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Influence of electrode morphology on electrochemical properties of lead dioxide electrodes ( β-PbO) for oxygen-ozone evolution reactions in acid medium was investigated using scanning electronic microscopy (SEM), cyclic voltammetry (CV), polarization curves (PC), and determination of the current efficiency ( Φ). Experimental findings revealed that application of high electrodeposition current densities furnishes more rough β-PbO films. Surface characteristics were verified by SEM images and the analysis of interfacial pseudo-capacitances and morphology factor ( φ). Kinetic study of the overall electrode process (O + O) based on the analysis of the Tafel slope revealed that the electrode morphology and electrolyte composition considerably affect the electrode kinetics. In most cases, the existence of two Tafel slopes distributed in the low and high overpotential domains was observed. Abnormal Tafel slopes ( b ≠ 120 mV) obtained for the primary water discharge step during water electrolysis were interpreted considering the apparent charge transfer coefficient ( α). Optimum conditions for the ozone production were obtained for the less rough β-PbO electrode immersed in a sulfuric acid solution (1.0 mol dm) containing KPF (30 × 10 mol dm), where the current efficiency of 15 mass % for the ozone production was obtained. [ABSTRACT FROM AUTHOR]

Abstract: A radiative transfer model and photochemical box model are used to examine the effects of clouds and aerosols on actinic flux and photolysis rates, and the impacts of changes in photolysis rates on ozone production and destruction rates in a polluted urban environment like Houston, Texas. During the TexAQS-II Radical and Aerosol Measurement Project the combined cloud and aerosol effects reduced j(NO2) photolysis frequencies by nominally 17%, while aerosols reduced j(NO2) by 3% on six clear sky days. Reductions in actinic flux due to attenuation by clouds and aerosols correspond to reduced net ozone formation rates with a nearly one-to-one relationship. The overall reduction in the net ozone production rate due to reductions in photolysis rates by clouds and aerosols was approximately 8 ppbv h−1. [Copyright &y& Elsevier]

Atmospheric oxidation processes are important to convert freshly emitted trace gases to secondary pollutants. RO x radicals (including hydroxyl radical (OH), hydroperoxyl radical (HO 2), and organic peroxyl radical (RO 2)) dominate the atmospheric oxidation capacity. In this study, measurements of RO x chemistry precursors and products are presented in Shanghai, a megacity in eastern China during late autumn. During the campaign, two types of air masses are identified, one of which is warm air parcel characterized by relatively higher concentrations of particulate matters and ozone. An observational based chemical box model is utilized to simulate the radical chemistry. HONO is the most important radical source contributing more than one-third of the total radical primary source. However, alkene ozonolysis reactions not only serve as a non-photolytic source but also become relative important during polluted cases indicating the important role in polluted conditions. The maximum ClNO 2 was 0.4 ppbv (5min averaged) with a 1h diurnal averaged maximum of 0.16 ppbv and 0.06 ppbv for polluted and clean cases, respectively. The contribution of ClNO 2 photolysis to the total primary radical production is <1% on 24h averaged based. Though the campaign was conducted in late autumn when ClNO 2 was considered as a relatively important radical source compared to summer conditions, our results suggest the contribution of ClNO 2 may vary from case to case. The role of Cl radical and OH radical in secondary pollution formation is explored. Although the model predicts that the concentrations of Cl radicals are orders of magnitude smaller than that of OH radicals, further model analysis highlight that the ozone production per VOC oxidation is more efficient due to Cl radical initiated the reaction chain compared to OH radical. The ubiquitous presence of ClNO 2 with large spatial and temporal variability demonstrates that the contribution of ClNO 2 to photochemical processes should be further investigated with field observations in variable environments/seasons. • ClNO 2 was measured at an urban site in Shanghai China during late-autumn. • AOC increased during polluted episode, contributing to pollution formation. • ClNO 2 photolysis contributed <1% to total ROx radical primary production. • Cl oxidation was found to be highly efficient (>95%) in ozone production. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Field measurements performed in the Keihin coastal industrial area during summer 2019 were used to characterize the air quality and ozone production potential. The total hydroxyl radical (OH) reactivity was found to be moderate, peaking with a 2-h average of 29.0 s−1, corresponding to an OH lifetime of ∼34 ms. The average hourly total OH reactivity was 11.4 ± 5.2 s−1 (average ± standard deviation), and the measured OH sinks (from over 90 trace species) accounted for 92.3% of the total OH reactivity. Compared with a previous series of campaigns in urban/suburban Japan, this field work investigated an area often overlooked for atmospheric observations and found the smallest missing OH reactivity (on average, 0.88 s−1). The near-zero missing OH reactivity indicated that photochemical procedures were less important to the Yokohama air quality study (AQUAS–Yokohama) than the ubiquitous substantial secondary products in other areas. This study also demonstrated that oceanic air masses may quickly flush coastal industrial areas and that a limited activity of photochemistry due to elevated NO x effectively terminates OH radical recycling. A comparison with other campaigns in Japan exhibited a positive correlation with oxidants (ozone and formaldehyde), indicating secondary products have a critical role in explaining missing OH reactivity. The ozone production potential was corresponding to a volatile organic compound (VOC)-limited regime, while the missing OH reactivity led to an ∼8% increase in ozone formation. Finally, a positive correlation was found between the ozone production rate and the reactivity ratio between VOCs and NO x , in both the current study and various other field campaigns in urban areas. • Moderate total OH reactivity (11.4 s−1) was obtained in a coastal industrial area with 8% of missing OH reactivity. • Ozone formation was constrained because of the termination of HO x by copious NO x. • A comparison over campaigns in Japan identified a positive correlation between missing OH reactivity and oxidants. • Ozone production rate in the VOC-limited regime areas will be likely stimulated by the increase of k VOC /k NOx ratio. [ABSTRACT FROM AUTHOR]

