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

2009 ◽  
Vol 9 (5) ◽  
pp. 19243-19278 ◽  
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 ◽  
Model Studies ◽  
Chemical Scheme ◽  
Best Fit ◽  
Malaysian Borneo

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. The largest contributors to the optimisation cost function at the point of best-fit are OH (41%), NO (18%) and total monoterpenes (16%). 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 50–70% 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 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 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 Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: comparison of measurements with the box model MECCA

2008 ◽  
Vol 8 (4) ◽  
pp. 15239-15289 ◽  
Author(s):  
D. Kubistin ◽  
H. Harder ◽  
M. Martinez ◽  
M. Rudolf ◽  
R. Sander ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropical Rainforest ◽  
Source Region ◽  
Degradation Process ◽  
Reaction Scheme ◽  
Box Model ◽  
Chemical Mechanism ◽  
Similar Amount ◽  
Oxidation Capacity ◽  
Mixing Ratios

Abstract. As a major source region of the hydroxyl radical OH, the Tropics largely control the oxidation capacity of the atmosphere on a global scale. However, emissions of hydrocarbons from the tropical rainforest that react rapidly with OH can potentially deplete the amount of OH and thereby reduce the oxidation capacity. The airborne GABRIEL field campaign in equatorial South America (Suriname) in October 2005 investigated the influence of the tropical rainforest on the HOx budget (HOx=OH+HO2). The first observations of OH and HO2 over a tropical rainforest are compared to steady state concentrations calculated with the atmospheric chemistry box model MECCA. The important precursors and sinks for HOx chemistry, measured during the campaign, are used as constraining parameters for the simulation of OH and HO2. Significant underestimations of HOx are found by the model over land during the afternoon, with mean ratios of observation to model of 12.2±3.5 and 4.1±1.4 for OH and HO2, respectively. The discrepancy between measurements and simulation results is correlated to the abundance of isoprene. While for low isoprene mixing ratios (above ocean or at altitudes >3 km), observation and simulation agree fairly well, for mixing ratios >200 pptV (<3 km over the rainforest) the model tends to underestimate the HOx observations as a function of isoprene. Box model simulations have been performed with the condensed chemical mechanism of MECCA and with the detailed isoprene reaction scheme of MCM, resulting in similar results for HOx concentrations. Simulations with constrained HO2 concentrations show that the conversion from HO2 to OH in the model is too low. However, by neglecting the isoprene chemistry in the model, observations and simulations agree much better. An OH source similar to the strength of the OH sink via isoprene chemistry is needed in the model to resolve the discrepancy. A possible explanation is that the oxidation of isoprene by OH not only dominates the removal of OH but also produces it in a similar amount. Several additional reactions which directly produce OH have been implemented into the box model, suggesting that upper limits in producing OH are still not able to reproduce the observations (improvement by factors of ≈2.4 and ≈2 for OH and HO2, respectively). We determine that OH has to be recycled to 94% instead of the simulated 38% to match the observations, which is most likely to happen in the isoprene degradation process, otherwise additional sources are required.

scholarly journals Examining the Impostor-Profile—Is There a General Impostor Characteristic?

2021 ◽  
Vol 12 ◽  
Author(s):  
Fabio Ibrahim ◽  
Johann-Christoph Münscher ◽  
Philipp Yorck Herzberg
Keyword(s):  
Convergent Validity ◽  
Factor Model ◽  
Second Order ◽  
Model Fit ◽  
Impostor Phenomenon ◽  
General Factor ◽  
Order Model ◽  
First Order ◽  
Order Factor ◽  
Best Fit

The Impostor-Profile (IPP) is a six-dimensional questionnaire measuring the Impostor Phenomenon facets. This study aims to test (a) the appropriateness of a total score, (b) measurement invariance (MI) between gender, (c) the reliability of the IPP, and (d) the convergent validity of the IPP subscales. The sample consisted of N = 482 individuals (64% female). To identify whether the scales of the IPP form a total score, we compared four models: (1) six correlating subscales, (2) a general factor model, (3) a second-order model with one second-order factor and six first-order factors, and (4) a bifactorial model with six group factors. The bifactorial model obtained the best fit. This supports the assumption of a total impostor score. The inspection of structural validity between gender subgroups showed configural, metric, and partial scalar MI. Factor mean comparisons supported the assumption that females and males differ in latent means of the Impostor Phenomenon expressions. The omega coefficients showed sufficient reliability (≥0.71), except for the subscale Need for Sympathy. Overall, the findings of the bifactor model fit and construct validity support the assumption that the measurement through total expression is meaningful in addition to the theoretically formulated multidimensionality of the Impostor Phenomenon.

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.

scholarly journals New insights into OH airglow modelling to derive night-time atomic oxygen and atomic hydrogen in the mesopause region

2018 ◽  
Author(s):  
Tilo Fytterer ◽  
Christian von Savigny ◽  
Martin Mlynczak ◽  
Miriam Sinnhuber
Keyword(s):  
Atomic Hydrogen ◽  
Atomic Oxygen ◽  
Box Model ◽  
Satellite Measurements ◽  
Night Time ◽  
Vibrationally Excited ◽  
Mesopause Region ◽  
Airglow Emissions ◽  
Instrument Configuration ◽  
Best Fit

