Urban Planning
Zeinab Adeli; Azin pirasteh
Abstract
Highlights
Comprehensive Assessment: Systematic, multi-scalar analysis of the correlation between 22 distinct urban form indicators and primary air pollutants across all 22 administrative districts of Tehran.
Spatial Determinism: Empirical confirmation of the decisive role of urban spatial structure ...
Read More
Highlights
Comprehensive Assessment: Systematic, multi-scalar analysis of the correlation between 22 distinct urban form indicators and primary air pollutants across all 22 administrative districts of Tehran.
Spatial Determinism: Empirical confirmation of the decisive role of urban spatial structure and morphological patterns in modulating air quality variations.
Introduction
Despite occupying less than three percent of the Earth’s surface, contemporary cities are the primary drivers of anthropogenic pollution, exposing a vast global population to hazardous air quality with severe public health and economic repercussions. While vehicular emissions and fossil fuel consumption are the dominant sources of atmospheric pollutants, local climatic conditions, complex topography, and—critically—urban form exert a profound influence on pollutant dispersion and concentration. Recent scholarship has increasingly focused on the nexus between urban morphology and air quality, suggesting that land-use patterns and spatial configurations can significantly attenuate or exacerbate the accumulation of pollutants. However, much of the extant research has been geographically limited or focused on restricted sets of environmental indicators.
Tehran, as a rapidly expanding megacity characterized by industrial development, high population density, and intensive motorized transport, serves as a critical case study for this environmental challenge. This research aims to investigate the complex relationship between various urban form indicators and air pollution levels across Tehran’s 22 districts. Specifically, the study seeks to answer: What are the primary morphological indicators affecting air quality, and what are the specific correlations between these urban form dimensions and major pollutants (CO, O₃, NO₂, SO₂, and PM2.5)? This understanding is essential for shifting towards more sustainable urban planning paradigms.
Theoretical Framework
This study conceptualizes the city as a dynamic system where physical form and environmental processes are inextricably linked. The research operationalizes urban form through 22 metrics categorized into four strategic dimensions: environmental design, land use, accessibility, and density. By meticulously calculating the quantitative values of these metrics for each district, the study provides a robust empirical basis for evaluating the spatial distribution and intensity of pollutants.
The correlation between these indicators and annual pollutant concentrations is analyzed to assess how spatial and design configurations influence urban environmental performance. This research adopts an applied analytical approach, utilizing quantitative spatial data to delineate the association between the dense urban fabric of Tehran and the magnitude of pollutants. Pearson’s correlation coefficient is employed as the primary statistical tool to establish the strength, direction, and structural significance of these bivariate dependencies. By integrating concepts from urban morphology and environmental science, this research offers a comprehensive understanding of how strategic spatial interventions can be leveraged to enhance urban environmental resilience.
Methodology
This research is an applied study utilizing a quantitative-statistical approach. The primary objective is to analyze the correlation between urban form indicators and air pollution across Tehran’s 22 districts. Data regarding the concentration of pollutants (CO, SO₂, NO, O₃, and PM2.5) were compiled from official air quality monitoring station archives and longitudinal environmental reports.
The indicators of urban form were categorized based on a thorough literature review, followed by the definition of standardized quantitative measures for each. Subsequently, the Pearson correlation test was performed to test the null hypotheses concerning the relationships between independent variables (urban form metrics) and dependent variables (pollutant concentration). This method allows for a clear evaluation of linear relationships within the high-density urban environment of Tehran, facilitating the identification of critical morphological factors that correlate with air quality degradation.
Results and Discussion
The Pearson correlation analysis revealed a diverse range of relationships between urban form and pollutant concentrations. Statistically significant positive correlations were observed between “residential unit density” and pollutants such as CO, SO₂, NO₂, and PM2.5, confirming that high-density residential areas—often associated with increased traffic and energy consumption—are more susceptible to air quality issues. Similar trends were noted for “gross population density” and “distance traveled,” which show a strong positive correlation with SO₂ and NO₂ emissions, underscoring the role of transport and human intensity in pollution cycles.
Conversely, indicators associated with sustainable urban design, such as “public transport network length” and “per capita green space,” demonstrated inverse relationships with several pollutants. For instance, increased green space coverage was negatively correlated with SO₂ and CO levels, suggesting a significant mitigating effect. However, the study also encountered complex nuances; for example, while some indicators like “pedestrian and bicycle path length” showed negative associations with SO₂, they exhibited positive correlations with others, indicating that the impact of urban form on air quality is multifaceted and highly dependent on the specific pollutant under examination.
