Estimation of ozone deposition over subalpine forest in Niwot Ridge, Colorado

Ground-level ozone can have detrimental effects on plants and ecosystems, increasing their sensitivity for environmental stresses, certain diseases, causing leaf damage and reduce in forest growth and potentially influence species diversity in ecosystems. The chemistry transport models which include deposition models have been developed to provide concentration and flux data to facilitate the evaluation of effects of air quality on ecosystems. There are several different approaches of parameterization schemes in gas deposition models, and the choice is usually a compromise between application determined needs and data availability.

The aim of this study is to evaluate the performance of three selected deposition models that are based on the big-leaf concept and characterized by different parameterization schemes. The three model estimations of ozone deposition over subalpine forest were validated using a six-month long dataset measured during the 2003 growing season using the eddy covariance technique at the Niwot Ridge AmeriFlux site in the Roosevelt National Forest in the Colorado Rocky Mountains. For our purpose, i.e. to get comparable results from different models, the model resistance schemes were adapted but the meteorological and radiation parameterizations (characteristics of moist air and solar radiation) were synchronized using one common scheme in order to obtain as objective results as possible regarding the performance of the models. We present here statistical and local sensitivity analysis to investigate the effect of the input values. Results show that model performance varies with time of the day, and the errors also have a seasonal pattern. During daytime over- or underestimation can occur depending on the season. Basically, the calculated nighttime ozone deposition data reveal a very good correlation with measured flux. Based on this comparative study that aims at a more precise simulation of the ozone fluxes and the cumulative ozone load over a region, the most appropriate method will be integrated into the REM-CALGRID urban/regional scale chemical transport model which has been developed in the Institute for Meteorology, FU–Berlin.