Comparing Particle Size Concentrations for Dust Filtered on the International Space Station Versus Residential Buildings in Downtown Toronto

Comparing Particle Size Concentrations for Dust Filtered on the International Space Station Versus Residential Buildings in Downtown Toronto
I. Coussons[1], J. Siegel[1], S. Haines[1]
[1] Department of Civil and Mineral Engineering, University of Toronto, Toronto ON, Canada
Keywords: High-Efficiency Particle Air Filter, Particulate Matter, Particle Size Distribution.
Topic: Atmospheric Aerosols, Quantitative Filter Forensics

Sources of particulate matter (PM) on the International Space Station (ISS) often originate from the activity of astronauts [1]. The PM is typically introduced into the air by activities such as the application of personal hygiene products, the interaction of astronauts with fitness equipment, and the consumption of food [2]. These particle emission sources are pertinent to the respiratory health of astronauts because PM generated on the ISS remains airborne due to negligible gravitational settlement [2]. To capture these particles the ISS employs Bacteria Filter Elements which are equipped with 20-mesh pre-screens and borosilicate HEPA media to achieve a 99.97% removal efficiency [3].

Research surrounding PM on the ISS largely focuses on bulk vacuum bag dust samples or samples of dust captured by the filter pre-screen. These studies do not consider the submicron PM that passes through the screen and is captured on the HEPA media. This investigation uses vacuum extraction and a laser particle sizer to examine the PM from a HEPA filter used on the ISS and employs dust samples from residential filters used in downtown Toronto as a benchmark for comparison [4].

The distribution of PM for the ISS sample showed two modes while the residential dust samples had one main mode concentrated around the 10-100 microns range. The difference in particle size distributions was measured using the Unusual Index with the ISS dust samples as the test sample and the residential dust samples acting as reference samples. The comparison resulted in a median Unusual Index of 0.795, where a value closer to 1 indicates high unusualness [5]. This indicates the dust captured by the ISS HEPA media is likely smaller in diameter than the dust captured by filters on Earth. The result can help to inform ventilation and filtration processes used for future commercial space travel.

References

[1] Meyer, M. E. (2017). Aerosol Sampling Experiment on the International Space Station.
[2] Meyer, M. E. (2018). Results of the Aerosol Sampling Experiment on the International Space Station.
[3] Perry, J. L. (2005). International Space Station Bacteria Filter Element Service Life Evaluation.
[4] Mahdavi, A., & Siegel, J. A. (2021). Quantitative filter forensics: Size distribution and particulate matter concentrations in residential buildings. Indoor Air, 31(4), 1050–1060. https://doi.org/10.1111/ina.12782
[5] Barry, J., Mason, C., McIntyre-Brown, L., & Cooper, K. M. (2021). Statistical comparisons of sediment particle size distributions. Continental Shelf Research, 228, Article 104548. https://doi.org/10.1016/j.csr.2021.104548