May Ecological Corridors at Urban Areas Help the Improvement of Air Quality and Outdoor Thermal Comfort in Winter Cities?

Research through Simulation in Erzurum

Abstract

Climate-sensitive urban planning research is crucial for improving city life quality, especially in winter-cities, providing to incorporate climatic elements to planning to promote outdoor activities and improving air quality. This study aims to examine the impact of ecological corridors on outdoor human thermal comfort and air pollution in winter cities. The study assessed how the urban environment in Erzurum, one of Turkey's coldest cities with low thermal comfort and high PM10 levels, responds to changing climatic conditions in regard to the implementation of proposed ecological corridors that involved opening closed stream lines. The winter 2023 analysis assessed the effectiveness of ecological corridors in mitigating winter disturbances caused by air pollution and thermal comfort conditions in the Erzurum, using maps generated from morphological, meteorological, and spatial data employing ENVI-met. It was found that newly established ecological corridors can mitigate the negative effects of high urban density, improper land use, lack of natural and green areas, and ventilation issues, leading to enhanced air quality and temperature. Same corridors, however, may decrease thermal comfort levels by inducing cold stress, especially in shaded areas. Thus, ecological corridors should be implemented with caution considering their potential negative and positive impacts on quality of city life.

Introduction

Urbanization plays a critical role in shaping Earth's climate system, as highlighted by the Intergovernmental Panel on Climate Change. The expansion of cities leads to significant changes in the environment, including increased greenhouse gas emissions, aerosols, altered land use patterns, and direct heat production (Yavaş, Dursun et al., 2023). These changes disrupt the natural relationship between the land surface and atmosphere, affecting water and energy exchange processes and contributing to global and local climate issues (Civerolo, Hogrefe et al., 2007; Vahmani, Sun et al., 2016). Among these challenges, poor air quality and reduced thermal comfort in urban areas have become prominent concerns (Aw and Kleeman, 2003; Burian and Shepherd, 2005; Chen, Zhang et al., 2018; Civerolo, Hogrefe et al., 2007; Fallmann, Forkel et al., 2016; Kalnay and Cai, 2003; Tao, Liu et al., 2015; Zhang, Li et al., 2019).

Urban characteristics such as building density, morphology, material use, street orientation, and vegetation levels greatly influence the local microclimate. Mixed-use housing and compact urban development strategies, have been shown to significantly reduce emissions and enhance urban sustainability by optimizing mobility and land use (Hasibuan, Asrofani et al., 2025). Research shows that these factors impact air quality and thermal comfort, which vary significantly based on the unique physical and climatic features of cities (Dursun, D and Yavaş, 2014; Dursun, D., Yavaş et al., 2020; Dursun, D. Y., M. , 2020; Irmak, Yilmaz et al., 2017; Li, Zhang et al., 2019). For instance, green spaces are known to reduce air pollution and moderate urban temperatures, but their effectiveness depends on their design and integration into the urban fabric (Rui, Buccolieri et al., 2019; Taleghani, Kleerekoper et al., 2015). Recent computational simulations confirm that strategically placed green open spaces can regulate airflow and pollutant dispersion in dense urban fabrics, contributing to both thermal comfort and air quality (Aini, Wikantiyoso et al., 2025). However, many studies assume that urban characteristics are homogeneous and fail to consider the complex interactions between different urban variables, such as street layouts, building heights, and material properties (Locosselli, de Camargo et al., 2019; Nowak, D. and Heisler, 2010; Nowak, D. J., Hirabayashi et al., 2018; Ozdemir, 2019). When examining the studies conducted in this context, it is noted that there is a deficiency in research concerning the effects of land use decisions on urban air quality at the micro scale (Deng, Ma et al., 2019; Shi, Ren et al., 2019; Taleghani, Clark et al., 2020; Yilmaz, Irmak et al., 2022; Yilmaz, Menteş et al., 2023; Yilmaz, Sezen et al., 2021b).

In Türkiye, cities face similar challenges of low air quality and poor thermal comfort due to rapid and unplanned urbanization. Given the different climate regions in Türkiye, it is also imperative to conduct site-specific studies. In cities with different climate characteristics such as cities with Mediterranean climate, black sea climate, and harsh continental climate, the effects of different spatial fabrics and green space applications on microclimate and air quality will differ. However, research exploring the relationship between urban planning decisions and environmental conditions, particularly at the city scale, remains limited. This highlights the need for site-specific studies that address the unique characteristics of urban environments in different climatic regions.

