O3 Removal Research Articles

Quantifying the impact of urban trees on air quality in Geneva, Switzerland

Atmospheric pollution threatens human health worldwide, with tropospheric ozone (O3) and particulate matter (PM) among the most harmful pollutants. Urban trees can reduce the concentration of air pollutants through dry deposition on their canopies and stomatal uptake. At the same time, urban trees can deteriorate air quality by emitting aerosol- and O3 precursors in the form of biogenic volatile organic compounds (BVOCs). O3 and PM removal, and BVOC emissions vary depending on the tree species. Therefore, the diversity and spatial distribution of urban trees significantly influence their impact on local air quality. This study employs a dual approach to assess and map the impact of urban trees on air quality in Geneva, Switzerland. Firstly, we use the i-Tree Eco model combined with a tree inventory (237,191 trees) to quantify BVOC emissions and PM10 (PM < 10 µm) and O3 removal at the genus level. Secondly, we develop a species-level parameterization using 51 common urban tree species to estimate the same variables and ozone-forming potential (OFP). Results show that the tree density is heterogeneous in the study area, leading to neighborhoods with greater biomass and, therefore, stronger influence by trees on local air quality. According to i-Tree Eco, urban trees in Geneva emitted 50 t of BVOCs, while removing 14 t of PM10 and 52 t of O3 in 2014. With the species-level parametrization, we estimate that urban trees removed about 66 ± 55 t of PM10 and 150 ± 96 t of O3 in 2014. However, they could also emit about 130 ± 52 t of BVOCs annually, which, under favorable conditions, can form 1153 ± 519 t of O3. Depending on the method, urban trees removed between 4 and 19 % of the anthropogenic PM10 emissions. The annual removal rates are comparable to findings in other European cities. The disparities between the two approaches are due to different parameterizations. This study could help urban planners to select adequate species for future planting programs in Geneva and more generally. It showed that the impact of urban trees on air quality is spatially heterogeneous but significant, and tightly linked to the species composition.

Phenology- and light-based parameterization of stomatal conductance model for urban woody species in northern China

Surface ozone (O3) poses a significant threat to urban vegetation health, and assessing the O3 risk across woody species is of vital importance for maintaining the health of urban infrastructure. In the present study, Jarvis-type stomatal conductance model was parameterized for ten urban species in northern China. Incorporating the effects of time of day and diurnal O3 concentration significantly enhanced the model performance. For different plant functional types (greening trees, greening shrubs, and orchard-grown trees), three parameterizations were established to estimate stomatal O3 uptake (POD1, phytotoxic O3 dose over an hourly threshold of 1 nmol m−2 s−1). The differences in POD1 between greening trees and shrubs were primarily due to the difference in their stomatal sensitivity to light. Orchard-grown trees displayed the lowest O3 removal capacity (lowest value of POD1) because of their shorter growing season despite of high stomatal conductance. These results indicated that plant phenology and light responsiveness determined stomatal O3 uptake, and the three parameterizations developed here could be applicable to various urban species in northern regions. Among climatic factors for O3 risk assessment, O3 concentration was the most important factor determining annual variation of POD1, which was primarily driven by air temperature. However, when O3 pollution decreased, O3 concentration exhibited less dependence on temperature and more dependence on light. These findings provide crucial insights for urban policy-makers and environmental scientists aiming to mitigate O3 pollution effects and enhance urban vegetation health.

Dominant mechanism underlying the explosive growth of summer surface O3 concentrations in the Beijing-Tianjin-Hebei Region, China

Despite the implementation of stringent emission reduction measures in China since 2013, ozone (O3) pollution remains a serious concern. Many O3 pollution processes are accompanied by the explosive growth of O3 concentration, meanwhile this explosive growth will trigger O3 pollution with a high probability. This study investigates the chemical and physical mechanisms behind the explosive growth of O3 in the summer within the Beijing-Tianjin-Hebei (BTH) region based on the atmospheric circulation clustering and WRF-CMAQ simulation. Ninety-four instances of O3 explosions from the summer of 2014–2021 were selected based on their day-to-day variation in O3 concentration, and the corresponding meteorological conditions were classified into four clusters using K-means analysis. Cluster 1 revealed that large-scale regional transmission of O3 and its precursors from the southern BTH region led to a renewed burst of O3 growth based on mild pollution. Nighttime reduction in NO2 concentration decreases titration consumption, causing a nocturnal rise in O3 concentration, detectable through observed data and progress analysis. In Cluster 2 and Cluster 3, the BTH region is located in the northeast wind area ahead of the ridge and northly wind area of post-trough situation, respectively. The vertical downward motion with the markable increase in surface solar radiation (SSR), 2-m temperature (T2M), and decrease in relative humidity (RH) contribute to photochemical O3 generation. Additionally, enhancements in boundary layer stability and reductions in dry deposition and vertical diffusion are favorable for the O3 accumulation. Cluster 4 showed the explosive growth after rainfall event, with the largest increment. The post-rain increase in SSR and T2M, coupled with decreased RH, promotes photochemical O3 formation. Moreover, progress analysis reveals the reduced cloud cover slows down O3 removal, contributing to O3 accumulation. The dominant mechanism behind the explosive growth of O3 will provide certain guidance for the prediction of O3.

