Iran
Shiraz, with a population of around 1.8 million (2016 census), is Iran's sixth most populous city. It is the capital of the province of Fars, and was also the capital of Iran under the reign of the Zand dynasty. It is located near the ruins of Persepolis and Pasargadae, two of the four capitals of the Achaemenid Empire.
Shiraz
During the Zand dynasty when Shiraz was the capital of Iran, it was a small village limited around the Arg of Karim Khan and naturally there were several villages near it. The north part of old Shiraz (now Qasr al-dasht and Chamran) was completely covered with gardens and green trees that still remain. A number of municipal laws prohibit construction in any of the garden areas. In another view, these gardens are the city's lungs and help to clean the dust, and haze or carbon dioxide that cars produce, by photosynthesis. On the other hand, we see Shiraz as being more likely to have clean air in Iran; this is when it is compared to big cities such as Tehran or Isfahan, and the reason behind it may lie in Shiraz's many gardens.