Conclusion
This study provides empirical evidence that urban form is a fundamental determinant of air pollution distribution. By analyzing 22 morphological indicators, the research confirms that structural characteristics—such as land-use intensity, density, and spatial connectivity—directly influence the accumulation of CO, SO₂, NO₂, and PM2.5. The results suggest that urban air quality is not merely a product of emissions, but also a result of how urban space is organized. Therefore, to mitigate air pollution, urban planners must move beyond traditional emission-control policies and embrace strategic spatial planning. Targeted interventions in density management, the enhancement of green infrastructure, and the optimization of accessibility can act as effective tools for long-term environmental management and sustainability in the Tehran metropolitan area.
Acknowledgment
We sincerely acknowledge all those who provided scientific support for this research.
Urban Ecology
Elham Ghasemi; Zahra Nazemi; Safoura Mokhtarzadeh; Mahdi Suleimany
Abstract
Highlights:
- Investigates the correlation between environmental factors and UHI intensity in the Isfahan metropolitan area over 10 years.
- Utilizes MODIS Aqua & Terra data alongside Landsat 8 imagery for comprehensive UHI analysis.
- Establishes a significant relationship between UHI ...
Read More
Highlights:
- Investigates the correlation between environmental factors and UHI intensity in the Isfahan metropolitan area over 10 years.
- Utilizes MODIS Aqua & Terra data alongside Landsat 8 imagery for comprehensive UHI analysis.
- Establishes a significant relationship between UHI and urban built density, vegetation, and water features.
- Determines vegetation as the most influential factor in mitigating UHI compared to other elements.
- Highlights the vital role of natural infrastructure in urban planning for UHI mitigation.
Introduction:
The Urban Heat Island (UHI) effect, characterized by a temperature increase in urban areas compared to their rural counterparts, presents considerable environmental challenges, impacting public health, urban energy systems, and city sustainability. This phenomenon, fueled by rapid urbanization and industrialization, exacerbates heatwaves, posing risks to public health. Understanding the UHI effect is essential for developing responsive urban planning strategies both spatially and institutionally. This study, centered on Isfahan, Iran, explores the correlation between UHI intensity and environmental factors, encompassing both built and natural attributes across five scenarios, including four seasons and one analyzing the ambient effect of the ZayandehRud river.
Theoretical Framework:
The UHI phenomenon involves complex interactions among various urban and environmental factors. The density of the built environment contributes to UHI exacerbation through heat storage and anthropogenic heat discharge. Air pollution, especially with greenhouse effects, directly influences heat-trapping and UHI formation. Conversely, green infrastructure and water bodies offer UHI mitigation through cooling effects. This study integrates theoretical basics from urban planning, climatology, and sustainable development for an analysis of how both natural and built elements correlate with UHI intensity in the Isfahan metropolitan area.
Methodology:
A mixed-method approach is adopted to address the multifaceted nature of Urban Heat Island (UHI) and its potentially correlated environmental factors. Land Surface Temperature (LST) data, crucial for delineating UHI, were extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard NASA's Aqua and Terra satellites, covering a decade from 2011 to 2021. This extended timeframe facilitates the exploration of UHI patterns across various seasons, examining specific impacts during both the flow and dry periods of the ZayandehRud river, as well as distinguishing LST differences between daytime and nighttime periods—unlike Landsat Satellite Images.
Additionally, Landsat 8 images are utilized to process the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) for mapping green infrastructures and water bodies. Air Quality Index (AQI) data from the year 2020 supplements the study, allowing for an investigation into the relationship between air pollution and UHI. The analysis of all datasets employs the Pearson correlation coefficient to ascertain the nature and extent of correlation among UHI and the identified environmental variables.
Results and Discussion:
The findings reveal the persistent prevalence of Urban Heat Island (UHI) during nighttime across all scenarios in Isfahan. However, during daytime hours, the trend shifts, giving rise to cooler zones within the city borders, indicating the emergence of urban cold islands. A noteworthy revelation from the study is the significant exacerbation of UHI attributed to the density of the urban built environment. Intriguingly, air pollution, though exerting a lesser impact on Land Surface Temperature (LST) compared to built density, still plays a role in elevating LST during daylight.
