O3 Removal Research Articles

In Situ Synthesis of Monolithic Cu2O–CuO/Cu Catalysts for Effective Ozone Decomposition

Nowadays, ozone (O3) has become a worldwide pollutant, and it is challenging to prepare monolithic O3 decomposition catalysts substituting the conventional complicated process of adhering catalyst powders onto porous substrates. Herein, monolithic Cu2O–CuO/Cu catalysts are obtained facilely by in situ thermal oxidizing–reducing copper foam. After optimization, the CuO nanowires (NWs) are first produced by annealing Cu foam in O2 at 400 °C for 2 h and then the NW surface is reduced into Cu2O by annealing in Ar/H2 at 350 °C for 2 h. The obtained Cu2O–CuO/Cu monolithic catalyst exhibits high catalytic activity to 20 ppm O3, maintaining 100% at a space velocity of 11,000 h–1 and even about 94% at 38,000 h–1. The catalytic ability toward O3 can be attributed to the generated Cu+/Cu2+ redox couples, the donor/acceptor-type point defects, and the Cu2O–CuO p–p heterojunction. This demonstrates the successful and convenient preparation of the monolithic catalyst for rapid, controllable, and productive O3 removal applications.

Investigation of Inactivatioin and Electrostatic Precipitation Effects by Corona Discharge

In recent years, infectious diseases have caused social and economic problems. To control such infectious diseases, various techniques are being developed and tested. In this study, the experimental apparatus as air purifier with corona discharge electrodes intersect to the gas flow was verified. We examined how the effects of air volume on O3 and NOx concentration and removal rate of virus. We found that the O3 and NOx concentrations decreased with air volume. The amount of viruses was decreased 84% by circulating air with viruses through the experimental apparatus four times.

Assessment of the Effects of the Spanish National Air Pollution Control Programme on Air Quality

During the last few decades, European legislation has driven progress in reducing air pollution in Europe through emission mitigation measures. In this paper, we use a chemistry transport model to assess the impact on ambient air quality of the measures considered for 2030 in the for the scenarios with existing (WEM2030) and additional measures (WAM2030). The study estimates a general improvement of air quality for the WAM2030 scenario, with no non-compliant air quality zones for NO2, SO2, and PM indicators. Despite an improvement for O3, the model still estimates non-compliant areas. For this pollutant, the WAM2030 scenario leads to different impacts depending on the indicator considered. Although the model estimates a reduction in maximum hourly O3 concentrations, small increases in O3 concentrations in winter and nighttime in the summer lead to increases in the annual mean in some areas and increases in other indicators (SOMO35 for health impacts and AOT40 for impacts on vegetation) in some urban areas. The results suggest that the lower NOx emissions in the WEM and WAM scenarios lead to less removal of O3 by NO titration, especially background ozone in winter and both background and locally produced ozone in summer, in areas with high NOx emissions.

1981–2020 winter ozone trends, Erzgebirge, Central Europe

Tropospheric ozone (O3) acts as greenhouse gas and air pollutant. Over the last 100 years, tropospheric O3 levels increased above background by factor 2.5 in the northern hemisphere and by factor 3–4 across Europe. The gas poses a potential risk to forest ecosystems in many mountain areas. There, O3 concentrations result from long-range transport and are influenced by removal processes (dry deposition, gas phase and cloud removal, reduction on wet aerosols). Most trend studies analyzed annual-mean concentrations. We focus on winter O3 trends at high altitudes in the German/Czech Erzgebirge (period 1981–2020) to avoid major noise from photochemical reactions and to better explain recent O3 behavior in Central Europe. Hourly air quality and meteorological data from four stations (Carlsfeld, CAR; Fichtelberg, FIB; Schwartenberg, SWB; Zinnwald, ZIW) were used to analyze O3 trends. The data can explain the complex O3 formation and removal behavior.Three distinct periods of O3-concentration trends can be discerned: i) Until the late 1980s, characterized by relatively low O3 concentrations. ii) Dramatic transformation in the 1990s with changing air pollution in Central Europe. Strong O3-concentration increase at FIB is corroborated by data from CAR and ZIW. iii) Stabilization as of 1997/98, when O3 concentrations remained at the same level for all four stations, despite general regional air pollution decrease. Key results are:a) Winter O3 trends mainly depend on O3 concentration of air masses transported to the stations and on the O3-removal potential (ORP) of clouds, not on local formation processes.b) ORP differs between clouds and fog, depending on droplet chemical composition. Fog from the North Bohemian Basin showed the highest ORP due to reaction with liquid phase S(IV). However, O3 reactions with O2− in fog droplets showed high ORP, too, depending on cloud-water pH values and NOx concentrations.c) So-called “Bohemian fog” decreased, and with it related ORP, while that of clouds from westerly and northwesterly air masses remained nearly unchanged since 1997/98.d) Decreasing ORP in clouds and fog (= higher O3 concentration) oppose decreasing O3 concentrations in westerly air masses. Both effects lead to unchanged O3 levels in the Erzgebirge since 1997/98.

