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In the field of electrochemical ozone production, electrodes need to have exceptional catalytic activity, long-term stability, and cost-effectiveness. In this case, TiO2-NTs/SnO2-Sb2O5-NiO electrodes were fabricated using a combination of anodization, electrochemical deposition, spin coating and annealing techniques. The coating of electrodes was analyzed using EDS, XRD and SEM techniques. According to the obtained cyclic voltammetry (CV) data, the TiO2-NTs/SnO2-Sb2O5-NiO electrode revealed a less positive potential for oxygen evolution compared to other constructed electrodes. The conversion of Ti to Ti-NTs improved the ozone production efficiency and resulted in higher concentrations of water-soluble ozone. To evaluate the performance of the electrodes and the corresponding electrocatalytic activity, a textile dye was used as a pollutant. The most effective modified electrode proved to have an impressive decomposition rate of 96% for the cationic yellow 28 dye within a 60-min timeframe. Furthermore, this modified electrode could substantially remove chemical oxygen demand (COD) of up to 53.6% during 60-min electrolysis. [ABSTRACT FROM AUTHOR]

Surface recombination in an oxygen DC glow discharge in a Pyrex (borosilicate glass) tube is studied via mesoscopic modelling and comparison with measurements of recombination probability. A total of 106 experimental conditions are assessed, with discharge current varying between 10 and 40 mA, pressure values ranging between 0.75 and 10 Torr, and fixed outer wall temperatures ( T w ) of −20, 5, 25 and 50 ∘ C . The model includes O+O and O+O2 surface recombination reactions and a T w dependent desorption frequency. The model is validated for all the 106 studied conditions and intends to have predictive capabilities. The analysis of the simulation results highlights that for T w = − 20 ∘ C and T w = 5 ∘ C the dominant recombination mechanisms involve physisorbed oxygen atoms ( O F ) in Langmuir–Hinshelwood (L-H) recombination O F + O F and in Eley–Rideal (E-R) recombination O 2 + O F , while for T w = 25 ∘ C and T w = 50 ∘ C processes involving chemisorbed oxygen atoms ( O S ) in E-R O + O S and L-H O F + O S also play a relevant role. A discussion is taken on the relevant recombination mechanisms and on ozone wall production, with relevance for higher pressure regimes. [ABSTRACT FROM AUTHOR]

Ozone (O3) pollution is a focus of the international community due to its health and environmental impacts. Organic peroxyl (RO2) radicals play a significant role in O3 initiation processes, which has implications for O3 mitigation. RO2 generated from volatile organic compounds (VOCs) sources contribute substantially to O3 formation. However, quantifying the RO2 from diverse sources is a great challenge. For the first time, we proposed a new hybrid Receptor‐Kinetic model to quantify sources contributions to RO2 from the perspective of molecular level and functional groups of VOCs. We revealed that 3‐Hydroxy‐2‐butylperoxy (BUT2OLO2), 4‐Hydroxy‐3‐methyl‐1‐butene‐3‐ylperoxy (ISOPBO2) and 1‐Hydroxypropane‐2‐ylperoxy (HYPROPO2) radicals were the dominant RO2, which were driven by reactions of cis/trans‐2‐butene (from Biogenic Emissions and Solvent Usage), isoprene (from Biogenic Emissions), and propylene (from Liquid Petroleum Gas Evaporation), respectively. The three dominant RO2 radicals contributed significantly to O3 production (28%, 10% and 14%), comparing with other 16 RO2. Sensitivity studies indicated that O3 production can be decreased effectively by reducing the dominant RO2 species for each source. Quantitative evidence suggested that targeting dominant RO2 sources can be a novel direction for O3 control. Plain Language Summary: Severe ozone (O3) pollution occurs frequently despite the strict air pollution control policies have been implemented in China. As a secondary pollutant, O3 formation is related to various photochemistry of radicals. However, it is a great challenge to quantify radicals due to the difficulty in measure. Here, we developed a new model to investigate the impacts of source on O3 from the perspective of organic peroxyl radicals (RO2). We found that VOCs sources emit a diverse variety of VOCs species to form various RO2 radicals, which are crucial for O3 formation. Sensitivity studies showed that O3 production can be decreased effectively by dominant RO2 reduction for each source. Therefore, foucusing on dominant RO2 sources can be a new direction for future O3 control. Key Points: A new hybrid Receptor‐Kinetic model was proposed to quantify sources contributions to O3 through photochemistry of RO2Sources emit a diverse variety of VOCs species to form various RO2 radicals, which are crucial for O3 formationO3 production can be decreased effectively by reducing the dominant RO2 species for each source [ABSTRACT FROM AUTHOR]

Current research directions indicate that vehicles with autonomous capabilities will increase in traffic contexts. Starting from data analyzed in R. E. Stern et al. (2018), this paper shows the benefits due to the traffic control exerted by a unique autonomous vehicle circulating on a ring track with more than 20 human-driven vehicles. Considering different traffic experiments with high stop-and-go waves and using a general microscopic model for emissions, it was first proved that emissions reduces by about 25%. Then, concentrations for pollutants at street level were found by solving numerically a system of differential equations with source terms derived from the emission model. The results outline that ozone and nitrogen oxides can decrease, depending on the analyzed experiment, by about 10% and 30%, respectively. Such findings suggest possible management strategies for traffic control, with emphasis on the environmental impact for vehicular flows. [ABSTRACT FROM AUTHOR]

Ozone production in a planar dielectric barrier discharge (DBD) in atmospheric oxygen in different discharge modes was investigated. Results show that the gas temperature in discharge channel depends strongly on discharge mode, with a value of 300–310 K in glow regime and 440–465 K in streamer regime. Ozone production yield in glow DBD is much higher than that in streamer one, with the best yield of 342.6 and 162.6 g/kWh, respectively. Gas temperature in discharge channel relates to the effective discharge area of DBD, which is a small fraction of the whole electrode surface in streamer DBD compared with nearly the whole surface in glow DBD. The gas temperature in the channel plays a decisive role in the conversion of oxygen atoms to ozone as well as the ozone equilibrium concentration. Excellent performance of glow DBD demonstrates the high energy efficiency and reliability for practical application of planar DBD-based ozone generator. [ABSTRACT FROM AUTHOR]