Ecological corridors have been proposed as a solution to improve urban air quality and outdoor thermal comfort by enhancing natural ventilation and integrating green infrastructure into the built environment, reflecting the multifunctional greenway planning strategy that emphasizes ecological connectivity and cultural integration as proposed by Ahern (2000). Acting as ventilation channels, these corridors connect less dense peripheral areas with city centers, facilitating airflow and improving air quality (Milosovicova, 2013). Properly designed corridors should have minimal obstacles, appropriate dimensions, and utilize parks, wide streets, and water bodies to optimize air circulation. While the theoretical benefits of ecological corridors are well-documented, their practical impacts on air quality and thermal comfort have rarely been quantified.

This study focuses on Erzurum, a city with a harsh winter climate and significant air pollution problems. Erzurum’s urbanization patterns, characterized by dense and unhealthy development, exacerbate its environmental challenges. Building on a previous project (Ecological Corridor Scenarios in Air Pollution: The City of Erzurum) supported by the Northeast Anatolia Development Agency (KUDAKA), which proposed ecological corridors (see Figure 1) as a solution to air pollution, this research aims to evaluate their effectiveness through simulation. The ENVI-met software is used to analyse how these corridors influence air quality and thermal comfort. In evaluating thermal comfort conditions, the authors employed the framework of thermal stress categories (Physiological Equivalent Temperature - PET), as proposed by Matzarakis and Mayer (1996). The study integrates detailed data on building characteristics, land use, and vegetation to assess the potential improvements that ecological corridors could bring to Erzurum’s urban environment. By addressing a gap in the existing literature, this research aims to provide concrete insights into the role of ecological corridors in enhancing air quality and thermal comfort in cities with challenging climatic conditions.

Figure 1. Proposed Ecological Corridors (Dursun, D and Yavaş, 2014; DURSUN, Doğan, YILMAZ et al., 2015)

Methods

The methodology followed in this study is based on the use of the ENVI-met program. Therefore, the method is directly linked to the operation of ENVI-met, a microclimate simulation program (see Figure 2). First, meteorological data, physical data, and air pollution data related to the study area are obtained and entered into the software interface. Based on these inputs, an appropriate simulation start date and time are selected. The program is then run for a simulation lasting approximately one month, during which results are generated. A validation analysis is conducted on the obtained results, and once satisfactory outcomes are achieved, the simulation results are evaluated. For thermal comfort assessments, Matzarakis and Mayer (1996) Thermal Stress Categories-PET are used. Simulation results are interpreted according to the values that correspond to these categories.

Figure 2. Methodology Diagram

Study area

The north-eastern Turkish city of Erzurum, which is situated at various elevations between 1758 and 2100 m, is selected as the field of research. The urban area in the northern Palandöken Mountain slopes is around 30 km2. In accordance with the decisions made regarding the spatial plan, which is easily amendable by the municipal council, the city continuously grows on both the flat Erzurum Plain in the north-northwest and west directions, and the mountainous areas to the southern outskirts of the Mountain (Cihangir-Çamur, Dursun et al., 2023; Dursun, Doğan, 2018; Dursun, Dogan and Yavas, 2015a, 2016; Yavaş, Dursun et al., 2023). Erzurum falls under the Dsb (Severe Winter, Dry and Cool Summer) subgroup of Koppen's climatic classification, which is characterized by monthly mean temperatures that are above 10 °C for at least four months and below 22 °C for the warmest months. The winter season lasts for more than six months, during which the temperature can drop as low as -37.2 °C. The time frame for snow cover is from mid-October to mid-May. Situated at an elevation of around 2000 meters, the centre of Erzurum is one of the biggest cities in the world (Kocaman, Zaman et al., 2008). Erzurum is situated on the edge of Palandöken Mountain, lying towards a plain at the base of a topography in the shape of a bowl that blocks most of the wind. The typologies regarding the components of the city, which have an impact on solar and wind insolation, also influence the characteristics of the urban climate of the city (Arslan, 2022; Dursun, D. and M., 2023; Dursun, Dogan and Yavas, 2016; Yavaş, Dursun et al., 2023).

