Infiltration and Surface Sampling Methodology for Assessing Indoor Deposition of Bushfire Ash
Bushfire events create extremely high ambient levels of fine particulate (PM 2.5) that travels long distances downwind. Infiltration to buildings is particle-size dependent, with a time delay to fine particle infiltration, but little attenuation. Public health advice is often not correct, suggesting that protection from bushfire particulate is provided by the indoor environment in the same manner that protection from pollen is offered by the indoors during allergy season. Indoor exposure to bushfire smoke can be important for epidemiologic research, and also for insurance purposes. Historical assessment of bushfire residue using soot and char scoring can lead to incorrect conclusions regarding the source of observed particulate. Bark and leaves contain stony minerals termed phytoliths, composed of calcium oxalate. These substances are present in ash, and travel many kilometres downwind from a bushfire, providing a fingerprint of the species of plants burned, the temperature of the fire, the distance from the source, and other information that forms a distinctive signature of the bushfire. Assemblage analysis of surface tapelift samples based on calcium oxalate detection can be utilised to distinguish between particulate from bushfires and other combustion sources common around homes. The particulate from bushfires remains present indoors on surfaces for many weeks or months, permitting contemporaneous as well as retrospective assessment of exposure and/or smoke damage.