In the present study, the Local Climate Zone (LCZ) scheme and Landsat 8 satellite images were used to extract urban land uses in Tehran. Then, FRAGSTATS software (version 4.2.1) was used to calculate land use metrics based on spatial patterns (composition and configuration) of each land use. Additionally, Sentinel-5P satellite images were used to calculate and evaluate air pollutants in summer (2020) and winter (2021). Finally, considering 22 districts of Tehran, Pearson correlation coefficient and multiple linear regression were used to investigate the relationship between the spatial composition and configuration of urban land uses and air pollutants, respectively (Fig. 1). It should be noted that land use maps were generated at the same scale used to generate the images for air pollutants, namely 1 km.
2. 1. The Case Of Study
Tehran as the most populous metropolis of Iran is located in the geographical position of 35°36'46'' N and 51°17'23" E. The area of the city is equal to 730 square kilometers and its population is about 9 million people, so it has the highest population density in Iran with a population density of 12,910 people per square kilometer. Tehran now has 22 regions (Fig. 2) and is the 25th most populous city and the 27th largest city in the world (www.tehran.ir). Due to the rapid population growth and increasing urbanization, the metropolis of Tehran includes various types of urban land uses. Additionally, the special geographical location of the city, which is surrounded by Shemiran heights in the north, Damavand in the east, and Karaj in the west and is open only from the south, has led to the increased concentration of pollutants in this metropolis (Zebardast & Riazi, 2015). It is ranked 27th in 2019 among the most polluted cities in the world (https://www.iqair.com/iran/tehran). Thus, to investigate the relationship between urban land uses and air pollution, the metropolis of Tehran was considered as the study case in the present research.
2. 2. Methods
The local climate zone (LCZ) scheme was used to extract urban land uses. The LCZ scheme is currently considered as a standard for linking landscape to air pollutants at an urban scale. Generally, this classification scheme can be applied in three areas: 1. study of urban heat islands (Alexander & Mills, 2014; Emmanuel & Krüger, 2012; Leconte et al., 2015; Lehnert et al., 2015), 2. Modeling (Alexander et al., 2015; Bokwa et al., 2015; Geletič et al., 2016), and 3. extraction of land cover maps based on different geometric features (Bechtel & Daneke, 2012; Danylo et al., 2016; Lelovics et al., 2014). One of the advantages of LCZ classification is the complete description of land-use types in an urban environment because it meets the standards for measuring physical properties and urban morphology (Stewart & Oke, 2010). This classification divides urban land uses into 10 types of man-made and built spaces (1-10) and 7 types of natural land cover (A-G) (Fig. 3)(Stewart & Oke, 2012). Each class can be identified using structural features and land cover that influence air temperature at a height of 1-2 meters above the ground (Das & Das, 2020). One of the methods for generating a map based on the LCZ classification is the remote sensing imagery-based method (Bechtel et al., 2016; Lin & Xu, 2016). Using this method, we followed three basic steps of pre-processing Landsat-8 satellite images (TM & OLI / TIR) (Summer, 2020; Winter, 2021) by SagaGIS software(Conrad et al., 2015), digitization of each class of land uses by Google Earth, and the classification of land uses based on the LCZ schema by SAGA GIS software.
After producing the classification maps based on the LCZ schema, we matched the detected data with the Google Earth map related to the time of extraction by ENVI5.3 software. Thus, we checked the classification accuracy using the kappa coefficient and overall accuracy. If the Kappa coefficient is above 85% and the overall accuracy is above 90% at this stage, the accuracy of the generated map can be considered acceptable (Kerle et al., 2004).
2. 3. Selected Metrics
After generating land use maps, the characteristics of the land uses were quantified using landscape metrics and the calculations were performed by FRAGSTATS 4.2.1 software. As Table(1) shows, 6 metrics with the following characteristics were selected: 1. significant role in theory and practice (Li & Wu, 2004; Peng et al., 2010; Zhou et al., 2011), 2. Ease of calculation and high interpretive power (Li et al., 2012; Zhou et al., 2011), and 3. The least exaggeration in the data (Li & Wu, 2004; Riitters et al., 1995; Zhou et al., 2011).

A wide range of studies have evaluated air pollution using satellite images at various scales (Alvarez-Mendoza et al., 2019; Basu et al., 2019; Fernández-Pacheco et al., 2018; Meng et al., 2016; Zhang et al., 2019). One of the satellites used for this purpose is Sentinel-5P (Table 2). It is an earth observation satellite that was launched on 13 October 2017 by the European Space Agency for the global monitoring of the environment and the air pollutants such as carbon dioxide, nitrogen dioxide, ozone, and sulfur dioxide with a resolution of 1 km*1 km and a very high speed (Sannigrahi et al., 2020; Veefkind et al., 2012). In this study, the spatial and temporal variation of air pollutants was investigated using the Sentile-5P satellite and its TROPOMI instruments on the Google Earth Engine (GEE) platform. GEE is a geographic data processor launched by Google in 2010 that allows users to access GEE through an Internet-based Application Programming Interface (API) and an interactive web-based development environment (Amani et al., 2020).
Table 2
Sentile-5P satellite information about air pollutants
Satellite
|
Name
|
Description
|
Min*
|
Max*
|
Unit
|
Sentinel-5p
|
CO
|
Vertically integrated CO column density
|
-279
|
4.64
|
mol/m^2
|
NO2
|
Total vertical column of NO2 (ratio of the slant column density of NO2 and the total air mass factor).
|
-0.0006
|
0.0096
|
SO2
|
SO2 vertical column density at ground level, calculated using the DOAS technique.
|
-48
|
0.24
|
O3
|
Total atmospheric column of O3 between the surface and the top of atmosphere, calculated with the [DOAS algorithm]
|
0.0047
|
0.272
|
* = Values are estimated, Earth Engine Code Editor (google.com) |