O2 Channel Research Articles

Effects of Window Green View Index on Stress Recovery of College Students from Psychological and Physiological Aspects

Students often experience high levels of daily academic pressure, spending extended periods within indoor classroom environments. Windows, as a medium of proximity to nature, play an important role in relieving stress. However, the broader implications of the Window Green View Index (WGVI) on individual well-being remain underexplored. This study aims to assess the effects of WGVI on stress recovery in college students by utilizing virtual reality technology to create five classroom environments with varying WGVI levels: 0%, 25%, 50%, 75%, and 100%. Twenty-four participants were subjected to the Trier Social Stress Test before engaging with the different WGVI scenarios for stress recovery. Both subjective assessments and objective physiological indicators were evaluated. Results indicated that participants exhibited the lowest Profile of Mood States (POMS) score (−4.50) and significantly improved systolic blood pressure recovery at a 25% WGVI level. The examination of EEG data revealed that the O2 channel in the occipital region exhibited the highest level of activity in the alpha frequency range during the experiment. Additionally, a significant association was observed between the EEG measurements and the subjective rating of stress. This study underscores the significance of incorporating WGVI into the design and planning of college buildings to promote mental health and well-being among students.

Level0 to Level1B processor for MethaneAIR

Abstract. This work presents the development of the MethaneAIR Level0–Level1B processor, which converts raw L0 data to calibrated and georeferenced L1B data. MethaneAIR is the airborne simulator for MethaneSAT, a new satellite under development by MethaneSAT LLC, a subsidiary of the Environmental Defense Fund (EDF). MethaneSAT's goals are to precisely map over 80 % of the production sources of methane from oil and gas fields across the globe to an accuracy of 2–4 ppb on a 2 km2 scale. Efficient algorithms have been developed to perform dark corrections, estimate the noise, radiometrically calibrate data, and correct stray light. A forward model integrated into the L0–L1B processor is demonstrated to retrieve wavelength shifts during flight accurately. It is also shown to characterize the instrument spectral response function (ISRF) changes occurring at each sampled spatial footprint. We demonstrate fast and accurate orthorectification of MethaneAIR data in a three-step process: (i) initial orthorectification of all observations using aircraft avionics, a simple camera model, and a medium-resolution digital elevation map; (ii) registration of oxygen (O2) channel grayscale images to reference Multispectral Instrument (MSI) band 11 imagery via Accelerated-KAZE (A-KAZE) feature extraction and linear transformation, with similar co-registration of methane (CH4) channel grayscale images to the registered O2 channel images; and finally (iii) optimization of the aircraft position and attitude to the registered imagery and calculation of viewing geometry. This co-registration technique accurately orthorectifies each channel to the referenced MSI imagery. However, in the pixel domain, radiance data for each channel are offset by almost 150–200 across-track pixels (rows) and need to be aligned for the full-physics or proxy retrievals where both channels are simultaneously used. We leveraged our orthorectification tool to identify tie points with similar geographic locations in both CH4 and O2 images in order to produce shift parameters in the across-track and along-track dimensions. These algorithms described in this article will be implemented into the MethaneSAT L0–L1B processor.

A new method to measure aquaporin-facilitated membrane diffusion of hydrogen peroxide and cations in plant suspension cells.