Synthesis of CeOx@SiO2 with tandem effect of mass transfer and activation for enhancing sulfanilamide degradation with ozone

In this work, a hollow mesoporous CeOx@SiO2 was synthesized and used to promote sulfanilamide (SA) mineralization in ozonation. SA mineralization was promoted to 68.2% by O3/CeOx@SiO2 in 120 min, but only 30.0% in O3 process. O3/CeOx@SiO2 behaved the better at acidic and alkaline condition than that at neutral condition. CeOx@SiO2 had the great ability in enhancing O3 utility rate. Silanol (SiOH) in pore channel of SiO2 shell was non-reactive with O3 but could provide transmission way for O3 to reach the inner CeOx core. Lewis sites, oxygen vacancies and surface hydroxyl groups induced by CeOx favored for the activation of O3. The excess electron at oxygen vacancies would be transferred to the absorbed O3 molecular, which then generated reactive oxygen species (ROS) to mineralize SA. Hydroxyl radicals (OH) and superoxide radicals (O2−) were the main ROS, which were recorded by EPR. The interfacial electron transfer process was revealed by LSV and ESI characterizations. SA degradation intermediates were also identified by HPLC-MS and IC, a possible degradation pathway was proposed. Moreover, CeOx@SiO2 showed a good reusability, no obvious decline of TOC removal was found in four times’ uses. Water matrix would complete ROS with SA, which inhibited the SA removal of both O3 and O3/CeOx@SiO2 processes, but the better TOC removal efficiency was still obtained by O3/CeOx@SiO2 in actual water.

Al2 O3 -Assisted Confinement Synthesis of Oxide/Carbon Hollow Composite Nanofibers and Application in Metal-Ion Capacitors.

Hollow micro-/nanostructures are widely explored for energy applications due to their unique structural advantages. The synthesis of hollow structures generally involves a "top-down" casting process based on hard or soft templates. Herein, a new and generic confinement strategy is developed to fabricate composite hollow fibers. A thin and homogeneous atomic-layer-deposition (ALD) Al2 O3 layer is employed to confine the pyrolysis of precursor fibers, which transform into metal (or metal oxide)-carbon composite hollow fibers after removal of Al2 O3 . Because of the uniform coating by ALD, the resultant composite hollow fibers exhibit a hollow interior from heads to ends even if they are millimeter long. V, Fe, Co, and Ni-based hollow nanofibers, demonstrating the versatility of this synthesis method, are successfully synthesized. Because of the carbon constituent, these composite fibers are particularly useful for energy applications. Herein, the as-obtained hollow V2 O3 -C fiber membrane is employed as a freestanding and flexible electrode for lithium-ion capacitor. The device shows an impressive energy density and a high power density.

Degradation of gas-phase o-xylene via combined non-thermal plasma and Fe doped LaMnO3 catalysts: Byproduct control

A series of Fe doped LaMnO3 catalysts were prepared to control the production of byproducts such as O3, N2O, and CO, during the degradation of volatile organic compounds with a non-thermal plasma. Eliminating these potentially toxic byproducts will make non-thermal plasma technologies applicable for a wider range of commercial applications. The modified LaMnO3 catalysts are combined in NTP-catalysis reactor with optimal configuration. Experimental results show that doping Fe on LaMnO3 catalysts can not only enhance the oxidation of o-xylene, but also lower the emission levels of byproducts. LaMn0.9Fe0.1O3 catalyst shows the best catalytic activity among the formulations tested herein. In addition to the strong mineralization of 88.1 %, the catalyst has the highest performance for o-xylene conversion (91.3 %), O3 inhibition efficiency (84.9 %), and N2O inhibition efficiency (61.2 %) due to the strong concentration of active oxygen species on the surface of the catalyst. Moreover, the high reducibility of Fe3+ demonstrated with H2-TPR (hydrogen temperature-programed reduction) further enhances the removal of O3 by oxygen species exchange between Mn3+/Mn4+ and Fe2+/Fe3+.

