Controls over ozone deposition to a high elevation subalpine forest

Andrew A Turnipseed,Sean P Burns,David J.P Moore,Jia Hu,Alex B Guenther,Russell K Monson

doi:10.1016/j.agrformet.2009.04.001

Andrew A Turnipseed, Sean P Burns + Show 4 more

https://doi.org/10.1016/j.agrformet.2009.04.001

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Ecosystem level ozone (O 3) fluxes during four different years were examined at a subalpine forest site in the Colorado Rocky Mountains. The local mountain–valley wind system and the proximity of the Denver Metropolitan area leads to high summertime ozone episodes on many afternoons. The timing between these episodes and the ecosystem processes controlling photosynthesis during the growing season plays a critical role in determining the amount of ozone deposition. Light and vapor pressure deficit (VPD) were the most dominant environmental drivers controlling the deposition of O 3 at this site through their influence on stomatal conductance. 81% of the daytime O 3 uptake was predicted to occur through the stomata. Stomatal uptake decreased at high VPD and temperatures leading to an overall decrease in O 3 flux; however, we did observe a non-stomatal conductance for O 3 that increased slightly with temperature before leveling off at higher values. During the growing season, O 3 deposition fluxes were enhanced after midday precipitation events and continued at elevated levels throughout the following night, implying a role for surface wetness. From nighttime data, evidence for both the presence of water films on the needles and non-closure of the plant stomata were observed. During the winter (non-growing) season, the ozone deposition velocity showed a consistent dependency on the latent heat flux. Although the mechanism is unclear, it is apparent that precipitation events play a role here through their influence on latent heat flux.

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Increases in ground-level ozone (O3) have been of great concern over the past 100 years (Vingarzan, 2004 and references therein)
In analyzing the wetness effects on O3 deposition, we have only looked at the variations in the total conductance (Gc), as models which predict stomatal conductance are not valid during wet conditions (Monteith and Unsworth, 1990)
In the present study we investigated the seasonal controls over and variability of O3 deposition at a high elevation subalpine forest that experiences periodic episodes of anthropogenic pollution

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Increases in ground-level ozone (O3) have been of great concern over the past 100 years (Vingarzan, 2004 and references therein). A large fraction of this deposition occurs through direct uptake by vegetation through the stomatal pores (Wesely, 1989; Wesely and Hicks, 2000) As quantitation of this loss is important toward predicting plant damage caused by O3, it has been argued that O3 concentration alone (as measured by many monitoring networks) is not adequate to predict damage to vegetation (US EPA, 1996; Musselman and Massman, 1999; Cieslik, 2004; Karlsson et al, 2004; Massman, 2004; Emberson et al, 2007). There have been numerous studies of ozone deposition to vegetation over the past 50 years (e.g., Regener, 1957; Wesely et al, 1978; Fuentes et al, 1992; Coe et al, 1995; Munger et al, 1996; Lamaud et al, 2002; Kurpius and Goldstein, 2003; Mikkelsen et al, 2004; Hogg et al, 2007), and these results have formed the basis for deposition models aimed at predicting vegetative ozone uptake (Wesely, 1989; Zhang et al, 2002)

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