Evaluation of a time-resolved method for aerosol deposition using the AMPAS device and a LiCl tracer

Background

Passive air sampling with settle plates measures particle deposition but is limited to a single, time-averaged interval and requires manual intervention. The Automated Multiplate Passive Air Sampler (AMPAS) enables sequential sampling, with previous studies assessing microbial deposition. Using microorganisms can have higher variability and chemical tracers offer a stable alternative with improved analytical precision. This study evaluates AMPAS performance with a LiCl tracer for characterising aerosol deposition under controlled ventilation.

Methods

A 10% LiCl solution was aerosolised into a mechanically ventilated chamber at two ventilation rates: 1.5 and 10 ACH. Deposition was collected using AMPAS devices with 30 and 60 min intervals across nine locations, with three consecutive repeated samples per location. Additional 55 and 90 mm plates assessed plate-size effects. Lithium was recovered and quantified using ICP-MS. Deposition rates were analysed using a linear mixed-effects model to test the effect of ventilation, sampling interval, location and experiment index. Plate-size effects and consecutive replicate variability were evaluated.

Results

Ventilation was the dominant determinant of deposition with 10 ACH producing a 58% reduction in normalised deposition rate relative to 1.5 ACH (p < 0.001). Sampling interval had no significant effect and location variability was minor compared with experiment variability. Deposition per unit area did not differ statistically between plate sizes.

Conclusion

AMPAS combined with a LiCl tracer provides a reproducible, sensitive, time-resolved method for aerosol deposition. It robustly detects ventilation-driven changes and supports the use of smaller plate sizes. It offers a framework for evaluating ventilation performance and validating models.