A pulsed power generator with a nanosecond pulsewidth has been developed and applied to ozone production. Coaxial reactors connected in parallel are used in the experiment. The system ozone production yield, which is evaluated from the initial energy in the primary storage capacitors, is approximately 190 g/kW. h when dry oxygen is used as the ingredient gas. A four- parallel chamber reactor gives higher concentrations of ozone and higher yields in the experimental conditions. This reactor seems to be most suitable to obtain the proper streamer corona volume and also to match the impedance of the generator. The connection between the generator and the reactor also affects the efficiency. [ABSTRACT FROM AUTHOR]

ESCOMPTE programme aims at studying the emissions of primary pollutants in industrial and urban areas, their transport, diffusion and transformation in the atmosphere. This experiment, carried out in southeast France, can be used to validate and to improve meteorological and chemical mesoscale models. One major goal of this experiment was to follow the pollutant plumes, and to investigate its thermodynamic and physico-chemical time evolution. This was realized by means of constant volume balloons, located by global position satellite (GPS) and equipped with thermodynamic and ozone sensors, flying at constant density levels. During the two ESCOMPTE campaigns that took place in June and July 2000 and 2001, 40 balloons were launched, 17 of them equipped with ozone sensors during the day from 0800 to 1800 UTC. Balloons’ altitudes flight levels ranged between 400 and 1200m altitude with Mistral (northerly synoptic flow) and Sea Breeze (southerly breeze) conditions. The atmospheric boundary layer (ABL) topography of the experimental domain is complex and varies strongly from day to day. Its depth presents a large gradient from the sea coast to the north part of the ESCOMPTE domain, and also more complex variability within the domain. The balloons’ trajectories describe the evolution of the pollutant plume emitted from the industrial area of Fos-Berre or from the Marseille urban area. Constant volume balloons give a good description of the trajectories of these two plumes. The balloons, which fly at an isopicnic level, cross different atmospheric layers chiefly depending on the ABL height in relation with the constant volume balloons flight level. Thus, each balloon flight is decomposed into different segments that correspond to the same atmospheric layer. In each segment, the ozone content variation is analyzed in relation to other thermodynamical parameters measured by the balloon and mainly to the vapor mixing ratio content. During ESCOMPTE campaign, the mean linear rate of chemical net ozone production at the top of the atmospheric boundary layer was found to be around 6ppbh−1. [Copyright &y& Elsevier]

An observation-based method (OBM) is developed to evaluate the ozone (O3) production efficiency (O3 molecules produced per NO x molecule consumed) and O3 production rate (P(O3)) during a field campaign in southern Taiwan. The method can also provide an estimate of the concentration of OH. A key step in the method is to use observed concentrations of two aromatic hydrocarbons, namely ethylbenzene and m,p-xylene, to estimate the degree of photochemical processing and amounts of photochemically consumed NO x and NMHCs by OH. In addition, total oxidant (O3+NO2) instead of O3 itself turns out to be very useful for representing ozone production in the OBM approach. The average O3 production efficiency during the field campaign in Fall (2003) is found to be about 10.2±3.9. The relationship of P(O3) with NO x is examined and compared with a one-dimensional (1D) photochemical model. Values of P(O3) derived from the OBM are slightly lower than those calculated in the 1D model. However, OH concentrations estimated by the OBM are about a factor of 2 lower than the 1D model. Fresh emissions, which affect the degree of photochemical processing appear to be a major cause of the underestimate. We have developed a three-dimensional (3D) OBM O3 production diagram that resembles the EKMA ozone isopleth diagram to study the relationship of the total oxidant versus O3 precursors. The 3D OBM O3 production diagram suggests that reducing emissions of NMHCs are more effective in controlling O3 than reducing NO x . However, significant uncertainties remain in the OBM, and considerable more work is required to minimize these uncertainties before a definitive control strategy can be reached. The observation-based approach provides a good alternative to measuring peroxy radicals for evaluating the production of O3 and formulating O3 control strategy in urban and suburban environments. [Copyright &y& Elsevier]

