scholarly journals Isoprene oxidation mechanisms: measurements and modelling of OH and HO<sub>2</sub> over a South-East Asian tropical rainforest during the OP3 field campaign

2011 ◽  
Vol 11 (13) ◽  
pp. 6749-6771 ◽  
Author(s):  
D. Stone ◽  
M. J. Evans ◽  
P. M. Edwards ◽  
R. Commane ◽  
T. Ingham ◽  
...  
Keyword(s):  
Tropical Rainforest ◽  
Geometric Mean ◽  
Atmospheric Composition ◽  
Peroxy Radicals ◽  
Unimolecular Decomposition ◽  
The Standard Model ◽  
Volatile Organic ◽  
Isoprene Oxidation ◽  
Oxidation Chemistry ◽  
Oxidation Mechanisms

Abstract. Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO2 in airmasses impacted with isoprene are 5.32−4.43+3.68 and 1.18−0.30+0.30 respectively, with 68 % of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.

scholarly journals Isoprene oxidation mechanisms: measurements and modelling of OH and HO<sub>2</sub> over a South-East Asian tropical rainforest during the OP3 field campaign

2011 ◽  
Vol 11 (3) ◽  
pp. 10343-10401 ◽  
Author(s):  
D. Stone ◽  
M. J. Evans ◽  
P. M. Edwards ◽  
R. Commane ◽  
T. Ingham ◽  
...  
Keyword(s):  
Tropical Rainforest ◽  
Geometric Mean ◽  
Atmospheric Composition ◽  
Peroxy Radicals ◽  
Unimolecular Decomposition ◽  
The Standard Model ◽  
Volatile Organic ◽  
Isoprene Oxidation ◽  
Oxidation Chemistry ◽  
Oxidation Mechanisms

Abstract. Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO2 in airmasses impacted with isoprene are 5.32−4.43+3.68 and 1.18−0.30+0.30 respectively, with 68% of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.

scholarly journals Changes to simulated global atmospheric composition resulting from recent revisions to isoprene oxidation chemistry

2021 ◽  
Vol 244 ◽  
pp. 117914
Author(s):  
M. Anwar H. Khan ◽  
Billie-Louise Schlich ◽  
Michael E. Jenkin ◽  
Michael C. Cooke ◽  
Richard G. Derwent ◽  
...  
Keyword(s):  
Atmospheric Composition ◽  
Isoprene Oxidation ◽  
Oxidation Chemistry

scholarly journals Secondary Organic Aerosol Reduced by Mixture of Atmospheric Vapours

2020 ◽  
Author(s):  
Thomas Mentel ◽  
Gordon McFiggans ◽  
Jürgen Wildt ◽  
Astrid Kiendler-Scharr ◽  
Keyword(s):  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Peroxy Radicals ◽  
Model Calculations ◽  
Volatile Organic ◽  
Single Precursor ◽  
Real Atmosphere ◽  
Isoprene Oxidation ◽  
Plant Emissions

&lt;p&gt;Biogenic volatile organic compounds (VOC) are important secondary organic aerosol (SOA) precursors. Whilst isoprene dominates VOC plant emissions globally, its yield of SOA mass is found to be modest in comparison to that of monoterpenes (MT). Tracers from isoprene oxidation have been observed in particles showing that they condense from the gas phase and yet new particle formation is suppressed by the presence of isoprene in mixtures of plant emissions containing MT.&lt;/p&gt;&lt;p&gt;Experiments were performed in the JPAC chamber in J&amp;#252;lich. We showed that isoprene can suppress both the instantaneous mass formation and overall yield of monoterpenes in mixtures by two effects: oxidant and product scavenging. Isoprene scavenged OH radicals from reacting with MT (oxidant scavenging). Subsequently, the resulting isoprene peroxy radicals reacted with highly oxygenated peroxy radicals from MT oxidation (product scavenging). These effects from isoprene, also demonstrated using CO or CH&lt;sub&gt;4&lt;/sub&gt;, reduced the yield of low-volatility, highly oxygenated molecules (HOM) from MT that would otherwise form SOA.&lt;/p&gt;&lt;p&gt;Our results show that in mixtures changes in particle mass and number are not additive, and yields from single precursor experiments cannot simply be linearly combined. Reactive, modest SOA yield compounds are not necessarily net SOA producers and isoprene oxidation can suppress both SOA number and mass. Global model calculations support that OH scavenging and product scavenging can also operate in the real atmosphere. Our results highlight a need for more realistic consideration of SOA formation in the atmosphere analogous to the treatment of ozone formation, where interactions between the mechanistic pathways involving peroxy radicals are recognised to be essential.&lt;/p&gt;

