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

Dry deposition of ozone (O) to vegetation is an important removal pathway for tropospheric O, while O uptake through plant stomata negatively affects vegetation and leads to climate change. Both processes are controlled by vegetation characteristics and ambient conditions via complex mechanisms. Recent studies have revealed that these processes can be fundamentally impacted by coastal effects, and by dry and warm conditions in ways that have not been fully characterized, largely due to lack of measurements under such conditions. Hence, we hypothesized that measuring dry deposition of O 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 O deposition to vegetation and stomatal uptake, providing important information for afforestation management and for climate and air-quality model improvement. To address these hypotheses, several measurement campaigns were performed at different sites, including pine, oak, and mixed Mediterranean forests, at distances of 20-59 km from the Eastern Mediterranean coast, under semiarid, Mediterranean and humid Mediterranean climate conditions. The eddy covariance technique was used to quantify vertical O flux (F) and its partitioning to stomatal flux (F) and non-stomatal flux (F). Whereas F 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 F/F of 8-11% during the summer. F in the area was predominantly controlled by relative humidity (RH), whereas increasing F with RH for RH < 70% indicated enhancement of F by aerosols, via surface wetness stimulation. At night, efficient turbulence due to sea and land breezes, together with increased RH, resulted in strong enhancement of F. Extreme dry surface events, some induced by dry intrusion from the upper troposphere, resulted in positive F events.