Ionizers work through two mechanisms:
1. Charged particles stick together, forming larger clumps that eventually drop out of the air.
2. Charged particles can build up on the surface of airborne pathogens, sometimes directly disrupting membranes or lipid layers, and if there is enough of a buildup they can induce an electric current through the organism that can kill / inactivate it.
One study on bipolar ionization showed antiviral efficiencies were 64.3, 89.1, and 97.4% with exposure times of 15, 30, and 45 min, respectively (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7094352/).
The advantage to ion generation based air purification systems is that they are able to actively operate in occupied spaces, not relying on air to get pumped out of a return duct and through a filter or UV system.
It's not possible for them to achieve an instantaneous elimination of airborne pathogens, but any significant percentage reduction can help to lower the total viral load that people in the room are being exposed to.
That being said, it's unlikely that what he's wearing around his neck will generate a sufficient quantity of ions to make much of a difference. It wouldn't be enough to fill the room, and the amount of time any such ions would have to act on a particle that comes close to him really isn't enough to have a large impact.
However, I would posit that the main reason for this discrepancy is that memory is linked to the level of stimulation, and we typically have developed to place a far higher weighting on our visual systems, not to mention the fact that the visual signal typically has a far higher information content, linking to many existing mental structures.
But this was done in a controlled environment where the subjects' full attention was focused on the audio. In such a case, it makes sense that retention rates would be comparable, as the same language centers in the brain are used for processing the input once it is transferred from the appropriate input sense.
The big problem with audiobook retention is that we typically listen to them whilst being involved in other tasks, and there are are a myriad of studies showing that humans are inherently extremely bad multi-taskers, with high task-switching costs even in people who claim to be otherwise.
Aside from just sitting with my eyes closed and listening, I find that retention is maximized with audiobooks when there is a split between System 1 and System 2 activity (ala Thinking, Fast and Slow by Daniel Kahneman). If I am doing something like driving, using System 1, my System 2 can be fully focused on the audiobook, until something darts out in the middle of the road and then I end up having to rewind and re-listen to what I missed.
The advantage to ion generation based air purification systems is that they are able to actively operate in occupied spaces, not relying on air to get pumped out of a return duct and through a filter or UV system.
It's not possible for them to achieve an instantaneous elimination of airborne pathogens, but any significant percentage reduction can help to lower the total viral load that people in the room are being exposed to.
That being said, it's unlikely that what he's wearing around his neck will generate a sufficient quantity of ions to make much of a difference. It wouldn't be enough to fill the room, and the amount of time any such ions would have to act on a particle that comes close to him really isn't enough to have a large impact.