  N95 respirators comprise a critical part of the personal protective equipment
used by frontline health-care workers, and are typically meant for one-time
usage. However, the recent COVID-19 pandemic has resulted in a serious shortage
of these masks leading to a worldwide effort to develop decontamination and
re-use procedures. A major factor contributing to the filtration efficiency of
N95 masks is the presence of an intermediate layer of charged polypropylene
electret fibers that trap particles through electrostatic or electrophoretic
effects. This charge can degrade when the mask is used. Moreover, simple
decontamination procedures (e.g. use of alcohol) can degrade any remaining
charge from the polypropylene, thus severely impacting the filtration
efficiency post decontamination. In this report, we summarize our results on
the development of a simple laboratory setup allowing measurement of charge and
filtration efficiency in N95 masks. In particular, we propose and show that it
is possible to recharge the masks post-decontamination and recover filtration
efficiency.
