Cosmogenic radiosulfur (³⁵S; half-life: 87.4 days) is transferred with the rain to the groundwater (as ³⁵SO₄²⁻) and can be used as residence time tracer for the detection of sub-yearly groundwater residence times. Due to the distinct but non-regular annual ³⁵S pattern in precipitation, related data evaluation requires consideration of a³⁵S input function that is based on representative rain samples. While minor rain events can easily be sampled quantitatively and hence representatively, a long-lasting rain event may get documented by a sample that represents only a certain sequence of the event, thus potentially resulting in a³⁵S activity concentration that might not be representative. With the aim to examine the magnitude of temporal variations of the ³⁵S activity concentration in rain during long-lasting rain events, we present and discuss two related exemplary ³⁵S time series. Furthermore, we evaluate the applicability of the parameters total sulfate and electrical conductivity (EC), both detected in rainwater as easily attainable ³⁵S proxies. The results of the study show (i) that the ³⁵S activity concentration may vary substantially during long-lasting rain events due to atmospheric migration processes and aerosol washout and (ii) that neither sulfate nor EC are suitable as ³⁵S proxies due to the different origin of ³⁵S on the one hand and sulfate/EC on the other. Hence, for the determination of a³⁵S activity concentration that is representative for a long-lasting rain event ³⁵S analyses of an adequate number of sub-samples cannot be avoided.

宇宙成因放射性硫（³⁵ S；半衰期：87.4 天）随雨水转移到地下水（作为³⁵ SO ₄ ^2-），可用作停留时间示踪剂，用于检测地下水次年停留时间。由于降水中独特但不规则的年度³⁵ S 模式，相关数据评估需要考虑基于代表性降雨样本的³⁵ S 输入函数。虽然小雨事件可以很容易地进行定量采样，因此具有代表性，但长期降雨事件可能会被仅代表事件特定序列的样本记录，因此可能导致³⁵可能不具有代表性的 S 活性浓度。为了检查长期降雨事件期间雨中³⁵ S 活动浓度的时间变化幅度，我们提出并讨论了两个相关的示例性³⁵ S 时间序列。此外，我们评估了参数总硫酸盐和电导率 (EC) 的适用性，这两个参数都在雨水中检测为容易获得的³⁵ S 代理。研究结果表明 (i)由于大气迁移过程和气溶胶冲刷，在长期降雨事件期间³⁵ S 活动浓度可能会发生很大变化，以及 (ii) 硫酸盐和 EC 都不适合作为³⁵ S 代理，因为不同的起源一方面是³⁵ S，另一方面是硫酸盐/EC。因此，为了确定代表长期降雨事件的³⁵ S 活动浓度，无法避免对足够数量的子样本进行³⁵ S 分析。