Source Of Hydroxyl Radicals Research Articles

Synthesis of a graft copolymer of polybutyl acrylate on fish collagen substratum using the RbTe1.5W0.5O6 complex oxide photocatalyst

In order to obtain a graft copolymer of polybutyl acrylate (PBA) on the substratum of emulsified fish collagen, RbTe1.5W0.5O6 complex oxide was used as a photocatalyst under visible light irradiation (λ = 400–700 nm). The emulsion was prepared by mixing the monomer and the aqueous collagen solution in a ratio of 1:2. Next, the catalyst was introduced into the resulting mixture, followed by stirring and ultrasound treatment. Before the reaction, the emulsion was bubbled with argon for 15 min. The reaction was carried out in an argon flow with continuous stirring. The radiation source was a 30 W visible light LED lamp placed at a distance of no more than 10 cm from the reaction mixture. At the end of the reaction, the emulsified organic phase was extracted with toluene, followed by phase isolation. In order to isolate the catalyst, the aqueous part of the solution was centrifuged for 30 min. Subsequently, the powder was repeatedly washed in distilled water at a temperature of 50 °C. The washed catalyst was dried, and the surface of the oxide after emulsion polymerization was examined using a scanning electron microscope. For the PBA–collagen graft copolymer emulsion isolated from the aqueous phase, molecular weight characteristics confirming the formation of a graft copolymer were obtained. It was established that the nitrogen content of amino acid residues in the PBA–collagen graft copolymer is significantly lower than in collagen, which indicates the formation of a graft copolymer. An analysis of films and sponges of PBA–collagen graft copolymer samples by scanning electron microscopy (SEM) showed a new structural-relief organization compared to collagen. A SEM analysis of the RbTe1.5W0.5O6 powder surface after the synthesis of the PBA–collagen graft copolymer detected fragments of polymer macromolecules on its surface. This can be explained by the fact that the catalyst used not only is a source of hydroxyl radicals, but сan also participate in the formation of a polymer on the powder surface due to the abstraction of a hydrogen atom from hydroxyl groups on its surface under the action of a hydroxyl radical.

Enhanced photo-degradation of N-methyl-2-pyrrolidone (NMP): Influence of matrix components, kinetic study and artificial neural network modelling

This study investigates the degradation of N-methyl-2-pyrrolidone (NMP) by UV-C and UV-C/PMS-treatment processes. The degradation of NMP was less than 2% by UV-C photolysis. To enhance the degradation, PMS was used as a source of sulphate (SO4• −) and hydroxyl (HO•) radicals in the UV-C photolysis treatment system. The operational parameters such as initial pH and concentration of NMP and PMS and water matrix elements were studied to understand their effects on degradation. At pH = 6.3, λ = 260 nm, initial concentration of NMP = 10 mg/L, PMS = 300 mg/L and carbonate ion = 150 mg/L, the degradation of NMP was found to be 97.5%, along with 26.86% of TOC removal. The bicarbonate ions, nitrate ions, and chloride ions showed the inhibitory effect on the degradation of NMP. The NMP degradation was governed by pseudo first order kinetics. SO4• − was found to be the dominating degradation species through the radical quenching studies. The intermediates formed during the degradation were identified through LC-MS analysis, and a degradation pathway was proposed. The experimental data was successfully validated through the application of the developed ANN model. The R2 between expected and experimental outcomes was 0.97. The developed ANN model was successful in predicting the degradation of NMP in the given reaction conditions with the prediction accuracy of 90.91% and RMSE of 3.54.

Mass Spectrometry and Cryogenic Electron Microscopy Illuminate Molecular-Level Mechanisms of the Oxidative and Structural Damage to Lipid Membranes by Radical-Bearing Graphene Oxide.

Biomedical applications of graphene in tumor and bacterial treatment have become cutting-edge fields due to its unique physical and chemical properties. However, a mechanistic understanding of the interactions and reactions between graphene-based material and biological systems such as lipid membranes remains elusive, especially at the molecular level. By using the unique field-induced droplet ionization mass spectrometry and cryogenic electron microscopy methodologies, we reveal the oxidation products of monolayer lipid membranes at the air-water interface and the change in the morphology of bilayer lipid membranes in an aqueous solution caused by the incorporation of graphene oxide bearing π-conjugated carbon radicals [hydrated graphene oxide (hGO)]. We discovered that hGO is an efficient source of hydroxyl radicals and that it is not only the incorporation of the hGO sheets but also the irregular packing of the lipid oxides from the hydroxyl radical oxidation that causes the structural distortions of the liposomes.

