Air quality is a critical indicator of environmental and public health, shaped by emissions, climate change, and socioeconomic factors. While advancements in policy, technology, and regulation have led to significant reductions in pollutant emissions across many regions, challenges persist—particularly in emerging and developing economies.

On the positive side, stricter environmental policies, the adoption of renewable energy, improved fuel quality, and the expansion of low-emission transportation have contributed to cleaner air in numerous countries. However, rapid urbanization, industrial growth, and increasing energy demands have led to worsening air pollution in some areas, especially in developing nations. Key pollutants such as particulate matter (PM_2.5 and PM₁₀), nitrogen oxides (NO_x), and ozone (O₃) pose severe health and environmental risks, including respiratory diseases and ecosystem disruptions. Additionally, climate change exacerbates air pollution through rising temperatures and more frequent wildfires.

Addressing global air quality challenges requires coordinated efforts, integrating emission control measures, climate-friendly technologies, and sustainable urban development. This study highlights air quality trends in different countries, with a particular focus on Mongolia and China. For instance, in Beijing, annual average PM_2.5 concentrations dropped from 84 µg/m³ in 2015 to 29 µg/m³ in 2022—a significant improvement. However, this remains far above the World Health Organization’s recommended annual limit of 5 µg/m³, underscoring the need for continued air pollution mitigation efforts.

Figure: Annual mean values of PM_2.5 concentration from 2015 to 2022 in various Chinese cities (Source: World Air Quality Report)

How to cite: Samad, A. and Vogt, U.: Enhancing Global Air Quality: Progress, Challenges, and Regional Developments, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-919, https://doi.org/10.5194/icuc12-919, 2025.

Air quality remains a serious threat to urban residents; it is the primary contributor to respiratory illnesses. Those living in densely populated neighborhoods are particularly vulnerable. Despite considerable advancements in our overall understanding of urban air pollution, our insights into neighborhood- and street-level pollution remain insufficient. Dense urban neighborhoods are dominated by tall buildings and high levels of traffic, leading to complex flow patterns and uneven distribution of primary pollutants. Herein, we delve into the street and neighborhood-scale pollution dynamics in New York City, harnessing both mobile and in-situ observations. We used a backpack fitted with research-grade instruments to monitor particulate matter (PM2.5) and ozone in the summer of 2023. Between July and August, nearly 50 runs were conducted, sampling multiple neighborhoods during various time periods. In-situation observations from multiple public air quality networks were also included in our analysis. Our results show a high degree of uniformity in street-level ozone concentration in NYC, while the particulate matter concentration varied significantly. On days impacted by synoptic disturbances, both ozone and particulate matter concentrations were nearly uniform throughout the city. The fixed ground stations were able to adequately capture the median PM2.5 concentration. However, they missed the extremes, which were, in some cases, two to five times the median value. The observations were also used to validate an urbanized WRF-Chem model and satellite-derived measurements. The numerical simulations conducted at 4km X 4km resolution performed better than the current forecast model in predicting both PM2.5 and ozone concentration.

How to cite: Ramamurthy, P. and Gaudel, A.: A multi-scale analysis of urban air quality, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-94, https://doi.org/10.5194/icuc12-94, 2025.

Mesoscale atmospheric chemical transport models, while widely used for studying atmospheric chemistry, face significant challenges in capturing fine-scale processes in complex environments such as urban areas and wildfire smoke plumes. The coarse spatial resolution of these models limits their ability to resolve turbulent transport, sharp concentration gradients, and nonlinear chemical interactions driven by subgrid-scale dynamics. To address these limitations, we apply the high-resolution Weather Research and Forecasting model with Large Eddy Simulation and Chemistry (WRF-LES-Chem) to two distinct cases: (1) investigating ozone formation in the Houston urban domain in Texas, U.S., characterized by complex emission sources and intricate coastal boundary layer processes, and (2) understanding in-plume chemistry during the Williams Flats Fire, a severe wildfire event in Washington State, U.S., where intense emissions and plume dynamics drive rapid chemical transformations. Our simulations demonstrate the advantages of high-resolution modeling in resolving small-scale chemical and meteorological interactions, improving the representation of observed diurnal and spatial variations in highly reactive chemicals, ozone, and secondary organic aerosols (SOA), and providing deeper insight into the role of radical chemistry in controlling ozone formation regimes and SOA formation. These applications highlight the importance of LES-Chem approaches in advancing air quality predictions and understanding atmospheric chemistry in dynamic and heterogeneous environments.