An ozone-generative electrostatic spore precipitator was developed to protect nursery-stage seedlings of tomato from both airborne conidia of powdery mildew ( Oidium neolycopersici) and root-infecting pathogen propagules of bacterial wilt ( Ralstonia solanacearum) and fusarium crown and root rot ( Fusarium oxysporum f.sp. radicis-lycopersici). The device was a cylindrical electrostatic spore precipitator (S2 cylinder) in which a positively charged straight conductor wire insulated with a transparent acrylic cylinder originated from a spore-precipitation cylinder (S1 cylinder) designed to physically control airborne conidia of tomato powdery mildew in greenhouses. The S2 cylinder consisted of two sites for conidial attraction and ozone production. The site for ozone production was located at the end of the cylinder, where an earthed copper conductor ring (as a cathode) was attached to the edge of the cylinder, responding to the anodal tip of a positively charged central conductor wire. Distinct types of discharge (corona, corona-streamer, streamer and arc discharge) occurred between the two electrodes and were dependant on the voltages applied to the wire and the distances between the electrodes. The highest ozone production was observed through streamer discharge. The remaining portion of the S2 cylinder, which was dielectrically polarized by a positively charged wire, created a non-uniform electric field outside the cylinder to attract conidia that came into the generated field. Hydroponic culture troughs to raise tomato seedlings in a nursery greenhouse were paralleled with S2 cylinders. The aim was to control rhizosphere pathogens R. solanacearum and F. oxysporum f.sp. radicis-lycopersici and to prevent them entering the hydroponic system during cultivation, while at the same time trapping O. neolycopersici conidia in the spaces between the cylinders. The results indicated that susceptible tomato plants in culture troughs attached to the S2 cylinders remained uninfected by both rhizosphere and aerial pathogens throughout the experimental period (2 and 3 weeks, respectively). This suggests that the present system will enable the dual control of both these pathogens in hydroponic systems in greenhouses. [ABSTRACT FROM AUTHOR]

Abstract: The effect of three factors on the ozone production was studied in this paper: air pressure, air flow and power. It was shown that for a given air flow, the concentration of produced ozone can be increased or decreased by increasing or decreasing the absorbed power; for a given power level, the concentration varies approximately inversely to air flow and for a given air flow and power level, the concentration of ozone varies inversely to air pressure. [Copyright &y& Elsevier]

In Europe, in case of the observation or the forecast of a photochemical event, punctual and local reductions in anthropogenic emissions can be triggered at the regional scale. Although the necessity for the establishment of such measures appears to be justified by bad air quality records over large European cities, individual short-term action plans (STAPs) have been blindly elaborated by regional authorities. Moreover, as they impose industrial and road traffic emission restrictions, these measures have an elevated economical cost. It is consequently crucial to determine their efficiency and potential for ozone peak reduction. The study presented in this paper aims to draw up an expertise on standard European STAPs, through the example of a French Mediterranean city. The objective is to determine and investigate the impact of current STAPs on ozone peak formation and to test ways to optimise their efficiency. In this frame, a set of emission scenarios has been elaborated and tested with the chemistry-transport model CHIMERE on the Berre–Marseille area. Simulations have shown that the tested action plans are not sufficient to eradicate severe ozone peaks and that more drastic restrictions on emissions are required to significantly affect ozone plumes. However, results also showed that the potential for ozone reduction remains small, with a maximum impact of only 5 ppbv for feasible STAPs. Finally, a temporal analysis of the ozone-emission relationship was engaged in order to optimise their application. [ABSTRACT FROM AUTHOR]

Abstract: Ozone has many industrial uses, including treatment of municipal water, wastewater, cooling towers, industrial process water, effluent water treatment, food processing, through to water fit for consumption and marine life. In this paper, we study the ozone production by negative electric corona discharge, witch involves passing the feed of gas, air rich, through an electrical discharge. This is done by applying a high voltage between two electrodes separated. The electrical charge between two surfaces creates a sequence of dissociation and subsequent collisions of oxygen with electrons creating ozone. So to describe this phenomenon we use (1D) numerical model for the charged particles. The electron number density and electric field are determined from solution of the one-dimensional coupled continuity equations of charge carriers and Poisson’s equation. Simulation result show the variation of the electrical field, charged particles density, and ozone (O3) particle density. [Copyright &y& Elsevier]

Abstract: Electrolysis of water by use of a simple solid polymer electrolyte sandwich with diamond anode, Nafion® polymer electrolyte and diamond cathode leads to efficient ozone production. The dependence of ozone production rate on current density, water flow rate and water conductivity have been investigated. Ozone production is favoured by high flow rate and low conductivity of the electrolysed water. [Copyright &y& Elsevier]

