Determination of particle-associated hydroxynitropyrenes with correction for chemical degradation on a quartz fibre filter during high volume air sampling

A correction method for the determination of atmospheric monohydroxylated derivatives of 1-nitropyrene (hydroxy-1-nitropyrenes, OHNPs) based on their degradation rates during high volume air sampling was established. OHNPs adsorbed directly on a quartz fibre filter (QFF) or on airborne particles collected on a QFF were exposed to ambient air passively or actively in a high volume air sampling system. The influence of ozone flux and exposure time on the degree of degradation of OHNPs was investigated. Up to 50% of OHNPs degraded over 1 h of exposure to ambient air containing ～60 ppbv of ozone in the active system. The degradation rate constants of OHNPs were found to correlate with the number of ozone molecules passing through the QFF in a unit time (N_O3) during high volume air sampling. The chemical loss of OHNPs under high volume air sampling conditions was successfully evaluated by the exposure time and the pseudo-first-order rate constant for OHNP degradation estimated from the correlation with N_O3. Concentrations of 3-, 6-, and 8-hydroxy-1-nitropyrenes in airborne particles collected in Osaka, Japan were determined using the established correction method.     

Nitroarene products from the gas-phase reactions of volatile polycyclic aromatic hydrocarbons with the OH radical and N2O5

The nitroarene products of the gas-phase reactions of acenaphthylene, acenaphthene, phenanthrene, and anthracene-d₁₀ with N₂O₅ and the OH radical (in the presence of NO_x) are reported. The calculated atmospheric lifetimes of these polycyclic aromatic hydrocarbons (PAH), as well as those of naphthalene, 1- and 2-methylnaphthalene, biphenyl, fluoranthene, pyrene, and acephenanthrylene, show that reaction with the OH radical is the dominant loss process for these PAH, with the exception of acenaphthylene, acenaphthene, and acephenanthrylene which contain an external cyclopenta-fused ring. For these latter PAH, reaction with the NO₃ radical, and for acenaphthylene and acephenanthrylene reaction with O₃, are also expected to be important atmospheric loss processes. The nitroarenes observed as products of the atmospherically-important gas-phase reactions of the PAH in environmental chamber studies are compared with the nitroarenes measured in ambient air samples collected in California. It is concluded that although nitroarenes are formed in low yields (?5%) from the OH radical-initiated reactions of the PAH, atmospheric formation of nitroarenes may contribute significantly to ambient nitroarene concentrations.     

Kinetics and mechanisms of the reaction of OH radicals with dimethyl sulfide

The rate constant of the reaction of OH with DMS has been measured relative to OH + ethene in a 420 l reaction chamber at 760 torr total pressure and 298 ± 3 K in N₂ + O₂ buffer gas using the 254 nm photolysis of H₂O₂ as the OH source. In agreement with a recent absolute rate determination of the reaction the measured effective rate constant was found to increase with increasing partial pressure of O₂ in the system, for 760 torr air a rate constant of (8.0 ± 0.5) × 10^?12 cm³ s^?1 was obtained. Product studies have been performed on the reaction in air using FTIR absorption spectrometry for detection of reactants and products. On a molar basis, SO₂ was formed with a yield of 70% and dimethyl sulfone (CH₃SO₂CH₃) with a yield of approximately 20%. These results are considerably different to those obtained in other product studies which were carried out in the presence of NO_x. These differences are compared and their relevance for the atmospheric oxidation mechanisms of DMS is discussed.     

Decomposition of Benzene Using a Pulse-Modulated DBD Plasma

To improve the energy yield (EY) of plasma volatile organic compound decomposition, a dielectric barrier discharge plasma driven by pulse-modulated AC power was used to experimentally study the abatement of benzene in atmospheric pressure air and at room temperature. The effects of the duty cycle on decomposition efficiency, EY, CO₂ selectivity and the formation of ozone and NO₂ were investigated. The results show that applying pulse modulation improves the EY and the CO₂ selectivity and greatly reduces the wall temperature of the reaction chamber.     

