title: Modeling short-term concentration fluctuations of semi-volatile pollutants in the soil-plant-atmosphere system.
abstract: Temperature changes can drive cycling of semi-volatile pollutants between different environmental compartments (e.g. atmosphere, soil, plants). To evaluate the impact of daily temperature changes on atmospheric concentration fluctuations we employed a physically based model coupling soil, plants and the atmosphere, which accounts for heat transport, effective gas diffusion, sorption and biodegradation in the soil as well as eddy diffusion and photochemical oxidation in the atmospheric boundary layer of varying heights. The model results suggest that temperature-driven re-volatilization and uptake in soils cannot fully explain significant diurnal concentration fluctuations of atmospheric pollutants as for example observed for polychlorinated biphenyls (PCBs). This holds even for relatively low water contents (high gas diffusivity) and high sorption capacity of the topsoil (high organic carbon content and high pollutant concentration in the topsoil). Observed concentration fluctuations, however, can be easily matched if a rapidly-exchanging environmental compartment, such as a plant layer, is introduced. At elevated temperatures, plants release organic pollutants, which are rapidly distributed in the atmosphere by eddy diffusion. For photosensitive compounds, e.g. some polycyclic aromatic hydrocarbons (PAHs), decreasing atmospheric concentrations would be expected during daytime for the bare soil scenario. This decline is buffered by a plant layer, which acts as a ground-level reservoir. The modeling results emphasize the importance of a rapidly-exchanging compartment above ground to explain short-term atmospheric concentration fluctuations.
authors.affiliation: Department of Geosciences, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany. Electronic address: zhongwen.bao@uni-tuebingen.de.
authors.forename: Zhongwen
authors.initials: Z
authors.lastname: Bao
authors.affiliation: Department of Geosciences, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Haberer
authors.affiliation: Geoscience Centre, Georg-August-Universität Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany.
authors.forename: Uli
authors.initials: U
authors.lastname: Maier
authors.affiliation: Department of Geology and Environmental Geosciences, College of Charleston, 202 Calhoun Street, Charleston, SC 29041, United States.
authors.forename: Barbara
authors.initials: B
authors.lastname: Beckingham
authors.affiliation: Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Amos
authors.affiliation: Department of Geosciences, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Grathwohl
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D018556:Crops, Agricultural / Q000378:metabolism*; D004784:Environmental Monitoring; D008956:Models, Chemical; D008962:Models, Theoretical; D012989:Soil Pollutants / Q000032:analysis*; D055549:Volatile Organic Compounds / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D012989:Soil Pollutants; D055549:Volatile Organic Compounds
keywords: Diurnal temperature changes; Numerical modeling; Photochemical transformation; Plants; Soil and atmosphere pollution