Chamber Studies of NO3 reactivity during the oxidation of isoprene

2020 ◽  
Author(s):  
Patrick Dewald ◽  
Justin Shenolikar ◽  
Nils Friedrich ◽  
Franz Rohrer ◽  
Ralf Tillmann ◽  
...  
Keyword(s):  
Oxidation Products ◽  
Research Centre ◽  
Biogenic Emissions ◽  
Organic Nitrates ◽  
Peroxy Radicals ◽  
Experimental Conditions ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Isoprene Oxidation ◽  
Chamber Studies

&lt;p&gt;Isoprene is the major volatile organic compound that is released into the environment via biogenic emissions and its oxidation can result in formation of secondary organic aerosol (SOA). Although isoprene emission occurs mainly at daytime, it can accumulate at nighttime and be oxidized by the nitrate radical (NO&lt;sub&gt;3&lt;/sub&gt;) to form organic nitrates that can partition to the particle phase. A detailed understanding of the reaction between isoprene and NO&lt;sub&gt;3&lt;/sub&gt; is thus required to predict its role in e.g. NO&lt;sub&gt;X&lt;/sub&gt; lifetimes and SOA formation.&lt;/p&gt;&lt;p&gt;The reaction between NO&lt;sub&gt;3&lt;/sub&gt; and isoprene was investigated under varying experimental conditions (high or low RO&lt;sub&gt;2&lt;/sub&gt;/HO&lt;sub&gt;2&lt;/sub&gt;, temperature, humidity, seed aerosols) during the NO3ISOP campaign at the atmospheric simulation chamber SAPHIR of the research centre in J&amp;#252;lich (Germany). Direct measurement of the NO&lt;sub&gt;3&lt;/sub&gt; reactivity was carried out with means of a flowtube coupled to a cavity-ring-down spectroscopy (FT-CRDS) setup which enabled the evolution of the NO&lt;sub&gt;3&lt;/sub&gt; lifetime during the isoprene oxidation process to be monitored.&lt;/p&gt;&lt;p&gt;By comparing direct NO&lt;sub&gt;3&lt;/sub&gt; reactivity measurements with those calculated from VOC mixing ratios and those calculated from a stationary-state analysis we identify the contributions of isoprene, secondary oxidation products and peroxy radicals to NO&lt;sub&gt;3&lt;/sub&gt; losses.&lt;/p&gt;

scholarly journals Simulating atmospheric composition over a South-East Asian tropical rainforest: performance of a chemistry box model

2010 ◽  
Vol 10 (1) ◽  
pp. 279-298 ◽  
Author(s):  
T. A. M. Pugh ◽  
A. R. MacKenzie ◽  
C. N. Hewitt ◽  
B. Langford ◽  
P. M. Edwards ◽  
...  
Keyword(s):  
Tropical Rainforest ◽  
Measurement Model ◽  
Model Fit ◽  
Box Model ◽  
Atmospheric Composition ◽  
Tropical Rainforests ◽  
Peroxy Radicals ◽  
Model Studies ◽  
Chemical Scheme ◽  
Best Fit

Abstract. Atmospheric composition and chemistry above tropical rainforests is currently not well established, particularly for south-east Asia. In order to examine our understanding of chemical processes in this region, the performance of a box model of atmospheric boundary layer chemistry is tested against measurements made at the top of the rainforest canopy near Danum Valley, Malaysian Borneo. Multi-variate optimisation against ambient concentration measurements was used to estimate average canopy-scale emissions for isoprene, total monoterpenes and nitric oxide. The excellent agreement between estimated values and measured fluxes of isoprene and total monoterpenes provides confidence in the overall modelling strategy, and suggests that this method may be applied where measured fluxes are not available, assuming that the local chemistry and mixing are adequately understood. The largest contributors to the optimisation cost function at the point of best-fit are OH (29%), NO (22%) and total peroxy radicals (27%). Several factors affect the modelled VOC chemistry. In particular concentrations of methacrolein (MACR) and methyl-vinyl ketone (MVK) are substantially overestimated, and the hydroxyl radical (OH) concentration is substantially underestimated; as has been seen before in tropical rainforest studies. It is shown that inclusion of dry deposition of MACR and MVK and wet deposition of species with high Henry's Law values substantially improves the fit of these oxidised species, whilst also substantially decreasing the OH sink. Increasing OH production arbitrarily, through a simple OH recycling mechanism , adversely affects the model fit for volatile organic compounds (VOCs). Given the constraints on isoprene flux provided by measurements, a substantial decrease in the rate of reaction of VOCs with OH is the only remaining option to explain the measurement/model discrepancy for OH. A reduction in the isoprene+OH rate constant of 50%, in conjunction with increased deposition of intermediates and some modest OH recycling, is able to produce both isoprene and OH concentrations within error of those measured. Whilst we cannot rule out an important role for missing chemistry, particularly in areas of higher isoprene flux, this study demonstrates that the inadequacies apparent in box and global model studies of tropical VOC chemistry may be more strongly influenced by representation of detailed physical and micrometeorological effects than errors in the chemical scheme.

