Deposition Velocities of Airborne Ionic Pollutants: Distribution Across Electronic Equipment Rooms.

In earlier studies, we reported on measurements of airborne concentrations and surface accumulations of ionic substances at electronic equipment installations at Wichita, Kansas and Lubbock, Texas. More extended studies were recently completed at equipment locations in Newark, New Jersey and Neenah, Wisconsin. From these and the previous studies it became evident that (1) reliable indoor/outdoor concentration ratios could be estimated from readily available air handling system parameters; and (2) deposition velocities, calculated as the ratio of the average surface accumulation rates to the airborne concentrations, are reasonably consistent for each of the dominant ions commonly present in fine or coarse particles, irregardless of location. While these ratios and deposition velocities enable reliable estimates of average surface accumulations to be made for unknown locations, it was also clear from the measurements that there is a substantial variation in the surface accumulation rate across equipment rooms. From the original data it could not be determined if these variations were a result of variations in airborne concentrations or variations in the deposition process. In this paper further measurements at Newark and Neenah are reported in which compact personal air sampling pumps have been used to collect total suspended particulates (TSP). The small size and low flow rates of these pumps allow a large number of them to be used in close proximity to the surface sampling locations. The airborne concentrations of ionic substances measured across the equipment room floors have been found to exhibit remarkably little variation. For example, the ranges in airborne sulfate associated with fine particles at Newark and Neenah were 0.83 - 1.08 and 0.73 - 0.81microns g/m sup 3 , respectively. In comparison, the ranges in surface accumulation rates for sulfate on vertical surfaces were 0.07 - 0.29 and 0.04 - 0.10micorns g/cm sup 2 yr, respectively. The ranges of the calculated deposition velocities obtained from the surface and airborne concentrations are 0.002 - 0. 010 and 0.002 - 0.004 cm/sec, respectively. These results demonstrate that: (1) the variation in surface accumulations is not attributable to the airborne concentrations and thus should be attributed to other factors probably related to air currents; and (2) airborne indoor concentrations of ionic substances are sufficiently constant across the equipment room floor to conclude that results obtained using a single dichotomous sampler are representative of the concentrations across the entire equipment room.