The interrelationship between vegetation and air-pollution

Ozone is the most prevalent and damaging air pollutant to affect natural vegetation, forests and crops (Global economic loss associated with ozone damage to crops is currently estimated to be $11-26 billion annually; Mills and Harmens, 2011). During the industrial age, anthropogenic emissions of fossil fuel have acted to approximately double the global mean tropospheric ozone concentration. Ozone is a secondary pollutant, formed in the atmosphere up to hundreds kilometers downwind of its precursor’s emission sources (volatile organic compounds, carbon monoxide and nitrogen oxides) in the presence of sunlight radiation. Ozone concentrations in Israel are high due to the strong anthropogenic emissions combined with relatively warm and dry weather conditions. The damaging effect of O3 is strongly related to its integrated uptake by plant stomata associated with stomatal closure, reduced CO2 uptake and photosynthesis and transpiration. Ozone-induced reduction in the CO2 uptake by plants leads to increase in atmospheric CO2 concentrations and therefore also global warming. Being a strong oxidant, ozone that enters the plant through its stomata leads to disturbances in biochemical and physiological processes.

Volatile organic compounds (VOCs) emitted from plants react with ozone, thereby protecting the plants on a local scale. However, the emitted VOCs can cause ozone formation at larger distances (up to more than ten kilometers) downwind of the emission sources. Once in the atmosphere, VOCs also play important roles in influencing radiation budget and precipitation, via changes in clouds properties and processes. The currently available knowledge about VOCs emission from plants and the associated impact on key atmospheric processes, as well as ozone uptake by plants is highly limited, especially for Mediterranean and Semi-arid climatic conditions.