How to cite: Li, Y.: Application of high-resolution large-eddy simulation in atmospheric chemistry studies for urban and fire environments , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-966, https://doi.org/10.5194/icuc12-966, 2025.

Urban Pollution Island (UPI) and Urban Heat Island (UHI) are two major issues affecting cities' liveability and sustainability, making them more vulnerable to climate change. The former phenomenon indicates the higher concentration of air pollutants in the city compared to its rural surroundings, while the latter refers to the higher air temperatures compared to rural neighboring, primarily due to the large extent of built-up.

Although the scientific community has now recognized that UPI and UHI could interact, making urban areas more susceptible to extreme weather and pollution events, the debate about the determination of the atmospheric mechanisms responsible for triggering or weakening the UPI-UHI relationship is still open.

This contribution aims to quantify and characterize the UPI in the urban area of Rome (Italy) by exploiting in-situ measurements of air pollutant concentrations collected over the period 2018-2023 by air quality stations belonging to the monitoring network managed by the Regional Agency for Environmental Protection (ARPA Lazio). The meteorological dataset is supplied by dense networks of instruments providing quality-checked datasets of WMO-compliant.

Different approaches for the determination of UPI are proposed and tested. Moreover, the temporal variability of the UPI Intensity is studied for both atmospheric particulate matters (PM10 and PM2.5) and the main trace gases present in metropolitan areas (NO2, NO, and O3). Furthermore, the UPI-UHI relationship during peculiar atmospheric events is investigated. For example, the UPI-UHI association is analyzed by selecting days with specific meteorological (heatwaves, calm wind, atmospheric stagnation) or air quality patterns (desert dust advection, lockdown period), mainly investigating the impact of atmospheric dynamics on UPI and UHI.

The results of the present study will help to deepen our understanding of UPI, providing useful information for the scientific community and stakeholders driving urban planning and pollution control actions.

How to cite: Di Bernardino, A., Argentini, S., Campanelli, M., Casasanta, G., Cecilia, A., Erriu, M., Falasca, S., and Siani, A. M.: Interaction between Urban Pollution Island and Urban Heat Island through in-situ observations in Rome (Italy) , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-381, https://doi.org/10.5194/icuc12-381, 2025.

Surface ozone levels are strongly influenced by temperature, with elevated concentrations commonly observed during summer. However, the ozone-temperature relationship requires further investigation due to the non-linear mechanisms governing ozone formation. In urban areas, anthropogenic heat emissions (AHE) contribute to local temperature increases, yet their effect on ozone levels remains uncertain and has not been fully quantified.
This study pioneers the coupling of distributed urban parameters in WRF's Single-Layer Urban Canopy Model (SLUCM) with atmospheric chemistry in WRF-Chem version 4.6. This version enables the representation of AHE and spatially varying urban morphological parameters (roughness length for momentum, displacement height, and sky-view factors). 
The Model for Ozone and Related Chemical Tracers (MOZART) coupled with the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) was used for gas-phase chemistry and aerosol representation. Chemical concentrations were initialized using output from the Whole Atmosphere Community Climate Model (WACCM), while biogenic emissions were derived from the Model of Emissions of Gases and Aerosols from Nature (MEGAN). Anthropogenic emissions were incorporated from the EDGAR HTAP_v3 inventory. Using this configuration, we examine the role of urban effects in driving surface ozone formation over the Kanto region of Japan for one week in August 2021, with a finest domain resolution of 1.5km.
Comparing simulations with and without AHE, we confirm that AHE significantly influences ozone transformation. In urban areas, AHE generally leads to an increase in ozone concentration. Notably, the increase in temperature (△T) and ozone (△ozone) reach their maximum in the evening, but their peaks do not coincide. The peak in △T occurs first, followed by the peak in △ozone after a lag of several hours. This temporal offset suggests complex interactions between AHE, meteorology, and atmospheric chemistry, which this study aims to determine by analyzing the mechanisms driving these interactions and their implications for urban air quality.

How to cite: Andal, M. D. C., Varquez, A. C. G., Kanda, M., Nagata, S., Takigawa, M., Patra, P. K., Griffiths, P., Kawano, N., Yamakami, A., and Doan, Q. V.: Investigating the influence of distributed anthropogenic heating to simulated ozone formation, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-570, https://doi.org/10.5194/icuc12-570, 2025.

Focusing on the Sino-European cities (Copenhagen, Paris and Hangzhou), this project aims to provide tools and case studies for optimizing multimodal traffic management, improving urban mobility, reducing traffic emissions, and finding new solutions towards greener mobility practices, climate-neutral and smart cities.