Graphitized Carbon-Supported Co@Co3O4 for Ozone Decomposition over the Entire Humidity Range.

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

Visible ozone detection and removal in two-dimensional Mn(ii)-based metal–organic frameworks

Highly stable and hydrophobic two-dimensional Mn(ii)-based MOFs effectively detect and remove trace O3 with discernible color change as the response.

Kill two birds with one stone: simultaneous removal of volatile organic compounds and ozone secondary pollution by a novel photocatalytic process.

Volatile organic compounds (VOCs) originating from diverse sources with complex compositions pose threats to both environmental safety and human health. Photocatalytic treatment of VOCs has garnered attention due to its high efficacy at room temperature. However, the intricate photochemical reaction generates ozone (O3), causing secondary pollution. Herein, our work developed a novel "synergistic effect" system for photocatalytic co-treatment of VOCs and O3 secondary pollution. Under the optimized reactor conditions simulated with computational fluid dynamics (CFD), MgO-loaded g-C3N4 composites (MgO/g-C3N4) were synthesized as efficient catalysts for the photocatalytic synergistic treatment process. Density functional theory (DFT) calculations, characterization, and electron paramagnetic resonance (EPR) tests revealed that the addition of MgO reduced the band gap of g-C3N4, and increased O3 molecule adsorption in the composites, efficiently harnessing the synergistic effect of O3 to generate a significant quantity of reactive oxygen radicals, thereby facilitating the removal of VOCs and O3. This study provides new insights for simultaneous elimination of VOCs and O3 secondary pollution by a photocatalytic process.

Hygroscopic La2O3 hybridized LaCoO3-based composite catalyst for efficient ozone decomposition under humidity conditions

Herein we first report the unique hygroscopic oxide hybrid LaCoO3-based composite catalyst derived from dual-metal metal organic framework (MOF) for ozone decomposition. First, dual-metal La,Co-MOF is synthesized by solvothermal method, then La,Co-MOF is calcined at high temperature, the hygroscopic oxide (La2O3) and active oxides (LaCoO3 and Co3O4) were uniformly hybridized to form porous microspheres. Benefiting from the hybrid action of the two types of oxides, this composite catalyst exhibits highly efficient O3 removal activity within 12 h over the entire humidity conditions. The outstanding humidity resistance is attributed to the preferential adsorption of water vapor on hygroscopic oxide (La2O3), preventing the adsorption of gaseous water molecules on the surface of active oxides. In-situ FTIR further indicates that this composite catalyst possesses superior humidity resistance in the ozone catalytic decomposition.

A “reserve” of regulating services: The importance of a remnant protected forest for human well-being in the Po delta (Italy)

During the last century the landscape of the Po delta (Italy), one of the most important European deltaic areas, was strongly altered by extended land reclamation and land use intensification. Consequently, the loss of the lowland forested area that was once extended along the region's coast took place. The present study aims to evaluate the ecosystem services provided by the Bosco Mesola woodland, a remnant-forested area of 1,058 ha located on an agriculture-dominated landscape, nowadays protected as a National Nature Reserve. Five ecosystem services were selected and evaluated both in biophysical and monetary terms, including provisioning (firewood production for industrial bioenergy and households’ heating purposes), regulating (air quality and climate regulation by carbon storage), and cultural services (eco-tourism), using experimental and collected data and modeling. The results underlined that the Reserve provides services for a total 10.4 M€ yr-1 and stores carbon for an estimated value of 7.2 M€. Notably, regulating services, such as air quality regulation (i.e. PM10 and O3 removal) accounts for 98.5% of the total annual value. While raising the issue related to the identification and conservation of ESs with no direct market value, whose socio-political and applicative fields have great relevance, this study demonstrates that remnant forests are exceptional providers of ecosystem services that can significantly contribute to reaching multiple sustainable development goals and whose preservation is largely remarked in EU Biodiversity Strategy for 2030. In this regard, the integration of different methods and data sources for ES assessment allow to capture a comprehensive range of ESs that may properly support the decision process.

