Seasonal deposition of housedusts onto household surfaces

Seasonal differences in the particle size fractions and mass loadings of ho usehold dust deposited on indoor surfaces were examined in four New Jersey homes. Housedust was collected during a 30-day period on non-electrostatic polyethylene sample plates on which a glass slide had been placed. In each home two samples were collected at a height of 1.5 m and two were collected at a height of 0.3 m above the floor. Dust samples were obtained from each home during a summer and winter collection period. Particle size measureme nt was completed using an adaptation of a Meridian ACAS 570 Interactive Las er Cytometer. Results indicated that the dust mass deposited on household s urfaces during the summer was greater than during the winter. The arithmeti c mean mass deposition rate for all houses was 0.37 +/- 0.13 mu g/cm(2)/day during the summer and 0.22 +/- 0.13 mu g/cm(2)/day during the winter. The total number of particles deposited, however, was greater during the winter than during the summer. The increase in winter time particle number was ca used by greater numbers of particles with an equivalent spherical diameter < 2.5 mu m. The most probable source of these particles was winter time com bustion emissions within the residences and the subsequent particle deposit ion on household surfaces. The greater mass loadings measured on the low sa mpling plates during the summer were associated with a greater number of pa rticles with an equivalent spherical diameter > 5 mu m. In the winter, howe ver, the particle mass and number loadings were similar at both heights. Th ese results suggested that ventilation of the house during the summer allow ed resuspended particles to enter which led to the higher levels of settled dust. Measurement of contaminant levels in housedust for exposure estimati on therefore, should account for the seasonal and height differences in dus t mass, and collect representative fractions of housedust that are availabl e for human contact. Furthermore, since over 99% of the particles on indoor surfaces were < 50 mu m any indirect sampling technique for dermal exposur e estimation should have collection efficiencies similar to the hand for pa rticles < 50 mu m.