In winter, wind velocity is already low if facade systems are inefficient and the inversion phenomena predominates due to terrain. Due to the unsuitability of the metropolitan structure for ventilation corridors, the contaminated air is not effectively removed by the prevailing southerly winds (WSW; West-Southwest; during the burning period), which blow in the opposite direction of the exit corridors (Dursun, Dogan and Yavas, 2015b; Dursun, D and Yavaş, 2014; Kopar and Zengin, 2009; Yavaş, Dursun et al., 2023). As a result, wind's ability to influence climate in a way that improves air quality throughout the winter is restricted. The wind speeds are lowest in January, February, and December, with averages of 2.1 m/s, 2.3 m/s, and 2.1 m/s respectively. According to the Erzurum Province's Clean Air Action Plan (CAAPEP), extremely significant increases in emission rates occur on days with extremely low air temperatures (CSB(Ministry of Environment, 2020). Significant increases in sulphur dioxide (SO2) and particulate matter emissions are observed, particularly between 6:00 and 11:00 in the morning and 18:00 and 21:00 in the evening, as a result of the initial firing and continuous loading of fuels burnt for heating.

Additionally, the CAAPEP states that during the winter, all stations surpass the 24-hour PM10 limit values. It is important to note that the PM10 values exceeding the limitations listed in the Air Quality Assessment and Management Regulation (Turkish State Ministry of Environment, Urbanism and Climate Change (2013). Air Quality Assessment and Management Regulation (AQAMR) issued on 09/09 2013 and with the number of 31677. [WWW document], URL https://www.mevzuat.gov.tr/File/GeneratePdf?mevzuatNo=12188&mevzuatTur=KurumVeKurulusYonetmeligi&mevzuatTertip=5 ), even while the annual SO2, NO2, and CO values continue to be below the limit value (CSB(Ministry of Environment, 2020). It is recognized that days with exceptionally high pollution are influenced by a number of climatic elements. The city's atmosphere becomes polluted and thick, especially on days when the meteorological high-pressure centre causes an inversion (Arslan, 2022; Yavaş, Dursun et al., 2023). The time it takes to surpass the limit values is also a result of the low wind speed, which also influences the duration of the air pollution (CSB(Ministry of Environment, 2020).

Within the scope of the article, a region where the transformation areas in the historical core of Erzurum are concentrated was selected as the study area (see Figure 3). The reason why this area was preferred for simulations is that it is a region where air pollution intensifies in winter months, has a closed stream line and is subject to urban transformation projects (DURSUN, Doğan, YILMAZ et al., 2015). The effect of two ecological corridors (Figure 1)(DURSUN, Doğan, YILMAZ et al., 2015), which were proposed in the area and based on the results of a previously completed project, on pollution and thermal comfort values were tested based on concrete scientific results. In addition, closed stream lines and water traces were included in the ecological corridors. 100-metre wide corridors were proposed with rows of trees on both sides of the corridors. In addition to thermal properties, the study characterised and tested the urban microclimate and air pollutants. It is estimated that in a short period of time the areas evacuated for transformation will reach 100% occupancy. In the area with dense residential use in the surrounding area, the building layout is split-layout and the buildings consist of 8-15 storeys. In the region, which will experience a rapid urbanisation process, it has been determined how air quality and thermal comfort values will change in case of development in advance and with different planning decisions (creating ecological corridors) with the ENVI-Met simulation model.

Figure 3. Satellite Image Showing the Boundaries and Spatial Structure of the Study Area, 2023 (Google Earth Pro V 7.3.6.9750. (July 7, 2022). Rabia Ana Mah., Erzurum, Turkey.39° 54' 10.70 “N, 41° 16” 46.49 ’E, Eye alt 3.67km, 1930m Elevation. DigitalGlobe 2022. http://www.earth.google.com [March 2, 2023])

Data

The National Air Quality Monitoring Network of the Turkish Ministry of Environment, Urbanization, and Climate Change publishes “hourly air quality data” from previous years on its official website database (havaizleme.gov.tr). The data is collected from measurement points dispersed across the country. In 2023, PM10 (µg/m3), SO2 (µg/m3), NO2 (µg/m3), and NOX (µg/m3) values were measured at two of measurement points at city centre: the Taşhan and Aziziye air quality measurement stations (Fig.4). These stations are located very close to the case study area and have been in operation since 2013. Measured data were used in the analysis and were taken from the database mentioned previously. In addition to collecting pollution data, this study also obtained hourly meteorological data for the same periods. This included air temperature (Ta; °C), relative humidity (RH; %), wind direction and wind velocity (wv; m/s).