The pollution of atmospheric ozone in China shows an obvious upward trend in the past decade. However, the studies on the atmospheric oxidation capacity and O 3 formation in four seasons in the southeastern coastal region of China with the rapid urbanization remain limited. Here, a four-season field observation was carried out in a coastal city of southeast China, using an observation-based model combining with the Master Chemical Mechanism, to explore the atmospheric oxidation capacity (AOC), radical chemistry, O 3 formation pathways and sensitivity. The results showed that the average net O 3 production rate (14.55 ppbv/hr) in summer was the strongest, but the average O 3 concentrations in autumn was higher. The AOC and RO x levels presented an obvious seasonal pattern with the maximum value in summer, while the OH reactivity in winter was the highest with an average value of 22.75 sec−1. The OH reactivity was dominated by oxygenated VOCs (OVOCs) (30.6%-42.8%), CO (23.2%-26.8%), NO 2 (13.6%-22.0%), and alkenes (8.4%-12.5%) in different seasons. HONO photolysis dominated OH primary source on daytime in winter, while in other seasons, HONO photolysis in the morning and ozone photolysis in the afternoon contributed mostly. Sensitivity analysis indicated that O 3 production was controlled by VOCs in spring, autumn and winter, but a VOC-limited and NO x -limited regime in summer, and alkene and aromatic species were the major controlling factors to O 3 formation. Overall, the study characterized the atmospheric oxidation capacity and elucidated the controlling factors for O 3 production in the coastal area with the rapid urbanization in China. [ABSTRACT FROM AUTHOR]

We present a synergistic investigation into ozone production dynamics within a high-voltage reaction chamber operating from 1.75 kV to 10 kV, at 60 Hz. The output ozone concentration dependence on a 60 Hz root mean square high-voltage for an air input pressure of 0.1 bar was measured using an ultraviolet-based sensor. A finite-element numerical model of the reaction chamber was developed and used for obtaining the reaction rate for the generated ozone for each level of input voltage and the internal distribution of the gas vector velocity field and ozone concentration. An expression to estimate the ozone reaction rates from the measured ozone concentrations was also derived. It was then compared and validated using the developed computational model. Therefore, in this work, a formula is proposed to estimate the ozone production by providing the experimental reaction rates. The other objective is to analyze the hysteresis phenomena observed in the partial discharges' levels in the reaction chamber and in the output ozone concentration. Finally, we establish a connection between the total power of partial discharges and the consequent ozone production, clarifying the role of cumulative partial discharges' power levels in governing the resultant output ozone concentration. [ABSTRACT FROM AUTHOR]

Ozone, O3, is a strong oxidizing agent often used for water purification. O3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O2, followed by three-body association reactions between O and O2. Previous studies on O3 formation in low-temperature plasma DBDs have shown that O3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N2 can suppress this phenomenon and increase the O3 production relative to using pure O2 in spite of power deposition being diverted from O2 to N2 and the production of nitrogen oxides, N x O y. The OZP is hypothesized to occur because O3 is destroyed on the surfaces in contact with the plasma. Including N2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O3 destruction. The effect of N2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O3 production with N2 admixtures. The mechanism includes O3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O2 and N2, and NO x reactions. Without these reactions on the surface, the density of O3 monotonically decreases with increasing N2 admixture due to power absorption by N2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O3 are maximum with a few tenths of percent of N2 depending on the O3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O3 density with N-based surface chemistry occurs when the surface destruction probability of O3 or the surface roughness was decreased. [ABSTRACT FROM AUTHOR]

With the coming of the “14th Five-Year Plan,” the coordinated control of particulate matter with an aerodynamic diameter no greater than 2.5 μm (PM2.5) and O3 has become a major issue of air pollution prevention and control in China. The stereoscopic monitoring of regional PM2.5 and O3 and their precursors is crucial to achieve coordinated control. However, current monitoring networks are currently inadequate for monitoring the vertical profiles of both PM2.5 and O3 simultaneously and support air quality control. The University of Science and Technology of China (USTC) has established a nationwide ground-based hyperspectral stereoscopic remote sensing network based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) since 2015. This monitoring network provides a significant opportunity for the regional coordinated control of PM2.5 and O3 in China. One-year vertical profiles of aerosol, NO2 and HCHO monitored from four MAX-DOAS stations installed in four megacities (Beijing, Shanghai, Shenzhen, and Chongqing) were used to characterize their vertical distribution differences in four key regions, Jing–Jin–Ji (JJJ), Yangtze River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SB), respectively. The normalized and yearly averaged aerosol vertical profiles below 400 m in JJJ and PRD exhibit a box shape and a Gaussian shape, respectively, and both show exponential shapes in YRD and SB. The NO2 vertical profiles in four regions all exhibit exponential shapes because of vehicle emissions. The shape of the HCHO vertical profile in JJJ and PRD was Gaussian, whereas an exponential shape was shown in YRD and SB. Moreover, a regional transport event occurred at an altitude of 600–1000 m was monitored in the southwest–northeast pathway of the North China Plain (NCP) by five MAX-DOAS stations (Shijiazhuang (SJZ), Wangdu (WD), Nancheng (NC), Chinese Academy of Meteorological Sciences (CAMS), and University of Chinese Academy of Sciences (UCAS)) belonging to the above network. The aerosol optical depths (AOD) in these five stations decreased in the order of SJZ > WD > NC > CAMS > UCAS. The short-distance regional transport of NO2 in the 700–900 m layer was monitored between WD and NC. As an important precursor of secondary aerosol, the peak of NO2 air mass in WD and NC all occurred 1 h earlier than that of aerosol. This was also observed for the short-distance regional transport of HCHO in the 700–900 m layer between NC and CAMS, which potentially affected the O3 concentration in Beijing. Finally, CAMS was selected as a typical site to determine the O3–NOx–volatile organic compounds (VOCs) sensitivities in vertical space. We found the production of O3 changed from predominantly VOCs-limited conditions to mainly mixed VOCs–NOx-limited condition from the 0–100 m layer to the 200–300 m layer. In addition, the downward transport of O3 could contribute to the increase of ground surface O3 concentration. This ground-based hyperspectral stereoscopic remote sensing network provide a promising strategy to support management of PM2.5 and O3 and their precursors and conduct attribution of sources.