Ground level ozone (O3) associated with radon (222Rn) and particulate matter (PM) concentrations in Bucharest metropolitan area and adverse health effects

The aim of this paper is to contribute with new information in the application of ground based radon (²²²Rn) observations to atmospheric research, namely its relation with air pollution due to ground-level ozone (O₃) and particle matter in two size fractions (PM10 and PM2.5) for Bucharest metropolitan area in Romania. During January 1–December 31, 2011, ground levels of radon, ozone and particulate matter (PM) have been continuously monitored in synergy with the main meteorological parameters (air temperature, humidity and pressure), and daily global air quality indices. A systematic analysis of surface ozone observations of ground level radon, ozone and PM is presented. Observational results indicate the following yearly daily mean ground level concentrations: 40.26 ± 7.54 Bq/m³ for radon, 90.51 μg/m³ for ozone, 35.96 μg/m³ for PM2.5, and 40.91 μg/m³ for PM10. The assessment of the results showed the influence of local and meteorological conditions on the daily mean radon, ozone and PM concentrations. However, in densely populated metropolitan area of Bucharest the mean daily values of ozone, PM2.5, PM10, and attached ²²²Rn are sometimes higher than European Community limit values leading to serious public concern during the last years. Due to the high risk of increased levels of O₃, PM2.5, PM10, and attached ²²²Rn on human health respiratory function (especially for children and older persons), and urban green, the results are very useful for atmospheric, radiological protection, epidemiological and environmental studies.     

Kinetics of Active Oxygen Species with Implications for Atmospheric Ozone Chemistry

Photochemical processes involving singlet oxygen (O₂(a¹Δ)), oxygen atoms_, and ozone are critical in determining atmospheric ozone concentrations. Here we report on kinetic measurements and modeling that examine the importance of the reactions of vibrationally excited ozone. Oxygen atoms and O₂(a¹Δ) were produced by UV laser photolysis of ozone. Time‐resolved absorption spectroscopy was used for O₃ concentration measurements. It was found that vibrationally excited ozone formed by O + O₂ + M → O₃(ν) + M recombination reacts effectively with O₂(a¹Δ) and O atoms. The reaction O₃(υ) + O₂(a¹Δ) → O + 2O₂ results in a reduction of the ozone recovery rate due to O atom regeneration, whereas the reaction O₃(υ) + O → 2O₂ removes two odd oxygen species, resulting in incomplete ozone recovery. The possible impact of these reactions on the atmospheric O₂(a¹Δ) and O₃ budgets at altitudes in the range of 80–100 km is considered.     

Polymer degradation under ionizing radiation: The role of ozone

Gamma-radiation degradation of poly(butadiene-co-styene) [SBR rubber] and poly(butadiene-co-acrylonitrile) [Buna-n rubber] in the presence of air has been investigated. Using a recently-developed modulus profiling techniques, it is shown that the degradation of these materials is very heterogenous through the sample thickness. There is a broad, paraboloidally-shaped modulus profile through the sample interior, together with a dramatic change in modulus in the surface regions. Mechanistic investigations lead to the conclusion that the radiation-inducted degradatoin of these materials results from two different process: (1) the standard free radical-mediated radiation chemistry, which gives rise to oxidation involving O₂ dissolved in the polymer and which leads to heterogenous oxidation due to oxygen diffusion effects; and (2) ozone chemistry in the surface regions of the samples, which results from attack by O₃ generated by the action of the ionizing radiation on the air atmosphere surrounding the samples. It appears that the intense role which this ozone mechanism can play in radiation-induced oxidative degradation of polymers has not been widely appreciated. This study provides evidence that the simultaneous action of ozone and ionizing radiation can in fact be strongly synergistic in their effect on organic materials     

Photochemical production of ozone in marine boundary layer in the sea of Japan: Results of the Rishiri Fall Experiment campaign