scholarly journals Anthropogenic enhancements to production of highly oxygenated molecules from autoxidation

2019 ◽  
Vol 116 (14) ◽  
pp. 6641-6646 ◽  
Author(s):  
Havala O. T. Pye ◽  
Emma L. D’Ambro ◽  
Ben H. Lee ◽  
Siegfried Schobesberger ◽  
Masayuki Takeuchi ◽  
...  
Keyword(s):  
Fine Particulate Matter ◽  
Peroxy Radicals ◽  
Dominant Component ◽  
Fine Particulate ◽  
Biogenic Voc ◽  
Aircraft Observations ◽  
Volatile Organic ◽  
Climate Interactions ◽  
Urban Plume

Atmospheric oxidation of natural and anthropogenic volatile organic compounds (VOCs) leads to secondary organic aerosol (SOA), which constitutes a major and often dominant component of atmospheric fine particulate matter (PM2.5). Recent work demonstrates that rapid autoxidation of organic peroxy radicals (RO2) formed during VOC oxidation results in highly oxygenated organic molecules (HOM) that efficiently form SOA. As NOxemissions decrease, the chemical regime of the atmosphere changes to one in which RO2autoxidation becomes increasingly important, potentially increasing PM2.5, while oxidant availability driving RO2formation rates simultaneously declines, possibly slowing regional PM2.5formation. Using a suite of in situ aircraft observations and laboratory studies of HOM, together with a detailed molecular mechanism, we show that although autoxidation in an archetypal biogenic VOC system becomes more competitive as NOxdecreases, absolute HOM production rates decrease due to oxidant reductions, leading to an overall positive coupling between anthropogenic NOxand localized biogenic SOA from autoxidation. This effect is observed in the Atlanta, Georgia, urban plume where HOM is enhanced in the presence of elevated NO, and predictions for Guangzhou, China, where increasing HOM-RO2production coincides with increases in NO from 1990 to 2010. These results suggest added benefits to PM2.5abatement strategies come with NOxemission reductions and have implications for aerosol–climate interactions due to changes in global SOA resulting from NOxinteractions since the preindustrial era.

scholarly journals Diel peroxy radicals in a semi industrial coastal area: nighttime formation of free radicals

2012 ◽  
Vol 12 (8) ◽  
pp. 19529-19570 ◽  
Author(s):  
M. D. Andrés-Hernández ◽  
D. Kartal ◽  
J. N. Growley ◽  
V. Sinha ◽  
E. Regelin ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Trace Gases ◽  
Peroxy Radical ◽  
Industrial Area ◽  
Diurnal Variations ◽  
Peroxy Radicals ◽  
Industrial Emissions ◽  
Air Masses ◽  
Volatile Organic ◽  
Organic Trace

Abstract. Peroxy radicals were measured by a PeRCA (Peroxy Radical Chemical Amplifier) instrument in the boundary layer during the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) campaign at a coastal, forested site influenced by urban-industrial emissions in Southern Spain in late autumn. Total peroxy radicals (RO2* = HO2 + ΣRO2) generally showed a daylight maximum between 10 and 50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 days of measurements. Emissions from the industrial area of Huelva often impacted the measurement site at night during the campaign. The processing of significant levels of anthropogenic organics leads to an intense nocturnal radical chemistry accompanied by formation of organic peroxy radicals at comparable levels to those of summer photochemical conditions with peak events up to 60–80 pptv. The RO2 production initiated by reactions of NO3 with organic trace gases was estimated to be significant but not sufficient to account for the concentrations of RO2* observed in air masses carrying high pollutant loading. The nocturnal production of peroxy radicals seems therefore to be dominated by ozonolysis of volatile organic compounds. RO2* diurnal variations were consistent with other HO2 measurements available at the site. HO2/RO2* ratios generally varied between 0.3 and 0.4 in all wind directions. Occasional HO2/RO2* ≥ 1 seemed to be associated with periods of high RO2* variability and with RO2 interferences in the HO2 measurement in air masses with high RO2 load.

scholarly journals Kinetics of the reactions of isoprene-derived hydroxynitrates: gas phase epoxide formation and solution phase hydrolysis

