# Stomatal and Non-Stomatal Turbulent Deposition Flux of Ozone to a Managed Peatland
## 1 Introduction  
Tropospheric ozone is an important greenhouse gas and is harmful to humans, as it impairs lung function [1]. Its average mixing ratio has more than doubled over the past 150 years [2]; the background mixing ratio today in Europe is approximately 30 ppb and is continuously increasing [3]. Ozone is not directly emitted into the atmosphere by anthropogenic emissions, but it is formed through photochemical reactions involving precursors--mainly nitrogen oxides (NO\({}_{x}\)) and volatile organic compounds (VOC)--from both natural and anthropogenic origins [4]. The sinks of tropospheric ozone are manifold and have been studied previously in detail: Ozone reacts with various trace gases such as hydroperoxyl radicals (HO\({}_{2}\)), biogenic VOC [5], and nitric oxide (NO) [6, 7]. It also reacts with aerosol particles [8, 9] and undergoes direct photolysis through short-wave solar radiation [6]. Another sink mechanism is its deposition on the earth's surface [10]. Once in contact with a given surface (vegetation, soil, or water), ozone will react readily and be decomposed; thus, its deposition is aterminal process [11; 12]. For vegetation, two ozone deposition pathways act in parallel: First, ozone is deposited on plants' surfaces, such as on their cuticles or twig and stem surfaces. Second, ozone can enter the plants' stomata, reach the sub-stomatal cavity and thus impact photosynthesis and other physiological processes [13; 14]. This may eventually cause alterations of plant morphology [15] and crop yield losses [16]. However, the stomatal ozone flux preceding these effects cannot be directly quantified on an ecosystem scale. Efforts to quantify this flux by indirect methods have only been made for a few ecosystems so far [17; 18; 19; 20; 21; 22; 23].  
In this study, we focus on the ozone deposition process on vegetation, specifically on the partitioning between stomatal and non-stomatal fluxes [24; 25; 22]. We performed this study on a mid-latitude peatland ecosystem, which is managed with the goal of bringing it back to a natural or at least semi-natural state. While most studies on ozone deposition to peat- and wetlands have been conducted using mesocosm and microcosm experiments [26; 27; 28; 29], only few studies have considered the larger picture and deal with ozone deposition to these ecosystems as a whole [30; 31; 32; 33]. To our knowledge, there is only one study on ozone deposition to a mid-latitude peatland on the ecosystem scale [21]; thus, here we aim to add valuable information that can improve the characterization of ozone deposition to these ecosystems.  
We applied the eddy covariance technique as well as the surface resistance analogy to first quantify the overall ozone deposition flux (\(F_{O_{3}}\)) and then partition this flux into stomatal (i.e., uptake by vegetation through stomatal gas exchange, \(F_{sto}\)) and non-stomatal fluxes (\(F_{nsto}\)) during the peak of the growing season. We performed a driver analysis of non-stomatal deposition velocities and analyzed the relationship between the stomatal ozone fluxes and gross primary productivity under different environmental ozone concentrations.