Global and Regional Patterns of Soil Nitrous Acid Emissions and Their Acceleration of Rural Photochemical Reactions

AbstractAbiotic and biotic releases of nitrous acid (HONO) from soils contribute substantially to the missing source of tropospheric HONO and hydroxyl radicals (OH). However, global and regional patterns of soil HONO emissions are rarely quantified, and the contributions of such emissions to atmospheric oxidization capacity are unclear. Here, we present that the best estimate of global soil HONO emissions in 2017 was 9.67 with a range of 7.36–11.99 Tg N yr−1, and cropland soils accounting for ∼79%. The analyses also indicate that regional soil HONO emissions enhanced ground OH concentrations by 10%–60% and ozone concentrations by 0.5–1.5 ppb in daytime in the ambient area of Shanghai, China. The impact of soil HONO emissions on OH budgets was more significant in rural than urban areas. These findings suggest that the soil HONO emissions, especially from cropland, could quicken photochemical reactions, and aggravate air pollution in rural areas.

Exploration of the atmospheric chemistry of nitrous acid in a coastal city of southeastern China: results from measurements across four seasons

Abstract. Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.45 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO2 to HONO in the nighttime was the highest in summer due to water droplets evaporating under high-temperature conditions. Based on a budget analysis, the rate of emission from unknown sources (Runknown) was highest around midday, with values of 4.51 ppb h−1 in summer, 3.51 ppb h−1 in spring, 3.28 ppb h−1 in autumn, and 2.08 ppb h−1 in winter. Unknown sources made up the largest proportion of all sources in summer (81.25 %), autumn (73.99 %), spring (70.87 %), and winter (59.28 %). The photolysis of particulate nitrate was probably a source in spring and summer while the conversion from NO2 to HONO on BC enhanced by light was perhaps a source in autumn and winter. The variation of HONO at night can be exactly simulated based on the HONO / NOx ratio, while the J(NO3-_R) × pNO3- should be considered for daytime simulations in summer and autumn, or 1/4× (J(NO3-_R) × pNO3-) in spring and winter. Compared with O3 photolysis, HONO photolysis has long been an important source of OH except for summer afternoons. Observation of HONO across four seasons with various auxiliary parameters improves the comprehension of HONO chemistry in southeastern coastal China.

Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics.

A prominent source of hydroxyl radicals (•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol, n-butanol, or formate as •OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO2-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO2-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2 for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.

Iron (III) hydroxocomplex-methyl viologen dication system as a prospective tool for determination of hydroxyl radical reaction rate constants with environmental pollutants.

Reactivity of oxidative species with target pollutants is one of the crucial parameters for application of any system based on advanced oxidation processes (AOPs). This work presents new useful approach how to determine the hydroxyl radical reaction rate constants (kOH) using UVA laser flash photolysis technique. Fe (III) hydroxocomplex at pH 3 was applied as a standard source of hydroxyl radicals and methyl viologen dication (MV2+) was used as selective probe for •OH radical. Application of MV2+ allows to determine kOH values even for compounds which do not generate themselves optically detectable transient species in reaction with hydroxyl radicals. Validity of this approach was tested on a wide range of different persistent pesticides and its main advantages and drawbacks in comparison with existing steady-state and time-resolved techniques were discussed.

Microplasma-assisted synthesis of TiO2–Au hybrid nanoparticles and their photocatalytic mechanism for degradation of methylene blue dye under ultraviolet and visible light irradiation

Plasmonic photocatalysts consisting of TiO2 and Au nanoparticles (NPs) have recently been intensively studied to overcome the limited photocatalytic activity of pristine TiO2 NPs. Here, we synthesized TiO2–Au hybrid NPs using atmospheric microplasma–liquid interaction and demonstrated their enhanced photocatalytic activity, under both ultraviolet (UV) and visible light irradiation, for the degradation of the organic dyes methylene blue (MB) in water. Through mechanism studies using a hole scavenger and external source of hydroxyl radicals, it was also revealed that the contribution of hole oxidation and electron reduction pathways for degradation of MB via hydroxyl radicals by the TiO2–Au hybrid NPs differed depending on the wavelength of irradiating light. This is because the MB dye is likely remotely oxidized under UV irradiation, but not under visible light. This systematic study on the role of hole and electron pathways for photocatalytic dye degradation by TiO2–Au hybrid NPs at different light and pH conditions is helpful for understanding and developing plasmonic photocatalysts.

