As the name implies, a green roof supports a veritable garden of plants. They offer a means of preserving green space in urban environments where almost every square inch of soil gets covered in asphalt, cement, and concrete.
Green roofs have many environmental benefits attributed to them. Their plants improve air quality by absorbing pollutants like carbon dioxide and ozone from the atmosphere, making it healthier to breathe.
They likewise help control runoff by absorbing much of the rainwater. By reducing the amount of water that washes various pollutants into local bodies of water, they improve the overall water quality.
Other environmental benefits include saving electricity by reducing the need for artificial cooling, reducing urban heat, and preserving roofing from wear and tear. It also improves urban biodiversity by providing homes for wildlife, enables growing food plants in urban spaces, and brings pleasant greenery to the eyes. (Related: Protect yourself from big city air pollution by taking these essential vitamins.)
The plants on a green roof absorb ozone from outdoor air
Researchers from Portland State University (PSU) wanted to measure the effects of green roofs on indoor air pollution of commercial spaces. They selected a big-box retail store in North Portland for their experiment.
The roof of the store consisted of a conventional white-painted membrane roof and a green roof with various plants. The researchers placed ozone-measuring devices on both the ordinary and green halves of the roof.
For two days, the researchers gauged the quality of the air that entered the retail store through the external intake vents mounted on the roof. They compared the ozone readings in the un-planted area with those in the green roof area.
Ozone is a chemical form of oxygen. While it screens much of the harmful ultraviolet light passing through the upper atmosphere, it is toxic to humans and animals that live down below.
At the end of their trial period, they noted that the air passing through the green roof displayed moderate reductions in ozone levels compared to the plant-less part of the roof. Upon further examination, they determined that the plants drew ozone from the air.
Get healthier indoor air by planting a green roof
The plants captured ozone through a means called dry deposition. It is a natural process that falls under the broader term "atmospheric deposition."
Over time, airborne pollutants will eventually "deposit" themselves on a surface due to various factors. Gravity might pull them down; they might run across a substance that attracts them on a physical or chemical level; or the surface they touch might dissolve them.
If the airborne pollutants come into contact with atmospheric moisture, they may get dissolved. When the moisture falls to earth as precipitation in the form of rain, snow, and the like, it is called "wet deposition." However, if the pollutants land on a dry surface, the term becomes "dry deposition."
Plants absorb gas from the air to help power vital processes such as photosynthesis. When ozone comes into contact with the surface of a plant, the gas gets gobbled up.
By capturing and storing ozone, the plants serve as a natural air filter. The PSU researchers concluded that the green roof improved the quality of the air that entered the building. They recommended further studies measure other air pollutants such as carbon dioxide.
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