Abstract: Satellite data (MODIS, GOME, and MOPITT) together with a chemical transport global model of the atmosphere (MOZART-2) are used to characterize air pollution in Eastern China and the Eastern US to assess the differences between the photochemical conditions in these two regions. Observations show that aerosol concentrations (both fine (radius<0.5μm) and coarse modes (radius>0.5μm)) are higher in Eastern China than in the Eastern US. The NO x concentrations in both regions are substantially higher than in remote regions such as over the oceans (150 compared to 5 (1014 #cm−2) over the Pacific Ocean). The CO concentrations are high in both urbanized areas (30 compared to 10 (1017 #cm−2) over the Pacific Ocean). However, the concentrations of non-methane hydrocarbons from both anthropogenic and biogenic sources are considerably lower in Eastern China than in the Eastern US. As a result, the rate of photochemical ozone production and ozone concentrations during summer is significantly lower in Eastern China (daily averaged concentrations of 40–50ppbv in summer) than in the Eastern US (daily averaged values of 60–70ppbv). The analysis also shows that in Eastern China, the O3 production is mainly due to the oxidation of carbon monoxide (54% of total O3 production), while, in the Eastern US, the O3 production is attributed primarily to the oxidation of reactive hydrocarbons (68% of total O3 production). The results also indicate that biogenic emissions of hydrocarbons contribute substantially to the production of O3 in the Eastern US. The O3 production due to the oxidation of biogenic hydrocarbons represents approximately one third of total O3 photochemical production in this region. Measurements of surface ozone in the Eastern US and Eastern China seem to support that the summer ozone production is lower in Eastern China than in the Eastern US. However, additional surface measurements, especially of reactive hydrocarbons and ozone are needed in Eastern China in order to improve the present analysis and to confirm our current conclusions. A sensitivity study shows that with increase in anthropogenic emissions of HCs, the surface ozone concentrations significantly increase in Eastern China, indicating that the increase in the emissions of HCs plays an important role for the enhancement in surface ozone in this region. [Copyright &y& Elsevier]

Atmospheric hydroxyl (OH), hydroperoxy (HO2), total peroxy (HO2 and organic peroxy radicals, RO2) mixing ratios and OH reactivity (first order OH loss rate) were measured at a rural site in central Pennsylvania during May and June 2002. OH and HO2 mixing ratios were measured with laser induced fluorescence (LIF); HO2 + RO2 mixing ratios were measured with chemical ionization mass spectrometry (CIMS). The daytime maximum mixing ratios were up to 0.6 parts per trillion by volume (pptv) for OH, 30 pptv for HO2, and 45 pptv for HO2 + RO2. A parameterized RACM (Regional Atmospheric Chemistry Mechanism) box model was used to predict steady state OH, HO2 and HO2 + RO2 concentrations by constraining the model to the measured OH reactivity and previously measured volatile organic compound (VOC) distributions. The averaged model calculations are generally in good agreement with the observations. For OH, the model matched the observations for day and night, with an average observed-to-modeled ratio of 0.80. In previous studies such as PROPHET98, nighttime NO was near 0 pptv and observed nighttime OH was significantly larger than modeled OH. In this study, nighttime observed and modeled OH agree to within measurement and model uncertainties because the main source of the nighttime OH was the reaction HO2 + NO → OH + NO2, with the NO being continually emitted from the surrounding fertilized corn field. The observed-to-modeled ratio for HO2 is 1.0 on average, although daytime HO2 is underpredicted by a factor of 1.2 and nighttime HO2 is over-predicted by a factor of ∼2. The average measured and modeled HO2 + RO2 agree well during daytime, but the modeled value is about twice the measured value during nighttime. While measured HO2 + RO2 values agree with modeled values for NO mixing ratios less than a few parts per billion by volume (ppbv), it increases substantially above the expected value for NO greater than a few ppbv. This observation of the higher-than-expected HO2 + RO2 with the CIMS technique confirms the observed increase of HO2 above expected values at higher NO mixing ratios in HO2 measurements with the LIF technique. The maximum instantaneous O3 production rate calculated from HO2 and RO2 reactions with NO was as high as 10–15 ppb h−1 at midday; the total daily O3 production varied from 13 to 113 ppbv d−1 and was 48 ppbv d−1 on average during this campaign. [ABSTRACT FROM AUTHOR]

Abstract: The development of environmental policies to reduce the ozone levels around large agglomerations requires a good understanding of the development of ozone episodes. In particular, it is necessary to know the location and photochemical activity of the plume where ozone is formed. Measurement campaigns make it possible not only to characterize the concentration fields of ozone and its precursors but also to identify the zones of strong ozone production, by means of specific measurements and kinetic calculations. The combination of the observation-based data with numerical simulations allows to better characterize photochemical pollution. This paper presents a study carried out within the ESCOMPTE program and based on the determination of ozone production rates by experimental and numerical methods: ground measurements of peroxy radicals, NO x at a rural site, airborne measurements of NO X and O3, Eulerian modeling. The reported case is of particular interest since it corresponds to an episode with very different photochemical situations. The diurnal variations of the peroxy radical concentration are analyzed in relation to those of ozone and its precursors. Ozone production rates—P(O3)–are studied over one particular day. The results show particularly high concentrations of RO2+HO2 at ground level (up to 200 pptv) under the influence of the urban and industrial plume, but also highlight very high production rates of ozone (60 to 80 ppbv h−1) a few tens of kilometers from the sources. The results show satisfactory agreement between the various approaches. Modeling provides a four-dimensional (4D) description of the plumes, in particular the relation between the ozone precursor concentrations and P(O3) on the ground. [Copyright &y& Elsevier]

