Emission rates and the personal cloud effect associated with particle release from the perihuman environment

Abstract

Inhalation exposure to elevated particulate matter levels is correlated with deleterious health and well-being outcomes. Despite growing evidence that identifies humans as sources of coarse airborne particles, the extent to which personal exposures are influenced by particle releases near occupants is unknown. In a controlled chamber, we monitored airborne total particle levels with high temporal and particle-size resolution for a range of simulated occupant activities. We also sampled directly from the subject's breathing zone to characterize exposures. A material-balance model showed that a sitting occupant released 8 million particles/h in the diameter range 1-10 µm. Elevated emissions were associated with increased intensity of upper body movements and with walking. Emissions were correlated with exposure, but not linearly. The personal PM 10 exposure increment above the roomaverage levels was 1.6-13 µg/m 3 during sitting, owing to spatial heterogeneity of particulate matter concentrations, a feature that was absent during walking. The personal cloud was more discernible among larger particles, as would be expected for shedding from skin and clothing. Manipulating papers and clothing fabric was a strong source of airborne particles. An increase in personal exposure was observed owing to particle mass exchange associated with a second room occupant. Keywords Human emissions, Personal exposure, Activity type, Particle size distribution, Crosscontamination, Particle sources Accepted ArticleThis article is protected by copyright. All rights reserved. Practical implicationsBetter understanding of the nature, scope and significance of human personal clouds is valuable for enhanced prediction and control of personal exposure, which is important in relation to how indoor air quality influences human health. The results of this work are of potential use in indoor air quality models and for improved ventilation design. The work also contributes to a better understanding of human occupants as sources of airborne particles, which could strengthen the design and interpretation of future air pollution exposure studies.

The particles around us

“…19 There may also be significant contributions caused by direct shedding from the human envelope, including the release of previously deposited particles from clothing surfaces, hair, or bare skin. 20 Among the best PM exposure studies was the PTEAM investigation, which showed a substantial personal cloud effect for PM 10 . 21 A recent study documents that a contribution to the personal cloud can result when coarse particles are released into the perihuman space of a seated occupant with subsequent upward transport into the breathing zone by the action of the metabolically generated thermal plume.…”

“…21 A recent study documents that a contribution to the personal cloud can result when coarse particles are released into the perihuman space of a seated occupant with subsequent upward transport into the breathing zone by the action of the metabolically generated thermal plume. 20 Exposure to ultrafine particles is likewise poorly characterized. In outdoor air, one dominant feature is the strong spatially varying concentrations near heavily trafficked roadways.…”

“…Such sources can include the resuspension of particles that had previously settled onto upward facing indoor surfaces . There may also be significant contributions caused by direct shedding from the human envelope, including the release of previously deposited particles from clothing surfaces, hair, or bare skin . Among the best PM exposure studies was the PTEAM investigation, which showed a substantial personal cloud effect for PM 10 .…”

“…Among the best PM exposure studies was the PTEAM investigation, which showed a substantial personal cloud effect for PM 10 . A recent study documents that a contribution to the personal cloud can result when coarse particles are released into the perihuman space of a seated occupant with subsequent upward transport into the breathing zone by the action of the metabolically generated thermal plume …”

Prediction of particle deposition around the cabin air supply nozzles of commercial airplanes using measured in-cabin particle emission rates

“…18 Several previous studies [19][20][21][22] experimentally measured the particle emission rates from clothed occupants and from various human activities in homes and classrooms, such as folding blankets, making a bed, vacuuming, walking around, and sitting. [23][24][25][26][27] They found that the factors affecting particle emission rates included the number of persons performing the activity, 22 the type and intensity of the activity, 24 the type of floor and seat cover, 23 the clothing level, 19 and the operational state of the mechanical ventilation system. 27 However, these factors would be very different in an airliner cabin environment from in an indoor environment in a building.…”