Plant aquaporins (AQPs) facilitate the membrane diffusion of water and small solutes, including hydrogen peroxide (H2 O2 ) and, possibly, cations, essential signalling molecules in many physiological processes. While the determination of the channel activity generally depends on heterologous expression of AQPs in Xenopus oocytes or yeast cells, we established a genetic tool to determine whether they facilitate the diffusion of H2 O2 through the plasma membrane in living plant cells. We designed genetic constructs to co-express the fluorescent H2 O2 sensor HyPer and AQPs, with expression controlled by a heat shock-inducible promoter in Nicotiana tabacum BY-2 suspension cells. After induction of ZmPIP2;5 AQP expression, a HyPer signal was recorded when the cells were incubated with H2 O2 , suggesting that ZmPIP2;5 facilitates H2 O2 transmembrane diffusion; in contrast, the ZmPIP2;5W85A mutated protein was inactive as a water or H2 O2 channel. ZmPIP2;1, ZmPIP2;4and AtPIP2;1 also facilitated H2 O2 diffusion. Incubation with abscisic acid and the elicitor flg22 peptide induced the intracellular H2 O2 accumulation in BY-2 cells expressing ZmPIP2;5. We also monitored cation channel activity of ZmPIP2;5 using a novel fluorescent photo-switchable Li+ sensor in BY-2 cells. BY-2 suspension cells engineered for inducible expression of AQPs as well as HyPer expression and the use of Li+ sensors constitute a powerful toolkit for evaluating the transport activity and the molecular determinants of PIPs in living plant cells.

Re-Examination of the N2O + O Reaction.

The reaction of N2O with O is a key step in consumption of nitrous oxide in thermal processes. It has two product channels, NO + NO (R2) and N2 + O2 (R3). The rate constant for R2 has been measured both in the forward and the reverse direction at elevated temperature and is well established. However, the rate constant for the N2 + O2 channel (R3) has been difficult to quantify and has significant error limits. The direct reaction on the triplet surface has a barrier of around 40 kcal mol-1, and it is too slow for the N2 + O2 channel to have any practical significance. Recently, Pham and Lin (2022) suggested an alternative low activation energy reaction path that involves intersystem crossing and reaction on the singlet surface. In the present work, we re-examined a wide range of experiments relevant for the N2O + O reaction through kinetic modeling, paying attention to the impact of artifacts such as impurities and surface reactions. Experimental results from shock tubes and batch reactors on the final NO yield in N2O decomposition, covering temperatures of 973-2200 K and pressures of 0.013-11.5 atm, support k3 ∼ 0, consistent with the high activation energy for reaction on the triplet surface and a low probability of ISC.

Complexity analysis from EEG data in congestive heart failure: A study via approximate entropy.

Congestive heart failure (CHF) is a very complex clinical syndrome that may lead to ischemic cerebral hypoxia condition. The aim of the present study is to analyze the effects of CHF on brain activity through electroencephalographic (EEG) complexity measures, like approximate entropy (ApEn). Twenty patients with CHF and 18 healthy elderly people were recruited. ApEn values were evaluated in the total spectrum (0.2-47 Hz) and main EEG frequency bands: delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-11 Hz), alpha 2 (11-13 Hz), beta 1 (13-20 Hz), beta 2 (20-30 Hz), and gamma (30-45 Hz) to identify differences between CHF group and control. Moreover, a correlation analysis was performed between ApEn parameters and clinical data (i.e., B-type natriuretic peptides (BNP), New York Heart Association (NYHA), and systolic blood pressure (SBP)) within the CHF group. Statistical topographic maps showed statistically significant differences between the two groups in the total spectrum and theta frequency band. Within the CHF group, significant negative correlations were found between total ApEn and BNP in O2 channel and between theta ApEn and NYHA scores in Fp1, Fp2, and Fz channels; instead, a significant positive correlation was found between theta ApEn and SBP in C3 channel and a nearly significant positive correlation was obtained between theta ApEn and SBP in F4 channel. EEG abnormalities in CHF are very similar to those observed in cognitive-impaired patients, suggesting analogies between the effects of neurodegeneration and brain chronic hypovolaemia due to heart disorder and underlying high brain sensitivity to CHF.