The Rishiri Fall Experiment (RISFEX ) campaign was performed in September 2003 at Rishiri island (45.07 N, 141.12 E, and 35 m asl) in the sea of Japan to investigate photochemical production of ozone in the marine boundary layer. Total peroxy radicals RO _x (HO₂ + RO₂) and NO _x (NO + NO₂) were measured together with other chemical species and physical parameters relevant to ozone production. The ozone production rate (P(O₃)) was estimated from measured peroxy radicals and was found to be highly variable between days, with 30-min averaged midday values varying from 0.2 to 1.7 ppbv/h (ppbv refers to part per billion by volume). The daytime mean P(O₃) for the air masses from relatively clean NE sector is close to zero, but significantly higher for air masses from more polluted W and SE sector, suggesting the impact of transport of pollutants on the remote local ozone production. The experimentally determined P(O₃) is compared with those derived from a time-dependent box model based on Regional Atmospheric Chemistry Modeling (RACM), and both the methods give the results generally in agreement. The model calculation shows that HO₂ + NO reaction contributes most to ozone production, ca. 60% at midday, followed by the reactions of CH₃O₂ and ISOP (peroxy radicals formed from isoprene) with NO which account for ca. 13% and 10% to ozone production, respectively, at noon. Sensitivity analysis indicates that the ozone production during the measurement period is within NO _x -limited regime.     

A Device for Preparing Standard Mixtures of Carbon Monoxide

Abstract

Accurate low concentrations of carbon monoxide, at levels comparable with those found in ambient air, are prepared by permeation through a thin silicone membrane at a constant temperature. The lowering in CO pressure into a diffusing phial is a measure of permeation rate. The device described permits the dynamic calibration and testing of atmospheric CO analyzers.     

Design and Operating Characteristics of a Simple and Reliable DBD Reactor for Use with Atmospheric Air

The paper reports on the construction and operating characteristics of a planar dielectric barrier discharge (DBD) plasma generator. The generator was powered from a commercial frequency inverter at 400 Hz through a high voltage transformer. It could be operated up to a specific energy density (power per gas flow) of 20 Wh/m³. The corresponding power density was about 0.5 W per cubic centimeter of discharge volume. Special emphasis was given to a simple and reliable construction, which was easy to assemble and is based on a new, nonexpensive barrier material with excellent electrical, mechanical, and thermal properties. The modular reactor design allows simple plasma power scale-up. The reactor works with undried ambient air without additional cooling. In the range up to 10 Wh/m³ the ozone generation from ambient air was directly proportional to the energy density at a rate of 60 g O₃ per kWh or 30 ppm/Wh/m³. Thus the generator can serve as an effective source for chemically active radicals in plasma gas cleaning applications.     

Development of Dipolar Proton Transfer Reaction Mass Spectrometer for Real-time Monitoring of Volatile Organic Compounds in Ambient Air

Volatile organic compounds (VOCs) in ambient air can participate in photochemical reactions, which lead to the generation of secondary pollutants such as ozone and aerosol. So real-time and accurate monitoring of atmospheric VOCs plays an important role in the study of the causes of air pollution. On the basis of proton transfer reaction mass spectrometry (PTR-MS) research, a novel dipolar proton transfer reaction mass spectrometer (DP-PTR-MS) for real-time and on-line monitoring of atmospheric VOCs was developed. Compared with conventional PTR-MS with one kind of reagent ion H₃O⁺, DP-PTR-MS had three kinds of reagent ions H₃O⁺, OH^?, (CH₃)₂COH⁺, which could be switched according to the actual detection need. So DP-PTR-MS can improve the qualitative ability and expand the detection range effectively. The reagent ion H₃O⁺ can be used for detecting VOCs whose proton affinities are greater than that of H₂O. The reagent ion OH^? can be used to identify VOCs cooperating with the reagent ion H₃O⁺, and can also be used for detecting some inorganic substances such as CO₂. The reagent ion (CH₃)₂COH⁺ can be used for accurately detecting NH₃ under interference elimination circumstances. The limit of detection (LOD) and sensitivity of DP-PTR-MS were measured by using six kinds of standard gases. The results showed that the LOD for detecting toluene was 7 × 10^?12 (V/V) and the sensitivity for detecting ammonia reached 126 cps/10^?9 (V/V). The ambient air in Hefei city was on-line and real-time monitored for continuous 78 h with DP-PTR-MS. The results showed that the newly developed DP-PTR-MS could be used for long-term and real-time monitoring atmospheric VOCs at the concentration of 10^?12 (V/V) level. DP-PTR-MS is an important tool to the study of the causes of atmospheric pollution and the monitoring of trace VOCs emissions.     