A Study on the Optimization about Peroxone(O3/H2O2-AOP)-Quenching Process in G Water Treatment Plant for 2-MIB Treatment and Residual Ozone Removal

Objectives In this study, Peroxone-Quenching process auto control system was developed and appropriate chemical was selected for 2-MIB treatment and residual O3 remove in G WTP. Methods In order to analyze the disinfection effect by the O3 process, the Giardia inactivation ratio by disinfection process (O3, Cl) was calculated by “Disinfection efficiency calculation program” made by Ministry of Environment. To optimize the Peroxone process, the 2-MIB removal rate was analyzed according to the operating conditions (O3 injection, H2O2/O3) and the equation of chemical injection rate was derived. To optimize the Quenching process, the correlation between dissolved O3 and atmospheric O3, the reduction rate of dissolved O3 concentration according to operation conditions (chemical injection rate, temperature, etc.) for each applied chemicals (H2O2, Na2S2O3) were analyzed. And the equation of chemical injection rate was derived. To appropriate chemical for Quenching process was selected by analyzing O3 removal efficiency and economic feasibility. Results and Discussion When water production increases, it is expected that the optimal operation of the O3 disinfection process will ensure the Giardia inactivation ratio over 1.0 in winter season. In the 2-MIB inflow, it was able to remove 70-100% of 2-MIB by Peroxone process operation. From the 2-MIB removal rate, an optimal O3 injection rate equation could be derived and optimal H2O2/O3 was confirmed to be 0.4. To reduce atmospheric O3, dissolved O3 remove is required. Factors affecting dissolved O3 removal by chemicals were injection rate, contact time, water temperature for H2O2, and injection rate, residual Cl for Na2S2O3. Using these factors, the equations of chemical injection rate for Quenching process were derived. As a result of the injection rate simulation for each chemicals, it is expected that the injection rate of Na2S2O3 can be lower than H2O2 (6-96%). Because O3 removal efficiency of Na2S2O3 is higher than H2O2, and Na2S2O3 is not affected by water temperature. The annual chemical purchase costs for Quenching process operation are estimated to be 131 million KRW for H2O2 and 87 million KRW for Na2S2O3. Considering to Quenching efficiency and economic feasibility, the application of Na2S2O3 was decided to be reasonable. Conclusions The Peroxone-Quenching process auto control system was installed and is operated now. It is expected to produce high quality tap water even with 2-MIB inflow by Peroxone process auto control system. And by the optimization of Quenching process, atmospheric O3 reduction for ensuring work place safety and economic operation would be expected. Key words: Ozone, AOP, Peroxone, Quenching, Residual Ozone Removal

Effect of exogenous catechin on alleviating O3 stress: The role of catechin-quinone in lipid peroxidation, salicylic acid, chlorophyll content, and antioxidant enzymes of Zamioculcas zamiifolia

Ozone (O3) can cause oxidative stress in plants and humans. Catechin is an antioxidant that enriches tea and can probably increase O3 tolerance in plants. To investigate the mechanism of catechin to alleviate O3 stress in plants, Zamiocalcus zamiifolia (an efficient plant for O3 phytoremediation) was sprayed with 5 mM catechin and was used to expose O3 (150-250) under long-term operation (10 cycles). We investigated whether exogenous catechin could enhance O3 removal and alleviate O3 stress through a balanced redox state in plants. Z. zamiifolia sprayed with catechin exhibited higher O3 removal (80.27±3.12%), than Z. zamiifolia without catechin (50.03±2.68%). O3 in the range of 150-250 ppb led to stress in plants, as shown by an increased malondialdehyde content (MDA) and salicylic acid (SA). Whereas under the presence of O3, exogenous catechin could maintain the MDA content and inhibit SA accumulation. Under Z. zamiifolia+catechin+O3 conditions, catechin reacted with O3, which led to the formation of catechin-quinone. The formation of catechin-quinone was confirmed by the depletion of reduced glutathione content (GSH). This catechin-quinone could induce GST and APX genes that are up-regulated approximately 35- and 5-fold, respectively. Hence, Z. zamiifolia+catechin+O3 conditions had higher performance for coping with oxidative stress than did Z. zamiifolia+O3 conditions. This evidence demonstrates that catechin could enhance O3 removal through a balanced redox state in plant cells. Finally, the application of tea extract for enhanced O3 removal is also shown in this study.