Limited research has been conducted on the formation mechanism of chemically active species in streamer discharges with respect to the oxygen concentration, which is critical to various applications such as ozone generation, air purification, and plasma-assisted combustion, among others. Herein, the oxygen concentration in an N2/O2 gas atmosphere is varied from 1% to 99% under atmospheric pressure and room temperature to investigate changes in the characteristics of streamer discharge propagation and generation of chemically active species. As the oxygen concentration increases from 10% to 90%, the decay rate of the discharge current, propagation velocity of the primary streamer, and ozone production efficiency increase. These phenomena are qualitatively explained by the electron attachment reaction to oxygen molecules and changes in the electron energy distribution function caused by the change in the oxygen concentration. However, the amount of discharge emission from N2(C) cannot be explained by changes in the fraction of electron energy lost in excitation of N2(C) and its quantum yield, implying that changes in the production of N2(C) in the primary and secondary streamers must be considered in a spatiotemporal manner. This study demonstrates that the ozone and N2(C) production characteristics in streamer discharges vary nonlinearly with respect to the oxygen concentration. [ABSTRACT FROM AUTHOR]

Ground surface ozone (O3) is an emerging concern in China due to its complex formation process. In August 2020, field measurements of O3, NOx, and volatile organic compounds (VOCs) were carried out in Hefei's western suburbs. The pollution features of VOCs and O3 formation were thoroughly analyzed. The total VOC concentration was 42.26 ppb, with the dominant contributor being oxygenated VOCs (OVOCs). Seven emission sources were recognized using the positive matrix factorization (PMF) model, including aged air masses, combustion sources, fuel evaporation, industrial emissions, vehicular emission, solvent utilization, and biogenic emission. Ozone generation mainly occurred under an NOx-limited regime based on the zero-dimensional box model analysis. According to the scenario analysis, the 13% cut in O3 might be achieved by the 10% and 30% reduction in NOx and VOCs, respectively. The O3 budget analysis demonstrates its high ozone production rate during the pollution period. The influence of regional transport cannot be ignored for high O3 pollution. This paper provides scientific evidence for O3 production and the strategies of reducing O3 by controlling its precursors. [ABSTRACT FROM AUTHOR]

We present a synergistic investigation into ozone production dynamics within a high-voltage reaction chamber operating from 1.75 kV to 10 kV, at 60 Hz. The output ozone concentration dependence on a 60 Hz root mean square high-voltage for an air input pressure of 0.1 bar was measured using an ultraviolet-based sensor. A finite-element numerical model of the reaction chamber was developed and used for obtaining the reaction rate for the generated ozone for each level of input voltage and the internal distribution of the gas vector velocity field and ozone concentration. An expression to estimate the ozone reaction rates from the measured ozone concentrations was also derived. It was then compared and validated using the developed computational model. Therefore, in this work, a formula is proposed to estimate the ozone production by providing the experimental reaction rates. The other objective is to analyze the hysteresis phenomena observed in the partial discharges’ levels in the reaction chamber and in the output ozone concentration. Finally, we establish a connection between the total power of partial discharges and the consequent ozone production, clarifying the role of cumulative partial discharges’ power levels in governing the resultant output ozone concentration.

We investigated the effect of various photocatalysts - titanium, zinc, barium, and tungsten oxides on ozone generation of the surface dielectric barrier discharge in air. The layers of these catalysts were deposited on the side of the glass plate opposite the active electrode so that the emission from the discharge irradiated them. We found that TiO2, ZnO, and BaTiO3 catalysts increase the concentration of ozone generated by the discharge. On the other hand, the presence of WO3 in the discharge does not affect the ozone concentration. All these catalysts show no substantial effect on the electrical parameters of the discharge.

This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO2) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO2 in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO2−) and nitrate (NO3−) in the water was proportional to treatment time up to 50 min. The concentration of NO3− was a power function of gas phase NO2 while the concentration of NO2− increased approximately linearly with gas phase NO2. The formation of NO2− and NO3− could be described by reactions between dissolved NO2 and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO2 concentrations, the formation of dinitrogen tetraoxide (N2O4) increased the formation rate of NO2− and NO3−. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO2− /NO3− in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO2 and NO concentrations. [ABSTRACT FROM AUTHOR]

We performed a comprehensive and intensive field experiment including ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurement at Raoyang (115°44′ E, 38°14′ N; 20 m altitude) in summer (13 June–20 August) 2014. The NO2 and HCHO profiles retrieved by MAX-DOAS take on different vertical distribution shapes, with the former declining with the increasing altitude and the latter having an elevated layer. The average levels of vertical column densities (VCDs) and near-surface volume mixing ratios (VMRs) were 1.02 ± 0.51 × 1016 molec·cm−2 and 3.23 ± 2.70 ppb for NO2 and 2.32 ± 0.56 × 1016 molec·cm−2 and 5.62 ± 2.11 ppb for HCHO, respectively. The NO2 and HCHO levels are closely connected with meteorological conditions, with the larger NO2 VCDs being associated with lower temperature, higher relative humidity (RH) and lower planetary boundary layer height (PBLH). With respect to the diurnal variations of vertical distribution, the NO2 in the residual layer gradually disappeared from 1.2 km height to the surface during the period of 7:00–11:00 Beijing time (BJ), and the near-surface NO2 had larger VMRs in the early morning and evening than in the later morning and afternoon. An elevated HCHO layer was observed to occur persistently with the lifted layer height rising from ~0.5 km to ~1.0 km before 10:00 BJ; the near-surface HCHO VMRs gradually increased and peaked around 10:00 BJ. The ratios of HCHO to NO2 (RHCHO-NO2) were generally larger than two in the boundary layer from 11:00 BJ until 19:00 BJ, the time period when ozone photochemistry was most active. Thus, ozone (O3) production was mainly in the NOx-limited regime during the observation campaign, which was closely related to relatively high temperatures and low RH. The O3 production regimes also changed with the wind's direction. These results are significant to reveal the formation mechanism of O3 pollution and develop strategies for controlling the O3 photochemical pollution over the North China Plain. [ABSTRACT FROM AUTHOR]

Ground surface ozone (O3) is an emerging concern in China due to its complex formation process. In August 2020, field measurements of O3, NOx, and volatile organic compounds (VOCs) were carried out in Hefei’s western suburbs. The pollution features of VOCs and O3 formation were thoroughly analyzed. The total VOC concentration was 42.26 ppb, with the dominant contributor being oxygenated VOCs (OVOCs). Seven emission sources were recognized using the positive matrix factorization (PMF) model, including aged air masses, combustion sources, fuel evaporation, industrial emissions, vehicular emission, solvent utilization, and biogenic emission. Ozone generation mainly occurred under an NOx-limited regime based on the zero-dimensional box model analysis. According to the scenario analysis, the 13% cut in O3 might be achieved by the 10% and 30% reduction in NOx and VOCs, respectively. The O3 budget analysis demonstrates its high ozone production rate during the pollution period. The influence of regional transport cannot be ignored for high O3 pollution. This paper provides scientific evidence for O3 production and the strategies of reducing O3 by controlling its precursors.