Radiation-Chemical Formation of Ozone in an Oxygen-Containing Gas Atmosphere

The process of ozone formation in an oxygen-containing gas atmosphere by the action of ionizing radiation was studied. A kinetic model of the process was constructed for the O₂–N₂ system. The effects of the main parameters of radiolysis on the O₃ formation rate were analyzed. The atmospheric emission of ozone from industrial-scale power units that employ electron-beam flue gas cleaning of harmful impurities was evaluated from the standpoint of its conceivable favorable effect on the Earth ozone layer.     

Influence of Power Modulation on Ozone Production Using an AC Surface Dielectric Barrier Discharge in Oxygen

The measurements of electro-optical discharge characteristics and concentration of produced ozone were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge (SDBD) in pure oxygen at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1 kHz, variable discharge duty cycle of 0.01–0.8 and oxygen flow rate of 2.5–10 slm. We observed asymmetric SDBD behaviour as evidenced by the variation in the ratio of the O^I/O₂ ⁺ emission intensities registered during the positive/negative half-periods and complemented by the transferred charge measurements through the Lissajous figures. We also found a strong dependence of O₃ concentration on the discharge duty cycle. The highest calculated ozone production yield reached 170 g/kWh with a corresponding energy cost of about 10 eV/molecule when combining the lowest inspected duty cycle with the lowest AC high voltage amplitude.     

Negative ion atmospheric pressure ionization mass spectrometry: Ionization of aromatic hydrocarbons

A corona discharge atmospheric pressure ionization source generates the reagent ions, OH^? and O^? ions in addition to better known O₂^? ions, when ambient air is used as the carrier. All three ions are gas-phase bases that could form negative ions from organics via proton abstraction. Ionization of simple aromatic hydrocarbons by O₂^? is thermodynamically not feasible. Simple aromatic hydrocarbons are ionized only by O^? and/or OH^? to form [M ? H]^? ions. However, [M ? H]^? ions do not appear in the mass spectrum as they undergo stabilization via clustering with predominantly oxygen atoms.     

Rate constants for the gas-phase reactions of Ozone with unsaturated Aliphatic Alcohols

The gas-phase reaction of ozone with unsaturated alcohols in air has been investigated at atmospheric pressure and ambient temperature (288–291 K). Cyclohexane was added to scavenge the hydroxyl radical which forms as a product of the ozone–unsaturated alcohol reaction. The reaction rate constants, in units of 10^?18 cm³ molecule^?1 s^?1, are 16.2 ± 0.7 for (±) 3-buten-2-ol, 17.9 ± 1.8 for 1-penten-3-ol, 10.0 ± 0.3 for 2-methyl-3-buten-2-ol, 169 ± 25 for cis-2 penten-1-ol, and 251 ± 41 for 2-buten-1-ol (mixture of isomers). Substituent effects on reactivity are discussed. The reactivity of unsaturated alcohols towards ozone is similar to that of their alkene structural homologues. Implications of these results with respect to the atmospheric persistence of unsaturated alcohols are briefly discussed. © 1994 John Wiley & Sons, Inc.     

