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Best practices for characterization of High Temperature-Aquifer Thermal Energy Storage (HT-ATES) potential using well tests in Berlin (Germany) as an example

Application of Aquifer Thermal Energy Storage with High Temperatures (HT-ATES) ranging from 60–90 °C is a promising technique to store large amounts of energy in urban areas. However, these areas typically lack information on hydrogeological and thermal parameters of the subsurface to determine the potential for energy storage. Moreover, conventional exploration methods as pumping tests do not account for the variation in density caused by the high temperature gradients or changes in salinity as encountered in HT-ATES operation. The objective of this study is therefore to develop best practices for characterizing the hydrogeological and thermal properties of groundwater wells and their surrounding formation that determine the potential performance of HT-ATES-systems. In addition to conventional pumping tests, a set of Push–Pull tracer Tests (PPTs) with cold and hot water are proposed and scrutinized using Berlin as case study. There, the research well Gt BChb 1/2015, which is characterized by a reservoir temperature of 17 °C at a depth between 220 und 230 m below ground surface was tested.In 2017, seven Slug-Withdrawal Tests (SWTs), a Step-Rate-Test (SRT), a production tests, and two Push–Pull tracer Tests (PPTs) with hot and cold water were performed during a period of 40 days. These tests were accompanied by Distributed-Temperature-Sensing (DTS) monitoring. The temperature measurements provide indications of injection areas based on the warmback period during a PPT with 81 °C hot water.The determined aquifer transmissibility T=3.2×10−5m2/s, the related Productivity Index (PI=2.0m3/(h bar)), and maximum flow rates of about 5m3/h indicate that the aquifer has potential for HT-ATES. However, the PPT and the DTS monitoring revealed cross flow between the target aquifer and an overlying aquifer. Thus, a new well with a design avoiding cross flow is required to utilize the aquifer’s energy storage potential. A set of best practices for characterizing HT-ATES potential was derived from the experiences in this study.

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Calibrating low-cost sensors to measure vertical and horizontal gradients of NO2 and O3 pollution in three street canyons in Berlin

Despite improvements in air quality over the last several decades, air pollution will continue to be a leading cause of harmful health effects in European cities as urban populations continue to grow. In recent years, the technology of low-cost sensors (LCS) has been adapted for use in expanding air pollution measurements at higher spatial resolution in cities across the globe. In a novel application, this exploratory study deploys metal oxide (MOS) and electrochemical (EC) low-cost sensors housed in EarthSense Zephyr sensor systems to measure nitrogen dioxide (NO2) and ozone (O3) concentrations in three street canyons in Berlin in winter, spring, and summer from 2017 to 2020. After calibration with reference instrumentation using the seven-step methodology outlined by Schmitz et al. (2021), we compare the measured concentrations with reference and urban background concentrations and investigate relationships with meteorology. We find that, following proper calibration, LCS capture expected patterns of urban pollution in association with diurnal chemistry and meteorology well. Additionally, EC sensors outperform MOS and allow for greater insights into local patterns of pollution. Furthermore, we measure concentrations of NO2 and O3 in street canyons that match expectations from modelling studies, indicating that high spatial resolution deployment of LCS could successfully yield new insights in urban microenvironments and inform model development. While LCS have a wider range of uncertainty than reference instruments, these results suggest that they can be reliably used for several new applications, such as validating urban street canyon models or measuring air pollution alongside changes to urban infrastructure.

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