The guidelines for improving air quality in homes, schools and other areas are well-known. Tropospheric ozone is the most notorious pollutant, responsible for more than 95% of every day in the United States. Ozone is particularly harmful to children and people who often work outdoors, as it inflames the lungs and increases the susceptibility and aggravation of respiratory diseases and infections. Vegetation, and trees in particular, can act as natural filters for both gases and particles in urban environments.
Particles are deposited on the surface of leaves, although particles can be re-suspended due to wind or rain or settle on the ground. Studies have shown that urban trees can reduce PM2.5 levels by up to 71.1 tons per year in some cities, resulting in a reduction of mortality rates of up to 7.6 people per year in New York alone. Additionally, air quality improvements attributed to urban trees ranged from 0.05% in San Francisco to 0.24% in Atlanta. Activity in outdoor green spaces has been associated with mental and physical benefits. People who use parks and open spaces are three times more likely to achieve recommended levels of physical activity than non-users, while those with access to a quiet side of their home were 40% less likely to be overweight or obese.
Green spaces can also reduce ambient noise by providing a barrier or screen, which can help improve cognitive thinking skills. Urban environments and busy lifestyles can be stressful, which can affect well-being and cause various ailments, as well as anxiety-related disorders. Visual stimuli and positive aesthetics, such as the presence of plants, can be used to relieve tension and reduce stress. Sounds of nature have also been shown to reduce stress. Over the past century, the climate has shown notable changes that affect human health, with populations in urban environments being more vulnerable due to residential density. The shade effect of trees and the cooling effects of the evapoperspiration of vegetation leaves reduce air temperature, while parks can extend their cooling effect to adjacent urban areas. Neighborhood green spaces can also improve people's perceptions of their own health.
Other factors that influence air quality include extreme heat, poverty-related stressors, racial disparities in access to green spaces, lack of income from any cause, mortality from circulatory diseases, physiological responses due to stress, health inequalities related to lack of income from any cause, mortality from circulatory diseases, physiological responses due to stress.