Abstract: High ozone concentrations are observed more and more frequently in the lower troposphere. The development of such polluted episodes is linked to a complex set of chemical, physical and dynamical parameters that interact with each other. To improve air quality, it is necessary to understand and quantify the role of all these processes on the intensity of ozone formation. The ESCOMPTE program, especially dedicated to the numerical simulation of photochemical episodes, offers an ideal frame to investigate details of the roles of many of these processes through 3D modeling. This paper presents the analysis, with a 3D eulerian model, of a severe and local episode of ozone pollution that occurred on the 21st of March 2001 in the ESCOMPTE region. This episode is particularly interesting due to the intensity of the observed ozone peaks (450 μg/m3 during 15 mn) but also because it did not occur in summer but at the beginning of spring. As part of the premodeling work of the ESCOMPTE program, this study focuses on the sensitivity of the simulated ozone peaks to various chemical and physical phenomena (long-range transport, industrial emissions, local dynamic phenomena…) to determine their influence on the rise of high local photooxidant concentrations and to better picture the photochemistry of the ESCOMPTE region. Through sensitivity tests to dynamical calculation resolution and emissions, this paper shows how the combination of sea and pond breezes with emissions of reactive VOCs can generate local intense ozone peaks. [Copyright &y& Elsevier]

An experimental study on the formation and transport of ozone in ambient air was performed in Tenerife (Canary Islands) in order to investigate the processes affecting ozone levels and air quality. The special features of Tenerife (prevalence of the trade wind pattern (NE), orography and the specific location of the local ozone sources) permit to quantify the role of the `long-range transport from northern latitudes'' versus the `formation and transport of ozone downwind of the main urban areas'' of Tenerife. Levels of O3, NO2 and OX were monitored in different types of environments to achieve this purpose. The results showed that: (1) upwind of the urban areas ozone is mainly transported from the ocean by trade winds, (2) local ozone titration (by NO) and ozone replenishment from the ocean are the main causes of ozone variations in urban and suburban areas, and (3) photochemical ozone production occurs downwind of the urban areas. Photochemical production causes daylight O3 and OX levels downwind of urban areas to be frequently (60% and 35% days/year, respectively) higher than upwind of the urban sites (O3 and OX excess frequently in the range 5–20 ppbv). Due to the above processes, different daily ozone cycles occur in short distances (<30 km), with maximum O3 levels during daylight or night depending on the site. Ozone phytotoxicity was assessed by calculating the AOT40 index upwind and downwind of the main urban areas. The critical value for the 5-day-AOT40 index was simultaneously exceeded at the two sites (few times/year) during long-range transport events. During the additional exceedances of the critical value downwind of the urban area, relatively high 5-day-AOT40 values were recorded upwind of the urban site. Thus, long-range transport from northern latitudes may produce relatively high 5-days-AOT40 levels in the oceanic boundary layer. These results are important for the protection of the large number of endemic plants in the Canaries. The conceptual model discussed in this study may be qualitatively applied to other islands which possess features similar to those of Tenerife. [Copyright &y& Elsevier]

Observed hydroxyl (OH) and hydroperoxy (HO2) radicals, collectively called HOx, were compared with OH and HO2 calculated by a box model that used the regional atmospheric chemistry mechanism and was constrained to the ancillary measurements during the PM2.5 Technology Assessment and Characterization Study-New York (PMTACS-NY) summer 2001 intensive in New York City. The measurements are described in the companion paper, Ren et al. (HOx concentrations and OH reactivity observations in New York City during PMTACS-NY2001, Atmospheric Environment, this issue). This comparison enables an investigation of HOx chemistry in this polluted urban atmosphere. For HO2, the observed concentrations and diurnal variation were usually well reproduced by the model calculations, with an observed-to-modeled ratio of 1.24, on average, for day and night. For OH, the model was generally able to match the measured concentrations during daytime with an observed-to-modeled ratio of about 1.10, but the calculations significantly underestimated OH during nighttime. The budgets of HOx show that its production was dominated by the photolysis of HONO, accounting for ∼56% of HOx production on average, during daytime due to relatively high HONO concentrations, while nighttime HOx production was mainly from the O3 reactions with alkenes. The OH reactivity measurements agree with the calculations to within 10% for both the composite diurnal variation and individual days. Calculations indicate that the reactions of OH with NO2, hydrocarbons, CO, NO, and carbonyls accounted for about 32%, 25%, 12%, 10% and 7% of total OH loss, respectively, in this urban area. Modeled instantaneous O3 production from HO2 and RO2 reactions with NO was 150±100 ppbv day−1. O3 production rates from measured HO2(P(O3)obsHO2) was greater than modeled HO2(P(O3)calcHO2) at higher values of NO. Average daily cumulative P(O3)obsHO2 was ∼140 ppbv day−1, a factor of 1.5, greater than average daily P(O3)calcHO2. [Copyright &y& Elsevier]

