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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]

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]

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]

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]

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 TiO 2 , ZnO, and BaTiO 3 catalysts increase the concentration of ozone generated by the discharge. On the other hand, the presence of WO 3 in the discharge does not affect the ozone concentration. All these catalysts show no substantial effect on the electrical parameters of the discharge. [Display omitted] • TiO 2 , ZnO, and BaTiO 3 catalysts increase O 3 concentration generated by the discharge. • These catalysts show no substantial effects on discharge electrical parameters. • WO 3 does not affect the concentration of generated ozone. • For the highest power and these catalysts, only a small difference in O 3 is indicated. [ABSTRACT FROM AUTHOR]

In the current study, kinetics of hydrogen formation from water vapour plasmolysis and ozone formation from air plasma are analysed. The hypothesis of this paper is that operating a plasma microreactor with residence time in the reactor approximately that of the timescale predicted by chemical kinetics simulation for the formation of hydrogen leads to a low power consumption mode of operation. However, this objective is difficult to assess with hydrogen formation from plasmolysis, as hydrogen concentration is difficult to monitor continuously as discussed in previous work and summarised here in section one as well. Ozone, however, is shown to have similar chemical kinetics and is readily analysed continuously, so is used as a proxy for the hydrogen hypothesis. Ozone was generated from air plasma using a Dielectric barrier discharge (DBD)-Corona hybrid discharge reactor. It was experimentally verified that time scale to achieve highest concentration of ozone is of the order of 10 −2 s at 0.8 L min −1 , 4.8 kV, 37 kHz, 3 cm electrode length and atmospheric pressure, in agreement with Lozano-Parada and Zimmerman [1] . This is the time scale to produce 99% of ozone. In previous work [2] , using kinetic modelling it was proposed a similar time scale to produce 99% hydrogen from water vapour plasmolysis under well mixed, batch reactors and hence supporting the claim made by Zimmerman and Lozano Parada [3] . Pressure and flow rate of the air, electrode material, length of external electrode and its configuration, applied power and frequency have been varied in this study, the results of which confirm the low power consumption mode is achieved by matching the residence time to the kinetics timescale. [ABSTRACT FROM AUTHOR]

Mitigating ozone pollution involves reducing ozone production and relies on complex air-quality models to design reduction strategies and determine their effectiveness. However, modeled ozone does not always agree with observations. A complementary approach is to measure the ozone production rate directly, leading to the development of the Measurement of Ozone Production Sensor (MOPS). Two improved second-generation MOPSv2s were deployed for NASA's DISCOVER-AQ field campaign in September 2013 at the University of Houston, 5 km south of downtown, and Smith Point, at the mouth of the Houston Ship Channel. Median September P(O 3 ) was low, consistent with the observed ambient ozone. The MOPSv2s provided statistically similar results when they were compared for 8 day sat the University of Houston. October measurements yielded a median ozone production rate of 27 ± 11 ppbv hr −1 , falling within the range of calculated P(O 3 ) from prior Houston field campaigns in 2006 and 2009. Additionally, diurnal patterns are similar to model-derived ozone production from these previous campaigns. An advection analysis for a high ozone event on 25 September 2013 indicates that the Houston site was in a local ozone source region, while Smith Point ozone was likely enhanced by transport from other areas. [ABSTRACT FROM AUTHOR]

We looked at 19 wildfire events that were observed in the summers of 2012 and 2013 at the Mt. Bachelor Observatory (MBO, 2.7 km a.s.l.), a mountaintop site located in central Oregon. We identified wildfire plumes using enhancement ratios (Δ Y /Δ X ), which we calculated for each plume by taking the Reduced Major Axis linear regression slope of various species. We reported the calculated enhancement ratios and explored their relationship with ozone production. We observed a negative correlation between ΔO 3 /ΔCO and ΔNO x /ΔNO y ( r = −0.72). This showed that the degree of NO x oxidation is a key predictor of ozone production. The highest ΔNO x /ΔNO y (0.57 pptv/pptv) was associated with ozone loss (ozone titration). Low ΔNO x /ΔNO y values (ranging from 0.049 to 0.15 pptv/pptv) are generally associated with ozone enhancement. We also found that even if ΔO 3 /ΔCO is low, ΔO 3 may still be significant if CO enhancements are large. We then explored events that are not associated with any O 3 enhancement/loss. Out of 19 fire events, 3 belong to this category. We discovered that these events are either BL-influenced (O 3 deposition), associated with low ΔNO y /ΔCO ratios, and/or associated with minimal photochemistry (due to nighttime transport). Absolute ozone enhancements ranged from 3.8 to 32 ppbv, while ozone production efficiencies (OPEs) ranged from 2.1 to 17. However, because PAN comprises most of the reactive nitrogen in fire plumes, the calculated OPEs underestimated the true ozone mixing ratios. OPEs may therefore be misleading indicators of ozone production in wildfires. Finally, we segregated the data into plume/non-plume time periods. From this we found that the average O 3 mixing ratio was significantly higher in fire plumes compared to non-plume time periods, and the noontime NO/NO 2 ratios were also higher. This later result gives insight into the photochemical environment in the fire plumes. [ABSTRACT FROM AUTHOR]

