Introduction

The increase in the growth rate of urbanization and the desire of people to live in cities has caused the temperature of cities to increase compared to their surroundings. If this temperature difference rises above a certain level, it will lead in problems and risks such as: change in biodiversity; changes in weather; disturbing the thermal balance; Greenhouse effects and other problems and environmental damage. The difference between levels in urban and non-urban areas in terms of three-dimensional stfucture of Built-up areas on the one hand and heat absorption of the building materials used, surface reflection and amount of coating Plants, on the other hand, bring about fundamental changes in the nature of built-up urban areas.The increase in temperature in urban areas and its small-scale climate changes are known as the urban heat island; Contrary to built-up areas, cities located in arid and semi-arid climates will have a lower surface temperature than their non-urban dry surroundings, this phenomenon is known as cold heat island. There are reciprocal relationships between the intensity of heat islands and atmospheric pollutants; This means that the intensity of heat islands can affect chemical reactions and be affected by them. A review of the literature related to the relationship between the urban heat island and air pollution in the last 30 years shows that it is better to investigate the synergistic effect of these two factors instead of investigating air pollution and urban heat island separately.
 

Methodology

In order to monitor the changes in thermal islands of Tehran province and investigation of its relationship with atmospheric pollutants, satellite remote sensing method combined with mathematical and statistical methods has been used. By writing the appropriate codes in the Google Earth Engine system, thermal islands and a map of temperature changes were produced; Also, by using the products of Sentinel-5 satellite in the Google Earth Engine system and using the methods of cluster analysis and path analysis, the relationship between climatic parameters and atmospheric pollutants of So2, CH4, Co, O3, NO2, HCHO and PM has been explained and described.
 

Results

According to the tables of beta coefficients, the daily temperature of the earth's surface with a beta coefficient of 0.315 had the greatest impact on the dependent variable of the nighttime temperature of the earth's surface. The research findings show that among the studied variables, the CO molecule was the main factor in increasing SO2 concentration. Likewise, the O3 molecule with the standard beta coefficient of -0.205 had the greatest reduction effect on the NO2 molecule, and other variables did not have a significant effect on the increase or decrease of NO2. According to the maps, the intensity of nighttime heat islands in the city of Tehran belongs to the central and southern areas of the city, which is due to the high concentration of residential structures and atmospheric pollutants. The maps of the temporal changes of the heat islands in the study area show that the main location of these islands is moving from the center of the city to its surroundings, which is caused by factors other than atmospheric pollutants. Among the ways of distinguishing this research from other researches conducted by other researchers, we can mention the use of atmospheric chemistry rules and its application in expressing and analyzing the role of atmospheric pollutants on the temperature near the earth's surface.
 

Discussion

In order to determine the direct and indirect effects of the studied variables on the night temperature of the earth's surface, the path analysis was performed step by step and path diagrams of intermediate dependent variables were drawn. Among the studied variables, the daily temperature of the earth's surface had the greatest impact on the nighttime temperature of the earth's surface. Beta tables and path charts indicate that CO had the greatest impact on the increase of SO2; Similarly, O3 has the most effect in reducing NO2. The map of the changes in the nocturnal heat islands between the years 2000 and 2022 shows the changes in the heat islands from the city of Tehran to the cities and satellite towns around it; It is similar to the process of changes and the direction of movement of thermal islands at night from the metropolis of Karaj to the cities and satellite towns around it.The average nightly heat island intensity map shows that during the years 2000 to 2022, the highest heat island intensity was in the central and southern regions of Tehran.   
 

Conclusion

The natural and political geography of Tehran province is one of its differences with other provinces of the country. The simultaneous mixing and interaction of the province's climatic, geomorphological and geopolitical conditions has caused the heat islands to acquire a special pattern. Based on the research done with the help of GEE system and under-desktop software; It was observed that the place of occurrence of thermal islands is moving and changing its place from the city of Tehran to the satellite cities and towns around it. According to the findings of this research, among the studied variables, the daily temperature of the earth's surface has the highest and PM particles have the least overall effect in reducing the nighttime temperature of the earth's surface.According to the obtained maps, charts and data; It was observed that among the 22 districts of Tehran, districts 11 and 12 were the permanent occurrences of nocturnal heat islands and had the highest occurrence frequency.
 
Acknowledgments
Atmospheric compounds, Google Earth engine, Surface temperature, Thermal islands, Tehran province, Path analysis