Figure 4. Ecological Corridors and Measurement Stations

In addition to pollution data, Elitech brand mobile measuring devices were procured for meteorological data to be measured in parallel for the same periods and calibrated in Erzurum Meteorological Regional Directorate. Assistance was received from the regional directorate officials for this process. Afterwards, mobile measurement devices were placed at three different points (for Measurement Point 1, the garden of the North East Anatolia Development Agency was determined, and the device was placed at the appropriate point to take hourly data records. For Measurement Point 2, a mobile measurement device was placed at a suitable point in the Agricultural Credit Cooperative campus. For Measurement Point 3, a measuring device was installed at a central point on the ecological corridor, in the garden of Kadama women's cooperative) and data were recorded for winter periods (see Figure 4). With these measuring devices, hourly temperature and humidity data at 2 metres above the ground were taken during the months of December (2022), January and February (2023). In addition, hourly temperature, wind speed (m/s), wind direction and relative humidity (g/m3) data were obtained from the Regional Directorate of Meteorology (Erzurum) for the same months.

Modelling

The ENVI-met model, one of the widely used dynamic simulation tools for microclimate analysis, has been used for microclimate research by more than 1900 registered users worldwide until 2017 (Bruse, M., 2018; Bruse, Michael and Fleer, 1998). In recent years, there has been a significant increase in ENVI-met studies and publications. In most of the studies, the model is used for both research and application purposes (Bruse, Michael and Fleer, 1998; Cortes, Rejuso et al., 2022; Dursun, D., Yavaş et al., 2020; Ebrahimnejad, Noori et al., 2017; Elraouf, ELMokadem et al., 2022; Kusumastuty, Poerbo et al., 2018; López-Cabeza, Galán-Marín et al., 2018; Tsoka, Tsikaloudaki et al., 2018; Yavaş, Dursun et al., 2023; Yilmaz, Külekçi et al., 2021a; Yilmaz, Mutlu et al., 2018). ENVI-met, a three-dimensional, non-hydrostatic microclimate model with a grid resolution of 0.5-10 metres, was developed to calculate and simulate climate variables in urban areas. The software considers total radiation (direct, reflected and diffuse solar radiation and longwave radiation) and models the evolution of climate variables during the day. In simulations using the laws of fluid dynamics and thermodynamics, the programme calculates the atmospheric state by combining the influence of buildings, vegetation, surface features, soils and climatic conditions. Furthermore, ENVI-met provides numerous tools to simulate and analyse air pollution in the simulation area. In addition to thermal characteristics, the urban microclimate is characterised by high levels of air pollutants, e.g. NOx and O3, especially during heat waves. Ozone is not a primary pollutant in the troposphere, i.e. - with the exception of nitrogen monoxide and nitrogen dioxide - it is not emitted directly into the atmosphere but is instead formed by photochemical reactions in the troposphere. In the absence of free radicals, the ozone concentration forms a photochemical equilibrium with the concentrations of nitrogen monoxide and nitrogen dioxide, where the ozone concentration depends on the ratio of NO2 and NO. Tropospheric ozone is formed mainly under the influence of NOx. Since cars and other vehicles are the main emitters of NOx, high O3 concentrations are clearly linked to the proximity of highly frequented streets. Atmospheric conditions (mainly shortwave radiation and ambient temperature) play a crucial role in the formation and destruction of O3 and cause its non-uniform distribution. With the high spatial resolution of ENVI-met, these local variations in the microclimate and hence their effects on the O3 concentration can be adequately simulated. This study demonstrates the ability of ENVI-met to analyse the air pollution concentration in a model area. Furthermore, ENVI-met offers numerous options for analysing active chemistry and dispersion in the model domain.

Thermal Comfort (PET)

Outdoor thermal comfort is related to the utilization pattern of urban open spaces. Thermally uncomfortable outdoor environments can discourage participation in outdoor activities and increase energy consumption of buildings for cooling (Aghamolaei, Azizi et al., 2023; Grifoni, Passerini et al., 2013). Especially for winter cities, urban layout from macro to micro scale has to be consistent with cold climate conditions.