Volatile organic compounds (VOCs) regulate atmospheric oxidation capacity, and the reactions of VOCs are key in understanding ozone formation and its mitigation strategies. When evaluating its impact, most previous studies did not fully consider the role of oxygenated VOCs due to limitations of measurement technology. By using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) combined with gas chromatography mass spectrometer (GC-MS) technology, we are able to quantify a large number of oxygenated VOCs in a representative urban environment in southern China. Based on the new dataset, we find that non - formaldehyde (HCHO) OVOCs can contribute large fractions (22-44%) of total RO[sub X]radical production, comparable or larger than the contributions from nitrous acid and formaldehyde. We demonstrate that constraints using OVOCs observations are essential in modeling radical and ozone production, as modelled OVOCs can be substantially lower than measurements, potentially due to primary emissions and/or missing secondary sources. Our results show that models without OVOC constraints using ambient measurements will underestimate P(RO[sub x] and ozone production rate, and may also affect the determination of sensitivity regime in ozone formation. Therefore, a thorough quantification of photodegradable OVOCs species is in urgent need to understand accurately the ozone chemistry and to develop effective control strategies. [ABSTRACT FROM AUTHOR]

Understanding of nitrous acid (HONO) production is crucial to photochemical studies, especially in polluted environments like eastern China. In-situ measurements of gaseous and particulate compositions were conducted at a rural coastal site during the 2018 spring Ozone Photochemistry and Export from China Experiment (OPECE). This data set was applied to investigate the recycling of reactive nitrogen through daytime heterogeneous HONO production. Although HONO levels increase during agricultural burning, analysis of the observation data does not indicate more efficient HONO production by agricultural burning aerosols than other anthropogenic aerosols. Box and 1-D modeling analyses reveal the intrinsic relationships between nitrogen dioxide (NO 2 ), particulate nitrate (pNO 3 ), and nitric acid (HNO 3 ), resulting in comparable agreement between observed and simulated HONO concentrations with any one of the three heterogeneous HONO production mechanisms, photosensitized NO 2 conversion on aerosols, photolysis of pNO 3 , and conversion from HNO 3 . This finding underscores the uncertainties in the mechanistic understanding and quantitative parametrizations of daytime heterogeneous HONO production pathways. Furthermore, the implications for reactive nitrogen recycling, ozone (O 3 ) production, and O 3 control strategies vary greatly depending on the HONO production mechanism. On a regional scale, the conversion of HONO from pNO 3 can drastically enhance O 3 production, while the conversion from NO 2 can reduce O 3 sensitivity to NOx changes in polluted eastern China.

An electric field in the dielectric barrier electrode system is necessary for ozone production because ozone is produced by the electric discharge of O2 under a high-intensity electric field. The gas discharge plasmas contain energetic particles, such as electrons, ions, atoms, and radicals. The recombination of the O atom and O2 in the plasma will form O3. In this paper, the dependence of DC electric field formation on electrode geometry and the gap between electrodes and dielectric materials were examined by using computational modeling. Thus, a set of electrode geometry, gap distance, and dielectric material were obtained for high-intensity and uniform electric field generation. The COMSOL Multiphysics software was used for the modeling. Among the electrode geometries of plate-plate, pin-plate and mesh-plate, the mesh-plate generated high-intensity and uniform electric field. In the modeling, dielectric materials, including quartz, mica, alumina, and water, were compared. The highest intensity of electric field occurred on the water surface. [ABSTRACT FROM AUTHOR]

Reducing ozone in the New York City (NYC) region requires understanding the nonlinearity of ozone production (PO 3) and its sensitivity to volatile organic compounds (VOCs) and nitrogen oxides (NO x = NO 2 + NO). Using observations from the Long Island Sound Tropospheric Ozone Study (LISTOS) in the late spring and summers of 2017–2019 and a 0-D box model, we test the sensitivity of PO 3 to ozone precursors. PO 3 is greater in the morning than the afternoon due to increased concentrations of NO 2 and VOC. This diurnal variation in PO 3 is enhanced in the late summer. Based on the model response of PO 3 to changes in initial NO 2 , 14% of samples are within a VOC-limited regime. The metric LRO x /LNO x , which compares the radical loss rates via self-reaction to their reaction with NO 2 , indicates an additional 17% of samples are in transition between NO x and VOC-limited regimes (0.30 <= LRO x /LNO x <= 1). We often find PO 3 to be VOC-limited in NYC and along the Connecticut coastline (I-95 corridor). In these samples, PO 3 is most sensitive to isoprene, propene, and isopentane, and individual VOCs have strong diurnal and seasonal variations. We further compare PO 3 calculations using the near explicit Master Chemical Mechanism (MCMv3.3.1) and Carbon Bond 6 revision 2 (CB6r2) for a more direct link to regulatory air quality models. Modeled PO 3 is 20% greater in MCMv3.3.1, due largely to the speciation of VOC and organic peroxy radicals, however the bounds of LRO x /LNO x used to determine the transition range between PO 3 regimes remain the same. • Ozone production is faster in the morning than in the afternoon. • VOC-limited ozone production is frequent along the Connecticut coastline and in NYC. • Ozone production sensitivity to biogenic and anthropogenic VOC varies with season and time of day. • Greater ozone production is calculated using MCMv3.3.1 compared to CB6r2, though both exhibit similar NO x sensitivity. [ABSTRACT FROM AUTHOR]

