Levels Of OH Radicals Research Articles

Brown carbon absorption in the Mediterranean basin from local and long-range transported biomass burning air masses

This study examines the impact of light absorption from biomass burning (BB) brown carbon (BrC) in the Mediterranean basin from local and distant fire incidents during a typical fire season in August 2019 and under severe fire activity in August 2021. The approaches of Saleh et al. (2014) and Wang et al. (2018) are used to describe the BrC absorption within the WRF-Chem model. Focusing on three regions in the Mediterranean (around the islands of Sicily, Malta, and Crete) that are most affected by BB activity, BrC absorption approximates 5 Mm−1 in OC concentrations up to 3 μg m−3 and can approach 15 Mm−1 in extreme conditions (up to 10 μg m−3). When photochemical bleaching is considered, BrC undergoes almost immediate bleaching upon emission due to high levels of OH radical in the Mediterranean atmosphere during summertime, decreasing light absorption between 56% and 75% under both average and extreme BB conditions. Cloud formation is facilitated above the PBL due to moisture increase induced by BrC at the area of fire events, while transported drier and warmer air masses tend to dissipate cloud formation further away from the BB source. The impact of BrC absorption on irradiances is small (up to −6 W m−2 in extreme conditions) and is often overlapped by the absorption from water vapour variations. BrC direct radiative effect (DRE) is estimated at 0.04 W m−2 (∼10% of BC) in average and 0.18 W m−2 in extreme BB activity under clear sky. Under all sky, low-level clouds dissipation in 2019 with average BB emissions enhances DRE (at 0.15 W m−2), while the higher clouds dissipation in 2021 limits DRE (at 0.11 W m−2) resulting in lower DRE despite the extreme BB conditions.

Superconducting-Magnet-Based Faraday Rotation Spectrometer for Real Time in Situ Measurement of OH Radicals at 106 Molecule/cm3 Level in an Atmospheric Simulation Chamber.

Atmospheric simulation chambers play vital roles in the validation of chemical mechanisms and act as a bridge between field measurements and modeling. Chambers operating at atmospheric levels of OH radicals (106-107 molecule/cm3) can significantly enhance the possibility for investigating the discrepancies between the observation and model predications. However, few chambers can directly detect chamber OH radicals at ambient levels. In this paper, we report on the first combination of a superconducting magnet with midinfrared Faraday rotation spectroscopy (FRS) for real time in situ measurement of the OH concentration in an atmospheric simulation chamber. With the use of a multipass enhanced FRS, a detection limit of 3.2 × 106 OH/cm3 (2σ, 4 s) was achieved with an absorption path length of 108 m. The developed FRS system provided a unique, self-calibrated analytical instrument for in situ direct measurement of chamber OH concentration.

Secondary organic aerosol formation from photo-oxidation of toluene with NOx and SO2: Chamber simulation with purified air versus urban ambient air as matrix

Chamber studies on the formation of secondary aerosols are mostly performed with purified air as matrix, it is of wide concern in what extent they might be different from the situations in ambient air, where a variety of gaseous and particulate components preexist. Here we compared the photo-oxidation of “toluene + NOx + SO2” combinations in a smog chamber in real urban ambient air matrix with that in purified air matrix. The secondary organic aerosols (SOA) mass concentrations and yields from toluene in the ambient air matrix, after subtracted ambient air background primary and secondary organic aerosols, were 9.0–34.0 and 5.6–12.9 times, respectively, greater than those in purified air matrix. Both homogeneous and heterogeneous oxidation of SO2 were enhanced in ambient air matrix experiments with observed 2.0–7.5 times higher SO2 degradation rates and 2.6–6.8 times faster sulfate formation than that in purified air matrix, resulting in higher in-situ particle acidity and consequently promoting acid-catalyzed SOA formation. In the ambient air experiments although averaged OH radical levels were elevated probably due to heterogeneous formation of OH on particle surface and/or ozonolysis of alkenes, non-OH oxidation pathways of SO2 became even more dominating. Under the same organic aerosol mass concentration, the SOA yields of toluene in purified air matrix experiments matched very well with the two-product model curve by Ng et al. (2007), yet the yields in ambient air on average was over two times larger. The results however were much near the best fit curve by Hildebrandt et al. (2009) with the volatility basis set (VBS) approach.