Based on big data, smart traffic management technologies, and integrated interdisciplinary methods, this project will build an Integrated Urban System (IUS) and key performance indicators for each city. With evolving urban planning, energy consumption, transport supply and demand, and group behaviours, the system will improve our understanding of interactions among urban multimodal mobility (e.g. combination of biking and trains), traffic emissions (e.g. switch to electric vehicles), air quality and climate change, and quantify these interactions for the Sino-European cities.

The results allow to quantify the leverage effects observed, and to highlight issues of environmental justice. The system is building multi-scenario simulations (e.g. reduced parking space for private cars) and proposing multi-mode transport schemes suitable for sustainable development, simultaneously optimizing mobility, and reducing emissions and health and climate risks.

Through collaborative analyses and cross simulations, a multi-mode transport scheme suitable for the sustainable development of Sino-European cities is further proposed. The results will establish a model for building smart cities, promoting Sino-European exchanges and cooperation, and jointly exploring climate neutrality pathways under future urbanization processes.

How to cite: Baklanov, A., Christensen, J. H., Yu, S., Coll, I., Li, P., Ketzel, M., Berthelsen, D., Etuman, A. E., Sahyoun, M., and Nuterman, R.: Integrated systems and analysis of urban Mobility for climate-neutral, environmental friendly and susTainable Cities in Europe and China (IMTECC) , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-836, https://doi.org/10.5194/icuc12-836, 2025.

This work presents the impacts on NOx emissions and concentrations of several mitigation strategies considering different meteorological conditions in a real air pollution hot spot. For this purpose, a methodology based on Computational Fluids Dynamics (CFD) has been used. The SUMO microscopic traffic simulator, coupled with an emissions model, is used to obtain road-traffic-related emissions for each selected scenario. These emissions are then used as input data to a set of steady-state CFD simulations which were previously performed for all wind direction sectors. Relevant meteorological variables are obtained from WRF simulations using the urban parameterization BEP-BEM. Finally, background NOx concentrations are obtained from an urban background air quality monitoring station (AQMS) in Madrid. 

Using this methodology, we have studied four periods:

Year 2016: Base case.

Year 2019: Reorganization of traffic flows by changing traffic directions in some streets.

Year 2022: Implementation of a Low Emissions Zone (ZBE) affecting the most polluting vehicles; with still some reduction of traffic due to the COVID-19 pandemic.

Year 2023: The recovery of traffic after the COVID-19 pandemic.

Results were evaluated using the observed concentrations at the AQMS in the study area. The impacts of the traffic variations are investigated for different meteorological conditions. The results show that the meteorological conditions affect both local and background concentrations and its net changes can be comparable to those due to emission reductions. Furthermore, we have considered two additional scenarios for each period considering different future levels of insertion of electric vehicles included in the Spanish National Energy and Climate Plan to assess their potential impact on emissions and air quality. Preliminary results show that the emissions reduction resulting from the replacement of fossil-fuelled vehicles with electric vehicles in the study area is not linear and depends on the composition of the traffic float prior to the replacement.

How to cite: Rodríguez Sánchez, A., Santiago, J. L., García Vivanco, M., Gamarra, A. R., Sanchez, B., Rivas, E., and Martín, F.: Microscale analysis of the introduction of electric vehicles in a real urban hot-spot for several meteorological and traffic conditions, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1051, https://doi.org/10.5194/icuc12-1051, 2025.

Urban decarbonization and sustainability plans highlight the importance of sustainable mobility strategies like cycling to reduce emissions and improve citizen well-being. Cities are increasingly investing in cycling infrastructure as a key urban strategy. However, widespread acceptance of these solutions requires careful planning and assessment of environmental stressors that cyclists encounter. Ensuring safe, inclusive cycling paths is crucial to encouraging their use.

This research develops a multidimensional exposure assessment for cyclists in the Brussels Capital Region (BCR). Using detailed spatial data, it analyzes environmental exposures such as air pollution, thermal conditions, and urban greenery along cycling paths. It measures negative exposures to pollutants and heat and positive exposures to urban green spaces and sky views. The Outdoor Thermal Comfort (OTC) is assessed using the UMEP-SOLWEIG model for Mean Radiant Temperature (Tmrt), while the Digital Surface Model (DSM) calculates the Sky View Factor (SVF).