An integrated study on air mitigation potential of urban vegetation: From a multi-trait approach to modeling

The ecosystem services provided by urban forests contribute to ameliorate air quality and human well-being in cities. An integrated approach based on direct measurements of leaf functional multi-traits and on estimation of the plant mitigation potential was used for predicting the species-specific impact on air quality of 29 species, including trees and shrubs, commonly present in the urban context. In addition, volatile organic compound (VOC) emissions and ozone forming potential (OFP) of each species were evaluated. At plant levels, pollution deposition equations and the i-Tree Eco model were applied for estimating particulate (PM10) and ozone (O3) removal potential and for calculating carbon dioxide (CO2) storage and sequestration by the studied species. The results highlight the plant species-specific ability to capture atmospheric pollutants based on their physiological (CO2 assimilation and stomatal conductance) and morphological (stomata, trichomes, waxes and cuticular ornamentation) leaf traits. Trees with abundant trichomes, waxes and wrinkled leaf surfaces are considered more suitable for capturing pollutants. Most of the studied species are suitable for urban planning programs as they result for the majority low VOC emitters and consequently are characterized by low or moderate OFP. Annual O3 and PM10 removal of the investigated trees species ranged from about 58–140 g plant−1 yr−1 and from about 17–139 g plant−1 yr−1, respectively. Total tree CO2 storage ranged from about 164–215 kg plant−1 and gross annual CO2 sequestration from 11 to 20 kg plant−1 year−1. Liriodendron tulipifera, Celtis australis, Acer campestre and Acer platanoides, were efficient species in capturing PM10 and absorbing O3. Prunus cerasifera, Quercus cerris, together with Celtis australis, Acer campestre and Acer platanoides, were efficient for carbon sequestration and storage. As aspected, lower potential of pollutant removal and CO2 storage and sequestration were estimated for shrubs, due to their smaller leaf area and structure.

Contribution of Bacillus cereus ERBP in ozone detoxification by Zamioculcas zamiifolia plants: Effect of ascorbate peroxidase, catalase and total flavonoid contents for ozone detoxification

Eighteen plant species were screened for ozone (O3) removal in a continuous system. Zamioculcas zamiifolia had the highest O3 removal efficiency. To enhance O3 removal by Z. zamiifolia, adding a compatible endophytic bacteria, Bacillus cereus ERBP into Z. zamiifolia was studied. After operating under an O3 continuous system (150–250 ppb) at a flow rate of 0.3 L min−1 for 80 h, inoculated plants (74%) exhibited higher O3 removal efficiency than non-inoculated ones (53%). In addition, after O3 exposure (80 h), the population of B. cereus ERBP in inoculated plants was significantly increased in both shoots approximately 35 folds and leaves 13 folds compared to inoculated plants without O3 exposure. The results also showed that B. cereus ERBP had the ability to protect Z. zamiifolia against O3 stress conditions. The increase in B. cereus ERBP populations was attributed to the significant increase in ascorbate peroxidase (APX) and catalase (CAT) activity. In addition, increasing B. cereus ERBP populations led to raise total flavonoid contents which is one of antioxidant compounds. Increasing APX, CAT activities, and total flavonoid contents can enhance O3 detoxification in plant tissues. The mechanism of B. cereus ERBP for enhancing O3 phytoremediation was proposed in this study. The results suggested that B. cereus ERBP was a potential tool for alleviating O3 stress on Z. zamiifolia and enhancing O3 phytoremediation efficiency.

