Aerosol Sampling Experiment (Aerosol Samplers) - 10.04.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Aerosols are small particles suspended in the air, and in Earth’s atmosphere, aerosols include soot, dust, pollen and a wide range of other natural and human-made materials. But smoke does not rise and dust does not settle in microgravity the way they do on Earth, causing aerosols to behave differently and pose hazards for crew members breathing the air. The Aerosol Sampling Experiment (Aerosol Sampler) collects airborne particles in the International Space Station’s (ISS) cabin air, and returns them to Earth so scientists can study the particles with powerful microscopes. For this experiment, particles collected on the cabin air samples are analyzed using a variety of microscopic techniques including: light microscopy, Raman spectroscopy, scanning electron microscopy, computer controlled scanning electron microscopy; and scanning transmission electron microscopy.
Science Results for Everyone
Information Pending

The following content was provided by Marit Meyer, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: Aerosol Samplers

Principal Investigator(s)
Marit Meyer, Ph.D., NASA Glenn Research Center, Cleveland, OH, United States

Co-Investigator(s)/Collaborator(s)
Information Pending

Developer(s)
RJ Lee Group, Inc., Monroeville, PA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Space Exploration

ISS Expedition Duration
September 2016 - September 2017; February 2018 - April 2019

Expeditions Assigned
49/50,51/52,55/56,57/58

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • ISS particulate matter requirements exist but there is no method of verifying whether they are met.
  • Our current knowledge of ambient aerosols in ISS air is based on sparse data and literature research on emission rates of particles from known sources on ISS.
  • Some airborne debris samples have been returned from ISS, but without the necessary delicate handling or not on collection substrates appropriate for exhaustive microscopic analysis of particles in size ranges of interest.
  • In the Aerosol Sampling Experiment, ISS airborne particles are sampled with two different collection devices (one commercial-off-the-shelf and the other custom-built).
    • The Passive Aerosol Sampler (PAS) consists of 5 collection surfaces in a metal housing which are exposed for different durations, on the order of days.
    • The Active Aerosol Sampler (AAS) has an internal pump and requires battery charging before sampling for approximately 6 hours.
  • The experiment is designed to generate data on ISS aerosols, to provide information for the design of future particulate monitors for long-term manned missions.
  • Another benefit of characterizing the particles in ISS air is to help design better spacecraft fire detectors which can discriminate between dust or background particles and smoke in order to reduce false alarms.
  • Data obtained from samples include long-term average particle number concentrations, size distributions, morphology and composition.
    • Sources of particles can often be identified with this information.
    • Particles a few nanometers to hundreds of micrometers can be collected (that’s a size range spanning six orders of magnitude).

Description

The ISS is a unique indoor environment that serves as both home and workplace for crew members. The ISS has some aerosol sources in common with buildings on Earth, but can be considered an isolated volume of air with only internally generated aerosols from occupants, their activities and ISS infrastructure. Spacecraft cabin air quality is of fundamental importance to crew health, with concerns encompassing both gaseous contaminants and particulate matter. Currently there is no particle measurement capability on the ISS; however, an aerosol source model developed for the purpose of filtration and ventilation systems design has been created and updated with emission rates from the literature. Since the initial modeling efforts, the number of crew members on board the ISS has increased from 3 to 6 and they are engaged in new processes and activities. Therefore, it is prudent to evaluate the current state of ISS ambient air quality in terms of particles.
 
Results from previous analyses of dust samples from ISS, combined with a literature review provide new predicted aerosol emission rates in terms of size-segregated mass and number concentration. The goal of the Aerosol Sampling Experiment (Aerosol Sampler)  is to provide data to verify that the current ISS filtration system is adequate and to get long-term average particle concentrations in different nodes and modules. This data on ISS aerosols is applicable to other spacecraft, and becomes more important as NASA considers future long term exploration missions, which precludes the opportunity for resupply of filtration products.
 
The 2 samplers that collect particles on ISS provide redundancy to maximize the success of the experiment and also expand size range of particles collected. Multiple simultaneous sampling operations also maximize the use of crew time in the experiment.
 
The Active Aerosol Sampler (AAS), which is battery powered, actively pulls in air and collects particles using the principal of thermophoresis. This is accomplished by flowing the sampled air through a large thermal gradient in a narrow channel. During this process, particles are driven to the cold side of the channel, where an electron microscope (EM) grid is held in place by a tiny magnet. When returned to Earth, these grids are easily removed and placed directly in the EM for analysis.
 