Facile Method to Create PdCe–MnOx Catalyst for Decomposing O3 under Humidity Conditions

Manganese oxides are one of the most promising candidates for ambient decomposition of O3. However, catalysts with high efficiency require complicated preparation processes to cultivate active microstructures. This study developed a simple and easy to scale up method to produce catalysts via thermal annealing of Mn precursor. With slight addition of Ce and Pd, the obtained PdCe–MnOx catalyst exhibited excellent O3 removal activity in the presence of water vapor. Numerous characterization methods, including X-ray diffraction, high-resolution transmission electron microscopy, mapping, Brunauer–Emmett–Teller, H2-temperature-programmed reduction, O2-temperature-programmed desorption, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy, were applied to explore the relationship between activity and structure. The slight addition of Pd and Ce not only boosts the formation of surface vacancy species but also enhances the water vapor resistance, all of which contribute to its excellent ozone decomposition performance.

Catalytic ozonation of methylethylketone over porous Mn–Cu/HZSM-5

The catalytic ozonation of methylethylketone (MEK) was performed at the room temperature (25 °C) using the synthesized Mn and Cu-loaded zeolite (ZSM-5, SiO2/Al2O3 = 80) catalysts. The ZSM-5 zeolite was used as a porous support material due to the large surface area and high capacity for adsorption of volatile organic compounds. Since Mn and Cu-loaded zeolite catalysts were effective for the catalytic ozonation of VOCs such as MEK, according to the loaded concentration of Mn and Cu, there are four types of metal loaded ZSM5 catalysts synthesized [5 wt% Mn/ZSM-5, 5 wt% Cu/ZSM-5, 5 wt% Mn-1 wt% Cu/ZSM-5 (5Mn1CuZSM), and 5 wt% Cu-1 wt% Mn/ZSM-5]. The catalytic efficiency for the removal of MEK and ozonation using the different catalysts was also studied. Based on various experimental analysis processes, the characteristics of the synthesized catalysts were explored and the removal efficiencies of MEK and O3 together with the COx concentration generated from the destruction of MEK and O3 were explored. The results for the decomposition of MEK and O3 at the room temperature indicated that the Mn dominant ZSM-5 catalysts showed better efficiency for the conversion of MEK and O3. The 5 wt% Mn/ZSM-5 outweighed the rest of them for the removal of MEK while the 5Mn1CuZSM showed the best catalytic reactivity for the conversion of O3 and the CO2 selectivity. It was ascertained that during the reaction time of catalyst and reactants of 120 min the Mn dominantly deposited bimetallic catalyst, 5Mn1CuZSM, was determined as the most effective for the removal of MEK and O3 due to the high capability of production of Mn3+ species and more available adsorbed oxygen sites compared to the other catalysts. Finally, the durability measurement for the 5Mn1CuZSM catalyst was performed together with the produced CO and CO2 concentration for 420 min.

Interstitial carbon-platinum electronic metal-support interaction structure boost synergistic removal of O3 and CH3SH via surface atomic oxygen

Carbon atoms in the interstitial sites of metal nanoparticles have strong influence on heterogeneous catalysis via electronic metal-support interactions (EMSI). Here, the Pt catalysts with interstitial C-Pt EMSI structures were first developed and identified to boost the removal of ozone (O3) and methyl mercaptan (CH3SH). Experimental results showed that the intrinsic activity of the catalysts with low Pt loading (wt%, 0.95 %) was 186 times higher than that of commercial MnO2. This excellent catalytic performance was attributed to dual-site catalytic structures to promote the adsorption/activation of O3 at interstitial C and capture/oxidation of CH3SH at Pt simultaneously. More importantly, the interstitial C sites retained surface atomic oxygen (*O) with excellent reactivity and lowered the energy barrier of CS bond breakage, thus achieving efficient decomposition of CH3SH into CO2/SO42-. This work provides high-performance catalysts and new mechanistic insights for the synergistic control of O3 and CH3SH.