Thermal comfort indices do not assess the impact of a single climate parameter on humans. It produces a result based on the temperature value by taking into account the combination of many parameters. In this study, thermal comfort assessment was carried out with PET, one of the thermal indices (Gulyás, Unger et al., 2006; Jamei and Rajagopalan, 2019; Mayer and Höppe, 1987; Potchter, Cohen et al., 2018). PET, considered as physiological equivalent temperature, is a thermal index derived from human energy balance. It is considered suitable for the assessment of the thermal component of different climates. In addition to having a detailed physiological basis, PET is preferred over other thermal indices because its unit is °C. Especially for urban planners, it makes the results more understandable than human-biometeorological terminology. PET results can be obtained as bioclimatic maps with the help of ENVI-met. Through these maps, spatial distribution can be easily monitored (Matzarakis, Mayer et al., 1999). Matzarakis and Mayer (1996) determined PET ranges (Table 1), which are valid for thermal perception and degree of physiological stress in humans. For the calculation of PET, six parameters were defined: air temperature, mean reflected temperature, wind speed, relative humidity, metabolic rate and thermal clothing insulation, and the values obtained are based on a nine-point psycho-physical scale ranging from 4^oC to 41^oC. In this study, urban microclimatic changes were measured by thermal comfort (PET) through ENVI-met and outdoor thermal comfort was evaluated according to the defined stress categories.

Table 1. The PET Index’s Thermal stress categories (Matzarakis and Mayer, 1996)

PET (0C)	Thermal Sensitivity/ Perception	Physiological Heat Stress Levels
< 4	Very cold	Extreme cold stress
4.1-8.0	Cold	Strong cold stress
8.1-13.0	Cool	Moderate cold stress
13.1-18.0	Slightly cool	Slight cold stress
18.1-23.0	Comfortable	No thermal stress
23.1-29.0	Slightly warm	Slight heat stress
29.1-35.0	Warm	Moderate heat stress
35.1-40.0	Hot	Strong heat stress
> 41.0	Very hot	Extreme heat stress

Mobil Data Entry

ENVI-Met version 5.5.1 was used for the simulations. The 3D simulation area for the whole area has a dimension of 240m×366m and a vertical height of 25m. The area was generated using a grid with a grid resolution of 5m×5m×5m×5m. In the focussed area within the study area, a grid resolution of 2m×2m×2m×2m with a dimension of 500m×300m and a vertical height of 45m was used to access more detailed data (see Figure 5). February was chosen for the analyses because it was measured as the coldest month of the year and because of the minimum differences between the average temperature in Erzurum and the temperature data of the study area. The model was tested for 30 hours, starting at 5:00 AM on February 12th, 2023, using meteorological parameters (Ta, Wv, Wd, RH) and the elements of air pollution (PM10, NO2, NOX). Wind direction was taken as 200^o and speed as 0.5 m/sec for the same day and 05:00.

Figure 5. A graphical representation of the research area, 2023

Validation of the ENVI-Met Model

ENVI-met calculations are largely validated depending on the grid size, detail in the model and input parameters. To validate the ENVI-met results of this study, the measured and simulated air temperature datasets were compared (Table 2). The graphs show that the increase and decrease of air temperatures for the two datasets occur at the same time of the day. The study evaluated the calibration between the measured values and modelling results with two different indicators. The agreement index (d), as the first indicator, takes a value between 0-1 and the closer this value is to 1, the more accuracy is ensured. RMSE (Root Mean Square Error) is another indicator that compares different prediction errors in a dataset and shows the accuracy. The smaller the value, the less error in the forecast. In this direction, the agreement index (between simulated and measured air temperature) d value and RMSE value were calculated for a period of 30 hours in February for the year 2023.

Table 2. Measurement Results

Measurement Month		Study Area	ERZURUM Average	Differences
December 2022	Temperature (oC)	(S1) -0.9 (S2) -1.4 (S3) -0.7 (Average)	-0.8	0.1
	Humidity (%)	64.7 (S1) 67.0 (S2) 72.6 (S3) 68.1 (Average)	78.9	-10.8
January 2023	Temperature (oC)	-0.9 (S1) -2.9 (S2) -3.6 (S3) -2.4 (Average)	-3.9	1.5
	Humidity (%)	52.2 (S1) 52.1 (S2) 63.4 (S3) 55.9 (Average)	63.6	-7.7
February 2023	Temperature (oC)	-3.0 (S1) -6.8 (S2) -7.1 (S3) -5.6 (Average)	-7.8	2.2
	Humidity (%)	62.3 (S1) 60.6 (S2) 73.9 (S3) 65.6 (Average)	68.7	-3.1

