Trees help to clean the air during spare the air days.
The San Francisco Examiner reported two days ago that the Mission District proper has the poorest air quality of any San Francisco neighborhood. The reason cited by a report from MIT entitled "Health and Urbanism" found that surrounding neighborhoods had better air quality because of more open space. This open space includes more areas with back yards planted with trees and shrubs.
The City of San Francisco is making an effort to plant more trees and shrubs according to the Examiner. The city is also granting permits for property owners to remove concrete areas and replace with soil areas that can be planted with trees and shrubs.
During this record breaking winter for spare the air days we are reminded that planting more trees helps to keep our air healthier. I recommend reading our article on "Choosing the Right Tree for your Home Landscape."