School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, P.R. China.
State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, Southern University of Science and Technology, Shenzhen, Guangdong 518055, P.R. China.
Environ Sci Technol. 2022 Feb 15;56(4):2355-2365. doi: 10.1021/acs.est.1c06009. Epub 2022 Feb 3.
During the lateral transport with subsurface flow, amounts of manufactured volatile organic chemicals and gases dissolved in groundwater are emitted into the atmosphere via upward diffusion through soils. Quantifying gas emissions is important for assessing environmental risk associated with these constituents (e.g., air pollution and global warming). It is widely recognized that the temperature would affect gas spreading in soils, which in turn regulates the gas emission from groundwater. However, the upward diffusive gas emission induced by the fluctuated ground surface temperature (GST) remains unexplored. A coupled heat transfer and gas transport model is developed to investigate emissions of tetrachloroethylene (PCE) and NO, a typical manufactured volatile organic chemical and a natural gas, from groundwater with seasonally fluctuating GSTs. The results indicate that both PCE and NO emissions vary significantly from month to month. Moreover, fluctuations of emissions lag obviously behind the fluctuation of GST due to the damping effects of both capillary fringe and soil sorption. The proposed model agrees with the observed data from a monolith lysimeter experiment well. The model is also applied to the estimations of NO emissions from 12 aquifers in Walloon Region, Belgium. The estimated NO emission is 12.6 μg N/m/d that falls in the estimated range (9.0-21.5 μg N/m/d) using the IPCC emission factor approach that commonly accounts for the NO emission of groundwater discharge to surface water only. It suggests that the upward diffusion is non-negligible for estimations of NO emission from groundwater.
在地下水流的横向迁移过程中，大量溶解在地下水中的人工挥发性有机化学品和气体通过向上扩散穿过土壤释放到大气中。量化气体排放对于评估与这些成分相关的环境风险（例如，空气污染和全球变暖）非常重要。人们普遍认识到温度会影响土壤中的气体扩散，这反过来又会调节地下水的气体排放。然而，波动的地表温度（GST）引起的向上扩散气体排放仍未得到探索。本研究建立了一个耦合的传热和气体传输模型，以研究具有季节性波动 GST 的地下水中四氯乙烯（PCE）和 NO 的排放，NO 是一种典型的人工挥发性有机化学品和一种天然气。结果表明，PCE 和 NO 的排放逐月变化很大。此外，由于毛管带和土壤吸附的阻尼作用，排放的波动明显滞后于 GST 的波动。所提出的模型与单块淋溶实验的观测数据吻合得很好。该模型还应用于比利时瓦隆地区 12 个含水层中 NO 排放的估算。使用仅考虑地下水排放到地表水的 IPCC 排放因子方法估算的 NO 排放量为 12.6μg N/m/d，落在估计范围内（9.0-21.5μg N/m/d）。这表明向上扩散对于估算地下水的 NO 排放是不可忽视的。