Results

Because of its user-friendliness and proven dependability in measuring changes in urban microclimate with respect to thermal comfort, ENVI-met was selected from a variety of numerical models for this investigation (Yang, Hu et al., 2021; Yavaş, Dursun et al., 2023). The temperature of the urban atmosphere is higher than that of the surrounding area because to modified radiative qualities, such as air quality, reduced velocity of the wind and albedo and roughness of the surface. Urban areas are also characterized by a high concentration of aerosols and air; such as NOX and O3, whose concentrations vary based on heat waves and human activities (Liang and Gong, 2020). Except for nitrogen monoxide and nitrogen dioxide, ozone is not a major pollutant in the troposphere, which means that it is created by photochemical processes in the troposphere rather than being released into the atmosphere (Brancher, 2021). Ozone concentration is determined by the NO2:NO2 ratio and it forms a photochemical equilibrium with concentrations of nitrogen monoxide and nitrogen dioxide without the presence of free radicals (Dursun, D. and M., 2023). NOX primarily influences the formation of tropospheric ozone (Archibald, Neu et al., 2020). High concentrations of O3 are unmistakably associated with the proximity of heavily trafficked streets, as automobiles and other vehicles are the primary sources of NOX emissions (Brancher, 2021). O3 is formed and destroyed in large part by atmospheric factors, namely shortwave radiation and ambient temperature, which results in its uneven distribution (Kroll, Heald et al., 2020). These localized variations in the microclimate and their consequences on the concentration of O3 can be sufficiently replicated because to ENVI-met's high spatial resolution (Simon, Fallmann et al., 2019; Yavaş, Dursun et al., 2023). This study also tests ENVI-met's ability to analyse air pollutant concentrations in a specific model area.

A simulation was conducted to evaluate concentrations of NO, NO2, and O3, as well as thermal comfort conditions during February 2023. The purpose was to gain insight into the relationship between the spatial distribution of air pollution parameters, thermal comfort conditions, and two proposed ecological corridors, including a restored stream line. The study focused on nitrogen oxides and O3 pollutants, as they have higher concentrations in the winter due to combustion and motor vehicle traffic, according to CAAPEP .

Validation of the ENVI-met Model

The validation of the ENVI-met model was conducted using two indicators: the correspondence index (d) and Root Mean Square Error (RMSE). The correspondence index (d), ranging from 0 (no agreement) to 1 (perfect agreement), was calculated as 0.75, indicating good agreement between measured and simulated air temperatures. The RMSE value, reflecting the magnitude of simulation errors, was 4.09, demonstrating that the model predictions have an acceptable level of accuracy (see Figure 6).

Figure 6. Correspondence index, RMSE, observed and simulated air temperature

Spatial Distribution of Air Pollution

The simulation results indicated that ecological corridors had a significant impact on reducing air pollutant concentrations. The concentrations of nitric oxide (NO) and ozone (O3) pollutants decreased substantially in areas where ecological corridors were implemented. Specifically, NO concentrations decreased by approximately 40 µg/m³, and ozone concentrations were reduced by around 6 µg/m³ (Figure 7, Figure 8, and Figure 9). Notably, the ecological corridors' effectiveness in reducing pollutant levels extended throughout the entire simulation area, not limited solely to the areas directly converted to green spaces.

Figure 7. Simulated distribution of NO concentration

Figure 8. Simulated distribution of NO2 concentration

Figure 9. Simulated distribution of O₃ concentration

Influence of Ecological Corridors on Air Temperature

Ecological corridors were found to raise local air temperatures by an average of 1°C. Simulations showed improvements of up to 0.8°C within the warmest areas of the study region. This increase can primarily be attributed to enhanced vegetation cover and the restoration of stream lines, both of which modify local radiative properties and the distribution of heat (Figure 10).

Figure 10. Distribution of simulated air temperature

Thermal Comfort Conditions

The evaluation of thermal comfort conditions based on PET values reveals that the presence of ecological corridors results in a roughly 5°C decrease in PET in the vacant areas and an 8°C decrease in PET in the surrounding built environment (see Figure 11). It is seen that there is a decrease of 1°C in the whole environment. The PET results indicate that the built environment falls within the 'strong cold stress' range due to the length of building shadows, particularly during the winter months. Although the thermal comfort of open areas is better than the built environment, “strong and moderate cold stress” ranges can be observed in those areas because of increasing wind and shade areas due to trees. Although the temperature increases throughout the area, PET values differ due to shade and wind conditions. Ecological corridors increased the ambient temperature slightly, but on the other hand created cold stress.