The Effects of Fuel Mixtures in Nonpremixed Combustion for a Bluff-Body Flame

A numerical investigation is presented assessing the effects of hydrogen compositions and nonflammable diluent mixtures on the combustion and NO emission characteristics of syngas nonpremixed flames for a bluff-body burner. An assessment of turbulent nonpremixed modeling techniques is presented and is compared with the experiments of Correa and Gulati (1992, “Measurements and Modeling of a Bluff Body Stabilized Flame,” Combust. Flame, 89(2), pp. 195–213). The realizable k–ε and the Reynolds stress (RSM) turbulence models were found to perform the best. As a result, increased hydrogen content caused the radial velocity and strain rate to decrease, which was important for mixing whereby NO production decreased. Also, the effectiveness of nonflammable diluent mixtures of N2, CO2, and H2O was characterized in terms of the ability to reduce NO emission in syngas nonpremixed flames. Results indicated that CO2 was the most effective diluent to reduce NO emission and H2O was more effective than N2. CO2 produced low levels of OH radical, which made CO2 the most effective diluent. Although H2O increased OH radicals, it was still effective to reduce thermal NO because of its high specific heat. It will be numerically shown that hydrogen concentration in the H2/CO/N2 flame does not significantly affect temperature but dramatically decreases NO emission, which is important for industrial applications that can use hydrogen in syngas flames.

Atmospheric SO2 oxidation efficiency over a semi-arid region: Seasonal patterns from observations and GEOS-Chem model

The oxidation efficiency of atmospheric SO2, measured as a molar ratio of SO42− to total SOx (SOx = SO2 + SO42−), referred as S-ratio, have been studied from a high altitude site (Gurushikhar, Mt. Abu: 24.6° N, 72.7° E, 1680 m ASL) in a semi-arid region of western India. A global 3-dimensional Chemical Transport Model (CTM), GEOS-Chem (v8-03-01), is employed to interpret the observed patterns. The S-ratios derived from time series SO2 and SO42− measurements exhibited a pronounced seasonality, with relatively low ratios in Feb–Mar 2010, high ratios in Nov–Dec 2009 and intermediate values in Sep–Oct 2009. The lower S-ratios for Feb ‘10 and Mar ‘10 (median values 0.10 and 0.08 respectively) have been attributed to the relatively high planetary boundary layer (PBL) heights – to reduce the SO2 loss from the atmosphere via dry deposition – as well as the lower OH radical levels and low ‘aged air mass influx’ during these months. On the other hand, low PBL heights and significant long range transport contributions are projected to be the possible causes for the higher S-ratios during Nov ‘09 and Dec ‘09 (median values 0.30 and 0.28 respectively). The seasonal patterns for the S-ratios predicted by the CTM for the GEOS-Chem 4° × 5° grid cell containing the sampling site showed highest ratios in Jul–Aug, and the lowest in Apr. The model has been employed further to study the contributions from various parameters to the S-ratios such as PBL, OH, RH, dust load, transport pattern and dry deposition. Sensitivity simulations showed the S-ratios enhancing with dust load with the peak in May (∼4.7% (median)). Similarly, the ‘dry deposition’ is seen to boost the S-ratios with the peak in August (∼66.3% (median)). Also, model simulations to assess the ‘altitudinal dependence of S-ratios’ have revealed a pronounced seasonal behaviour.

Nitrous acid (HONO): An emerging indoor pollutant

Abstract Nitrous acid (HONO) is an emergent household pollutant exhibiting adverse health effects. It can be easily photodissociated by the solar light penetrating through the windows leading to an important production of hydroxyl radical (OH) which in turn controls the oxidative capacity of indoor atmospheres. Indeed, recent campaign performed in a school classroom in Marseille, France revealed high levels of OH radicals in order of 10 6 cm −3 which were directly associated with the photolysis of HONO. Chamber experiments confirmed that photolysis of HONO is the main source of OH radicals indoors. Very recent laboratory measurements have demonstrated that the photo-enhanced reaction of NO 2 on various surfaces commonly found indoors is a powerful source of HONO indicating that indoor surfaces are not only physical but also photochemical substrates that play an active role in the enhancement of the production of HONO indoors. These results provided a significant contribution towards a comprehensive understanding of HONO chemistry indoors, a knowledge that should be implemented in photochemical models in order to properly describe the indoor air chemistry.