• CabECO® cells can be successfully used as electro-ozonizers. • Need for high availability of oxygen to reach high efficiencies. • Need for temperature regulation to improve efficiency. • Very important role of ozone scavengers reflected on a decay in ozone concentration. This work intends to go a step further in the application of electrochemical technology to produce ozone, by evaluating the production of ozone with a commercial cell registered as CabECO®, which has been previously used to disinfect heavily polluted water in a successful manner, with a view to ascertaining whether this success may be related to the production of ozone. The CabECO® cell is a PEM electrolyzer; that is to say, one in which anode and cathode are connected through a PEM membrane. Since ozone production on the electrolyte is important and depends on the composition of the liquid, attention must be paid to the electrochemical production of scavengers. Dosing of oxygen as microbubbles has a very positive effect on the production of ozone, while temperature regulation is as well considerably important, as the increase in temperature generated by ohmic losses can lead to important decreases in the efficiency of ozone electrogeneration. Rates within the range 0.06–0.60 mg O 3 min−1 are observed; this means that the maximum current efficiency reached is as high as 6.11% (considering oxygen as raw matter). These results are extremely promising as compared with other references in the literature, at once they also indicate there is room for further improvements and a long way to prevent the effect of scavengers and increase the efficiency of the process. [Display omitted] [ABSTRACT FROM AUTHOR]

San Antonio, the second-most populous city in Texas and the seventh-most populous city in the United States (US), has been designated a marginal non-attainment area by the US Environmental Protection Agency with respect to the 2015 ozone (O 3) National Ambient Air Quality Standard. While stationary air quality monitoring sites are operated in the region by the Texas Commission on Environmental Quality (TCEQ), there are limited in situ field measurements for O 3 and its precursors in the urban core. To better understand O 3 dynamics in San Antonio, a suite of meteorological and gas instruments was deployed during May 2017. We incorporate field measurements from two campaign sites and one TCEQ stationary monitoring site into a zero-dimensional O 3 model to characterize the local formation and destruction rates of O 3 , hydroxyl radical (OH) reactivity of volatile organic compounds (VOCs), O 3 production efficiency, and O 3 formation regime in the urban core and directly downwind of San Antonio. Upwind/downwind differences indicate the importance of photochemical processing of VOCs with carbon-carbon double bonds. San Antonio was mostly in a nitrogen oxide (NO X)-sensitive regime throughout the daytime during the campaign period, with O 3 formation peaking at noon in the city center and early afternoon at the downwind region. Formaldehyde (HCHO), isoprene, and alkenes dominated VOC reactivity, with alkenes and isoprene from San Antonio's core (upwind) likely contributing to the downwind formation of HCHO and enhancing its OH reactivity. However, their direct impact on downwind O 3 production was not observed. Model results suggest further strengthening NO X emission controls to decrease O 3 formation in San Antonio. • Meteorological and gas instruments were deployed in San Antonio during May 2017. • Photochemical processing of VOCs with carbon-carbon double bonds is important. • San Antonio was mostly in a nitrogen oxide (NO X)-sensitive regime. • Upwind alkenes and isoprene contribute to the downwind formation of HCHO. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to assess the possibility of using different kinds of electrical discharges operating in dry air under normal conditions as ozone generators. The ozone production and NOx destruction efficiency are investigated as a function of discharge parameters such as the reduced electric field, the energy deposition, and the electron density. The specific energy deposition becomes a key parameter to compare the different classes of ozonators. During the operative phase the electric discharge produces an appreciable amount of nitrogen oxides. Taking into consideration both the active phase of flue gas processing and the post-discharge phase it is possible to achieve a good NOx-removal efficiency even for initial concentrations as high as 1000 ppm. The main processes and characteristic times are discussed. [ABSTRACT FROM AUTHOR]

Simultaneous observations for the total column densities of NO , O and HO were carried on using the portable Spectrometer (438-450 nm and 400-450 nm) and the visible Spectrometer (544.4-628 nm) during premonsoon thunderstorms and embedded hail storm activity at Pune (18°32'N & 73°51'E), India. These observations confirm the fact that there is an increase in O and NO column densities during thunderstorms. The increase in O was observed following onset of thunderstorm, while the increase in NO was observed only after the thunder flashes occur. This implies that the production mechanisms for O and NO in thunderstorm are different. The observed column density of NO value (1 to 3 × 10molecules · cm) during thunderstorm activity is 10 to 30 times higher than the value (1 × 10molecules · cm) of a normal day total column density. The spectrometric observations and observations of thunder flashes by electric field meter showed that 6.4 × 10molecules / flash of NO are produced. The increased total column density of ozone during thunderstorm period is 1.2 times higher than normal (clear) day ozone concentration. The multiple scattering in the clouds is estimated from HO and O absorption bands in the visible spectral region. Considering this effect the calculated amount of ozone added in the global atmosphere due to thunderstorm activity is 0.26 to 0.52 DU, and the annual production of ozone due to thunderstorm activity is of the order of 4.02 × 10 molecules / year. The annual NO production may be of the order of 2.02 × 10molecules / year. [ABSTRACT FROM AUTHOR]