High crop yield losses induced by potential HONO sources — A modelling study in the North China Plain

Nitrous acid (HONO) is a major source of hydroxyl radicals in the troposphere through its photolysis, and can significantly influence ozone (O3) levels, thereby causing considerable crop yield losses. Previous studies have assessed relative crop yield losses by using exposure-response equations with observed or simulated O3, however, the contribution of enhanced O3 due to potential HONO sources to the crop yield losses has never been quantified. In this study, for the first time, we evaluated the crop yield losses caused by potential HONO sources in the North China Plain (NCP), which is one of the major grain-producing areas in China suffering from heavy O3 pollution, by using the Weather Research and Forecasting/Chemistry (WRF-Chem) model during the wheat and maize growing seasons of 2016. HONO simulations were significantly improved after including six potential HONO sources in the WRF-Chem model. The potential HONO sources produced a daily maximum 8-h O3 enhancement of 8.1/8.2 ppb during the wheat/maize growing seasons, respectively, and led to ~11.4%/3.3% relative yield losses for wheat/maize, respectively, corresponding to approximately US$3.78/0.66 billion losses, respectively, in NCP in 2016. The above results suggest that potential HONO sources play a significant role in O3 formation and could induce high crop yield losses globally.

A Stochastic Characterization of Hydrogen Peroxide-Induced Regulated Cell Death in Microcystis aeruginosa.

Regulated cell death (RCD) encompasses the activation of cellular pathways that initiate and execute a self-dismissal process. RCD occur over a range of stressors doses that overcome pro-survival cellular pathways, while higher doses cause excessive damage leading to passive accidental cell death (ACD). Hydrogen peroxide (HP) has been proposed as a potential tool to control harmful cyanobacterial blooms, given its capacity to remove cyanobacterial cells and oxidize cyanotoxins. HP is a source of hydroxyl radicals and is expected to induce RCD only within a limited range of concentrations. This property makes this compound very useful to better understand stress-driven RCD. In this work, we analyzed cell death in microcystin-producing Microcystis aeruginosa by means of a stochastic dose response model using a wide range of HP concentrations (0, 0.29, 1.76, 3.67, 7.35, 14.70, and 29.5 mM). We used flow cytometry and unsupervised classification to study cell viability and characterize transitional cell death phenotypes after exposing cells to HP for 48 and 72 h. Non-linear regression was used to fit experimental data to a logistic cumulative distribution function (cdf) and calculate the half maximal effective concentration (EC50). The EC50 of M. aeruginosa exposed to HP were 3.77 ± 0.26 mM and 4.26 ± 0.22 mM at 48 and 72 h, respectively. The derivative of cdf (probability density function; pdf) provided theoretical and practical demonstration that EC50 is the minimal dose required to cause RCD in 50% of cells, therefore maximizing the probability of RCD occurrence. 1.76 mM HP lead to an antioxidant stress response characterized by increased reactive oxygen species (ROS) levels and HP decomposition activity. The exposure of 3.67 mM HP induced a dose-related transition in cell death phenotype, and produced several morphological changes (a less dense stroma, distortion of the cell membrane, partial disintegration of thylakoids, extensive cytoplasmic vacuolation and highly condensed chromatin). The EC50 and the stochastic cdf and pdf together with the multidimensional transitional phenotypic analysis of single cells contribute to further characterize cell death pathways in cyanobacteria.

PM1.0-Nitrite Heterogeneous Formation Demonstrated via a Modified Versatile Aerosol Concentration Enrichment System Coupled with Ion Chromatography.

Particulate nitrite is a critical source of hydroxyl radicals; however, it lacks high-resolution methods due to its low abundance and stability to explore its formation mechanism. In this study, a modified versatile aerosol concentration enrichment system (VACES) coupled with ion chromatography (IC) was used to measure particulate NO2- hourly online and achieve a lowered detection limit of 10-3 μg m-3. VACES-IC was used to observe a high- and low-concentration events of PM1.0-NO2- in Shanghai, corresponding to the ambient-level concentrations of 0.34 and 0.05 μg m-3, respectively. The morning peak concentrations of NO2- even exceeded 3σ (standard deviation) in the high-concentration event due to the reduction of NO2 by aerosol SO32- based on kinetics and regression analysis. This implies that controlling SO2 emissions would be an effective strategy to decrease morning NO2- concentrations, correspondingly reducing the kinetic formation of SO42- by 20.8-34.8%. However, after sunrise, NO2- formation was primarily attributed to NO2 hydrolysis at pH 4.97-6.14. In the low-concentration event, NO2 hydrolysis also accounted for an overwhelming proportion (∼90%) of NO2- formation. This work estimates the contribution of different paths to particulate NO2- formation based on newly established high-resolution measurements.