Relationships between EEG and thermal comfort of elderly adults in outdoor open spaces

We investigated the relationship between variation in EEG signal characteristics (α, β, θ and δ frequency bands) of elderly adults and their thermal perceptions in outdoor environments in Xi'an, China using meteorological measurement, subjective questionnaire survey and EEG signal monitoring. We found that: 1) the δ, θ and β relative powers of the frontal lobe were significantly correlated with physiological equivalent temperature (PET), globe temperature (Tg), wind speed (Va), mean radiant temperature (Tmrt) and global radiation (G). The α, δ and β relative powers of parietal lobe were significantly correlated with PET, Tg, air temperature (Ta) and relative humidity (RH). 2) The α relative power of the frontal lobe varied with an inverted U-shape with an increase in thermal sensation. The α wave of the frontal lobe was the most accurate index to evaluate elderly adults' thermal sensation. 3) The α wave of the right cerebral hemisphere can be used to identify elderly adults' thermal comfort, particularly the O2 channel of the occipital lobe. 4) Ta and Va were dominant influences of the EEG among elderly adults. The meteorological factors that affected the EEG changed as thermal stress fluctuated; most meteorological factors were positively related to thermal stress. Our results provide theoretical evidence of the predictive accuracy of outdoor thermal comfort models for elderly adults and contribute to the practical bioclimatic design of outdoor open spaces for vulnerable groups.

Mental performance classification using fused multilevel feature generation with EEG signals

ABSTRACT Mental performance classification is a critical issue for brain-computer interfaces. Accurate and reliable classification of good or bad mental performance gives important clues for the preliminary diagnosis of some diseases and mental stress. In this work, we put forward an objective artificial intelligence model to quantify the clarity of thought during mental arithmetic tasks. The proposed model consists of: (i) multilevel feature extraction based on statistical and texture analysis methods, (ii) feature ranking and selection with a Chi2 method, (iii) classification, and (iv) weightless majority voting classifier. The novelty of the presented model comes from multilevel fused feature generation. The presented model was developed using 20 channel electroencephalography data from 36 subjects. The signals were captured while the subjects were performing mental arithmetic tasks. The individual datasets were labeled as either good or bad, based on the task results. We have obtained an accuracy of 96.77% using O2 channel with a k-nearest neighbor classifier and reached 100.0% accuracy with the majority voting classifier. Our results indicate that it is possible to determine mental performance with artificial intelligence. That might be a steppingstone to establish objective measures for the clarity of thought during a wide range of mental tasks.

Time-frequency Analysis of Electroencephalogram Signals in a Perceptual Decision-Making Task of Random Dot Kinematograms

Purpose: Perceptual decision-making is the act of choosing one option from a set of alternatives based on available sensory information. Regarding the serious role of this act in human personal and social lives, the neurophysiological analysis of the brain during this type of decisions is of great interest. In this research, the underlying neural mechanism of these decisions is investigated using a perceptual decision-making Electroencephalogram (EEG) dataset with a perceptual discrimination task.
 Materials and Methods: An online available dataset containing the pre-processed EEG signals of 24 healthy participants during the perceptual decision-making task of Random Dot Kinematograms was used. After a secondary pre-processing stage, clean EEG signal was divided into 1.3-second segments and averaged for Event-Related Potential (ERP) and Event-Related Spectral Perturbation (ERSP) calculations. The task engagement index was also calculated and averaged among all participants.
 Results: According to the results, the amplitude of the N200 component in O1 and O2 channels was larger for correct choices than incorrect ones. Furthermore, in the O2 channel, it was observed that the average alpha power near 200 milli-seconds after stimulus onset was slightly higher in high and low confidence choices than medium confidence choices. The beta band power in the PO2 channel was also higher for correct choices rather than incorrect ones in this interval. Moreover, the results represented that the task engagement index was higher in medium confidence choices, especially in occipital and parieto-occipital channels.
 Conclusion: The larger N200 amplitude and the higher beta power for correct choices, and the lower alpha power for medium confidence choices may be due to more attention of the individuals to the stimuli. This phenomenon can be observed in the task engagement indices as well. This could be because the user expended more effort in medium confidence to bring one of the choices to the decision threshold.