A comparative study of rotational temperatures using diatomic OH,O2 and N2+ molecular spectra emitted from atmospheric plasmas

From the application point of view, gas temperature is one of the most important parameters for atmospheric plasmas. Based on the fact that the gas temperature is closely related with the rotational temperature of an atmospheric plasma, a spectroscopic method of measuring the rotational temperature is described in this work by analyzing OH, O₂ and N₂⁺ molecular spectra emitted from the atmospheric plasma in ambient air. The OH and N₂⁺ molecular spectra are emitted because of the oxygen, hydrogen and nitrogen atoms existing in the ambient air. The O₂ diatomic molecular spectrum is emitted from the oxygen plasma that is frequently produced for atmospheric plasma applications. In order to utilize a spectrometer with modest spectral resolution, a synthetic diatomic molecular spectrum was compared with the experimentally obtained spectrum. The rotational temperatures determined by the above three different molecular spectra are in good agreement within 2.4% error. In the case of a plasma with low gas temperature, the temperature measured by a thermocouple was compared to verify the accuracy of the spectroscopic method, and the results show excellent agreement. From the study, it was found that an appropriate diatomic molecular species can be chosen to be used as a thermometer depending on experimental circumstances.     

Thin films of vanadium oxide grown on vanadium metal: oxidation conditions to produce V2O5 films for Li‐intercalation applications and characterisation by XPS,AFM, RBS/NRA

Thin films of vanadium oxide were grown on vanadium metal surfaces (i) in air at ambient conditions, (ii) in 5 mM H₂SO₄ (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10^?5 mbar) at temperatures between 350 and 550 °C and (iv) at near‐atmospheric oxygen pressure (750 mbar) at 500 °C. The oxide films were investigated by atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed of V₂O₃. In air and in aqueous solution at RT, the oxide films are ultra‐thin and hydroxylated. At 500 °C, nearly atmospheric oxygen pressure is required to form crystalline V₂O₅ films. The oxide films grown at pO₂ = 750 mbar for 5 min are about 260‐nm thick, and consist of a 115‐nm outer layer of crystalline V₂O₅. The inner oxide is mainly composed of VO₂. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 °C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well‐crystallized V₂O₅ film, formed by oxidation for 5 min at 500 °C and 750 mbar O₂, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright © 2005 John Wiley & Sons, Ltd.     

Production of radicals in the ozonolysis of propene in air

Radical production in the ozonolysis of propene in air was monitored directly by a peroxy radical chemical amplification (PERCA) instrument at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The ozonolysis reactions were conducted in a flow tube under pseudo-first-order conditions for ozone. The decay in ozone was calculated based on reaction time tr and effective rate constant keff (keff = k1[C3H6]0)) for the ozone-propene reaction. The total radical yields relative to consumed ozone were d...     

Photocatalytic performance of Pt-loaded TiO2 in the decomposition of gaseous ozone

Gas-phase catalytic and photocatalytic decomposition of ozone (O₃) was investigated using TiO₂ and Pt-loaded TiO₂ (Pt/TiO₂) at room temperature and atmospheric pressure. The nominal weight loading of Pt was less than 1 wt.%. Results of this study indicate that both the overall conversion of O₃ to O₂ and other products with UV irradiation and without UV irradiation (dark reaction) can be improved by using Pt-loaded TiO₂. Photocatalytic conversion of O₃ on pure TiO₂ decreased with increasing water vapor. In contrast, Pt/TiO₂ was active for the decomposition of ozone under the humidity condition at room temperature.     

整体式担载型Pt基催化剂上航空煤油的裂解:助剂SrO和BaO的影响

考察了整体式担载型Pt基催化剂上国产3号航空煤油(RP-3)的常压裂解反应,着重探讨了添加BaO和SrO助剂对裂解效果的影响,以及裂解时间对积炭量的影响.采用全自动吸附仪、程序升温还原、X射线光电子能谱以及X射线衍射和扫描电镜等方法对催化剂进行了表征.结果表明,在整体式担载型Pt基催化剂上RP-3裂解的总产气量比热裂解提高了39.7%;BaO或SrO助剂的添加又使其总产气量又分别提高了25.6%和37.0%;同时添加BaO和SrO的催化剂,其催化裂解总产气量则提高了96.5%.BaO和SrO助剂均可有效地抑制积炭的生成,而两者间的协同作用,进一步抑制了RP-3催化裂解过程中积炭的生成.