SATPC0039101 TAB 04 4 SOW REV.pdf

July 3, 2025

STATEMENT OF WORK

for

“Investigation of surface films as reservoir for volatile methylsiloxane SVOCs and updated phase partitioning analysis using ISS gas and particle concentration data”

NASA Lead Contact

Dr. Claire Fortenberry Research Aerospace Engineer Universities Space Research Association NASA Glenn Research Center claire.fortenberry@nasa.gov 434-284-3681

Project Summary

Plans for future long-duration missions, including long-term Lunar habitations, Martian transit, and Martian surface vehicles, necessitate a comprehensive understanding of airborne toxicant dynamics to ensure the health and safety of mission crew. Surface films, which are ubiquitous in indoor air on Earth, can act as reservoirs for semivolatile organic compounds (SVOCs), which can subsequently partition into the gas and particulate phases, affecting crew exposure mechanisms and durations. Although previous research and technology demonstrations have characterized the microbial environment on ISS surfaces, the composition of SVOCs in surface films on the ISS is not well understood.

Previously, phase partitioning parameters, including gas-water partitioning coefficients, saturation ratios, and gas-particle partitioning coefficients, were generated for volatile methylsiloxane (VMS) oxidation products, which were selected as a target species based on observations from NASA’s Aerosol Sampling Experiment. This project will extend this model to include VMS surface film partitioning parameters as a function of surface film thickness, which itself is expected to be a function of time and crew activity. Parameters to be studied include gas-surface partitioning coefficients and timescales for previously identified semivolatile VMS oxidation products, as well as additional reaction products.

Additionally, this project will update gas-particle partitioning coefficients generated in previous work using higher-fidelity aerosol mass concentration data from the Exploration Aerosol Monitors (ExAM) ISS technology demonstration. Additional data from the ISS, including relative humidity, temperature, pressure, and SVOC concentrations as available, will be supplied to validate the model. Finally, a final report will describe how this model framework may be generalizable so it may be applied to better understand long-term exposure of other toxicants relevant for long-duration space missions.

mailto:claire.fortenberry@nasa.gov

Milestones

Project period of performance is 13 months from approval of funding award.

Task 1: Generate surface partitioning coefficients and timescales for target VMS species identified in previous work

Task 2: Evaluate possible contributions of non-OH-driven oxidation to VMS chemistry and partitioning dynamics

Task 3: Update gas-particle phase partitioning parameters from previous report for VMS oxidation products using data from ExAM and other ISS systems as they are available

Task 4: Conference presentation and model revisions Paper submitted for presentation at the International Conference on Environmental Systems in July 2026. Revisions to models made based on feedback from ICES paper reviewers and Dr. Fortenberry.

Task 5: Final report Comprehensive final report summarizing methods, results, discussion of findings, and conclusions.

Table 1. Task schedule.

CY2025 CY2026

Task 7 8 9 10 11 12 1 2 3 4 5 6 7