We report the recovery and characterization of a new urban micrometeorite collection derived from the rooftop of an industrial building in Germany. We identified 315 micrometeorites (diameter: 55–515 µm, size peak: ˜150 µm, size distribution slope exponent: −2.62). They are predominantly S-type cosmic spherules (97.2%) but also two G-type spherules (0.6%), an unmelted coarse-grained single-mineral micrometeorite, and eight scoriaceous particles (2.5%) or particles transitional between scoriaceous micrometeorites and porphyritic spherules. Their analysis details how the magnetite rim on partially melted micrometeorites is progressively diluted as the melt fraction increases during heating. At least 10 micrometeorites contain platinum group nuggets (PGNs). They have chondritic compositions but are depleted in volatile Pd. However, a single nugget preserves chondritic Pd concentrations. We suggest that an Fe-Ni-S bead originally containing the PGN escaped its host cavity and wet the particle exterior, creating an Fe-rich melt that protected the nugget from evaporation. This melt layer oxidized forming magnetite—indicating that wetting events can affect the texture and composition of micrometeorites. Utilizing the well-constrained surface area (8400 m²) and rooftop age (21 yr), we attempted the first global mass flux estimate based on urban micrometeorite data. This produced anomalously low values (13.4 t yr^–1), even when correcting for losses due to sample processing (<89.7 t yr^–1). Our value is approximately two orders of magnitude lower than previous estimates, indicating that >99% of particles are missing, having been lost via drainage and cleaning. Rooftop collection sites have limited potential for mass flux calculations unless problems of loss can be resolved. However, urban micrometeorite collections have other advantages, notably exceptionally well-preserved particles with extremely young terrestrial ages and the ability to extract many micrometeorites from accessible sites. Urban micrometeorites should be considered complementary to Antarctic and deep-sea collections with potential for citizen science and educational exploitation.

中文翻译：

---

评估城市微陨石作为研究资源——从单一屋顶收集的大量人口

我们报告了来自德国工业建筑屋顶的新城市微陨石系列的恢复和表征。我们鉴定了 315 颗微陨石（直径：55–515 µm，尺寸峰值：~150 µm，尺寸分布斜率指数：-2.62）。它们主要是 S 型宇宙小球体 (97.2%)，但也有两个 G 型小球体 (0.6%)、一个未熔化的粗粒单矿物微陨石和 8 个渣质颗粒 (2.5%) 或介于渣质微陨石和斑状陨石之间的颗粒小球。他们的分析详细说明了部分熔化的微陨石上的磁铁矿边缘如何随着加热过程中熔体分数的增加而逐渐稀释。至少有 10 颗微陨石含有铂族金块 (PGN)。它们具有球粒状成分，但缺乏挥发性 Pd。然而，单个金块保留球粒状 Pd 浓度。我们建议最初含有 PGN 的 Fe-Ni-S 珠子脱离了它的宿主腔并润湿了颗粒的外部，形成了一种富含铁的熔体，保护了金块免于蒸发。该熔体层氧化形成磁铁矿——表明润湿事件会影响微陨石的质地和成分。利用良好约束的表面积 (8400 m² ) 和屋顶年龄（21 年），我们尝试了基于城市微陨石数据的第一个全球质量通量估计。这产生了异常低的值 (13.4 t yr ^–1 )，即使校正由于样品处理造成的损失 (<89.7 t yr ^–1）。我们的值比之前的估计值低大约两个数量级，这表明超过 99% 的颗粒已通过排水和清洁丢失。除非可以解决损失问题，否则屋顶收集点的质量通量计算潜力有限。然而，城市微陨石收藏还有其他优势，特别是保存异常完好的粒子，具有极年轻的地球年龄，并且能够从可到达的地点提取许多微陨石。城市微陨石应被视为对南极和深海收藏的补充，具有用于公民科学和教育开发的潜力。