A continuous measurement of ambient volatile organic compounds (VOCs) was carried out from May to June 2018 at a background site, the Wudang Mountain (Mt. Wudang) in Central China. The characteristics, sources of VOCs and their contributions to ozone formation were investigated for the first time in this area. Based on the National Ambient Air Quality Standard, 29 O 3 non-attainment days were identified. The average mixing ratio of 82 total VOCs (∑VOCs) was 12.17 ± 3.66 ppb. Higher mixing ratios of individual species were found compared with those measured at global baseline sites. The results revealed that the dominant VOCs components were alkanes and OVOCs, accounting for 79.92%. Five sources, i.e. industrial processes, fuel evaporation, vehicular exhaust, solvent utilization and biogenic emission were identified by the positive matrix factorization (PMF) model. From potential source contribution function (PSCF) analysis, local area and the adjacent provinces especially Shaanxi province, had some extent influence on Mt. Wudang. The OH radical loss rate (L OH) and ozone formation potential (OFP) calculations revealed that biogenic emission and vehicular exhaust were both the major sources for ozone formation. Through the Observation-Based Model (OBM) simulation, the daytime average net ozone production rate was 4.1 ppb/h and the ozone production pathway was dominated by the reaction of HO 2 + NO. This study shows that local emission and long-range transport of air pollutants should be taken into account for developing the science-based air pollution control strategies at Mt. Wudang. Unlabelled Image • First study on the characteristics and sources of VOCs, and the contributions to ozone formation at Mt. Wudang. • The mixing ratios of ozone depleting substances at Mt. Wudang were much lower than the mean global baseline values. • Vehicular exhaust and biogenic emission were the dominant sources for the photochemical ozone formation at Mt. Wudang. • The daytime net photochemical ozone production rate was 4.1 ppb/h and the main production pathway was HO 2 + NO reaction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The introduction of aggressive emission control policies propelled three decades ago has led to significant reductions of ozone (O 3) levels in the Mexico City Metropolitan Area (MCMA). However, in recent years the levels have stalled, and there is evidence that the production of secondary pollutants may have started to rebound. Similar responses to changes in O 3 precursors observed in other urban areas suggest major changes in atmospheric reactivity and O 3 production P(O 3), prompting the introduction of new emission control policies. In this study, we evaluate the changes in VOC-OH reactivity and P(O 3) using data of O 3 , volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxides (NO x) collected from the 1990s to 2019 by the local air quality monitoring network and during two dedicated 6-week field measurement campaigns in the MCMA. The results show a reduction of VOC-OH reactivity from 38 s−1 in 2003–2006 to about 19 s−1 in 2018 within the urban core, a slight increase from around 8 s−1 to 9 s−1 for the northern peripheral urban sites in the same period, and a small decrease from about 18 s−1 to 15 s−1 during 2014–2016 in the south of the city. Alkanes are still key contributors to VOC-OH reactivity, whereas the contribution from aromatic and alkene species has decreased, in agreement with reductions of VOC emissions from mobile sources. Changes in P(O 3) suggest that increases in the relative contributions from highly oxygenated volatile chemical products from solvents consumption, personal care and other products are responsible for sustained high O 3 levels in recent years. We also found that there is a marked spatial dependency of P(O 3) in the northern, central, and southern areas of the city, suggesting spatially different VOC and NO x sensitivity regimes. Finally, significant increases in NO 2 /NO ratios suggest changes in the pathways for the nighttime accumulation of HO x radicals and NO y species that could impact the morning photochemistry and radical budgets for secondary aerosol formation. These results strongly suggest a need for new measurements of radical budgets in the MCMA, the expansion of a continuous measurement network of VOCs with the addition of oxygenated species, and the use of these data to support comprehensive modeling studies for the design of effective emission control strategies. Image 1 • Changes in atmospheric reactivity and P(O 3) suggest a need for new emission controls. • Observed decreases in early morning VOC-OH reactivity with sustained high O 3 levels. • NO 2 /NO increases suggest changes in radical budgets for secondary aerosol formation. • Marked spatial P(O 3) dependency suggests spatially different O 3 sensitivity regimes. • Emerging sources of VOCs relevant for P(O 3) should be part of air quality management. [ABSTRACT FROM AUTHOR]

The weekly cycle and weekend effect in the O 3 , NO, NO 2 , CO, CH 4 , SO 2 , NMHC, and PM 10 concentrations were investigated in the Moscow megacity using in-situ measurements from January 1, 2005 to December 31, 2014 at 49 stations of the Moscow Environment Monitoring network. Daily variations in the CO, NO x , NMHC, and PM 10 concentrations depend mainly on motor transport emissions and the atmospheric boundary layer vertical stratification. The characteristic feature of Moscow is the time coincidence of rush hours and surface temperature inversion during the cold season, which results in pollutant accumulation in the atmospheric surface layer. It was found that the surface concentrations of the pollutants (except ozone and methane) decrease on weekends. Weekday (Tuesday–Friday)-Sunday differences in the daytime (08:00–22:00 LT) NO, NO 2 , CO, SO 2 , NMHC, and PM 10 concentrations relative to those of weekday period averaged for all stations over 2005–2014 amounted to 23.9 ± 5.8, 16.7 ± 2.8, 13.6 ± 3.3, 7.6 ± 6.5, 6.3 ± 2.2, and 14.5 ± 5.1%, respectively. The ozone concentration increased on Sunday by 16.5 ± 4.8%. The methane concentration on weekends was the same as on weekdays. The weekend effects in all pollutant concentrations were weakened within the greenbelt around Moscow. In different sectors of Moscow the pollutant weekend effects except that in SO 2 were approximately the same. The vertical structure of the NO, NO 2 , and CO weekend effects was analyzed based on data obtained from measurements at the TV tower 500 m in height. These weekend effects decreased nonlinearly with height. Estimates obtained for basic criteria of activity of photochemical processes determining the formation of the weekly cycle and weekend effect of ozone (NMHC/NO x ratio, fraction of radical loss via NO x chemistry, concentration of O x) show that the VOC-limited chemistry is characteristic of Moscow. • Daily and weekly cycles in O 3 , CO, CH 4 , NO, NO 2 , SO 2 , NMHC, and PM 10 were analyzed. • Measurements at 49 sites in 2005–2014 were used for species weekend effect studies. • Weekend effect in pollutants depends on PBL stratification, city sectors and height. • The VOC-limited chemistry of O 3 formation is characteristic of Moscow atmosphere. [ABSTRACT FROM AUTHOR]