Source contributions of surface ozone in China using an adjoint sensitivity analysis

Air pollution has become an adverse environmental problem in China, resulting in serious public health impacts. This study advanced and applied the CMAQ adjoint model to quantitatively assess the source-receptor relationships between surface ozone (O3) changes over different receptor regions and precursor emissions across all locations in China. Five receptor regions were defined based on the administrative division, including northern China (NC), southern China (SC), Pearl River Delta region (PRD), Yangtz River Delta region (YRD), and Beijing-Tianjin-Hebei region (BTH). Our results identified the different influential pathways of atmospheric processes and emissions to O3 pollution. We found that the atmospheric processes such as horizontal and vertical advection could offset the O3 removal through chemical reactions in VOC-limited areas inside the receptor regions. In addition, O3 pollution can be induced by transport of O3 directly or its precursors. Our results of relative source contributions to O3 show that transboundary O3 pollution was significant in SC, NC and YRD, while the O3 pollution in PRD and BTH were more contributed by local sources. Anhui, Hubei and Jiangsu provinces were the three largest source areas of NOx and VOC emissions to O3 in SC (>52%) and YRD (>69%). NOx and VOC emissions from Tianjin and Beijing were the largest contributors to O3 in NC (>34%) and BTH (>51%). PRD was the dominant source areas of NOx (>89%) and VOC emissions (~98%) to its own regional O3.

Trends in air pollutants and health impacts in three Swedish cities over the past three decades

Abstract. Air pollution concentrations have been decreasing in many cities in the developed countries. We have estimated time trends and health effects associated with exposure to NOx, NO2, O3, and PM10 (particulate matter) in the Swedish cities Stockholm, Gothenburg, and Malmö from the 1990s to 2015. Trend analyses of concentrations have been performed by using the Mann–Kendall test and the Theil–Sen method. Measured concentrations are from central monitoring stations representing urban background levels, and they are assumed to indicate changes in long-term exposure to the population. However, corrections for population exposure have been performed for NOx, O3, and PM10 in Stockholm, and for NOx in Gothenburg. For NOx and PM10, the concentrations at the central monitoring stations are shown to overestimate exposure when compared to dispersion model calculations of spatially resolved, population-weighted exposure concentrations, while the reverse applies to O3. The trends are very different for the pollutants that are studied; NOx and NO2 have been decreasing in all cities, O3 exhibits an increasing trend in all cities, and for PM10, there is a slowly decreasing trend in Stockholm, a slowly increasing trend in Gothenburg, and no significant trend in Malmö. Trends associated with NOxand NO2 are mainly attributed to local emission reductions from traffic. Long-range transport and local emissions from road traffic (non-exhaust PM emissions) and residential wood combustion are the main sources of PM10. For O3, the trends are affected by long-range transport, and there is a net removal of O3 in the cities. The increasing trends are attributed to decreased net removal, as NOx emissions have been reduced. Health effects in terms of changes in life expectancy are calculated based on the trends in exposure to NOx, NO2, O3, and PM10 and the relative risks associated with exposure to these pollutants. The decreased levels of NOx are estimated to increase the life expectancy by up to 11 months for Stockholm and 12 months for Gothenburg. This corresponds to up to one-fifth of the total increase in life expectancy (54–70 months) in the cities during the period of 1990–2015. Since the increased concentrations in O3 have a relatively small impact on the changes in life expectancy, the overall net effect is increased life expectancies in the cities that have been studied.

Heat treatment of MnCO3: An easy way to obtain efficient and stable MnO2 for humid O3 decomposition

The competitive water adsorption in the practical environment usually causes severe deactivation of the O3 decomposition catalysts. In this study, MnCO3 was used as precursor to prepare efficient and stable MnO2 catalyst for gaseous O3 decomposition in humid stream. The sample S-300, prepared by calcining MnCO3 at 300 °C for 6 h, exhibited 63% (80%) of removal efficiency for 120 (43) ppm of O3 under a high space velocity of 600 L g−1 h−1 and 50% (40%) of relative humidity at 25 °C, which is superior to the commercial O3 scrubber (oxide compound of Cu and Mn) and α-MnO2. However, even lower or higher treatment temperature did not further promote humid O3 decomposition. Thorough characterizations, especially by the temperature programmed and in situ DRIFTs experiments, demonstrate that the large amount of active oxygen vacancies and strong Lewis-acid sites together with the easy recovery of the occupied oxygen vacancies and weak interaction with water molecules accounted for the excellent O3 decomposition activity in humid stream. Besides, the developed pores by thermal decomposition of MnCO3 might also facilitate O3 removal. This study provides an easy and rational design of affordable and efficient catalysts for environmental application.