Figure 11. Distribution of simulated PET values

Discussion

According to the 2020 World Air Quality Report by IQAir, Turkey ranks 46th among 106 nations in air quality, with Erzurum identified as one of Turkey’s three most polluted cities. This highlights the need to evaluate Erzurum's urban planning considering three critical factors: air pollution, rapid urbanization, and its cold climate conditions. Despite their significance, existing literature exploring the intersection of air pollution, urbanization, and spatial development in cold regions remains limited. One notable exception is Yavaş, Dursun et al. (2023), which demonstrated how urban expansion and increased human activity elevate pollution levels and deteriorate microclimatic conditions. The research emphasizes the role urban form and functional layout play in exacerbating thermal discomfort and air pollution.

Our findings align with the literature, emphasizing that strategic green infrastructure, specifically ecological corridors, positively influences urban air quality and microclimate. However, as Nowak, D. and Heisler (2010) suggest, tree placement must be carefully planned; incorrect alignment, particularly in prevailing wind directions, might inadvertently trap pollutants. The present study affirms that ecological corridors, when designed considering prevailing winds and spatial organization, can effectively reduce pollutant concentrations and enhance air circulation.

While interest in the relationship between urbanization and climate change has increased significantly over the past decade (Zhou, An et al., 2022), most research continues to focus on macroscale implications. Studies since the 1990s have predominantly addressed theoretical aspects, energy comfort, and microclimate modelling (Yavaş, Dursun et al., 2023). Our study contributes by examining practical microscale implications of ecological corridors on air quality, thermal comfort, and urban temperatures, providing essential insights for informed urban planning and redevelopment strategies.

Furthermore, this research assesses the specific impacts of ecological corridors—100 meters wide with bilateral tree plantations—on Erzurum's air quality, highlighting the nuanced interactions between green infrastructure and pollution. The complex nature of these interactions necessitates careful design to optimize benefits, as discussed extensively by various scholars(Abhijith, Kumar et al., 2017; Cariñanos and Casares-Porcel, 2011; Eisenman, Churkina et al., 2019; Gallagher, Baldauf et al., 2015; Kumar, Druckman et al., 2019; Lee and Maheswaran, 2011; Shaneyfelt, Anderson et al., 2017; Van den Berg, Maas et al., 2010). While our findings affirm the pollutant-mitigating capabilities of ecological corridors, they do not delve into species-specific effects, highlighting an important area for future research.

Despite their advantages, green urban areas in cold climates can increase heating energy demands, as noted by Simpson and McPherson (1998). Still, numerous studies indicate that green infrastructure significantly reduces air pollutants like CO, NO₂, PM₁₀, PM₂.₅, and SO₂ (Cavanagh and Clemons, 2006; Selmi, Weber et al., 2016). Given these varying outcomes, further research focused on detailed local and regional analyses is required to build a comprehensive database supporting precise urban planning decisions (Pataki, Carreiro et al., 2011; Salmond, Tadaki et al., 2016).

Our investigation extends the preliminary findings of the "Scenarios for Ecological Corridors in Air Pollution: Erzurum City" project (Dursun, Dogan and Yavas, 2015a). That project recommended ecological corridors based on pollution hot spots, urban transformation sites, prevailing winds, and natural hydrological paths (covered streambeds). Despite clearly outlined plans, the current uncertainties surrounding the utilization of expropriated areas, intended for ecological corridors, raise concerns regarding potential prioritization of short-term economic benefits (e.g., housing or commercial development) over long-term ecological solutions. Our findings strongly suggest maintaining these areas as ecological corridors could significantly mitigate pollution and enhance air quality, challenging the perception that such investments yield inadequate financial returns.

Critically, our study underscores the importance of site-specific assessments beyond general assumptions. Detailed micro-level planning is essential, particularly in cold climates with prolonged heating periods and persistent air pollution, as seen in Erzurum. By evaluating microclimatic impacts, this research highlights tangible improvements achievable in air quality, temperature regulation, and thermal comfort through targeted urban design and green infrastructure integration.

