Fate and Transport of Indoor Particles: How Human Activity Effects Pollutant Exposure

By Andrea Ferro, Ph.D., P.E.

Particulate pollutants enter indoor environments by passing through building walls, being carried indoors on shoes, or from sources already present indoors. Particulate pollutants include lead, pesticides, dioxins, spores, and biological allergens . Once inside, particulate pollutants will attach to surfaces (such as walls, furnishing, and floorings) and use them as particle reservoirs. Human inhalation exposure and the residence time of the particle pollutant indoors depend on the resuspension of the pollutant due to human activity (i.e. dusting, vacuuming, walking, and folding clothes).

In one set of experiments , three types of particulate matter (PM) measurements (indoor, outdoor, and personal) were collected using real-time laser particle counters and integrated filter samples inside a home. Inductively coupled plasma with mass spectrometry (ICP-MS) was used to analyze the filter samples for elemental ions. Two models were then used to estimate how much outdoor air and indoor human activity contributed to indoor PM. The two models used were the Chemical Mass Balance Receptor Model Version 8 (CMB8) and an indoor-outdoor (I-O) model based on the mass balance of the indoor environment.

In a follow up study , tracer particles were released inside a test house in Redwood City, California. The concentrations of the particles were monitored over time while a regular cycle of typical human activity was maintained. The indoor residence time of the PM and the human exposure to the PM were predicted using a mass balance which assumed the particles were introduced as a pulse source. The result of these studies illustrate the effect that deposition and resuspension (due to human activity) have on the particle concentration in indoor environments.