New insight into the enhanced activity of ordered mesoporous nickel oxide in formaldehyde catalytic oxidation reactions

Highly ordered mesoporous materials synthesized by a nanocasting method offer vast opportunities in catalytic applications. However, considerable debates remain as to the mechanism by which the mesoporous structure results in enhanced performance. We demonstrate new insights into the role of ordered mesoporous metal oxides in the catalytic oxidation reaction by preparing nickel (II) oxide (NiO) rather than a multiple valence compound such as Co3O4 as model catalyst. Mesoporous NiO using KIT-6 as a template (m-NiO-k) achieved total formaldehyde (HCHO) mineralization at 90 °C using oxygen (O2) as oxidant, while bulk NiO (b-NiO-c) oxidized HCHO completely at 170 °C. Moreover, using ozone (O3) as oxidant, m-NiO-k attained increased HCHO conversion by ∼34% with a twofold increase in CO2 selectivity and a 100% O3 decomposition rate. We conclude that the surface sodium functionalization of m-NiO significantly promotes the total oxidation of HCHO with O2, likely via contribute to hydroxyl regeneration during reaction. Furthermore, the extra active oxygen species and undercoordinated NiO on the mesoporous surface owing to the properties of mesoporous structures contribute almost exclusively to the high activity and selectivity in the simultaneous catalytic removal of HCHO and O3, which are also involved in the further enhanced activity for HCHO oxidation using m-NiO with O2. These findings provide additional new insight into engineering efficient mesoporous metal oxides for VOCs catalysis under mild condition. Furthermore, they provide an innovative perspective on optimizing other reactions employing nanocast mesoporous catalysts.

Catalytic decomposition performance for O3 and NO2 in humid indoor air on a MnOx/Al2O3 catalyst modified by a cost-effective chemical grafting method

Processes based on non-thermal plasma (NTP) for indoor air treatment inevitably lead to the formation of toxic by-products such as ozone (O3) and nitrogen oxides (NOx). Adding a step of heterogeneous catalysis in series with NTP could allow for the decomposition of the by-products. Therefore, different catalysts were developed based on transition metal oxides, such as NiOx, CoOx and MnOx with different weight percentage 1, 5 and 10wt.%, deposited on a γ-Al2O3 support. The O3 removal efficiency (ORE) and the NOx removal efficiency (NRE) were very encouraging in dry air: about 65% and 80%, respectively, by using 2g 5wt.% MnOx/Al2O3 catalyst under the experimental conditions. However, strongly negative effects of relative humidity (RH) on the catalytic decomposition performance were observed. To overcome this limitation, the catalyst surface was modified to make it hydrophobic using a cost-effective chemical grafting method. This treatment consisted in impregnating the 5wt.% MnOx/Al2O3 catalyst with different trichloro(alkyl)silanes (TCAS). The effects of different linker lengths and amounts of TCAS for the hydrophobicity and the decomposition performance of surface-modified catalysts under humid conditions were investigated. Our results show that the surface-modified catalyst with the shortest linker and 0.25mmol/gcat of modifying agent represents the best catalytic decomposition performance for O3. Its ORE is 41% at 60% RH, which is twice that of the non-modified catalyst.

Meteorological and Chemical Factors Controlling Ozone Formation in Seoul during MAPS-Seoul 2015

Author(s): Kim, H; Choi, WC; Rhee, HJ; Suh, I; Lee, M; Blake, DR; Kim, S; Jung, J; Lee, G; Kim, DS; Park, SM; Ahn, J; Lee, SD | Abstract: To understand the chemical mechanisms of controlling factors in ozone (O3) formation in early summer in Seoul, a comprehensive study encompassing measurement and modeling was conducted under the Megacity Air Pollution Study-Seoul (MAPS-Seoul) campaign. From May 18 to June 12, 2015, O3 and peroxyacetyl nitrate (PAN) were measured, along with their precursors, including NOx and volatile organic compounds (VOCs), at the Korea Institute of Science and Technology, located in northeast Seoul. VOCs were sampled in a canister twice a day (at 09:30 and 15:00) and analyzed via gas chromatography. The meteorological conditions and chemical regimes of the air masses were clearly distinguished during the study period. In May, NOx concentrations were higher with more pronounced diurnal cycles of precursors and O3 under constant westerly winds. By contrast, stagnant conditions developed in June, which reduced the inflow of primary emissions from the downtown area but increased the influence from the neighboring forest under high temperatures. As a result, the ratio of O3 to odd oxygen was higher in June, indicating a less efficient removal of O3 by NOx. In the same context, the air mass was chemically more aged with a higher NO2/NOx ratio and enhanced OH reactivity of oxygenated and biogenic VOCs in June. The overall measurement results suggest that O3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O3 concentrations are the highest of the year.