Detecting slow eye movements with bimodal-LSTM for recognizing drivers’ sleep onset period

Slow eye movements (SEMs) indicate sleep onset period but are rarely studied in the field of driver fatigue detection. Through visual observation and statistical analysis we find that SEMs occur during eye-closed periods and have a high overall coverage rate during driving, which makes it feasible to utilize detecting SEMs to recognize drivers’ sleep onset period. To detect SEMs, we adopt a bimodal Long Short-Term Memory (LSTM) network to deal with temporal information and multimodal information in physiological signals. To extend the distinguishing information, we define a novel horizontal sum (HSUM) signal, which is sum of signals from two horizontal electrooculogram (EOG) channels. Electroencephalogram (EEG)-related features are extracted from the HSUM signal in contrast to those from the traditional O2 signal. EOG features are extracted from the horizontal EOG (HEOG) signals. The results demonstrate that features from multimodal signals (HSUM and HEOG signals, or O2 and HEOG signals) achieve better classification results than features from the single HEOG signal. And the EEG-related features extracted from self-defined HSUM signals achieve comparable results to those from traditional O2 signals, thus avoiding using extra O2 channel. The proposed method of detecting SEMs using the bimodal LSTM to classify features from HSUM and HEOG signals achieves the average F-score of 76.5%, which is higher than the classic support vector machine by 7.5%. This method of detecting SEMs using only two channels helps to build a user acceptable and feasible system for recognizing drivers’ sleep onset period.

Application of advanced technology to build a vibrant environment on planet mars

In order to make Mars a better planet, in this paper, photo-dissociation technology, mathematical modeling, and a series of chemical reaction methodology have been proposed to create a vibrant ecosystem and balance the atmosphere on Mars. Since CO2 is a stable compound, breaking it down into C and O2 always is challenging, but exciting thought. Interestingly, my recent research revealed that photo-dissociation by utilizing UVV (laser) could be an exciting technology to split CO2 into C + O2 since the theoretical reaction suggested that the production of C + O2 channel from CO2 photo-exciting technology releases the energetic level threshold of C(3P2) + O2(X3∑ g − ) that can be detected by ultraviolet laser pump-probe spectroscopy. Subsequently, a mathematical model for creating of ocean on Mars by breaking its substantial polar ice has been performed considering algorithms for surface and coordinate between the barotropic momentum and continuity equations, and interestingly the calculation suggested that it is very much possible to flow ocean on Mars surface to meet its water demand. Subsequently, proposed series of chemical reaction technology suggested that implementation of carbonator looping and plasma reaction paths can convert photo-dissociated carbon (C) into N2 and NH3 to enrich Mars’ soil in order to grow vegetation as well as to create a balance ecosystem in Mars eventually. Finally, sustainable green technology has been proposed for the development of Mars to be a complete balanced planet to deliver all basic and modern needs to run daily life smoothly. Thus, implication of chemical reaction technologies along with sustainable development plans can indeed make the Mars a vibrant environment to live there in clean and green.

ChemInform Abstract: Evidence for Direct Molecular Oxygen Production in CO2 Photodissociation.

AbstractVacuum UV laser pump‐probe spectroscopy and velocity‐map imaging detection of C(3PJ) give direct experimental evidence for the C + O2 channel with a yield of 5% in CO2 photodissociation.

Photochemistry. Evidence for direct molecular oxygen production in CO₂ photodissociation.

Photodissociation of carbon dioxide (CO2) has long been assumed to proceed exclusively to carbon monoxide (CO) and oxygen atom (O) primary products. However, recent theoretical calculations suggested that an exit channel to produce C + O2 should also be energetically accessible. Here we report the direct experimental evidence for the C + O2 channel in CO2 photodissociation near the energetic threshold of the C((3)P) + O2(X(3)Σ(g)(-)) channel with a yield of 5 ± 2% using vacuum ultraviolet laser pump-probe spectroscopy and velocity-map imaging detection of the C((3)PJ) product between 101.5 and 107.2 nanometers. Our results may have implications for nonbiological oxygen production in CO2-heavy atmospheres.