Taxifolin mitigates oxidative DNA damage in vitro and protects zebrafish (Danio rerio) embryos against cadmium toxicity

Taxifolin (TAX) is a natural source of bioflavonoid found in various conifers. In this study, initially we investigated the antioxidant potential of TAX under in vitro assays such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), ferric-ion reducing power (FRAP) and hydroxyl radical (OH). The activities of DPPH, ABTS, FRAP and OH radical levels were significantly inhibited by TAX with an IC50 values of 16.48, 66.34, 18.17 and 11.42μg/ml, respectively. Secondly, TAX exhibited a strong protection against OH mediated DNA damage on pUC19 plasmid DNA at 1.0μg/ml. Finally, we evaluated the protective mechanism of TAX against cadmium intoxicated zebrafish embryos (Danio rerio). We found that embryos exposed to 100μM Cd exhibited significantly reduced survival, delayed hatching and phenotypic abnormalities at 24, 48, 72 and 96hours post fertilization (hpf). Similarly, Cd intoxicated embryos showed significantly increased cardiac function (131beats/min) at 60hpf. Conversely, treatment with TAX (0.1, 1.0 and 10μM) significantly enhanced the antioxidant enzyme levels (SOD, CAT, GPx and GR) by reducing the lipid peroxidation (MDA) in zebrafish embryos. Collectively, our results concluded that TAX could act as a potent redox scavenger against oxidative DNA damage and also functions as a crucial suppressor of Cd toxicity in zebrafish embryos.

Development of revised SAPRC aromatics mechanisms

The representation of the gas-phase atmospheric reactions of aromatic hydrocarbons in the SAPRC-07 chemical mechanism has been updated to give better simulations of recent environmental chamber experiments carried out under lower NOx conditions than used to develop SAPRC-07. SAPRC-07 consistently underpredicted NO oxidation and O3 formation rates observed in most of the newer experiments. The new aromatics mechanisms, designated as SAPRC-11, gave better simulations of O3 formation in almost all experiments, except for higher (>100 ppb) NOx benzene and (to a lesser extent) toluene experiments where O3 formation rates were consistently overpredicted. This overprediction at higher NOx can be corrected if the aromatics mechanism is parameterized to include a new NOx dependence on photoreactive product yields, but that parameterization was not incorporated in SAPRC-11 because it is inconsistent with available laboratory data. The mechanisms for phenolic compounds were also significantly revised to better simulate the new experiments. The base mechanism for SAPRC-11 incorporates a few minor updates, but otherwise is the same as SAPRC-07. The light source used in the chamber experiments had no significant effect on mechanism evaluation results, except possibly for cresols. The mechanisms still underpredict OH radical levels and further studies are needed to reduce uncertainties in aromatics mechanisms.

28 GENERATION OF REACTIVE OXYGEN SPECIES IN BOVINE CULTURED SOMATIC CELLS AND SOMATIC CELL NUCLEAR TRANSFER EMBRYOS DURING MICROMANIPULATION PROCEDURES AND EARLY IN VITRO DEVELOPMENT

The present study was conducted to examine the reactive oxygen species (ROS) generation levels in the donor cells, recipient oocytes, and somatic cell nuclear transfer (SCNT) embryos during nuclear transfer procedures. Bovine ear skin cells were classified by serum starvation, confluence, and cycling cells. Bovine metaphase II (MII) oocytes matured in vitro for 22 h and denuded by vortexing were enucleated and electrofused with serum-starved donor cells, then activated by a combination of Ca-ionophore and 6-dimethylaminopurine culture for 4 h. In vitro fertilization (IVF) was performed for controls. SCNT and IVF embryos were cultured in CR1aa supplemented with 3 mg mL–1 BSA for ∼36 h. Donor cells, recipient oocytes, and SCNT embryos were stained in 10 μM dichlorohydrofluorescein diacetate (DCHFDA) or 10 μM HPF dye each for 30 min at 39°C to measure the H2O2 or ·OH radical levels after various micromanipulation steps. SCNT and IVF embryos were also stained at the 1-, 2-, and 4-cell stages after 8, 24, and 42 h of fusion or insemination, respectively. The fluorescent emissions from the samples were recorded as JPEG file using a digital camera (F5.0, 4 s) attached to a fluorescent microscope with filters at 450 to 480 nm for excitation and at 515 nm for emission. The images were analysed using ImageJ software 1.37 (NIH) by the intensity of fluorescence (pixels) in each cell (total 70 to 75 cells in each group), oocyte and embryo (total 50 to 60 eggs or embryos in each group). 4 to 7 replicates were performed for each experiment, and data were analysed by Duncan′s multiple-range tests. H2O2 and ·OH radical levels of cultured somatic cells were high in confluence group and significantly low in serum starvation group (P < 0.05). During micromanipulation, H2O2 levels in recipient oocytes and SCNT embryos were increased by enucleation (37.2 pixels), electrofusion (49.7 pixels), and activation (40.6 pixels) treatments (P < 0.05) compared to that in MII oocytes (33.1 pixels), and the level of H2O2 was extremely increased immediately after electrofusion. ·OH radical levels were significantly higher during manipulation procedures (51.6 to 55.7 pixels; P < 0.05) compared to MII oocytes. During in vitro culture, the H2O2 and ·OH radical levels of SCNT embryos were significantly higher (P < 0.05) compared to IVF embryos at 1- (32.4 v. 17.3 and 52.0 v. 29.6 pixels, respectively), 2- (27.2 v. 22.0 and 33.4 v. 26.0 pixels, respectively), and 4-cell (25.1 v. 16.5 and 26.9 v. 20.7 pixels, respectively) stages. These results suggest that the culture type of donor cells can affect the ROS generation level and the cellular stress during micromanipulation procedures also can generate the ROS in bovine SCNT embryos, which may lead the cellular damages in bovine SCNT embryos. This work was supported by National Research Foundation of Korea Grant funded by the Korean Government (KRF-2008–313-F00067).

