The interrelationship between vegetation and air‑pollution

Scientific background: This research is collaboration between the Hebrew University and UC Berkeley, U.S. The project is aimed at studying the relationship between air pollution, plants functoning (e.g., photosynthesis and transpiration) and climate change. 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.

Methods:  In order to approach the objectives of the study, ecosystem-atmosphere gas exchange will be used to quantify the fluxes of water vapor (H2O), carbon di-oxide (CO2), ozone (O3) and VOCs in Yatir forest and Ramat Hanadiv Shrubbery. The eddy covariance technique allows calculating the flux rate by placing meteorological and chemical (specific for the investigated gases) sensors over the ecosystem. All used sensors need to be highly precise and operate at high frequency (>10Hz). The water vapor and carbon di-oxide measurement enables us to follow the plants activity and functioning. The ozone flux measurement allows to determine the ozone flux through the plants stomata, based on the water and carbon di-oxide fluxes. The VOCs fluxes will be determined using the Proton-Transfer-Reaction-Time-of-Flight Mass Spectrometry (PTR-ToF-MS). This newly developed methodology currently enable us the measurement of a much larger number of VOCs species compared with previous studies, allowing the simultaneous quantification of hundreds of species, while many of them were not recognized as being emitted from vegetation so far (Park et al., 2013). During the research the concentration of other gases will be continuously measured including, carbon monooxide, nitrogen oxides and sulfur di-oxide. The quantification of these gases along with complementary measurement data will enable us to follow air pollution processes and sources.

References :
Mills G. and H. Harmens. 2011. Ozone Pollution: A hidden threat to food security Report
prepared by the ICP Vegetation. Centre for Ecology and Hydrology, Environment Centre Wales,
Park J.-H., Goldstein A.H., Timkovsky J., Fares S., Weber R., Karlik J. & Holzinger R., (2013) Active atmosphere-ecosystem exchange of the vast majority of detected volatile organic compounds, Science, 341, 643–647.

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