2.1.3 AAPCV - Annual Amount of Pollutants Captured by Vegetation
Version 2.2 by Emily West on 2022/01/10 14:39
2.1.3 AAPCV - Annual Amount of Pollutants Captured by Vegetation
| Topic | Urban challenges | Sub-challenges |
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| Environment | 2 - Air Quality | 2.1.1 Air Quality at District/ City Scale |
Description | Annual amount of pollutants captured by vegetation indicates the amount of particulate and gaseous emissions through deposition and dispersion. Trees affect air quality through the direct removal of air pollutants, altering local microclimates and building energy use, and through the emission of volatile organic compounds (VOCs), which can contribute to O3 and PM2.5 formation. However, integrative studies have revealed that trees, particularly low VOC emitting species, can be a viable strategy to help reduce urban O3 levels. Trees remove gaseous air pollution primarily by uptake via leaf stomata, though some gases are removed by the plant surface. For O3, SO2 and NO2, most of the pollution is removed via leaf stomata. Once inside the leaf, gases diffuse into intercellular spaces and may be absorbed by water films to form acids or react with inner-leaf surfaces. Trees directly affect particulate matter in the atmosphere by intercepting particles, emitting particles (e.g., pollen) and resuspension of particles captured on the plant surface. Some particles can be absorbed into the tree, though most intercepted particles are retained on the plant surface. The intercepted particles often are resuspended to the atmosphere, washed off by rain, or dropped to the ground with leaf and twig fall. During dry periods, particles are constantly intercepted and resuspended, in part, dependent upon wind speed. The accumulation of particles on the leaves can affect photosynthesis and therefore potentially affect pollution removal by trees. During precipitation, particles can be washed off and either dissolved or transferred to the soil. Consequently, vegetation is only a temporary retention site for many atmospheric particles, where particles are eventually moved back to the atmosphere or moved to the soil. |
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