The study underscores the pivotal role of urban green infrastructure and water bodies in mitigating heat islands. Among these elements, green spaces, particularly vegetation, emerge as highly influential, surpassing the cooling effects of both water bodies and polluted air. The seasonal variation in vegetation cover also influences UHI intensity, with reduced vegetative cover in colder, drier seasons contributing to heightened UHI effects. These spatial and temporal dynamics emphasize the intricate balance between UHI and environmental factors, offering valuable insights for decision-makers. Such insights can guide targeted strategies in urban planning and design to address the challenges posed by UHI.
Conclusion:
The study emphasizes the importance of considering UHI in urban planning, design, and sustainability discussions. Strategies include reducing built density and integrating green and blue infrastructures. Addressing air quality and vegetation cover in shaping urban thermal landscapes suggests comprehensive policies. Guarding against UHI through natural space preservation and innovative design solutions tailored to Isfahan's climate can enhance urban livability. Future work should quantify contributions of different elements for comprehensive UHI mitigation models. This Isfahan case study serves as a cornerstone for wider applications across similar cities, aiding in combatting global warming and UHI effectively.
Urban Ecology
Mostafa Karimi; Samaneh Khosnavaz; Aliakbar Shamsipour; Masoumeh Moghbel
Abstract
Today, urban development and air pollution are the most important issues concerning urban climate that can affect the quality of urban life. Despite the significant progress made in the fuel and engine technology, emission of pollutants in urban environments is still prevalent. As in many other countries, ...
Read More
Today, urban development and air pollution are the most important issues concerning urban climate that can affect the quality of urban life. Despite the significant progress made in the fuel and engine technology, emission of pollutants in urban environments is still prevalent. As in many other countries, the environmental issue is particularly evident in the large cities of Iran such as Tehran, Tabriz, Isfahan, Shiraz, Arak, and Karaj. The rapid urbanization, industrialization, and increasing trend in the use of motor vehicles have caused numerous environmental issues, including the production and distribution of different types of air pollutant, especially in Tehran, the capital. Tehran’s confinement by mountains and meteorological factors such as temperature inversion, the persistence of high-pressure systems with cold air, and local winds exacerbate pollution. Hence, numerous studies have been conducted on air pollution in Tehran. The results have indicated that 73% to 85.5% of the air pollution observed at urban stations is caused by temperature inversions, which are influenced by high pressure and surface radiation. According to the above research, the key factors involved in the spread of pollution over the streets besides the spatial and natural factors that can affect the distribution of air pollutants (i.e. geographic location, topography, etc.) include the arrangement of the buildings, particularly in terms of street width and orientation, distance, and intersections. It should be noted given the significance of the issue that the pollution can have extensive effects although it occurs at the street level, due to the interaction of the dispersal and diffusion of pollutants through meteorological conditions (wind speed and direction and atmospheric stability), the configuration of buildings, and the orientation of streets. Therefore, the main purpose of this research was to specify the characteristics of pollutant flow and dispersion on urban passages in micro scale. For that purpose, the meteorological data, including air temperature, relative humidity, and wind speed and direction, were extracted from Iran Meteorological Organization (IMO) Geophysics Weather Station (the closest station to the area under investigation) for a 20-year statistical period (1991-2010). Two areas (1 and 2) in Municipal District 6 were specified as making up the area under study in this research. Then, the pollutant dispersion data were obtained based on the relationship between traffic volume and pollutant production during two winter and summer months (July and January) and at three times of the day (morning, midday, and afternoon). Finally, the distribution of air pollutants was simulated using the ENVI-met microscale model for building configuration and street orientation in the area under investigation. The results demonstrated that street and pathway orientation plays an important role in the accumulation or distribution of pollutants. Accordingly, the density of pollutants is higher in streets that are perpendicular to the prevailing wind direction. Furthermore, the concentration of pollutants in the main streets of the area under study exhibited a significant relationship with their directions. Pollutant concentration was moderate in streets with prevailing north winds, while the highest and lowest amounts of pollutant concentration were observed in streets with south and southwest winds, respectively. It can be concluded that consideration of the climate conditions in urban design and development (wind speed/direction in particular) can be effective in improvement of air quality in urban areas. Air Pollution, Street Orientation, Wind Speed/Direction, Tehran, ENVI-met Model.
