Ozone deposition to a Sierra Nevada, California ponderosa pine plantation

The main focus of this dissertation is analyzing ozone flux to a ponderosa pine plantation in the Sierra Nevada Mountains and its controlling factors. Climate (specifically, photosynthetically active radiation, vapor pressure deficit, air temperature, and soil moisture or water potential) was found to have a major impact on ozone deposition. The relationship of the climate variables with ozone deposition was found to be dynamic and to change with phenology and water status. Consequently, concentration based metrics proved inadequate to protect tree health because actual ozone dose to trees was controlled by many factors in addition to concentration. A strong seasonality on ozone deposition was observed. Cumulative ozone flux was found to be higher in the summer than any other individual season but the majority (∼two-thirds) of the total ozone deposited to this system occurred in non-summer months. The transpiration study showed that strong coupling between the leaf surface and airstream and a low threshold for stomatal closure caused transpiration and canopy conductance to be limited on an hourly basis but allowed the trees to remain active all summer. Finally, ozone flux was partitioned into the main ozone sinks: FO3=Fstom+Fsurf +Fchem. Both stomatal uptake and chemical reactions—likely with NO and hydrocarbons—were equally important ozone sinks at this site, while deposition to non-stomatal surfaces was a relatively minor component.; Overall, the major processes controlling ozone deposition to this site could be summarized as: FO3=f PAR,VPD,Tair, Y,phenology+ f&parl0;LAI,u*, ra,rb,s oilwetness&parr0;+ fTair, where $FO3$ is ozone flux, PAR is photosynthetically active radiation, VPD is vapor pressure deficit, T_air is air temperature, $Y$ is water potential, LAI is leaf area index, u_∗ is friction velocity, r_a is aerodynamic resistance, and r_b is boundary layer resistance.