Tehran is the capital of Iran and the most populous city in West Asia, as well as the second most significant metropolitan area in the Middle East, with an estimated population of 15 million in the Greater Tehran metropolis (surpassed only by Cairo). Tehran experiences a continental climate characterized by Mediterranean rainfall patterns and a cold semi-arid climate according to the Köppen climate classification (BSk). Summers in Tehran are typically long, hot, and dry, with limited rainfall.

Tehran is notorious for being one of the world’s most polluted cities. Recent research suggests that over 4,000 people in Tehran die prematurely each year due to ambient PM2.5 air pollution. Higher levels of air pollution in Tehran are associated with increased hospital admissions, particularly for respiratory issues. Much of this air pollution is a direct result of vehicle emissions, compounded by the use of substandard and poor-quality fuels in these vehicles.

As a response to these environmental challenges, Mohammedreza conducted a study addressing the critical urban environmental issues of UPI (Urban Pollution Island) and UHI (Urban Heat Island) in Tehran. His research focused on the role of green spaces in mitigating these urban challenges.

Initially, Mohammedreza sought to identify common greening patterns, including the choice of plant species, their locations, and specific characteristics. Subsequently, he examined the behavior of these greening patterns by analyzing specific hourly meteorological data. Based on our investigation, he identified optimal greening patterns that could address various challenges presented by urban canyons, such as UPI and UHI. These optimal patterns took into account various aspects of urban life, including ecological, environmental, cultural, social, and aesthetic considerations, making them comprehensive solutions suitable for urban designers and landscape architects to implement.

Our results confirmed the importance of wind speed and relative humidity in air pollution at the pedestrian level. In a way, the patterns that recorded the lowest wind speed had the highest air pollution deposition. These results confirm previous studies in this field.

The correlation coefficient of meteorological parameters on urban canyon phenomena (Urban Pollution Island and Urban heat Island) and each other in different seasons was a point that was investigated. The Results showed that grass and side hedges with a height of 1.2 meters were not noticeable and effective in depositing air pollution or intensifying adverse effects on Thermal comfort in urban canyons.

Based on the results, it can be said that the”Tree center” patterns have a better effect on improving thermal comfort conditions and reducing air pollution in urban canyons than the “Tree sides” patterns at the pedestrian level.

Graphs show that moving deciduous trees from the sidewalks to the median strip has effectively reduced air pollution at the pedestrian level by 67% in summer and 54% in winter. By the Same reposition for the coniferous trees, air pollution (PM2.5) has been reduced by 200% in summer and 90% in winter.

Also, by examining the type of species, it can be stated that deciduous trees have been more effective in reducing these phenomena (UPI and UHI) than coniferous trees. The results confirm these statements in both the winter and summer seasons.

Therefore, the ideal greenery pattern in urban canyons in the studied site (Tehran) can deciduous trees in the median strip and shrubs and bushes with a height of fewer than 1.2 meters scattered on the sidewalks. Following such a planting plan while reducing phenomena such as UPI and UHI preserves the aesthetic and scenic aspects of urban sidewalks, preserves the connection of urban pedestrians with the urban green space, and can It can meet the needs of landscape architects and urban designers.

Greeneries’ features, especially the Leaf area density (LAD) and its changes in the seasons, was one of the things that were given less attention in previous studies. Scenarios with the same tree position but different LAD values have achieved different results ( especially for deciduous trees because of  seasonal changes) . The LAD effect on wind speed as the main factor affecting air pollution deposition shows the importance of this parameter, which requires more investigation and attention.