C 2–C 8 NMHCs over the Eastern Mediterranean: Seasonal variation and impact on regional oxidation chemistry

More than 2500 measurements of C 2–C 8 non-methane hydrocarbons (NMHCs) have been conducted at Finokalia sampling station on the island of Crete over a thirty-month period (September 2003–February 2006), to investigate the factors controlling NMHC levels and estimate their role in the oxidizing capacity of the Eastern Mediterranean atmosphere. Atmospheric concentrations of NMHCs range from below the detection limit (5 pptv) to a few ppbv and present a hydroxyl radical (OH) driven seasonal pattern with lower values during summer. The diel variability was also influenced by the reaction of the NMHC with the OH radical, exhibiting a nighttime maximum and a midday or early afternoon minimum. Long-lived compounds demonstrate higher concentrations under the influence of the northern sector (European continent), indicating that besides chemistry, transport significantly contributes to NMHCs levels in the area. Based on the observed NMHCs diurnal cycles, mean OH radical levels of 3.5 × 10 6 molecules cm −3 have been derived for May–October period.

Photodissociation dynamics of acetoxime in gas phase

The dynamics of photodissociation of acetoxime at 193 nm, leading to the formation of (CH3)2C=N and OH fragments, has been investigated. The nascent OH radicals, which are both rotationally and vibrationally excited, were probed by laser photolysis-laser induced fluorescence technique. OH fragments in both v" = 1 and v" = 0 vibrational states were detected with a ratio of population in the higher to lower level of 0.07+/-0.01. The rotational temperatures of v" = 0 and 1 levels of OH radicals are 2650+/-150 K and 1290+/-20 K, respectively. More than 30% of the available energy, i.e., 115+/-21 kJ mol(-1) is partitioned into the relative translational energy of the fragments. The results of excited electronic state and transition state calculations at the configuration interaction with single electronic excitation level suggest that the dissociation takes place with an exit barrier of approximately 126 kJ mol(-1) at the triplet state (T2) potential energy surface, formed by internal conversions/intersystem crossing from the initially populated S2 state. Using the calculated transition state geometry and its energy, the observed energy distribution pattern can be reproduced by the hybrid model within experimental uncertainties. The presence of an exit barrier is further supported by the observation of N-OH dissociation upon 248 nm excitation, where the relative translational energy of the fragments is found to be approximately 96 kJ mol(-1). The photodissociation dynamics of acetoxime is compared with C-OH dissociation in enols and carboxylic acid and N-OH dissociation in nitrous acid. The observed emission (lambda(max)=430 nm) and the N-OH dissociation dynamics indicate crossing of the initially populated state to an emissive state of acetoxime, which is different from the dissociative state.