Efficient Degradation of Toluene over MnO2/TiO2 Nanobelts under Vacuum Ultraviolet Irradiation

Toluene, as a kind of volatile organic compounds, not only causes pollution to the atmosphere and water but also damages human health. Although vacuum ultraviolet (VUV) can effectively promote the degradation of toluene, it will produce a large amount of O3, which will cause secondary pollution. Therefore, it is very important to study catalysts that can promote both toluene degradation and ozone decomposition. In this work, a MnO2/TiO2 catalyst with uniformly dispersed MnO2 was prepared using the immersion reduction method, which was used to degrade toluene under VUV. The toluene removal efficiency was improved by the utilization and elimination of O3. The toluene removal efficiency over the prepared MnO2/TiO2 catalyst was 88%, and the O3 removal rate was 97%. The toluene removal efficiency under VUV was 4.9 times that of UV. The synergistic effect of VUV and multifunctional catalyst effectively improved the toluene removal efficiency.

Unmanned aerial systems for modelling air pollution removal by urban greenery

Urban greenery plays an important role in reducing air pollution, being one of the often-used, nature-based measures in sustainable and climate-resilient urban development. However, when modelling its effect on air pollution removal by dry deposition, coarse and time-limited data on vegetation properties are often included, disregarding the high spatial and temporal heterogeneity in urban forest canopies. Here, we present a detailed, physics-based approach for modelling particulate matter (PM10) and tropospheric ozone (O3) removal by urban greenery on a small scale that eliminates these constraints. Our procedure combines a dense network of low-cost optical and electrochemical air pollution sensors, and a remote sensing method for greenery structure monitoring derived from Unmanned aerial systems (UAS) imagery processed by the Structure from Motion (SfM) algorithm. This approach enabled the quantification of species- and individual-specific air pollution removal rates by woody plants throughout the growing season, exploring the high spatial and temporal variability of modelled removal rates within an urban forest. The total PM10 and O3 removal rates ranged from 7.6 g m-2 (PM10) and 12.6 g m-2 (O3) for mature trees of Acer pseudoplatanus to 0.1 g m-2 and 0.1 g m-2 for newly planted tree saplings of Salix daphnoides. The present study demonstrates that UAS-SfM can detect differences in structures among and within canopies and by involving these characteristics, they can shift the modelling of air pollution removal towards a level of individual woody plants and beyond, enabling more realistic and accurate quantification of air pollution removal. Moreover, this approach can be similarly applied when modelling other ecosystem services provided by urban greenery.

Catalytic ozone decomposition and adsorptive VOCs removal in bimetallic metal-organic frameworks

Atmospheric ozone has long been a threat to human health, however, rational design of high-performance O3-decomposition catalysts remains challenging. Herein, we demonstrate the great potential of a series of isomorphous bimetallic MOFs denoted as PCN-250(Fe2M) (M = Co2+, Ni2+, Mn2+) in catalytic O3 decomposition. Particularly, PCN-250(Fe2Co) showed 100% O3 removal efficiency for a continuous air flow containing 1 ppm O3 over a wide humidity range (0 ‒ 80% RH) at room temperature. Mechanism studies suggested that the high catalytic performance originated from the introduction of open Co(II) sites as well as its porous structure. Additionally, at low pressures around 10 Pa, PCN-250(Fe2Co) exhibited high adsorption capacities (89 ‒ 241 mg g−1) for most VOCs, which are not only a class of hazardous air pollutants but also the precursor of O3. This work opens up a new avenue to develop advanced air purification materials for O3 and VOCs removal in one.

Multivariate model-based investigation of the temperature dependence of ozone concentration in Finnish boreal forest

Tropospheric ozone (O3) concentrations are observed to increase with temperature in urban and rural locations. We investigated the apparent temperature dependency of daytime ozone concentration in the Finnish boreal forest in summertime based on long-term measurements. We used statistical mixed effects models to separate the direct effects of temperature from other factors influencing this dependency, such as weather conditions, long-range transport of precursors, and concentration of various hydrocarbons. The apparent temperature dependency of 1.16 ppb °C−1 based on a simple linear regression was reduced to 0.87 ppb °C−1 within the canopy for summer daytime data after considering these factors. In addition, our results indicated that small oxygenated volatile organic compounds may play an important role in the temperature dependence of O3 concentrations in this dataset from a low-NOx environment. Summertime observations and daytime data were selected for this analysis to focus on an environment that is significantly affected by biogenic emissions. Despite limitations due to selection of the data, these results highlight the importance of considering factors contributing to the apparent temperature dependence of the O3 concentration. In addition, our results show that a mixed effects model achieves relatively good predictive accuracy for this dataset without explicitly calculating all processes involved in O3 formation and removal.