The study investigated the reactive dissolution of gas phase nitrogen-oxides and ozone in water. Mixtures with variable composition of nitrogen oxides were produced by mixing nitric oxide (NO) with ozone. Pure NO in Ar carrier gas resulted in the production of NO2− but its production rate was limited by low NO solubility. The presence of NO2 in the gas increased the production of NO2− while NO3− was also produced. The presence of N2O5 in the gas abruptly increased the production of NO3− due to higher solubility of N2O5. In the present configuration, about 8% of NO2 was dissolved in the water while for N2O5 the fraction was 78%. [ABSTRACT FROM AUTHOR]

We performed a comprehensive and intensive field experiment including ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurement at Raoyang (115°44′ E, 38°14′ N; 20 m altitude) in summer (13 June–20 August) 2014. The NO2 and HCHO profiles retrieved by MAX-DOAS take on different vertical distribution shapes, with the former declining with the increasing altitude and the latter having an elevated layer. The average levels of vertical column densities (VCDs) and near-surface volume mixing ratios (VMRs) were 1.02 ± 0.51 × 1016 molec·cm−2 and 3.23 ± 2.70 ppb for NO2 and 2.32 ± 0.56 × 1016 molec·cm−2 and 5.62 ± 2.11 ppb for HCHO, respectively. The NO2 and HCHO levels are closely connected with meteorological conditions, with the larger NO2 VCDs being associated with lower temperature, higher relative humidity (RH) and lower planetary boundary layer height (PBLH). With respect to the diurnal variations of vertical distribution, the NO2 in the residual layer gradually disappeared from 1.2 km height to the surface during the period of 7:00–11:00 Beijing time (BJ), and the near-surface NO2 had larger VMRs in the early morning and evening than in the later morning and afternoon. An elevated HCHO layer was observed to occur persistently with the lifted layer height rising from ~0.5 km to ~1.0 km before 10:00 BJ; the near-surface HCHO VMRs gradually increased and peaked around 10:00 BJ. The ratios of HCHO to NO2 (RHCHO-NO2) were generally larger than two in the boundary layer from 11:00 BJ until 19:00 BJ, the time period when ozone photochemistry was most active. Thus, ozone (O3) production was mainly in the NOx-limited regime during the observation campaign, which was closely related to relatively high temperatures and low RH. The O3 production regimes also changed with the wind’s direction. These results are significant to reveal the formation mechanism of O3 pollution and develop strategies for controlling the O3 photochemical pollution over the North China Plain.

Measurements of CO and 15 volatile organic compounds (VOCs) at the IAP-RAS (A.M. Obukhov Institute of Atmospheric Physics) site located in the center of Moscow were analyzed. Acetaldehyde, ethanol, 1.3-butadiene, isoprene, toluene and C-8 aromatics were established to be the main ozone precursors in the observed area, providing up to 82% of the total ozone formation potential of the VOCs measured. Diurnal and seasonal variations of the compounds are discussed. The concentrations of anthropogenic VOCs (acetaldehyde, benzene, 1.3-butadiene, toluene, and C-8 aromatics) did not exceed their maximum permissible levels, reaching their maxima in summer and autumn in the morning and evening hours. Biogenic ethanol and isoprene were the highest in summer midday but their concentrations were low enough (up to 4 and 0.4 ppbv, respectively) due to small vegetation area around the site. Emission ratios (ERs) for the main ozone precursors—acetaldehyde, ethanol, 1.3-butadiene, isoprene, toluene, and C-8 aromatics—were estimated from two-sided linear regression fits using benzene and CO as tracers for anthropogenic emissions, with spatial and temporal filters being applied to account for the influence of chemistry and local emission sources. The best estimates of ERs were obtained using benzene as a reference species. Anthropogenic fractions of VOCs (AFs) were then estimated. As expected, acetaldehyde, toluene, 1.3-butadiene, and C8aromatics were entirely anthropogenic and emitted mainly from urban vehicle exhausts throughout the day, both in summer and in winter. AFs of isoprene and ethanol did not exceed 30% and 50% in summer, respectively, during both daytime and nighttime hours. In winter, the anthropogenic fractions of isoprene and ethanol were slightly higher (up to 35% and 60%, respectively).

This paper presents the first results of the measurements of trace gases and aerosols at three surface sites in and outside Beijing before and during the 2008 Olympics. The official air pollution index near the Olympic Stadium and the data from our nearby site revealed an obvious association between air quality and meteorology and different responses of secondary and primary pollutants to the control measures. Ambient concentrations of vehicle-related nitrogen oxides (NO(x)) and volatile organic compounds (VOCs) at an urban site dropped by 25% and 20-45% in the first two weeks after full control was put in place, but the levels of ozone, sulfate and nitrate in PM(2.5) increased by 16%, 64%, 37%, respectively, compared to the period prior to the full control; wind data and back trajectories indicated the contribution of regional pollution from the North China Plain. Air quality (for both primary and secondary pollutants) improved significantly during the Games, which were also associated with the changes in weather conditions (prolonged rainfall, decreased temperature, and more frequent air masses from clean regions). A comparison of the ozone data at three sites on eight ozone-pollution days, when the air masses were from the southeast-south-southwest sector, showed that regional pollution sources contributed > 34-88% to the peak ozone concentrations at the urban site in Beijing. Regional sources also contributed significantly to the CO concentrations in urban Beijing. Ozone production efficiencies at two sites were low (similar to 3 ppbv/ppbv), indicating that ozone formation was being controlled by VOCs. Compared with data collected in 2005 at a downwind site, the concentrations of ozone, sulfur dioxide (SO(2)), total sulfur (SO(2)+PM(2.5) sulfate), carbon monoxide (CO), reactive aromatics (toluene and xylenes) sharply decreased (by 8-64%) in 2008, but no significant changes were observed for the concentrations of PM(2.5), fine sulfate, total odd reactive nitrogen (NO(y)), and longer lived alkanes and benzene. We suggest that these results indicate the success of the government's efforts in reducing emissions of SO(2), CO, and VOCs in Beijing, but increased regional emissions during 2005-2008. More stringent control of regional emissions will be needed for significant reductions of ozone and fine particulate pollution in Beijing.