Modeling ozone uptake by urban and peri-urban forest: a case study in the Metropolitan City of Rome.

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O3), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O3 removal in different contexts. The present study modeled the O3 stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O3 fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O3 uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.

Relationships of CO2 assimilation rates with exposure- and flux-based O3 metrics in three urban tree species

The relationships of CO2 assimilation under saturated-light conditions (Asat) with exposure- (AOTX, Accumulated Ozone exposure over a hourly Threshold of X ppb) and flux-based (PODY, Phytotoxic Ozone Dose over a hourly threshold Y nmol·m−2·s−1) O3 metrics was studied on three common urban trees, Fraxinus chinensis (FC), Platanus orientalis (PO) and Robinia pseudoacacia (RP). Parameterizations for a stomatal multiplicative model were proposed for the three species. RP was the species showing lower species-specific maximum stomatal conductance (gmax) and experiencing lower cumulative O3 uptake along the experiment, but in contrast it was the most sensitive to O3. PODY was slightly better than AOTX metric at estimating relative Asat (R-Asat)for PO and RB but not for FC. The best fittings obtained for the regressions between R-Asat and AOTX for FC, PO and RP were 0.904, 0.868, and 0.876, when the thresholds of X were 60ppb, 55ppb and 30ppb, respectively. However, AOT40 performed also well for all of them, with R2 always >0.83. For PODY, the highest R2 values for FC, PO and RB were 0.863, 0.897 and 0.911 at thresholds Y=7, 5 and 1nmolO3m−2s−1, respectively. Given the potentially higher O3 removal capacity of FC and PO by stomatal uptake and their lower sensitivity to this pollutant than RP, the former two species would be appropriate for urban gardens and areas where O3 levels are high. Parameterization and modeling of stomatal conductance for the main urban tree species may provide reliable estimations of the stomatal uptake of O3 and other gaseous pollutants by vegetation, which may support decision making on the most suitable species for green urban planning in polluted areas.

A spatially-explicit method to assess the dry deposition of air pollution by urban forests in the city of Florence, Italy

Urban forests (UF) provide a range of important ecosystem services (ES) for human well-being. Relevant ES delivered by UF include urban temperature regulation, runoff mitigation, noise reduction, recreation, and air purification. In this study the potential of air pollution removal by UF in the city of Florence (Italy) was investigated. Two main air pollutants were considered – particulate matter (PM10) and tropospheric ozone (O3) – with the aim of providing a methodological framework for mapping air pollutant removal by UF and assessing the percent removal of air pollutant.The distribution of UF was mapped by high spatial resolution remote sensing data and classified into seven forest categories. The Leaf Area Index (LAI) was estimated spatially using a regression model between in-field LAI survey and Airborne Laser Scanning data and it was found to be in good linear agreement with estimates from ground-based measurements (R2=0.88 and RMSE%=11%). We applied pollution deposition equations by using pollution concentrations measured at urban monitoring stations and then estimated the pollutant removal potential of the UF: annual O3 and PM10 removal accounted for 77.9t and 171.3t, respectively. O3 and PM10 removal rates by evergreen broadleaves (16.1 and 27.3g/m2), conifers (10.9 and 28.5g/m2), and mixed evergreen species (15.8 and 31.7g/m2) were higher than by deciduous broadleaf stands (4.1 and 10g/m2). However, deciduous forests exhibited the largest total removal due to the high percentage of tree cover within the city. The present study confirms that UF play an important role in air purification in Mediterranean cities as they can remove monthly up to 5% of O3 and 13% of PM10.