Development and testing of a novel sulfur dioxide sonde

Abstract. A novel technique has been developed to measure sulfur dioxide (SO2) using a modification of the existing electrochemical concentration cell (ECC) ozonesonde technology. The current sonde-based method to measure SO2 (i.e., the dual-sonde approach) involves launching two ozonesondes together, with one of the sondes having a filter to remove SO2 at the inlet. The SO2 profile is determined by taking the difference between the measurements from the two instruments. The dual-sonde method works well in typical tropospheric conditions when [O3]&gt;[SO2] but saturates when [SO2]&gt;[O3] and has large uncertainties in the upper troposphere and lower stratosphere that would limit its effectiveness in measuring SO2 from an explosive volcanic eruption. Due to these limitations, several modifications were made to create a single-sonde system that would directly measure SO2 (i.e., the SO2 sonde). These modifications included (1) a positively biased ECC current, (2) the addition of an O3 removal filter, and (3) the addition of a sample dryer. The SO2 sonde measures SO2 as a reduction in the cell current. There was a strong correlation (r2&gt;0.94) between the SO2 sonde and a Thermo 43c analyzer during controlled laboratory tests and pre-flight tests. Varying humidity levels affected the SO2 sonde's sensitivity (avg =84.6±31.7 ppbv µA−1, 1σ RSD =37 %) during initial field tests, which was resolved by adding a sample dryer upstream of the O3 removal filter and pump inlet. This modification significantly reduced the variability and increased the sensitivity of the SO2 measurements (avg =47±5.8 ppbv µA−1, 1σ RSD =12 %). Field tests included measurements near Kīlauea volcano (before and during the 2018 eruption of the Lower East Rift Zone), Costa Rica's Turrialba volcano, and anthropogenic plumes from the Athabasca oil sands region of Alberta, Canada. This single-SO2-sonde system is an effective, inexpensive instrument for measuring both ground-based and vertical profiles of SO2 from anthropogenic and natural sources (i.e., volcanic eruptions) over a wide range of concentrations.

Highly efficient ozone elimination by metal doped ultra-fine Cu2O nanoparticles

Nowadays, ozone contamination becomes dominant in air and thus challenges the research and development of cost-effective catalyst. In this study, metal doped Cu2O catalysts are synthesized via reduction of Cu2+ by ascorbic acid in base solutions containing doping metal ions. The results show that compared with pure Cu2O, the Mg2+ and Fe2+ dopants enhance the O3 removal efficiency while Ni2+ depresses the activity. In specific, Mg-Cu2O shows high O3 removal efficiency of 88.4% in harsh environment of 600,000 mL/(g·hr) space velocity and 1500 ppmV O3, which is one of the highest in the literature. Photoluminescence and electron paramagnetic spectroscopy characterization shows higher concentration of crystal defects induced by the Mg2+ dopants, favoring the O3 degradation. The in-situ diffuse reflectance Fourier transform infrared spectroscopy shows the intermediate species in the O3 degradation process change from O22− dominant of pure Cu2O to O2− dominant of Mg-Cu2O, which would contribute to the high activity. All these results show the promising prospect of the Mg-Cu2O for highly efficiency O3 removal.

Integrated process analysis retrieval of changes in ground-level ozone and fine particulate matter during the COVID-19 outbreak in the coastal city of Kannur, India

The Community Multi-Scale Air Quality (CMAQ) model was applied to evaluate the air quality in the coastal city of Kannur, India, during the 2020 COVID-19 lockdown. From the Pre1 (March 1–24, 2020) period to the Lock (March 25–April 19, 2020) and Tri (April 20–May 9, 2020) periods, the Kerala state government gradually imposed a strict lockdown policy. Both the simulations and observations showed a decline in the PM2.5 concentrations and an enhancement in the O3 concentrations during the Lock and Tri periods compared with that in the Pre1 period. Integrated process rate (IPR) analysis was employed to isolate the contributions of the individual atmospheric processes. The results revealed that the vertical transport from the upper layers dominated the surface O3 formation, comprising 89.4%, 83.1%, and 88.9% of the O3 sources during the Pre1, Lock, and Tri periods, respectively. Photochemistry contributed negatively to the O3 concentrations at the surface layer. Compared with the Pre1 period, the O3 enhancement during the Lock period was primarily attributable to the lower negative contribution of photochemistry and the lower O3 removal rate by horizontal transport. During the Tri period, a slower consumption of O3 by gas-phase chemistry and a stronger vertical import from the upper layers to the surface accounted for the increase in O3. Emission and aerosol processes constituted the major positive contributions to the net surface PM2.5, accounting for a total of 48.7%, 38.4%, and 42.5% of PM2.5 sources during the Pre1, Lock, and Tri periods, respectively. The decreases in the PM2.5 concentrations during the Lock and Tri periods were primarily explained by the weaker PM2.5 production from emission and aerosol processes. The increased vertical transport rate of PM2.5 from the surface layer to the upper layers was also a reason for the decrease in the PM2.5 during the Lock periods.