An extensive set of measurements was made in and around Mexico City as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiments in March 2006. Simulations with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4), a global chemical transport model, have been used to provide a regional context for these observations and assist in their interpretation. These MOZART-4 simulations reproduce the aircraft observations generally well, but some differences in the modeled volatile organic compounds (VOCs) from the observations result from incorrect VOC speciation assumed for the emission inventories. The different types of CO sources represented in the model have been "tagged" to quantify the contributions of regions outside Mexico, as well as the various emissions sectors within Mexico, to the regional air quality of Mexico. This analysis indicates open fires have some, but not a dominant, impact on the atmospheric composition in the region around Mexico City when averaged over the month. However, considerable variation in the fire contribution (2-15% of total CO) is seen during the month. The transport and photochemical aging of Mexico City emissions were studied using tags of CO emissions for each day, showing that typically the air downwind of Mexico City was a combination of many ages. Ozone production in MOZART-4 is shown to agree well with the net production rates from box model calculations constrained by the MILAGRO aircraft measurements. Ozone production efficiency derived from the ratio of O-x to NOz is higher in MOZART-4 than in the observations for moderately polluted air. OH reactivity determined from the MOZART-4 results shows the same increase in relative importance of oxygenated VOCs downwind of Mexico City as the reactivity inferred from the observations. The amount of ozone produced by emissions from Mexico City and surrounding areas has been quantified in the model by tracking NO emissions, showing little influence beyond Mexico's borders, and also relatively minor influence from fire emissions on the monthly average tropospheric ozone column.

The aim of present study was to investigate the influence of oxygen percentage (1–80%), temperature (20 and 100 °C) and the addition of TiO2 catalyst on the production of ozone O3 and nitrous oxide N2O by DBD. The production efficiency of O3 increased with O2 percentage while the production efficiency of N2O had a maximum at approximately 20% of O2. The production of O3 slightly decreased with the increase of temperature while the production of N2O increased. The presence of TiO2 considerably increased the production efficiency of N2O production. The O3 production efficiency was enhanced by TiO2 at 20 °C and reduced at 100 °C. [ABSTRACT FROM AUTHOR]

Toluene and benzene are used for assessing the ability to measure disjunct eddy covariance (DEC) fluxes of Volatile Organic Compounds (VOC) using Proton Transfer Reaction Mass Spectrometry (PTR-MS) on aircraft. Statistically significant correlation between vertical wind speed and mixing ratios suggests that airborne VOC eddy covariance (EC) flux measurements using PTR-MS are feasible. City-median midday toluene and benzene fluxes are calculated to be on the order of 14.1 +/- 4.0 mg/m(2)/h and 4.7 +/- 2.3 mg/m(2)/h, respectively. For comparison the adjusted CAM2004 emission inventory estimates toluene fluxes of 10 mg/m(2)/h along the footprint of the flight-track. Wavelet analysis of instantaneous toluene and benzene measurements during city overpasses is tested as a tool to assess surface emission heterogeneity. High toluene to benzene flux ratios above an industrial district (e. g. 10-15 g/g) including the International airport (e. g. 3-5 g/g) and a mean flux (concentration) ratio of 3.2 +/- 0.5 g/g (3.9 +/- 0.3 g/g) across Mexico City indicate that evaporative fuel and industrial emissions play an important role for the prevalence of aromatic compounds. Based on a tracer model, which was constrained by BTEX (BTEX Benzene/Toluene/Ethylbenzene/ m, p, o-Xylenes) compound concentration ratios, the fuel marker methyl-tertiary-butylether (MTBE) and the biomass burning marker acetonitrile (CH3CN), we show that a combination of industrial, evaporative fuel, and exhaust emissions account for > 87% of all BTEX sources. Our observations suggest that biomass burning emissions play a minor role for the abundance of BTEX compounds in the MCMA (2-13%).

Isoprene is emitted from vegetation to the atmosphere in significant quantities, and it plays an important role in the reactions that control tropospheric oxidant concentrations. As future climatic and land-cover changes occur, the spatial and temporal variations, as well as the magnitude of these biogenic isoprene emissions, are expected to change. This paper presents a study of the change in biogenic isoprene emissions that would result from both anthropogenic land-cover and climate-driven changes. Annual global isoprene emissions were estimated to be 522 Tg yr-1 under current climatological and land-cover conditions. When climate-driven land-cover changes are predicted, but climate does not change, total global emissions did not change significantly, although regional impacts were important. However, the use of future temperature and land-cover drivers to estimate isoprene emissions produced a global estimate of 889 Tg yr-1. Anthropogenic land-cover changes, such as urbanization and changes of natural vegetation to plantation forests, can also have substantial impacts on isoprene emissions (i.e., up to 717 Tg yr-1, a 37% increase, when land-cover changes but temperature remains at current-day values). The Model for Ozone and Related Tracers, version 2 (MOZART-2) was run with the different isoprene emission scenarios to simulate the potential changes in global atmospheric chemical composition. The simulated regional surface ozone concentrations changed as much as -9 to 55 ppbv under certain emission and climate scenarios. These results were used to evaluate changes in the ozone production chemistry under different emission scenarios. As expected, the impacts of changing isoprene emissions are regionally dependent, with large changes in China, the Amazon, and the United States.

Local ozone production and loss rates for the arctic free troposphere (58-85° N, 1-6 km, February-May) during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1-3 km layer and a factor of 7 in the 3-6 km layer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1-3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratios up to ∼300 pptv in February and for NOx mixing ratios up to ∼500 pptv in May. These NOx limits are an order of magnitude higher than median NOx levels observed, illustrating the strong dependence of gross ozone production rates on NOx mixing ratios for the majority of the observations. The threshold NOx mixing ratio needed for net positive ozone production was also calculated to increase from NOx ∼ 10 pptv in February to ∼25 pptv in May, suggesting that the NOx levels needed to sustain net ozone production are lower in winter than spring. This lower NOx threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NOx needed to produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1-3 km layer and net ozone production for the 3-6 km layer throughout the campaign. © 2004 Kluwer Academic Publishers.

