The measurement and assessment of indoor air quality in terms of respirable particulate constituents is relevant, especially in light of the COVID-19 pandemic and associated infection events. To analyze indoor infectious potential and to develop customized hygiene concepts, the measurement monitoring of the anthropogenic aerosol spreading is necessary. For indoor aerosol measurements usually standard lab equipment is used. However, these devices are time-consuming, expensive and unwieldy. The idea is to replace this standard laboratory equipment with low-cost sensors widely used for monitoring fine dust (particulate matter—PM). Due to the low acquisition costs, many sensors can be used to determine the aerosol load, even in large rooms. Thus, the aim of this work is to verify the measurement capability of low-cost sensors. For this purpose, two different models of low-cost sensors are compared with established laboratory measuring instruments. The study was performed with artificially prepared NaCl aerosols with a well-defined size and morphology. In addition, the influence of the relative humidity, which can vary significantly indoors, on the measurement capability of the low-cost sensors is investigated. For this purpose, a heating stage was developed and tested. The results show a discrepancy in measurement capability between low-cost sensors and laboratory measuring instruments. This difference can be attributed to the partially different measuring method, as well as the different measuring particle size ranges. The determined measurement accuracy is nevertheless good, considering the compactness and the acquisition price of the low-cost sensors.

Most FFP (Filtering Face Piece) masks are made from nonwoven filter media that are electrostatically charged, resulting in the additional electrostatic capture mechanism of particles. The protective effect of these masks is therefore mainly dependent on the electric field surrounding the charged fibers. Upon prolonged wear, the mask becomes saturated with exhaled air, resulting in humidification on the wearer’s side. However, speaking, coughing, or sneezing also generate droplets, which can deposit on the mask from the person wearing it, as well as from other people. In order to investigate this influence on the filtration efficiency and the existing electric field, an experimental study was carried out. To imitate human breathing, a test setup was constructed using a Sheffield Head with different types of masks. This was followed by the cyclical humidification and drying of the masks through simulated breathing. By observing these phases in detail using sample sections, it was possible to continuously record the water content in the samples, the relative humidity, and the pressure drop (breathing resistance). The results demonstrate that moisture has an impact on the filtration efficiency of the electret FFP masks when worn under real-life conditions and that the initial condition can be restored with sufficient drying time.

Electret filter media are electrostatically charged during the manufacturing process to activate effective electrical separation mechanisms. In order to investigate the influence of humidity on these mechanisms, the electric field, and filtration efficiency, a Direct Numerical Simulation (DNS) study of the aerosol deposition within wetted fibrous nonwoven filter media used in masks was carried out. Initial experimental investigations determined key properties of the filter material, including porosity, fiber diameter, and surface charge density. Using Micro-Computed Tomography (µCT), preferred locations for droplet deposition within the filter were identified. Additional experiments quantified the amount of water absorbed by the filter medium and assessed its impact on the existing electric field. Numerical simulations examined various models with differing porosity and fiber diameter, incorporating different levels of water content to analyze the changes in the electric field, flow velocity, and resulting filtration efficiency. The results provide valuable insights into the significant effects of fiber change on filtration performance, demonstrating the electret filter’s ability to partially compensate for the negative impacts of water.