Evaluation of Combustion Mechanisms Using Global Uncertainty and Sensitivity Analyses: A Case Study for Low‐Temperature Dimethyl Ether Oxidation

ABSTRACTA global uncertainty analysis is performed for three current mechanisms describing the low‐temperature oxidation of dimethyl ether (Aramco Mech 1.3, Metcalfe et al., Int J Chem Kinet 2013, 45, 638–675; Zheng et al., Proc Combust Inst 2005, 30, 1101–1109; Liu et al., Combust Flame 2013, 160, 2654–2668) with application to simulations of species concentrations (CH2O, H2O2, CH3OCHO) corresponding to existing data from an atmospheric pressure flow reactor and high‐pressure ignition delays. When incorporating uncertainties in reaction rates within a global sampling approach, the distributions of predicted targets can span several orders of magnitude. The experimental profiles, however, fall within the predictive uncertainty limits. A variance‐based sensitivity analysis is then undertaken using high dimensional model representations. The main contributions to predictive uncertainties come from the CH3OCH2 + O2 system, with isomerization, propagation, chain‐branching, secondary OH formation, and peroxy–peroxy reactions all playing a role. The response surface describing the relationship between sampled reaction rates and predicted outputs is complex in all cases. Higher order interactions between parameters contribute significantly to output variance, and no single reaction channel dominates for any of the conditions studied. Sensitivity scatter plots illustrate that many different parameter combinations could lead to good agreement with specific sets of experimental data. The Aramco scheme is then updated based on data from a recent study by Eskola et al. (J Phys Chem A, in press), which presents quite different temperature and pressure dependencies for the rates of CH3OCH2O2 → CH2OCH2O2H and CH2OCH2O2H → OH+2CH2O compared with currently used values and includes well skipping channels. The updates from Eskola worsen the agreement with experiments when used in isolation. However, if the rate of the CH2OCH2O2H + O2 channel is subsequently reduced, very good agreement can be achieved. Owing to the complex nature of the response surface, the tuning of this channel remains speculative. Further detailed studies of the temperature and pressure dependence of the CH3OCH2O2 + O2, CH2OCH2O2H + O2 system are recommended to reduce uncertainties within current dimethyl ether mechanisms for low‐temperature conditions.

Estimation of Eye Closure Degree Using EEG Sensors and Its Application in Driver Drowsiness Detection

Currently, driver drowsiness detectors using video based technology is being widely studied. Eyelid closure degree (ECD) is the main measure of the video-based methods, however, drawbacks such as brightness limitations and practical hurdles such as distraction of the drivers limits its success. This study presents a way to compute the ECD using EEG sensors instead of video-based methods. The premise is that the ECD exhibits a linear relationship with changes of the occipital EEG. A total of 30 subjects are included in this study: ten of them participated in a simple proof-of-concept experiment to verify the linear relationship between ECD and EEG, and then twenty participated in a monotonous highway driving experiment in a driving simulator environment to test the robustness of the linear relationship in real-life applications. Taking the video-based method as a reference, the Alpha power percentage from the O2 channel is found to be the best input feature for linear regression estimation of the ECD. The best overall squared correlation coefficient (SCC, denoted by r2) and mean squared error (MSE) validated by linear support vector regression model and leave one subject out method is r2 = 0.930 and MSE = 0.013. The proposed linear EEG-ECD model can achieve 87.5% and 70.0% accuracy for male and female subjects, respectively, for a driver drowsiness application, percentage eyelid closure over the pupil over time (PERCLOS). This new ECD estimation method not only addresses the video-based method drawbacks, but also makes ECD estimation more computationally efficient and easier to implement in EEG sensors in a real time way.

Conserved glycine 232 in the ligand channel of ba3 cytochrome oxidase from Thermus thermophilus.