Identification of Elusive Keto and Enol Intermediates in the Photolysis of 1,3,5-Trinitro-1,3,5-Triazinane.

Enols have emerged as critical reactive intermediates in combustion processes and in fundamental molecular mass growth processes in the interstellar medium, but the elementary reaction pathways to enols in extreme environments, such as during the decomposition of molecular energetic materials, are still elusive. Here, we report on the original identification of the enol and keto isomers of oxy-s-triazine, as well as its deoxygenated derivative 1,3,5-triazine, formed in the photodecomposition processes of 1,3,5-trinitro-1,3,5-triazinane (RDX)-a molecular energetic material. The identification was facilitated by exploiting isomer-selective tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) in conjunction with quantum chemical calculations. The present study reports the first experimental evidence of an enol intermediate in the dissociation domain of a nitramine-based energetic material. Our investigations suggest that the enols like 1,3,5-triazine-2-ol could be the source of hydroxyl radicals, and their inclusion in the theoretical models is important to understand the unprecedented chemistry of explosive materials.

Enhanced photocatalytic degradation of water pollutants using bio-green synthesis of zinc oxide nanoparticles (ZnO NPs)

Chemical pollutants released from textile industries are becoming a major concern for water pollution, causing hazardous diseases around the globe. Strategies developed against the treatment of effluents from textile industries are becoming a mere failure. Therefore, metal oxide nanoparticles (MO NPs) came into rescue as an alternative to the already available dye treatment techniques. So far, numerous research data have been published on the applications of MO NPs in antimicrobial and anticancer applications, photocatalysis, and wastewater treatment. In recent trends, Zinc Oxide nanoparticles (ZnO NPs) have been reported to possess strong photocatalytic properties depending upon the sources of energy, UV irradiation and surface hydroxyl radicals. The biological synthesis route has provided a better, safer, and efficient way of fabricating ZnO NPs for bioremediation purposes. The present study is the first and foremost report on the synthesis of ZnO NPs using Ruellia tuberosa for antimicrobial and bioremediation purposes. The physical and chemical compositions of ZnO NPs analysed using UV–Vis spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FT-IR), Energy dispersive X-ray spectroscopy (EDAX), and Transmission electron microscopy (TEM) revealed rod shaped NPs with a size of 40–50 nm. ZnO NPs exhibited higher antibacterial activity against Gram negative bacteria, especially Escherichia coli. Further, textile fabrics were coated with ZnO NPs to prevent the growth of Escherichia coli. In an environmental perspective, ZnO NPs degraded 94% and 92% of methylene blue (MB) and malachite green (MG), respectively. Thus, the present study will give a brief idea on the application of ZnO NPs in the textile industry for the degradation of synthetic dyes and inhibition of pathogenic bacteria. The present study is novel, simple, compatible and hence, can be utilized for future biomedical and environmental applications.

Simulation Verification of Barrierless HONO Formation from the Oxidation Reaction System of NO, Cl, and Water in the Atmosphere.

Nitrous acid (HONO) is a major source of hydroxyl (OH) radicals, and identifying its source is crucial to atmospheric chemistry. Here, a new formation route of HONO from the reaction of NO with Cl radicals with the aid of one or two water molecules [(Cl) (NO) (H2O)n (n = 1-2)] as well as on the droplet surface was found by Born-Oppenheimer molecular dynamic simulation and metadynamic simulation. The (Cl) (NO) (H2O)1 (monohydrate) system exhibited a free-energy barrier of approximately 0.95 kcal mol-1, whereas the (Cl) (NO) (H2O)2 (dihydrate) system was barrierless. For the dihydrate system and the reaction of NO with Cl radicals on the droplet surface, only one water molecule participated in the reaction and the other acted as the "solvent" molecule. The production rates of HONO suggested that the monohydrate system ([NO] = 8.56 × 1012 molecule cm-3, [Cl] = 8.00 × 106 molecule cm-3, [H2O] = 5.18 × 1017 molecule cm-3) could account for 40.3% of the unknown HONO production rate (Punknown) at site 1 and 53.8% of Punknown at site 2 in the East China Sea. This study identified the importance of the reaction system of NO, Cl, and water molecules in the formation of HONO in the marine boundary layer region.

