Characterization and source apportionment of the coarse-mode fraction of settled dust in a public school classroom

Dust settled onto surfaces in indoor environments is a complex mixture of particles generated from numerous outdoor, indoor, occupant and occupant activity related sources. This project developed a methodology for the systematic collection and analysis of settled dust in an indoor environment. Samples were analyzed using polarized light microscopy for the purpose of determining its composition and to investigate the relative contributions of various particle sources.Prior to the field study, several operations were undertaken to ensure the collection of representative samples and acquisition of statistically significant data. First, a reference database of particle types common to indoor environments was compiled. To evaluate the performance of settled dust collection techniques, a dust settling chamber was designed, built and performance tested. Using this settling chamber, adhesive tape and microvacuum sampling were compared to direct deposition, both methods were found to collect representative samples. The analytical parameters of a light microscopic analysis protocol were optimized. A three dimensional sampling array was then developed to ensure systematic sampling of settled dust, and implemented in two elementary school classrooms.Field study results identified 39 different particle types in settled dust samples including organic particles such as skin, starch grains, and plant/insect debris; particle aggregates; the minerals silica, calcium carbonate, clay, and gypsum; cellulose, cotton, synthetic and carpet fibers; synthetic vitreous fibers; black and white opaque particles, residue from cleaning solutions, waxes and polishes; and paint residue from children\u27s arts and craft paint. Twenty different particle types were found to comprise 94% of the particles characterized. The sources for these 20 particle types were found to originate from outdoors, indoors and from the occupants and their activities. Each was found to contribute about a third of the different particle types identified in the settled dust. Although this method was used in the investigation of a \u27non-problem\u27 school and determined the composition of a \u27normal\u27 dust, this method can easily be used to assess many different types of buildings and environments including those with known problems