A006-0001
Investigation of ozone deposition to vegetation under warm and dry conditions near the Eastern Mediterranean coast

Monday, 7 December 2020
Poster
Eran Tas1, Qian Li2, Maor Gabay1, Yoav Rubin2, Shira Raveh-Rubin3, Shani Rohatyn3, Fyodor A. Tatarinov3, Eyal Rotenberg3, Efrat Ramati3, Uri Dicken3, Yakir Preisler3, Erick Fredj4 and Dan Yakir3, (1)Hebrew University of Jerusalem, Soil & Water Sciences, Jerusalem, Israel, (2)Hebrew University of Jerusalem, Soil & Water Sciences, Rehovot, Israel, (3)Weizmann Institute of Science, Rehovot, Israel, (4)The Jerusalem College of Technology, Jerusalem, Israel
Abstract:
Dry deposition of ozone (O3) to vegetation is an important removal pathway for tropospheric O3, while O3 uptake through plant stomata negatively affects vegetation which can in turn influence climate, by reducing carbon assimilation. Both processes are controlled by ambient conditions via complex mechanisms. Recent studies have revealed that these processes can be fundamentally impacted by coastal effects1, and by dry and warm conditions in ways that have not been fully characterized, largely due to lack of measurements under such conditions2,3. Hence, we hypothesized that measuring dry deposition of O3 to vegetation along a sharp spatial climate gradient, and at different distances from the coast, can offer new insights into the characterization of these effects on O3 deposition to vegetation, providing important information for climate and air-quality model improvement. To address these hypotheses, several measurement campaigns were performed at different forests, 4–59 km from the Eastern Mediterranean coast, under semiarid, Mediterranean and humid Mediterranean climate conditions3,4. The eddy covariance technique was used to quantify vertical O3 flux (Ftot) and its partitioning to stomatal flux (Fst­) and non-stomatal flux (Fns).

At night, efficient turbulence due to sea and land breezes significantly enhanced nighttime O3 deposition to vegetation, dozens of kilometers from the sea, while ~3.5km from the coast nighttime O3-deposition velocity (Vd) was smaller than daytime Vd by only ~20–37%. While previous studies under Mediterranean conditions revealed important contribution of chemical reactions, mainly of biogenic volatile organic compounds, to O3 deposition, under the conditions studied here, relative humidity was found to be the most important factor controlling O3 deposition rate, via enhancement of Fns at all sites. Extreme dry surface events, some induced by dry intrusion from the upper troposphere, resulted in positive Fns events. Whereas Fst tended to peak around noon under humid Mediterranean and Mediterranean conditions in summer, it was strongly limited by drought under semiarid conditions from spring to early winter, with minimum average Fst/Ftot of 8–11% during the summer, reflecting minimal effect of O3 deposition to vegetation on carbon assimilation under semiarid conditions.

[1] Li, Q. et al. 2018. Measurement-based investigation of ozone deposition to vegetation under the effects of coastal and photochemical air pollution in the Eastern Mediterranean. Sci. Total Environ. 645, 1579–1597.

[2] Fowler, D. et al. 2009. Atmospheric composition change: ecosystems–atmosphere interactions. Atmos. Environ. 43 (33), 5193–5267. https://doi.org/10.1016/j.atmosenv.2009.07.068.

[3] Emberson, L.D. et al. 2000. Modelling of stomatal conductance and ozone flux of Norway spruce: comparison with field data. Environ. Pollut. 109, 393–402.

[4] Li, Q., et al. 2019. Investigation of ozone deposition to vegetation under warm and dry conditions near the Eastern Mediterranean coast. Sci. Total Environ. 658, 1316-1333.

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