields significant HOM-ACCs, which have high potentially important at low-NOx conditions.

Language: Английский

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