Based on these insights, we recommend several strategic actions for urban planners and policymakers. It is essential to enhance technical infrastructure and invest in human resources dedicated to simulation and environmental modelling, facilitating advanced assessments of urban development projects and their environmental impacts prior to implementation. Comprehensive green infrastructure and natural surface expansion policies should be developed and rigorously supported through meticulous planning, continuous monitoring, and thorough evaluation processes. Furthermore, urbanization policies must be clearly defined with climate-specific considerations, extending beyond basic zoning principles to encompass integrated urban design and thorough environmental impact analyses. It is also crucial to elevate urban ecological strategies, such as ecological corridors, from localized initiatives to national policy priorities, thus promoting sustainable development practices across Turkish cities. Ultimately, ecological corridors hold substantial potential for improving air quality, thermal comfort, and overall urban resilience, provided that their implementation is guided by detailed, evidence-based urban planning principles.

Conclusion

The study's findings lead to the following conclusions:

• Urban ecological corridors can reduce the rate of air pollution by facilitating appropriate spatial planning and land use decisions.

• Restoring the blue (stream line) and green (ecological corridor) areas and planting more trees therein reduces the concentrations of NO, NOX, and O3 in the air.

• The most obvious elements influencing air temperature and thermal comfort levels in the neighbourhood are green spaces and trees, simulations show rising temperatures but falling PET values (by reducing thermal comfort to strong cold stress).

• It becomes clear that, in order to improve air quality and thermal comfort in cities situated at high elevations with prevailing mountainous and cold climate conditions, extra care must be taken with spatial planning to ensure that less green space and dense urban development are not permitted over the central area.

• Incorporating green corridors into spatial plans should be based on detailed spatial and climatic analyses. This includes considering cold climate characteristics, the design of the built environment and the length of the heating season. Additionally, planning decisions must take into account the disadvantages of a city's topographical and geographical location, such as inversion.

• An intriguing finding of the study is that the suggested ecological corridors had favourable effects on temperature and air pollution, but unfavourable effects on thermal comfort. To ensure favourable outcomes, it is crucial to strictly adhere to spatial design and planning principles that are appropriate for the local climate circumstances. This applies to all interventions and decisions made in urban development plans. Ecological corridors' effects on cold stress should be considered in cities with cold climates.

• This study highlights the aspects that may impact urban thermal comfort and air quality, such as building density, land use types, vegetation cover and restricted wind velocity.

• This simulation study also shows the relationship between vegetation, surface features, and the spatial organization of urban areas and the circumstances of air pollution, heating, and cooling in urban environments.

• This study highlights the need to produce input data on microclimate factors in order to work on design solutions by connecting the issue of air pollution in city centres with ecological corridor design.

The results of the study indicate that ecological corridors increase air temperature and reduce pollution concentrations during winter; however, an important point to remember is that ecological corridors, as tested in the simulation, can also increase cold stress in urban areas. In cold climate cities such as Erzurum, planning for ecological corridors should take various parameters into account; especially in urban areas that are likely to experience high levels of pedestrian traffic. Detailed urban design projects should be prepared using these parameters in order to create areas with high thermal comfort. The influence of wind, ground surface variety, and vegetation on air temperature and pollution levels is well documented. However, the results of the ENVI-met model demonstrate that these factors are not solely functions of vegetation cover or surface materials. Furthermore, it is recognised that these factors are contingent upon the quality, configuration and disposition of urban spaces. Therefore, a key takeaway from this study is that an urban area's air pollution issue is related to planning decisions and spatial design and should serve as an input for planning and design solutions based on microclimate parameters. When considering these inputs, urban space design should involve comprehensive testing of solutions through various trials, addressing elements such as building and street orientations, street widths, green space proportions, tree planting patterns, natural and artificial surface ratios, and material details for paved surfaces. It can be concluded from this study that an urban area's air pollution issue is related to planning decisions and spatial design. Consequently, this should serve as an input for planning and design solutions based on microclimate parameters. In light of these considerations, it is imperative that urban space design incorporates a comprehensive testing of solutions through a multitude of trials. This process should encompass an array of elements, including building and street orientations, street widths, green space proportions, tree planting patterns, ratios of natural and artificial surfaces, and the specifics of paved materials.

Author Contributions

Conceptualization, D.D., M.Y.; methodology, D.D., M.Y.; software, M.Y.; investigation, D.D., M.Y.; resources, D.D.; data curation, D.D., M.Y; writing—original draft preparation, D.D., M.Y. and D.D.; writing—review and editing, D.D., M.Y. and D.D.; supervision, D.D. All authors have read and agreed to the published version of the manuscript.

Ethics Declaration

The authors declare that they have no conflicts of interest regarding the publication of the paper.

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