Evaluation of hydroxyl radical and reactive chlorine species generation from the superoxide/hypochlorous acid reaction as the basis for a novel advanced oxidation process

The reaction of hypochlorous acid (HOCl) with superoxide radical (O2•–) – a source of hydroxyl radical (HO•) and various reactive chlorine species (RCS) – was investigated as the basis for a novel non-photochemical advanced oxidation process (AOP). Moderately stable (t1/2 ~ minutes) aqueous O2•– stocks were prepared by several approaches at pH>12 and either (a) added directly to aqueous free available chlorine (FAC; i.e., HOCl/OCl–) at circumneutral pH, or (b) premixed with alkaline FAC and then acidified to pH 7, to degrade various organic probe compounds via in situ generated HO• and RCS. Radical production was optimal at [HO2•/O2•–]0/[FAC]0 ~ 2, with ~0.8 mol HO• formed/mol FAC consumed, and HO• and RCS exposures reaching ~5×10−10 and ~10−9 M×s, respectively. Similar trends were observed in natural waters and organic matter-amended phosphate buffer containing up to 5 mgC/L of dissolved organic carbon. Direct formation of oxyhalides, trihalomethanes (THMs), and haloacetic acids (HAAs), was minimal, though THM and HAA formation was moderately enhanced during post-chlorination of O2•–/FAC-treated solutions. This process could provide a beneficial addition to the range of available AOPs due to its high radical exposures, simplicity, rapid time-scales, potential for on-site O2•– generation, and widespread accessibility of FAC and other reagents.

Efficiency assessment of municipal landfill leachate treatment during advanced oxidation process (AOP) with biochar adsorption (BC)

Leachate generated in landfills are characterized by high toxicity related to, high concentrations of organic and non-organic pollutants, therefore, it is advisable to use highly effective methods of their purification to prevent environmental contamination. The aim of this study was to determine the treatment efficiency of landfill leachate during the application of integrated processes: advanced oxidation (AOP) and biochar adsorption (BC). In the case of the AOP, the chemical process was the Fenton reaction in which the source of hydroxyl radicals was H2O2 (system I) and SPC - sodium percarbonate (system II). Leachate was derived from the regional municipal waste landfill in Silesian Province (Poland) which was characterized by the pH of 8.40, COD value was 3155 mg L−1 and BOD was under 165 mg L−1. The BOD/COD ratio was at a low level (0.053) that indicated low biodegradability. The applied systems allowed of the COD reduction index to the level of 549 mg L−1 (H2O2+BC) and 944 mg L−1 (SPC+BC) where the limit threshold is 125 mg L−1. In the same case of the TOC index, these values were respectively 119 and 186 mg L−1, where the limit value is 30 mg L−1.This study has been aimed to estimate the toxicity of leachate treatment in integrated systems: AOP processes + biochar adsorption. Toxicity of treated and untreated leachate has been analysed by Sinapis alba and Lepidium sativum plants-based tests. It was found that while conducting the Fenton process as system I (H2O2) at all reagent doses, the removal efficiency of COD and TOC was 17% and 12% higher, respectively, compared to system II. The most advantageous dose of regents was 2.5:1 and biochar - 2 g L−1. It was observed that in the SPC+BC system the roots of L. sativum and S. alba were on average 34% and 28% longer compared to the H2O2+BC system. Higher germination index (GI) of both tested plants, indicating lower wastewater toxicity, was recorded for the SPC+BC system.

Plasma-catalytic Efficiency on the Discolouration of Sunset Yellow FCF in a Glidarc Plasma Reactor in Presence of WO₃ Used as Catalyst

In this work, we highlight the plasma-catalytic effect of gliding arc discharge on the bleaching of azo dye sunset yellow FCF in aqueous solution. The effect has been studied in the presence of tungsten oxide as a catalyst in the glidarc reactor. The catalyst has been synthesized via acid precipitation process. The product obtained was characterized by X-ray powder diffraction (XRD), Fourier Transform Infrared (FTIR) and Nitrogen Physisorption. The results showed firstly monoclinic structure of WO3 catalyst. The maximum bleaching rates obtained are 17% and 52.5% after 30 min for initial dye concentration of 25 mg.L-1 for plasma alone and plasma-catalyst, respectively. These results have clearly shown that gliding arc discharge has a double effect, in on hand as a source of hydroxyl radical and on other hands as a source of radiation able to excite the catalyst. The effects of initial pH and photocatalyst loading have been studied.

