Single-particle elemental analysis of vacuum bag dust samples collected from the International Space Station by SEM/EDX and sp-ICP-ToF-MS

Air quality on board the International Space Station (ISS) is a significant concern for the long-term health of astronauts living on the station. Aerosolized particles are generated from a variety of sources, such as on-board equipment, electronics, and the astronauts themselves. Airborne particles can remain suspended for significant amounts of time due to the absence of gravitational settling. In this work we examine the particulate matter on board the ISS through scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) and single-particle multi-element inductively coupled plasma time-of-flight mass spectrometry (sp-ICP) analysis of two vacuum bag dust samples collected with a handheld vacuum cleaner used to clean surfaces and filter faces inside the ISS. SEM/EDX analysis shows that many large particles were collected. These particles are most commonly clothing fibers or of biological origin, along with smaller numbers of carbonaceous particles that may be from polymer and halopolymer materials. sp-ICP analysis quantitatively determined metal concentrations in particles approximately <10 µm in diameter and was able to identify several distinct particle compositions. Some of these, such as stainless steel (Fe-Cr-Ni-Mn), antiperspirant (Al-Zr), silver (Ag), and titanium oxide (Ti) particles, are consistent with particle types identified through past aerosol and vacuum bag sampling and analyses. Other types, including Fe-Al and other types of Al and Zr particles, do not have a clear origin consistent with past work. SEM/EDX and sp-ICP provide different but complementary information regarding the composition of particles obtained from vacuum bag dust samples. The material analyzed was obtained through the Divert Unwanted Space Trash (DUST) experiment on ISS, which returned vacuum bags to Earth for the purpose of understanding airborne particles in the unique ISS environment.

国际空间站（International Space Station，ISS）舱内空气质量，对于长期驻留该空间站的宇航员身体健康而言，是一项至关重要的关注点。舱内气溶胶颗粒的来源十分多样，涵盖舱载设备、电子器件以及宇航员自身等多个渠道。由于缺乏重力沉降作用，空气悬浮颗粒可在舱内长时间悬浮。本研究采用扫描电子显微镜-能量色散X射线光谱仪（scanning electron microscopy coupled with energy dispersive X-ray spectroscopy，SEM/EDX）与单颗粒多元素电感耦合等离子体飞行时间质谱仪（single-particle multi-element inductively coupled plasma time-of-flight mass spectrometry，sp-ICP），对两份真空袋粉尘样本开展分析。该样本由用于清洁ISS舱内表面与过滤器表面的手持式吸尘器采集获得。扫描电子显微镜-能量色散X射线光谱分析结果显示，本次采集到大量大尺寸颗粒，其中占比最高的为衣物纤维或生物源性颗粒，另有少量碳质颗粒，其来源大概率为聚合物与卤聚合物材料。单颗粒多元素电感耦合等离子体飞行时间质谱分析可对直径约小于10μm的颗粒实现金属浓度定量检测，并成功识别出多种具有独特组分的颗粒类型。其中部分颗粒组分与过往气溶胶及真空袋采样分析结果一致，例如不锈钢（Fe-Cr-Ni-Mn）、止汗剂相关（Al-Zr）、银（Ag）以及氧化钛（Ti）颗粒。其余颗粒类型，包括铁铝（Fe-Al）颗粒及其他铝基、锆基颗粒，其来源暂未明确，无法与过往研究结果形成对应。扫描电子显微镜-能量色散X射线光谱与单颗粒多元素电感耦合等离子体飞行时间质谱，二者可为真空袋粉尘样本的颗粒组分分析提供各具特色且互为补充的信息。本次分析所用的粉尘样本，源自ISS上的转移冗余空间垃圾（Divert Unwanted Space Trash，DUST）实验，该实验将真空袋带回地球，旨在探究独特空间站环境中的空气悬浮颗粒特性。