The analysis reveals spatial and temporal variations in these exposures, identifying cycling paths needing improvements. It also examines the role of green infrastructure in alleviating environmental stress, considering its types and placements along routes. This research provides a foundation for urban design policies aimed at optimizing green infrastructure and enhancing cycling path effectiveness. By pinpointing high-stress areas and times, urban planners can implement interventions to improve environmental quality for cyclists and soft mobility users. The findings offer valuable insights for shaping future urban planning strategies to promote sustainable living and soft mobility in crowded urban areas like BCR.]

How to cite: Huang, Y.-S., Llaguno-Munitxa, M., and Manoli, G.: Multidimensional environmental exposure assessment of soft mobility users; a case study in the Brussels Capital Region, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-686, https://doi.org/10.5194/icuc12-686, 2025.

Climate change and air quality research are closely related research areas that have often been investigated with different objectives. However, addressing both topics as a joint approach can lead to synergies and help to avoid counteracting effects, where mitigating one may exacerbate the other. A convergence of methods and approaches is necessary to consider on the one hand the climate trend and forcing in mitigation scenarios applied by the air quality community and on the other hand to better understand and describe the impact of short-lived climate pollutants.

The project FOCI aims to analyse non-CO2 forcings on both climate and air quality and therefore requires a joint approach. The project applies regional climate and urban scale models driven by global earth system models to describe continental to urban scale air quality under present and future climate conditions.

The present and future anthropogenic emissions required for such model investigations need to be consistent with CMIP6 historical climate reconstruction and future scenario simulations. One critical aspect is that pollutants considered in CMPI6, which is based on CEDS, do not include particulate matter (PM2.5/PM10) but only its black and organic carbon (BC/OC) components. This would cause a significant underestimation of particulate matter concentrations and raises the need to define a method to estimate the non-speciated PM emissions from the available information.

In order to derive historical and future PM emissions consistent with CEDS we investigate a number of approaches based on the use of different proxies from the EDGAR database. These estimated datasets of consistent CEDS and particulate matter emissions are used in the FOCI project numerical models to describe continental to urban scale air quality under present climate conditions as well as for different SSP projections to ultimately evaluate the impact of key radiative forcers on climate and societal systems.

How to cite: Grawe, D., Arghavani, S., Alyuz, U., Boorman, P., Finardi, S., Halenka, T., Radice, P., Samland, M., Sokhi, R., and Troccoli, A.: Harmonisation of historical and future emission data for climate and air quality modelling, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-701, https://doi.org/10.5194/icuc12-701, 2025.

Prolonged high temperature events (hot extremes) have increased globally and on a regional scale. Traditional data processing methods to understand air quality changes in hot extremes may not adequately describe variations in directly emitted air pollutants like nitrogen oxides (NO_x) or volatile organic compounds (VOCs) and then their influence on secondary species like ozone (O₃). In Houston, TX (USA), the TROPOMI NO₂ (4.92%) and HCHO (21.25%) column observe an increase in hot extremes, but spatially and temporally the increase and resulting air quality vulnerability on populations is not uniform and can go unrecognised. Lee and Wang (2023) developed a clustering algorithm CLASP (CLustering of Atmospheric Satellite Products) rooted in density-based clustering which can capture variation and describe high magnitude features captured in TROPOMI observations on their spatial, magnitude, and temporal axes. CLASP qualified variation in hot extremes driven by biogenic and anthropogenic variables, by identifying increases in the magnitude and frequency of high magnitude hotspots in Houston. CLASP readily identified unique column increases in hot extremes which could be attributed to a regional airport and a peaking power plant. Population-weighted TROPOMI columns together with CLASP inform how Hispanics and Blacks or African Americans observe higher weighted population columns, and that these groups experience a higher frequency and magnitude of NO₂ and HCHO compared to other population groups, which intensifies in hot extremes. Surface ozone sees an overall increase of 14.80% in hot extremes, but similarly, increases are not homogenous as different extreme periods see varying degrees of change. In taking an observational approach to describe ozone air quality, we show how CLASP can help inform of variation captured in the TROPOMI column as well as identified limitations which prompts a need to further untangle how hot extremes effect ozone air quality in a region that may experience further exacerbated extremes.

How to cite: Lee, T. and Wang, Y.: The Influence of NOx and HCHO in Hot Extremes Observed from Space on Urban Populations and Ozone: A Case Study in Houston, TX (USA), 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-809, https://doi.org/10.5194/icuc12-809, 2025.