Gaining quantitative information about the HO x cycle involved in ozone (O 3) production is important for reduction of tropospheric O 3. In this study, we evaluated the impacts of both the missing OH reactivity and the heterogeneous loss of HO 2 due to ambient aerosol uptake on the photochemical O 3 production potential and regime analysis during the Air QUAlity Study (AQUAS)-Kyoto summer campaign in 2018. We examined the missing OH reactivity, which was 50% of the averaged total OH reactivity (9.8 ± 3.8 (1σ) s−1), and the uptake loss rate of HO 2 on ambient aerosols of 0.0017 ± 0.0015 s−1. The real-time uptake loss rate of HO 2 was measured by employing a versatile aerosol concentration enrichment system (VACES). The O 3 production potential increased by a factor of two when the missing OH reactivity was considered and decreased by ∼20% when the HO 2 loss due to aerosol uptake was considered. In addition, the missing OH reactivity and the HO 2 loss due to aerosol uptake decreased the relative sensitivity of the O 3 production rate to volatile organic compounds (VOCs) and increased that to NO x (= NO + NO 2). Consequently, the NO x limited regime period, the period in which the relative sensitivity of the O 3 production rate to NO x was higher than that to VOCs, was expanded by a few hours. Finally, the effect of aerosol uptake on O 3 production was anti-correlated with the NO concentration and peaked around noon when the NO concentration was the minimum. It is concluded that aerosols likely affect tropospheric O 3 production in suburban and rural areas, where the concentrations of NO x , particularly NO, are very low ([NO] < 0.3 ppb). • Measurements of OH reactivity and uptake loss rate of HO 2 onto ambient aerosols. • Ozone production potential and regime during the AQUAS-Kyoto summer campaign in 2018. • Impacts of missing OH reactivity and aerosols on the photochemical ozone production. [ABSTRACT FROM AUTHOR]

Within the framework of the RONOCO (ROle of Nighttime chemistry in controlling the Oxidising Capacity of the atmOsphere) campaign a daytime flight over the metropolitan area of London were carried out to study the nitrogen oxide chemistry and its role in the production and loss of ozone (O3) and alkyl and multifunctional nitrate (ΣANs). The FAAM BAe-146 aircraft, used for these observations, was equipped with instruments to measure the most relevant compounds that control the lower troposphere chemistry, including O3, NO, NO2, NO3, N2O5, HNO3, peroxy nitrates (SPNs), ΣANs, OH, and HO2. In the London's flight a strong ozone titration process was observed when flying above Reading (downwind of London) and when intercepting the London plume. The coupled cycles of NOx and HOx can have different terminations forming SPNs, ΣANs, HNO3 or peroxides (H2O2, ROOH) altering the O3 production. In the observations reported here, we found that a strong ozone titration (ΔO3 = -16 ppb), due to a rapid increase of NOx (ΔNOx = 27 ppb), corresponds also to a high increase of ΣANs concentrations (ΔΣANs = 3 ppb), and quite stable concentrations of HNO3 and SPNs. Unexpectedly, compared with other megacities, the production of ΣANs is similar to that of Ox (O3 + NO2), suggesting that in the London plume, at least during these observations, the formation of ΣANs effectively removes active NOx and hence reduces the amount of O3 production. In fact, we found that the ratio between the ozone production and the alkyl nitrates production (observed) approximate the unity; on the contrary the calculated ratio is 7. In order to explain this discrepancy, we made sensitivity tests changing the alkyl nitrates branching ratio for some VOCs and we investigated the impact of the unmeasured VOCs during the flight, founding that the calculated ratio decreases from 7 to 2 and that, in this condition, the major contribution to the ΣANs production is given by Alkanes. Observations and analysis reported here suggest that in the London plume the high NOx emissions and the chemistry of some VOCs (mainly Alkanes) produce high concentrations of ΣANs competing against the local ozone production. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the dependence of ozone-forming potential on temperature was analysed based on data from two stations (with an industrial and rural background, respectively) in North Rhine-Westphalia, Germany, for the period of 1983–2007. After examining the interrelations between ozone, NO x and temperature, a projection of the days with ozone exceedance (over a limit value of a daily maximum 8-h average≥120 μg m−3 for 25 days per year averaged for 3 years) in terms of global climate change was made using probability theory and an autoregression integrated moving average (ARIMA) model. The results show that with a temperature increase of 3 K, the frequency of days when ozone exceeds its limit value will increase by 135% at the industrial station and by 87% at the rural background station. [Copyright &y& Elsevier]

Abstract: Tropospheric ozone (O3) negatively impacts human health and ecosystems, and is a greenhouse gas. Wildfires are a source of tropospheric O3, and studies show that wildfires are increasing in North America. In this study, we present a critical review of O3 production from wildfires focusing on three key topics: the influence of wildfire emissions on O3 production; the influence of photochemistry on wildfire O3 production; and regulatory issues associated with wildfire O3 production in the United States. Observations of ΔO3/ΔCO range from approximately −0.1 to 0.9, and are caused by the interplay of numerous factors including fire emissions, efficiency of combustion, chemical and photochemical reactions, aerosol effects on chemistry and radiation, and local and downwind meteorological patterns. Using average ΔO3/ΔCO ratios for major biomes, we estimate global wildfires produce approximately 170 Tg of O3 per year, which is 3.5% of all global tropospheric O3 production. Areas of uncertainty in wildfire O3 production include the net effect of aerosols on chemical and photochemical reactions within a fire plume, the impact of oxygenated volatile organic compounds and nitrous acid on O3 production, and the interplay of variables that lead to extreme ΔO3/ΔCO values. Because wildfire frequencies are likely increasing and have been shown to contribute to elevated O3 at air quality monitoring sites, it is important to better understand the emissions, photochemistry and impacts of these fires. [Copyright &y& Elsevier]

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]

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]

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]

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]

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]

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]

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]

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 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]