Assessment of air pollutants removal by green infrastructure and urban and peri-urban forests management for a greening plan in the Municipality of Ferrara (Po river plain, Italy)

Air pollution is a serious concern for human health and is even more worrying in areas that are known to be “pollution hotspots”, such as the Po Plain in northern Italy. The Urban Green Infrastructure (UGI), which includes urban and peri-urban forests, enhances human health and wellbeing delivering a wide range of ecosystem services, including air quality improvement. In this research, we analyzed, in biophysical and monetary terms, the role of the UGI in removing PM10 and O3 from the atmosphere in the Municipality of Ferrara using established removal models. We used a multiscale approach that includes geospatial data, field sampling and laboratory analysis. Then, using a local green areas database, we located public areas that could potentially undergo forestation actions without requiring any land conversion and evaluated the benefit in terms of ESs provision that these actions may exert. We found that, in 2019, the UGI in the Municipality of Ferrara removed about 19.8 Mg of PM10 and 8.6 Mg of O3, for a monetary benefit of € 2.12 million € and 147*103 respectively. We then identified about 121 ha within the urban core of the Municipality that could potentially be forested. Such an action would increase the PM10 and O3 removal by about 49% and 18%, respectively. Our findings comply with the EU Biodiversity strategy for 2030, which calls for the development of an ambitious greening plan for cities with more than 20,000 inhabitants.

Land use and anthropogenic heat modulate ozone by meteorology: a perspective from the Yangtze River Delta region

Abstract. With the rapid advance in urbanization, land use and anthropogenic heat (AH) dictated by human activities significantly modify the urban climate and in turn the air quality. Focusing on the Yangtze River Delta (YRD) region, a highly urbanized coastal area with severe ozone (O3) pollution, we estimate the impacts of land use and AH on meteorology and O3 using the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem). These results enhance our understanding of the formation of O3 pollution in rapidly developing city clusters with place-specific topography, as most of our results can be supported by previous studies conducted in other regions around the world. Regional O3 pollution episodes occurred frequently (∼ 26 times per year) in the YRD from 2015 to 2019. These O3 pollution episodes are usually in calm conditions characterized by high temperature (over 20 ∘C), low relative humidity (less than 80 %), light wind (less than 3 m s−1) and shallow cloud cover (less than 5 okta). In this case, O3 pollution belts tend to appear in the converging airflows associated with the sea and the lake breezes. On the other hand, rapid urbanization has significantly changed land use and AH in this region, which subsequently affects meteorology and O3 concentration. The largest change in land use comes from urban expansion, which causes an increase in 2 m temperature (T2) by a maximum of 3 ∘C, an increase in planetary boundary layer height (PBLH) by a maximum of 500 m, a decrease in 10 m wind speed (WS10) by a maximum of 1.5 m s−1 and an increase in surface O3 by a maximum of 20 µg m−3. With regard to the sea and lake breezes, the expansion of coastal cities, like Shanghai, can enhance the sea breeze circulation by ∼ 1 m s−1. During the advance of the sea breeze front inland, the updraft induced by the front causes strong vertical mixing of O3. However, once the sea breeze is fully developed in the afternoon (∼ 17:00 LT), further progression inland will stall. Then O3 removal by the low sea breeze will be weakened, and surface O3 can be 10 µg m−3 higher in the case with cities than in the case with no cities. The expansion of lakeside cities, such as Wuxi and Suzhou, can extend the lifetime of lake breezes from noon to afternoon. Since the offshore flow of the lake breeze transports high O3 from the land to the lake, the onshore flow brings high O3 back to the land. Surface O3 in lakeside cities can increase by as much as 30 µg m−3. Compared to land use, the effects of AH are relatively small. The changes mainly appear in and around cities where AH fluxes are large. There are increases in T2, PBLH, WS10 and surface O3 when AH fluxes are taken into account, with increments of approximately 0.2 ∘C, 75 m, 0.3 m s−1 and 4 µg m−3, respectively. AH contributes largely to the urban environment, altering meteorological factors, O3 concentration and urban breeze circulation, but its effect on the sea and the lake breezes seems to be limited.