Modeling long-term uptake and re-volatilization of semi-volatile organic compounds (SVOCs) across the soil-atmosphere interface.
Soil-atmosphere exchange is important for the environmental fate and atmospheric transport of many semi-volatile organic compounds (SVOCs). This study focuses on modeling the vapor phase exchange of semi-volatile hydrophobic organic pollutants between soil and the atmosphere using the multicomponent reactive transport code MIN3P. MIN3P is typically applied to simulate aqueous and vapor phase transport and reaction processes in the subsurface. We extended the code to also include an atmospheric boundary layer where eddy diffusion takes place. The relevant processes and parameters affecting soil-atmosphere exchange were investigated in several 1-D model scenarios and at various time scales (from years to centuries). Phenanthrene was chosen as a model compound, but results apply for other hydrophobic organic compounds as well. Gaseous phenanthrene was assumed to be constantly supplied to the system during a pollution period and a subsequent regulation period (with a 50% decline in the emission rate). Our results indicate that long-term soil-atmosphere exchange of phenanthrene is controlled by the soil compartment - re-volatilization thus depends on soil properties. A sensitivity analysis showed that accumulation and transport in soils in the short term is dominated by diffusion, whereas in the long term groundwater recharge and biodegradation become relevant. As expected, sorption causes retardation and slows down transport and biodegradation. If atmospheric concentration is reduced (e.g. after environmental regulations), re-volatilization from soil to the atmosphere occurs only for a relatively short time period. Therefore, the model results demonstrate that soils generally are sinks for atmospheric pollutants. The atmospheric boundary layer is only relevant for time scales of less than one month. The extended MIN3P code can also be applied to simulate fluctuating concentrations in the atmosphere, for instance due to temperature changes in the topsoil.
University of Tübingen, Department of Geosciences, Hölderlinstr. 12, 72074 Tübingen, Germany. Electronic address: zhongwen.bao@uni-tuebingen.de.
Zhongwen
Z
Bao
University of Tübingen, Department of Geosciences, Hölderlinstr. 12, 72074 Tübingen, Germany.
Christina
C
Haberer
Helmholtz Center for Environmental Research - UFZ, Department of Hydrogeology, Permoserstr. 15, 04318 Leipzig, Germany.
Uli
U
Maier
College of Charleston, Department of Geology and Environmental Geosciences, 202 Calhoun Street, 29401 Charleston, SC, United States.
Barbara
B
Beckingham
Carleton University, Department of Earth Sciences, 1125 Colonel By Drive, K1S 5B6 Ottawa, ON, Canada.
Richard T
RT
Amos
University of Tübingen, Department of Geosciences, Hölderlinstr. 12, 72074 Tübingen, Germany.
Peter
P
Grathwohl
D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere / Q000737:chemistry; D004784:Environmental Monitoring / Q000379:methods*; D008956:Models, Chemical; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D055549:Volatile Organic Compounds / Q000032:analysis*; D014835:Volatilization
D000393:Air Pollutants; D012987:Soil; D012989:Soil Pollutants; D055549:Volatile Organic Compounds
Biodegradation; Diffusion; Groundwater recharge; Phenanthrene; Soil and atmosphere pollution; Sorption