Superoxide and Nitrous Acid Production from Nitrate Photolysis Is Enhanced by Dissolved Aliphatic Organic Matter

Nitrate anion (NO3–) is ubiquitous in the environment, and its photochemistry produces nitrous acid (HONO), a major source of tropospheric hydroxyl radical (OH). Enhanced HONO(g) emissions have been observed from NO3–(aq) photolysis in field studies, although the underlying reasons for this enhancement are debated. Here, we show that the enhancement is in part caused by changes in secondary nitrate anion photochemistry due to dissolved aliphatic organic matter (DAOM). Increased yields of superoxide radical (O2–) and HONO were observed when NO3– solutions (pH 6) were photolyzed in the presence of DAOM surrogates of varying solubility. In an additional experiment, nitrate titrated with additional DAOM showed a further simultaneous increase in the levels of O2–(aq) and HONO(g) with decreased yields of gaseous nitric oxide (NO) and nitrogen dioxide (NO2). To the best of our knowledge, this is the first time that superoxide was directly observed as an intermediate in nitrate photolysis experiments, produced through DOAM oxidation by OH(aq). Herein, we suggest that enhanced HONO(g) emissions from NO3–(aq) photolysis result from the reaction of O2–(aq) with NO2(aq) and NO(aq) to form peroxynitrate (OONO2–) and peroxynitrite (OONO–), respectively, which are precursors to nitrite (NO2–). Overall, this points to an important role of O2–(aq) in aqueous aerosol chemistry, which is currently underappreciated.

Unexpectedly High Indoor HONO Concentrations Associated with Photochemical NO2 Transformation on Glass Windows.

Nitrous acid (HONO) is an important gaseous pollutant contributing to indoor air pollution because it causes adverse health effects and is the main source of hydroxyl radicals (OH). Here, we present direct measurements of HONO produced through light-induced heterogeneous reactions of NO2 with grime adsorbed on glass window. The uptake coefficients of NO2 [γ(NO2)] on the glass plates from the kitchen increased markedly from (2.3 ± 0.1) × 10-6 at 0% RH to (4.1 ± 0.5) × 10-6 at 90% RH. We report a significant quantity of daytime HONO produced in the kitchen, compared to the living room and bedroom. Kinetic modeling suggests that phase state and bulk diffusivity play important roles in the NO2 uptake; the best fit to the measured uptake coefficients is obtained with fixed diffusion coefficients. Photon scattering may be occurring at the surface of the films, leading to enhanced photon-excitation rates of polycyclic aromatic hydrocarbons. By taking these effects into account, the results from this study indicate that the HONO yields obtained in this study can explain the missing HONO in the photochemical models describing the indoor air chemistry.

Influence of ship direct emission on HONO sources in channel environment

Abstract Nitrous acid (HONO) is the primary source of hydroxyl radical (OH) during daytime and significantly contribute to the formation of secondary organic compounds (SOA) and atmospheric oxidizing capacity. One month simultaneous observations at ship channel site (SCS) and background site (BGS) in Shanghai, China were conducted to aim at estimating the HONO concentration from ship direct emission and analyzing the nocturnal budget of HONO during non-clean period in SCS. The HONO average concentrations at both BGS and SCS during non-clean period were 0.37 ± 0.42 ppbv and 0.91 ± 0.78 ppbv, respectively. The diurnal variation of HONO from ship direct emission presented a double-peak trend with a maximum value 0.38 ± 0.18 ppbv at 07:00 in the morning. The proportion of HONO emission from ships was in a range of 43%~74% in the daytime, while, the proportions were 42%~63% and 14%~28% at night in clean and non-clean periods, respectively. HONO nocturnal conversion frequencies from NO2 were 0.29%/h at both sites in non-clean period, during which the deposition velocities of HONO were 0.21–1.4 cm/s and 0.34–1.4 cm/s at BGS and SCS, respectively.