Abstract. An OH airglow model was developed to derive night-time atomic oxygen (O(3P)) and atomic hydrogen (H) from satellite OH airglow observations in the mesopause region (~ 75–100 km). The OH airglow model is based on the zero dimensional box model CAABA/MECCA-3.72f and was empirically adjusted to fit four different OH airglow emissions observed by the satellite/instrument configuration TIMED/SABER at 2.0 μm and at 1.6 μm as well as measurements by ENVISAT/SCIAMACHY of the transitions OH(6-2) and OH(3-1). Comparisons between the Best fit model obtained here and the satellite measurements suggest that deactivation of vibrationally excited OH(v) via OH(v ≥ 7) + O2 might favour relaxation to OH(v' ≤ 5) + O2 by multi-quantum quenching. It is further indicated that the deactivation pathway to OH(v' = v − 5) + O2 dominates. The results also provide general support of the recently proposed mechanism OH(v) + O(3P) → OH(0 ≤ v' ≤ v − 5) + O(1D) but suggest slower rates of OH(v = 7,6,5) + O(3P). Additionally, deactivation to OH(v' = v − 5) + O(1D) might be preferred. The profiles of O(3P) and H derived here are plausible between 80 km and 95  km. The values of O(3P) obtained in this study agree with the corresponding TIMED/SABER values between 80 km and 85 km, but are larger from 85 to 95 km due to different relaxation assumptions of OH(v) + O(3P). The H profile found here is generally larger than TIMED/SABER H by about 30–35 % from 80 to 95 km, which might be attributed to too high O3 night-time values.

scholarly journals New chemical scheme for giant planet thermochemistry

2020 ◽  
Vol 634 ◽  
pp. A78 ◽  
Author(s):  
O. Venot ◽  
T. Cavalié ◽  
R. Bounaceur ◽  
P. Tremblin ◽  
L. Brouillard ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Giant Planet ◽  
Brown Dwarfs ◽  
Planetary Atmospheres ◽  
Atmospheric Composition ◽  
Planetary Formation ◽  
Hot Jupiters ◽  
Chemical Scheme ◽  
High Level ◽  
Kinetics Of

Context. Several chemical networks have been developed to study warm (exo)planetary atmospheres. The kinetics of the reactions related to the methanol chemistry included in these schemes have been questioned. Aims. The goal of this paper is to update the methanol chemistry for such chemical networks based on recent publications in the combustion literature. We also aim to study the consequences of this update on the atmospheric compositions of (exo)planetary atmospheres and brown dwarfs. Methods. We performed an extensive review of combustion experimental studies and revisited the sub-mechanism describing methanol combustion in a scheme published in 2012. The updated scheme involves 108 species linked by a total of 1906 reactions. We then applied our 1D kinetic model with this new scheme to the case studies HD 209458b, HD 189733b, GJ 436b, GJ 1214b, ULAS J1335+11, Uranus, and Neptune; we compared these results with those obtained with the former scheme. Results. The update of the scheme has a negligible impact on the atmospheres of hot Jupiters. However, the atmospheric composition of warm Neptunes and brown dwarfs is modified sufficiently to impact observational spectra in the wavelength range in which James Webb Space Telescope will operate. Concerning Uranus and Neptune, the update of the chemical scheme modifies the abundance of CO and thus impacts the deep oxygen abundance required to reproduce the observational data. For future 3D kinetics models, we also derived a reduced scheme containing 44 species and 582 reactions. Conclusions. Chemical schemes should be regularly updated to maintain a high level of reliability on the results of kinetic models and be able to improve our knowledge of planetary formation.

Aerosol Dynamics Box Model Studies on the Connection of Sulphuric Acid and New Particle Formation

2007 ◽  
pp. 1013-1017
Author(s):  
Sanna-Liisa Sihto ◽  
Henri Vuollekoski ◽  
J. Leppä ◽  
Ilona Riipinen ◽  
Veli-Matti Kerminen ◽  
...  
Keyword(s):  
Sulphuric Acid ◽  
Particle Formation ◽  
Box Model ◽  
New Particle Formation ◽  
Aerosol Dynamics ◽  
Model Studies

scholarly journals In situ measurements of isoprene and monoterpenes within a south-east Asian tropical rainforest

2011 ◽  
Vol 11 (14) ◽  
pp. 6971-6984 ◽  
Author(s):  
C. E. Jones ◽  
J. R. Hopkins ◽  
A. C. Lewis
Keyword(s):  
Tropical Rainforest ◽  
East Asian ◽  
Ground Level ◽  
Ambient Air ◽  
Tropical Rainforests ◽  
Light Conditions ◽  
Mixing Ratios ◽  
Volatile Carbon ◽  
Malaysian Borneo

Abstract. Biogenic volatile organic compounds (BVOCs) emitted from tropical rainforests comprise a substantial fraction of global atmospheric VOC emissions, however there are only relatively limited measurements of these species in tropical rainforest regions. We present observations of isoprene, α-pinene, camphene, Δ-3-carene, γ-terpinene and limonene, as well as oxygenated VOCs (OVOCs) of biogenic origin such as methacrolein, in ambient air above a tropical rainforest in Malaysian Borneo during the Oxidant and Particle Photochemical Processes above a south-east Asian tropical rainforest (OP3) project in 2008. Daytime composition was dominated by isoprene, with an average mixing ratio of the order of ~1 ppb. γ-terpinene, limonene and camphene were the most abundant monoterpenes, with average daytime mixing ratios of 102, 71 and 66 ppt respectively, and with an average monoterpene toisoprene ratio of 0.3 during sunlit hours, compared to 2.0 at night. Limonene and camphene abundances were seen to be related to both temperature and light conditions. In contrast, γ-terpinene emission continued into the late afternoon/evening, under relatively low temperature and light conditions. The contributions of isoprene, monoterpenes and other classes of VOC to the volatile carbon budget and OH reactivity have been summarised for this rainforest location. We observe good agreement between surface and aircraft measurements of boundary layer isoprene and methacrolein above the natural rainforest, suggesting that the ground-level observations are broadly representative of isoprene emissions from this region.

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