The COVID-19 lockdown presented a peculiar opportunity to study a shift in the photochemical regime of ozone production in Quito (Ecuador) before and after mobility restrictions. Primary precursors such as NO and CO dropped dramatically as early as 13 March 2020, due to school closures, but ambient ozone did not change. In this work we use a chemical box model in order to estimate regimes of ozone production before and after the lockdown. We constrain the model with observations in Quito (ozone, NO x , CO, and meteorology) and with estimations of traffic-associated VOCs that are tightly linked to CO. To this end, we use the closest observational data of VOC/CO ratios at an urban area that shares with Quito conditions of high altitude and is located in the tropics, namely Mexico City. A shift in the chemical regime after mobility restrictions was evaluated in light of the magnitude of radical losses to nitric acid and to hydrogen peroxide. With reduced NO x in the morning rush hour (lockdown conditions), ozone production rates at 08:30-10:30 increased from 4.2-17 to 9.7-23 ppbv h -1 , respectively. To test further the observed shift in chemical regime, ozone production was recalculated with post-lockdown NO x levels, but setting VOCs to pre-lockdown conditions. This change tripled ozone production rates in the mid-morning and stayed higher throughout the day. In light of these findings, practical scenarios that present the potential for ozone accumulation in the ambient air are discussed., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2020 Turkish National Committee for Air Pollution Research and Control. Production and hosting by Elsevier B.V.)

Despite the central role of reactive organic carbon (ROC) in the formation of secondary species that impact global air quality and climate, our assessment of ROC abundance and impacts is challenged by the diversity of species that contribute to it. We revisit measurements of ROC species made during two field campaigns in the United States: the 2013 SOAS campaign in forested Centreville, AL, and the 2010 CalNex campaign in urban Pasadena, CA. We find that average measured ROC concentrations are about twice as high in Pasadena (73.8 μgCsm -3 ) than in Centreville (36.5 μgCsm -3 ). However, the OH reactivity (OHR) measured at these sites is similar (20.1 and 19.3 s -1 ). The shortfall in OHR when summing up measured contributions is 31%, at Pasadena and 14% at Centreville, suggesting that there may be a larger reservoir of unmeasured ROC at the former site. Estimated O 3 production and SOA potential (defined as concentration × yield) are both higher during CalNex than SOAS. This analysis suggests that the ROC in urban California is less reactive, but due to higher concentrations of oxides of nitrogen and hydroxyl radicals, is more efficient in terms of O 3 and SOA production, than in the forested southeastern U.S.

Increasing carbon monoxide and ozone concentrations have been observed in the lower troposphere of the Brazilian Amazon region in recent years (1989-1995). Carbon monoxide and ozone have been measured in the region continuously; from observations at a single site and many sporadic field missions, there is a clear indication that the chemical activity in the troposphere is growing, with increasing concentrations especially during the dry season. On the other hand, the most recent deforestation assessment by the Brazilian Government, performed by the Instituto Nacional de Pesquisas Espaciais (INPE) using Landsat data, shows yearly rates rising from the 11,130 km year minimum of the 1990/91 survey, to 13,786 km year for the 1991/92 period, and 14,896 km year for the period 1992/94. It is argued that the increase in deforestation/biomass burning activities in 'Amazonia' have produced larger carbon monoxide and ozone concentrations in the lower atmosphere. [ABSTRACT FROM AUTHOR]

The sensitivity of ozone production to increasing temperature and a decreasing concentration of precursors, namely nitrogen oxides and non-methane hydrocarbon, has been estimated with probability theory using observation data for 2004–2015 for the Kanto region, Japan. The sensitivity of ozone, in terms of the number of high ozone concentration days, to temperature was higher at the beginning of the observation period when precursor concentrations were high but lower in more recent years when the precursor concentrations were lower. Analysis of the high ozone concentration days showed that a 10-percent reduction of both precursor concentrations yields a reduction in the number of high concentration ozone days of approximately 4 days per year, whereas a 0.2 °C temperature increase leads to less than a 1-day increase per year. This indicates that precursor concentration is more important than temperature for determining ozone concentration. • Impact of temperature rise and precursor reductions on ozone production is studied. • Simple probability theory is applied to observation data in our analysis. • Impact of temperature on ozone production depends on precursor concentrations. • Precursor concentrations are more important than temperature for ozone production. [ABSTRACT FROM AUTHOR]