Knowing how the protein environment modulates ligand pathways and redox centers in the respiratory heme-copper oxidases is fundamental for understanding the relationship between the structure and function of these enzymes. In this study, we investigated the reactions of O2 and NO with the fully reduced G232V mutant of ba3 cytochrome c oxidase from Thermus thermophilus (Tt ba3) in which a conserved glycine residue in the O2 channel of the enzyme was replaced with a bulkier valine residue. Previous studies of the homologous mutant of Rhodobacter sphaeroides aa3 cytochrome c oxidase suggested that the valine completely blocked the access of O2 to the active site [Salomonsson, L., et al. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 11617–11621]. Using photolabile O2 and NO carriers, we find by using time-resolved optical absorption spectroscopy that the rates of O2 and NO binding are not significantly affected in the Tt ba3 G232V mutant. Classical molecular dynamics simulations of diffusion of O2 to the active site in the wild-type enzyme and G232V mutant show that the insertion of the larger valine residue in place of the glycine appears to open up other O2 and NO exit/entrance pathways that allow these ligands unhindered access to the active site, thus compensating for the larger valine residue.

Measurement of Visual Eeg Signals Stimulated By Yellow Color Photons of Specific Wave Length At Different Intensities

Electroencephalography (EEG) is a diagnostic tool that records the electrical activity of the brain using numerous electrodes placed on various regions to the scalp, or in special cases on the cortex. The resulting traces are known as an electroencephalogram and represent so-called brainwaves.There are many types of stimulators (physical, chemical , and mechanical )that are affect the special senses sensitive areas in the brain which are collected as electrical signals. This research is concerned with photo stimulator (yellow color with frequency of ≈ 515 THz that is transmitted by visual nerve and the generated electrical signal waves are recorded by EEG. The sample of the research consists of 18 normal vision volunteers divided equally between males and females. All precautions of wave interference or artifacts that are due to physiological or external electrical source are taken into account and minimized into the ignored level.The results clearly showed that, the mean relative action potential amplitude recorded from O2 for males were the same in low and higher intensities ; when intensity was increased than that recorded from O1, and O2 channel for females also the same at low intensities then increased with increasing intensity than that recorded from O1.The fitting equation of the mean relative action potential amplitude versus the intensity of O1 and O2 channels for males are y = 0.053x2-3.161x + 47.23 with R2 = 0.969 and y = 0.044x2- 2.619x + 39.19 with R2 = 0.987, and for females are y = 0.046x2 – 2.693x + 39.60 with R2 = 0.894 and y = 0.043x2- 2.483x + 36.59 with R2 = 0.880 respectively.To compare the EEG electrical signals that are recorded from O1 and O2 channels for males and females, the mean relative action potential amplitudes are higher in males than in females for both channels. The deduced fitting curves for males O1 channel is y =0.046x2 – 2.693x + 39.60 with R2 = 0.894 and for females, O1 channel y =0.043x2 - 2.483x + 36.59 with R2 = 0.880 and that for male O2 channel is y = 0.044x2 – 2.619x + 39.19 with R2 = 0.987 and for female O2 channel y = 0.05x2 – 3.61x + 47.23 with R2 = 0.969.

Effect of nucleobase sequence on the proton-transfer reaction and stability of the guanine–cytosine base pair radical anion

The formation of base pair radical anions is closely related to many fascinating research fields in biology and chemistry such as radiation damage to DNA and electron transport in DNA. However, the relevant knowledge so far mainly comes from studies on isolated base pair radical anions, and their behavior in the DNA environment is less understood. In this study, we focus on how the nucleobase sequence affects the properties of the guanine-cytosine (GC) base pair radical anion. The energetic barrier and reaction energy for the proton transfer along the N(1)(G)-H···N(3)(C) hydrogen bond and the stability of GC˙(-) (i.e., electron affinity of GC) embedded in different sequences of base-pair trimer were evaluated using density functional theory. The computational results demonstrated that the presence of neighboring base pairs has an important influence on the behavior of GC˙(-) in the gas phase. The excess electron was found to be localized on the embedded GC and the charge leakage to neighboring base pairs was very minor in all of the investigated sequences. Accordingly, the sequence behavior of the proton-transfer reaction and the stability of GC˙(-) is chiefly governed by electrostatic interactions with adjacent base pairs. However, the effect of base stacking, due to its electrostatic nature, is severely screened upon hydration, and thus, the sequence dependence of the properties of GC˙(-) in aqueous environment becomes relatively weak and less than that observed in the gas phase. The effect of geometry relaxation associated with neighboring base pairs as well as the possibility of proton transfer along the N(2)(G)-H···O(2)(C) channel have also been investigated. The implications of the present findings to the electron transport and radiation damage of DNA are discussed.