Photodissociation of Unsaturated Alcohols. Energy Distribution in the Nascent OH Radicals

The photodissociation of allyl and propargyl alcohols at 193 nm, which involves π−π* electronic transition and leads to the formation of OH, has been studied by using a laser photolysis−laser-induced fluorescence technique. The nascent OH radicals formed from both these molecules are found to be rotationally and vibrationally excited. The vibrational distributions are found to be similar, described by vibrational temperatures of 2070 ± 380 and 2130 ± 440 K for allyl and propargyl alcohols, respectively. The rotational temperatures of both v‘ ‘ = 0 and 1 levels of OH radicals from allyl alcohol are found to be almost the same, viz., 1960 ± 150 and 1900 ± 250 K, respectively, and close to the vibrational temperature. On the other hand, the rotational temperatures of OH radicals, 1760 ± 130 K at the v‘ ‘ = 0 level and 690 ± 120 K at the v‘ ‘ = 1 level, are very different from each other, in the case of propargyl alcohol. In both molecules, a significant part of the available energy is partitioned into the re...

Kinetic modeling of Fenton oxidation of phenol and monochlorophenols

A kinetic model, consisting of 28 reactions, was proposed to understand the key mechanism of the Fenton oxidation of phenol and o-, m-, and p-chlorophenols. Particular attention is paid to the interactions of the organic intermediates with the Fe species. The proposed model reasonably predicts the decomposition kinetics and by-product formation for the different phenols at widely varying levels of Fe 2+, H 2O 2, and the phenols. For the phenols and intermediates, change in concentrations with time was predicted within 20–30% deviation from the measured data. The single model predicts the overall kinetics of Fenton oxidation of all the tested phenols by adjusting the rate constant of hydroxyl radical for each phenol. Sensitivity analysis indicates that the key reactions are those that directly govern the levels of OH radical and Fe 2+. Both the model prediction and the experimental results show that the decomposition rate could be complicated particularly by the availability of Fe 2+. Understanding the interactions of the organic intermediates with Fe 2+ is thus of critical importance to improve the decomposition performance.

Environmental chamber study of maximum incremental reactivities of volatile organic compounds

The effects of 26 individual volatile organic compounds (VOCs) on ozone formation, NO oxidation, and OH radical levels were measured by adding them to reactive organic gas (ROG)-NO x -air environmental chamber irradiations representing a simplified model photochemical smog system. These experiments had relatively low ROG NO x ratios to represent conditions where ozone formation is most sensitive to VOC additions. The compounds studied included representative alkanes, alkenes, aromatic hydrocarbons, aldehydes, alcohols, and CO. The addition of formaldehyde, methylbenzenes, alkenes and methanol all caused increased integrated OH radical concentrations, and caused the most NO oxidation and ozone formation per molecule reacted. The C 6+ n-alkanes had the most inhibiting effects on OH radicals, and caused reduced NO oxidation and ozone formation in these experiments. The other compounds had smaller negative effects on OH radicals, but moderate positive effects on ozone formed and NO oxidized. The implications of these results in terms of the atmospheric reaction mechanisms of these compounds are discussed.

Experimental investigation of chamber‐dependent radical sources

AbstractWhile environmental chamber data have been widely used to generate and validate computer models of the chemistry occurring in polluted atmospheres, the effects of the chambers on the gas‐phase chemistry being studied have been poorly characterized. In order to investigate such chamber effects, a series of NOx—air irradiations, with trace levels of organics present to monitor OH radical concentrations, have been carried out in four different environmental chambers (ranging in volume from ∼100 to 40,000 L) at varying temperatures, humidities, pressures, and reaction conditions. In addition, a number of control experiments have been carried out to validate the technique for measuring OH radical levels in these irradiations. The data show that unknown sources of OH radicals are present in all of the chambers studied. The data are consistent with the presence of two distinct radical sources: (1) the photolysis of initially present HONO, whose importance increases with increasing NO2/NO concentration ratios, but which is a minor contributor to the overall radical flux after 30–60 min of irradiation, and (2) a constant (for these NOx—air irradiations) radical source which dominates beyond approximately the first 60 min of irradiation. The radical input rates, after the first ∽30–60 min of irradiation, are independent of the NO concentration, increase with increasing temperature, humidity, and NO2 concentration, are proportional to light intensity, and are dependent on the chamber employed. Although the exact nature of this radical source is still undetermined, results of experiments reported here allow a number of possible mechanisms to be ruled, out, and these are discussed.

Determining population of OH-radical levels by the method of bright-line absorption and emission, taking into account unresolved doublet structure

Determining population of OH-radical levels by the method of bright-line absorption and emission, taking into account unresolved doublet structure

High resolution tunneling spectroscopy of “hot” molecules

Improved resolution in inelastic tunneling experiment has allowed the observation of structure, which we believe to be rotation-vibration levels of OH radicals heated by tunneling electrons.