The Passive Aerosol Sampler (PAS) was designed with individual drawer-like collection surfaces covered with sticky carbon tape which are open to ISS air for 5 different exposure durations (2, 4, 8, 16 and 32 days). PAS are mounted on the edge of air vents where the drawers directly intercept the air pulled into the ISS ventilation system. These vents often have a build-up of dust that is removed in weekly vacuuming chores, so depending on the sampling location, the longer duration samples are expected to contain visible amounts of airborne debris.
 
Upon return to Earth the AAS samples will be analyzed using high resolution electron microscopes including a Hitachi S-5500 scanning electron microscope/scanning transmission electron microscope (SEM/STEM); Hitachi HD-2300 STEM; Tescan Mira-3 field emission SEM (FESEM). These microscopes are equipped with energy dispersive X-ray spectroscopy (EDS) technology for determination of elemental composition.
 
The PAS samples are examined using a combination of light microscopy, Raman spectroscopy (Horiba LabRAM HR), SEM (Tescan variable pressure Vega-3) and computer controlled SEM; (Tescan Mira-3 incorporating RJ Lee Group IntelliSEM particle analysis software).

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Applications

Space Applications
Crew members on the ISS are breathing more or less the same fixed volume of air that has been on the ISS for years. There is no chance to get ‘fresh air’ as we do on Earth, but an advanced air revitalization system processes and cleans the air continuously. Crew members in space have complained of allergies and nose and eye irritation, which suggests the ISS cabin air has a high concentration of tiny particles that can be inhaled. The ISS filtration system is designed to remove these particles, but researchers have no way to verify the efficiency or cleanliness of the air. This investigation generates new data to characterize the quality of the air on the ISS, in terms of particles. Future space travelers may benefit from this data, as they can be used in the design and selection of particle detectors appropriate for low gravity. Long-term manned space missions need aerosol measurement capability to ensure crew health and comfort.

Earth Applications
There are no Earth applications for the experimental data generated, however, the samplers used in this experiment originated with Earth applications and were adapted for low gravity. The ISS PAS is modified from a commercial-off-the-shelf sampler design that relies on gravity to collect particles. The ISS AAS is a commercially available device that has been used on Earth for particle collection in a variety of aerosol science applications, for example, environmental monitoring, such as air pollution studies or occupational health related research.

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Operations

Operational Requirements and Protocols
In order to develop particle measuring instruments that work for long periods of time in low gravity, it is important to understand the nature and sizes of particles in a spacecraft. This data was obtained many years ago for the Space Shuttle in an experiment during an 11-day mission, but airborne particulate matter has never been characterized for the ISS, even though it has a much larger volume of air and has been inhabited for over 15 years.  Humans and their activities generate particles, so for a fixed filtration design, it is expected that longer missions and larger crews affect the number of particles in the air. One way to find out how well the filtration system is working is to capture particles in ISS air and bring them back to Earth and analyze them.  The Aerosol Samplers Payload collects particles using two types of samplers, one is called ‘Active,’ as it is battery powered and has a small pump that samples the air. The other one is called ‘Passive’ because it collects particles on sticky surfaces which are placed over ISS vents, in the flow path of incoming particle-laden air. Seven sampling locations are chosen in the U.S. segments of ISS to provide information on air cleanliness where different activities take place. Once the samples are returned to Earth, individual particles are analyzed with a variety of microscopic techniques to understand how many particles are in ISS air, what sizes and shapes, what they are made of, and understand the sources of these particles. Sampling with the AAS takes place within 2 feet of the PAS during the 32-day deployment and is scheduled during particle-producing activities, such as crew exercise, cargo vehicle docking, and in the hygiene compartment. Using the PAS and AAS in the same area allows for the collection of a larger size range of particles (from a few nanometers for hundreds of micrometers). PAS are mounted with Velcro near air intakes of the ISS ventilation system to take advantage of incoming ‘dirty’ air flow. Upon initial deployment, all 7 sampling surfaces are exposed to collect particles. Crew members close off the individual sampling surfaces (like drawers) after exposure times: after 2, 4, 8, 16, and 32 days. The purpose of multiple exposure times is to obtain at least one long-term sample with optimal particle coverage for microscopic analysis with not too few particles, and not too many particles (overlapping or touching each other). When the last drawers are closed, the crew member removes the PAS and stows them.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Results Publications

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites

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Imagery

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Active Aerosol Sampler (NASA Image).

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Passive Sampler on Air Return Vent (NASA Image).

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