Evidence of Roaming Dynamics and Multiple Channels for Molecular Elimination in NO3 Photolysis

We report correlated state distributions arising from NO3 photolysis at 588 nm using velocity map ion imaging. State-selected NO images reveal clear evidence for two dissociation pathways for the NO + O2 channel. Vibrationally excited O2 (3Σg−, ν = 5−10) is formed in coincidence with low rotational states of NO (2Π) in the dominant mechanism. We also observe a small channel consisting of low vibrational levels of O2 (3Σg−, ν = 0−4) coincident with high NO rotational states. We discuss the results in the context of the recent studies of formaldehyde dissociation and postulate the involvement of roaming-type dynamics.

Radiative signature of increasing atmospheric carbon dioxide in HIRS satellite observations

We examine the cause and implications of decadal trends observed in the High‐Resolution Infrared Radiation Sounder (HIRS) CO2 channels over the period 1980–1999 in conjunction with Microwave Sounding Unit (MSU) O2 channel measurements and climate model simulations. Simulated HIRS brightness temperatures (TBs) from the climate model with constant carbon dioxide indicate a global warming trend (∼0.2 K/decade) consistent with the corresponding MSU observations. By contrast, simulations with observed time‐varying CO2 concentration result in a global decreasing TB trend (∼−0.3 K/decade), indicating a greater influence of increased CO2 on the HIRS radiances compared to the tropospheric warming. Moreover, comparison between observation and simulations suggests that there may be important regional variations in the CO2 trends, particularly over the northern hemisphere midlatitudes downstream from major CO2 sources (U.S. and China). Thus the HIRS CO2 radiances may provide one opportunity to supplement existing surface networks by constraining regional patterns of decadal CO2 variability.

Water formation at low temperatures by surface O2 hydrogenation I: characterization of ice penetration

Water is the main component of interstellar ice mantles, is abundant in the solar system and is a crucial ingredient for life. The formation of this molecule in the interstellar medium cannot be explained by gas-phase chemistry only and its surface hydrogenation formation routes at low temperatures (O, O(2), O(3) channels) are still unclear and most likely incomplete. In a previous paper we discussed an unexpected zeroth-order H(2)O production behavior in O(2) ice hydrogenation experiments compared to the first-order H(2)CO and CH(3)OH production behavior found in former studies on hydrogenation of CO ice. In this paper we experimentally investigate in detail how the structure of O(2) ice leads to this rare behavior in reaction order and production yield. In our experiments H atoms are added to a thick O(2) ice under fully controlled conditions, while the changes are followed by means of reflection absorption infrared spectroscopy (RAIRS). The H-atom penetration mechanism is systematically studied by varying the temperature, thickness and structure of the O(2) ice. We conclude that the competition between reaction and diffusion of the H atoms into the O(2) ice explains the unexpected H(2)O and H(2)O(2) formation behavior. In addition, we show that the proposed O(2) hydrogenation scheme is incomplete, suggesting that additional surface reactions should be considered. Indeed, the detection of newly formed O(3) in the ice upon H-atom exposure proves that the O(2) channel is not an isolated route. Furthermore, the addition of H(2) molecules is found not to have a measurable effect on the O(2) reaction channel.