Urban air flow is affected by topography, built environment and meteorology in a way that can be difficult to predict. The deliberate release of inert, non-toxic tracers can provide measurements of air flow. A series of experiments in Bristol, UK, have used inert perfluorocarbon tracers to investigate the dispersion effects. Tracer data can be used to validate wind tunnel models and large eddy simulations of the test area.
The River Avon, flows from the Severn Estuary through a gorge to the west of the city of Bristol into the Harbour. Hills of up to100 m elevation surround this location and tracer campaigns have been conducted in the Cotham area uphill and to the north. Modelling has shown the gorge to be important for the circulation of winds in the city, and a vehicle fire in the South East in January 2021 provided an example of pollutants being recirculated through the city.
Tracers were released for 15 minutes and air sampled for 30 minutes in Tedlar bags in multiple locations for offline analysis by GCMS. Three releases from the North West in June 2021 with wind speeds between 1 and 4 m s-1 were detected 1.5 km downwind from the release point, but measurements from a similar distance from the South, North and South West in January 2022 at ~1 m s-1 were more disperse. Tracer releases with a southerly wind of up to 2 m s-1 in the Cotham area in September 2024 have shown that over the short distance scale, tracers follow street networks in the predominant wind direction. Perfluoromethylclohexane released on a street at the bottom of a hill was measured at 1741 ppq 320 m up the hill, but less than 550 ppq on side streets 400 m up the hill in the predominant wind direction.

How to cite: Matthews, J., Khan, A., Barlow, J., Tong, Z.-X., and Shallcross, D.: Tracer release experiments to interpret pollutant dispersion in Bristol, UK., 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-720, https://doi.org/10.5194/icuc12-720, 2025.

Air quality continues to be an issue for cities around the world, causing public health and environmental problems. Actions to improve air quality must address emissions, but secondary pollutants, such as tropospheric ozone, are difficult to control, not only because of the complexity of reactions that form them but also because of the number of their precursor sources and the interactions caused by atmospheric transport and dispersion. This work analyzes regional interactions of ozone precursors over three metropolitan regions in Sao Paulo state, Brazil, and how they contribute to the spatial and temporal ozone concentration during a high concentration episode. The metropolitan regions are Sao Paulo, Campinas, and Baixada Santista, located in the southeast part of Brazil, and approximately aligned in a northwest-southeast axis. They form a relevant economic axis, bringing the agricultural production of the countryside, that concentrates in Campinas, where there is relevant industrial production, passing through the greatest city of the country, Sao Paulo, with massive vehicular emissions, and exiting in the port of Santos, in Baixada Santista, to be shipped abroad. Baixada Santista also has industrial emissions. Most of the transportation is road-based. The northwest-southeast axis is also the prevalent direction of the wind, shaping the atmospheric interaction between these sites. Results show relevant interactions between the metropolitan areas: the sea breeze brings the marine air and the air pollutants from Baixada Santista to Sao Paulo; the prevalent east-northeast wind takes the pollution from Sao Paulo to Campinas. Mostly at night, the wind comes from the northwest, rotating the transport of pollutants. Sea breeze also influences the vertical transport and dispersion of pollutants, affecting ozone concentration. In conclusion, to improve air quality, actions must be aware of the regional interactions and decisions must consider the complexity of regional economic activities and pollution sources.

How to cite: Valdambrini, N. M. and Ribeiro, F.: Impacts of regional interactions on spatial and temporal variation of ozone and its precursors, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-97, https://doi.org/10.5194/icuc12-97, 2025.

Dry deposition is a crucial process responsible for the removal of air pollutants from the atmosphere, significantly impacting air quality in urban environments. Currently, existing regional air quality models typically parameterize the turbulent transport and dry deposition of air pollutants in the atmospheric surface layers (ASL) based on the Monin-Obukhov similarity theory (MOST), which assumes that the underlying surface is flat and homogeneous. However, in modern cities, high-rise buildings with heights comparable to the ASL depth (approximately 100 meters) are prevalent. In this condition, applying MOST to parameterize turbulent transport in these urban settings may lead to inaccurate air quality predictions. To address this issue, this study investigates the effects of urban geometry on the turbulent transport and dry deposition of air pollutants in the ASL using a building-resolving large-eddy simulation (LES) method. Specifically, we develop an LES approach to simulate the dry deposition of ultrafine aerosol particles over four distinct real urban surfaces, each with unique morphological characteristics. By considering the turbulent transport within urban canopies and the deposition of aerosols on building roofs and facades, our results indicate that traditional parameterization methods may overestimate turbulent transport over urban surfaces and underestimate the corresponding aerodynamic resistance by 28% to 52%.

How to cite: Cheng, W.-C. and Fu, T.-M.: Investigation of the dry deposition of air pollutants over urban surfaces using a building-resolving large-eddy simulation method, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-89, https://doi.org/10.5194/icuc12-89, 2025.