Environmental decontamination is a major challenge due to the rapid growth of industrial and technological development, requiring an important consumption of fossil energies. Nowadays, a new way to treat polluting molecules based on the use of nonequilibrium reactive plasmas, is under development. These plasmas are generated by electrical discharges at atmospheric pressure, for neutralizing or transforming the toxic oxides. In this respect, the goal of the present work is to analyze the possibilities of treatment of NOx molecules and ozone generation by pulsed discharge. The study was carried out by using a one-dimensional model based on the parallel resistor network concept, consisting in dividing the discharge volume into plasma elements which are connected in no way but through their contribution to the total resistance of the plasma. The model calculations indicate the effect of gas heating and inhomogeneous preionization on the ozone production and NOx destruction. [ABSTRACT FROM AUTHOR]

In this paper, simultaneous maximization of generated ozone concentration and minimization of electrical energy consumption is investigated in a laboratory-scale electrochemical ozone production system (EOP). Neural network simulation of EOP was carried out for generated ozone concentration prediction by Abbasi et al. (Chem Eng Res Des 92(11):2618–2625, 2014). In this study, neural network models (as black box models) were developed to predict both generated ozone concentration and electrical energy consumption. The models then were used for optimization. Altruistic non-dominated sorting genetic algorithm with jumping gene variant and termination criterion was used for MOO. Generational distance and spread were used in the termination criterion in order to stop algorithm after the right number of generations. Moreover, several optimal solutions from the Pareto-optimal set are chosen and then validated experimentally. [ABSTRACT FROM AUTHOR]

Abstract During two growing seasons of a maritime pine stand, in 2014 and 2015, ozone (O 3) fluxes have been determined using the eddy covariance (EC) method and compared to the outputs of a big-leaf O 3 deposition model including stomatal, cuticular and soil pathways. The model developed in this study generally allowed to properly reproduce the measured ozone deposition. Ozone fluxes showed a strong reduction during two water stressed periods in September 2014 and July 2015. The model partly explain this fall due to the reduction of stomatal deposition. Despite this stomatal closure, measured O 3 fluxes presented systematically lower negative values than the model outputs, and sometimes even positive values around midday during periods marked by strong water stress. In other words, the difference between observed and modelled O 3 fluxes (hereinafter referred to as the residual O 3 flux) is systematically positive on daytime during these water-stressed periods. This positive residual flux traduced the existence of an O 3 source below the flux measurement level, responsible for positive fluxes that counterbalance deposition fluxes. We developed an O 3 production module based on a terpene emission algorithm and an OH concentration proxy, to try to explain the observed ozone production. As this parametrisation allowed us to reproduce well the daily and inter-daily dynamics of the residual O 3 flux, it confirms that the latter actually resulted from O 3 production processes. This ozone production is here highlighted for the first time using O 3 fluxes measurements by the EC method. The chemical reactions possibly involved in O 3 production processes in this maritime pine forest have been discussed and different mechanisms are proposed, based on peroxy radicals chemistry or stress-induced BVOCs. Highlights • Ozone (O 3) fluxes have been measured and modelled over a maritime pine stand. • Two water-stressed periods provoked a strong reduction of O 3 deposition. • Comparison between modelled and measured O 3 fluxes highlighted an O 3 production during water-stressed periods. • O 3 production seems to be related to BVOCs photochemistry. [ABSTRACT FROM AUTHOR]

This study presented a quantitative evaluation of the performance of a low power miniaturized SDBD source for the production of ozone and nitrogen oxides as benchmarks of long-lived RONS. The effects of varying oxygen and humidity on the trend of the production efficiency are investigated. The oxygen content and the humidity had no noticeable effect on the total power consumed, but their level in the feeding gas has a strong impact on the production of NxOy. It is found also that there is an optimum level of the oxygen content and the humidity for the production of NO2 and N2O. The analysis of the results indicated that the nitrogen excited species, especially N2A3Σu+ and N(2D) play vital roles in the production of the nitrogen oxides, particularly the NO, which considered as the main source for the other NxOy in the present system. Interestingly, it is found that the humidity has a positive effect on the NO2 production, while it has a negative effect on the N2O and O3, which implied that the present SDBD is a strong oxidizer for the formed NO. The rise in the gas temperature in the present SDBD was negligible and has no effect on the production of nitrogen oxides, while the temperature of the plasma channel might affect the RONS production efficiency. Investigating the production mechanisms and the energy efficiency, of the formed nitrogen oxides, unravels for the first time the performance of the SDBD for nitrogen fixation. [ABSTRACT FROM AUTHOR]

Results from the Intergovernmental Panel on Climatic Change (IPCC) tropospheric photochemical model intercomparison (PhotoComp) are presented with a brief discussion of the factors that may contribute to differences in the modeled behaviors of HOx cycling and the accompanying O3 tendencies. PhotoComp was a tightly controlled model experiment in which the IPCC 1994 assessment sought to determine the consistency among models that are used to predict changes in tropospheric ozone, an important greenhouse gas. Calculated tropospheric photodissociation rates displayed significant differences, with a root-mean-square (rms) error of the reported model results ranging from about ±6–9% of the mean (for O3 and NO2) to up to ±15% (H2O2 and CH2O). Models using multistream methods in radiative transfer calculations showed distinctly higher rates for photodissociation of NO2 and CH2O compared to models using two-stream methods, and this difference accounted for up to one third of the rms error for these two rates. In general, some small but systematic differences between models were noted for the predicted chemical tendencies in cases that did not include reactions of nomnethane hydrocarbons (NMHC). These differences in modeled O3 tendencies in some cases could be identified, for example, as being due to differences in photodissociation rates, but in others they could not and must be ascribed to unidentified errors. O3tendencies showed rms errors of about ±10% in the moist, surface level cases with NOx concentrations equal to a few tens of parts per trillion by volume. Most of these model to model differences can be traced to differences in the destruction of O3 due to reaction with HO2. Differences in HO2, in turn, are likely due to (1) inconsistent reaction rates used by the models for the conversion of HO2 to H2O2 and (2) differences in the model-calculated photolysis of H2O2 and CH2O. In the middle tropospheric “polluted” scenario with NOx concentrations larger than a few parts per billion by volume, O3 tendencies showed rms errors of ±10–30%. These model to model differences most likely stem from differences in the calculated rates of O3 photolysis to O(1 D), which provides about 80% of the HOx source under these conditions. The introduction of hydrocarbons dramatically increased both the rate of NOx loss and its model to model differences, which, in turn, are reflected in an increased spread of predicted O3. Including NMHC in the simulation approximately doubled the rms error for O3concentration.