2014 ◽  
Vol 14 (8) ◽  
pp. 12121-12165 ◽  
Author(s):  
M. I. Jacobs ◽  
W. J. Burke ◽  
M. J. Elrod
Keyword(s):  
Gas Phase ◽  
Hydrolysis Rate ◽  
Ionization Mass ◽  
Volatile Organic ◽  
Isoprene Oxidation ◽  
Gas Phase Oxidation ◽  
Acid Catalyzed ◽  
Regional Formation ◽  
A Minor ◽  
Kinetics Of

Abstract. Isoprene, the most abundant non-methane volatile organic compound (VOC) emitted into the atmosphere, is known to undergo gas phase oxidation to form eight different hydroxynitrate isomers in "high NOx" environments. These hydroxynitrates are known to affect the global and regional formation of ozone and secondary organic aerosol (SOA), as well as affect the distribution of nitrogen. In the present study, we have synthesized three of the eight possible hydroxynitrates: 4-hydroxy-3-nitroxy isoprene (4,3-HNI) and E/Z-1-hydroxy-4-nitroxy isoprene (1,4-HNI). Oxidation of the 4,3-HNI isomer by the OH radical was monitored using a flow tube chemical ionization mass spectrometer (FT-CIMS), and its OH rate constant was determined to be (3.64 ± 0.41) × 10−11 cm3 molecule−1 s−1. The products of 4,3-HNI oxidation were monitored, and a mechanism to explain the products was developed. An isoprene epoxide (IEPOX) – a species important in SOA chemistry and thought to originate only from "low NOx" isoprene oxidation – was found as a minor, but significant product. Additionally, hydrolysis kinetics of the three synthesized isomers were monitored with NMR. The bulk, neutral solution hydrolysis rate constants for 4,3-HNI and the 1,4-HNI isomers were (1.59±0.03 × 10−5 s−1 and (6.76 ± 0.09) × 10−3 s−1, respectively. The hydrolysis reactions of each isomer were found to be general acid-catalyzed. The reaction pathways, product yields and atmospheric implications for both the gas phase and aerosol-phase reactions are discussed.

scholarly journals CRI-HOM: A novel chemical mechanism for simulating Highly Oxygenated Organic Molecules (HOMs) in global chemistry-aerosol-climate models

2020 ◽  
Author(s):  
James Weber ◽  
Alexander Archibald ◽  
Paul Griffiths ◽  
Scott Archer-Nicholls ◽  
Torsten Berndt ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Radiative Forcing ◽  
Organic Molecules ◽  
Climate Models ◽  
Global Climate Models ◽  
Chemical Mechanism ◽  
Atmospheric Composition ◽  
Climate Modelling ◽  
Particle Nucleation ◽  
Peroxy Radicals

Abstract. We present here results from a new mechanism, CRI-HOM, which we have developed to simulate the formation of highly oxygenated organic molecules (HOMs) from the gas phase oxidation of α-pinene, one of the most widely emitted BVOCs by mass. This concise scheme adds 12 species and 66 reactions to the Common Representative Intermediates (CRI) mechanism v2.2 Reduction 5 and enables the representation of semi-explicit HOM treatment suitable for long term global chemistry- aerosol-climate modelling, within a comprehensive tropospheric chemical mechanism. The key features of the new mechanism are (i) representation of the autoxidation of peroxy radicals from the hydroxyl radical and ozone initiated reactions of α-pinene, (ii) formation of multiple generations of peroxy radicals, (iii) formation of accretion products (dimers) and (iv) isoprene-driven suppression of accretion product formation, as observed in experiments. The mechanism has been constructed through optimisation against a series of flow tube laboratory experiments. The mechanism predicts a HOM yield of 4–6 % under conditions of low to moderate NOx, in line with experimental observations, and reproduces qualitatively the decline in HOM yield and concentration at higher NOx. The mechanism gives a HOM yield that also increases with temperature, in line with observations, and our mechanism compares favourably to some of the limited observations of [HOM] observed in the boreal forest in Finland and in the south east USA. The reproduction of isoprene-driven suppression of HOMs is a key step forward as it enables global climate models to capture the interaction between the major BVOC species, along with the potential climatic feedbacks. This suppression is demonstrated when the mechanism is used to simulate atmospheric profiles over the boreal forest and rainforest; different isoprene concentrations result in different [HOM] distributions, illustrating the importance of BVOC interactions in atmospheric composition and climate. Finally particle nucleation rates calculated from [HOM] in present day and pre- industrial atmospheres suggest that sulphuric acid free nucleation can compete effectively with other nucleation pathways in the boreal forest, particularly in the pre-industrial, with important implications for the aerosol budget and radiative forcing.

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