Volatile organic compounds (VOCs), ozone (O3), nitrogen oxides (NOx), carbon monoxide (CO), meteorological parameters, and total non-methane hydrocarbons (NMHC) were analyzed from simultaneous measurements at the MSU-IAP (Moscow State University—Institute of Atmospheric Physics) observational site in Moscow from 2011–2013. Seasonal and diurnal variability of the compounds was studied. The highest O3 concentration in Moscow was observed in the summer daytime periods in anticyclonic meteorological conditions under poor ventilation of the atmospheric boundary layer and high temperatures (up to 105 ppbv or 210 μg/m3). In contrast, NOx, CO, and benzene decreased from 8 a.m. to 5–6 p.m. local time (LT). The high positive correlation of daytime O3 with secondary VOCs affirmed an important role of photochemical O3 production in Moscow during the summers of 2011–2013. The summertime average concentrations of the biogenic VOCs isoprene and monoterpenes were observed to be 0.73 ppbv and 0.53 ppbv, respectively. The principal source of anthropogenic VOCs in Moscow was established to be local vehicle emissions. Yet, only about 5% of the observed isoprene was safely attributed to anthropogenic sources, suggesting significant contribution of biogenic sources into the total levels of ozone precursors. The non-linear O3–NOx dependence shows a decrease in ground-level O3 with an increase in NOx during the summers of 2011–2013, which is typical for the VOC-sensitive photochemical regime of O3 formation. Nevertheless, during the elevated ozone episodes in July 2011, the photochemical regime of ozone production was either transitional or NOx-sensitive. Contribution of various anthropogenic and biogenic VOCs into the measured ozone values was evaluated. The ozone-forming potential (OFP) of total VOCs was 31–67 μg/m3 on average and exceeded 100 μg/m3 in the top 10% of high ozone events, reaching 136 μg/m3. Acetaldehyde, 1.3-butadiene, and isoprene have the highest ozone production potential in Moscow compared to that of other measured VOCs.

Chlorine (Cl) radicals from photolabile chlorine species are highly reactive and can affect the fate of air pollutants in the atmosphere. Although several campaigns have been conducted, typically in coastal environments, long-term observations of reactive chlorine species and their impacts on atmospheric oxidation capacities (AOCs) are lacking. Here, we report nearly full-year observations of Cl 2 and ClNO 2 levels in Beijing and evaluate their impacts on the AOC with a box model coupled with Cl chemistry. Cl radicals promote the circulation of OH-HO 2 -RO 2 by accelerating the OH chain lengths by up to 12.6% on average, hence boosting the AOC, especially in the winter or spring. This promotion effect is nonlinearly dependent on the VOC and NO x concentrations, thus leading to a slight shift in ozone formation from a VOC-sensitive regime to a transition regime with seasonal differences. Given the ubiquitous reactive chlorines in polluted inland urban regions, the AOCs and the formation of secondary pollutants will be underestimated if the reactive chlorine species are neglected.

Particulate matter (PM), especially those with an aerodynamic particle size of less than 10 μm (PM 10 ), is typically emitted from transboundary forest fires. A large-scale forest fire may contribute to a haze condition known as a high particulate event (HPE), which has affected Southeast Asia, particularly Peninsular Malaysia, for a long time. Such event can alter the photochemical reactions of secondary pollutants. This work investigates the influence of PM on ground-level ozone (O 3 ) formation during HPE. Five continuous air quality monitoring stations from different site categories (i.e., industrial, urban and background) located across Peninsular Malaysia were selected in this study during the HPEs in 2013 and 2014. Result clearly indicated that O 3 concentrations were significantly higher during HPE than during non-HPE in all the sites. The O 3 diurnal variation in each site exhibited a similar pattern, whereas the magnitudes of variation during HPE and non-HPE differed. Light scattering and atmospheric attenuation were proven to be associated with HPE, which possibly affected O 3 photochemical reactions during HPE. Critical conversion time was used as the main determining factor when comparing HPE and non-HPE conditions. A possible screening effect that resulted in the shifting of the critical transformation point caused a delay of approximately of 15–30 min. The shifting was possibly influenced by the attenuation of sunlight in the morning during HPE. A negative correlation between O 3 and PM 10 was observed during the HPE in Klang in 2013 and 2014, with −0.87. Essentially, HPE with a high PM concentration altered ground-level O 3 formation. [ABSTRACT FROM AUTHOR]

Observations of ground-level ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), particulate matter (PM10) and meteorological parameter (temperature, relative humidity and wind speed) fluctuations during high particulate event (HPE) and non-HPE in Malaysia have been conducted for 2 years (2013 and 2014). The study focuses on urban areas, namely, Shah Alam, Petaling Jaya and Bandaraya Melaka. The diurnal variations of ground-level O3 concentration were higher during HPE than those during non-HPE in all urban areas. The concentration of O3 fluctuated more in 2014 than 2013 due to the higher incidences of HPE. Temperature and wind speed fluctuated with higher PM10, NO2 and NO concentrations during HPE than those during non-HPE in all urban sites. Relative humidity was lower during HPE than that during non-HPE. Positive correlations were found between PM10 and ozone during HPE for Shah Alam and Petaling Jaya with 0.81 and 0.79, respectively. Meanwhile, negative correlation (− 0.76) was recorded for Bandaraya Melaka. The non-HPE correlation of PM10 and O3 showed negative values for all locations except Petaling Jaya (0.02). Temperature and wind speed shows a strong positive correlation with ozone for all locations during HPE and non-HPE with the highest at Shah Alam (0.97). Inverse relationships were found between relative humidity and O3, in which the highest was for Shah Alam (− 0.96) in 2013 and Shah Alam (− 0.97) and Bandaraya Melaka (− 0.97) in 2014. The result of the ozone best-fit equation obtained an R2 of 0.6730. The study parameters had a significant positive relationship with the ozone predictions during HPE. [ABSTRACT FROM AUTHOR]

This paper describes the influence of gas pressure on the conversion of O2 to O3 and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O2 to O3 is continuously enhanced by the increase of gas pressure (0.1-0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0-0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2-0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD. [ABSTRACT FROM AUTHOR]