OK, it is easy to understand that there would be fewer suspended droplets in the air above a toilet flushed with a closed lid.
Admittedly I didn’t read the entire article because I didn’t care to sign up.
But perhaps you can tell me did the test the air above the toilet after the lid was opened on the closed lid toilets after a flush.
I can see that opening the lid on a toilet creates air turbulence in the bowl and would possibly carry suspended water droplets out of the bowl and on to your hands and face.
If you are going to do a study like this you have to consider how people actually use the device.
They make a device to stop this from happening and it also prevents odor from permeating the room, I was trying to get someone to pay me to install one in the 1990s but no one ever wanted to spend the money for installation.
It was a suction device, and would have been great on small boats and motor homes.
Unless you really slam open the lid on your toilet, you’re not going to create enough turbulence to lift any water out of the bowl. The problem lies in the actual flush. When the toilet is flushed it splashes. Some droplets are big, others are much smaller (and these are the ones that stay airborne longer). A closed toilet is going to keep most of those droplets inside the bowl, where the vacuum created by the flush process will pull the majority of them back down. Without the lid, the droplets can get far enough away from the bowl that they won’t be pulled back down.
Also, regarding the new versus the old toilets, the old ones probably weren’t quite as bad for germ spreading, since most of them didn’t have the flush jet at the bottom, but they still had some splash even if it wasn’t easily noticeable; they just dumped the water in from the rim until enough had gone through to theoretically evacuate the bowl. Those bottom jets in the new design toilets are probably a big cause of the splashing, since less water means more positive pressure is needed to move things along.
The problem with most old toilets was, even though there was enough water to theoretically flush the thing, it was used very inefficiently. The old toilets, as noted, relied on the weight of the water in the bowl to flush, and only filled from small outlets around the rim. If they did become clogged, they were much more likely to overflow if you didn’t get the tank lid off and the valve shut in time.
New toilets flush much more efficiently, but often don’t have enough total fluid to do the job right, and the u-bend dimensions are therefore much more critical, since it has to be big enough not to clog but small enough that the tiny water volume will still work. Usually designers get the second part right, and fail on the first.
The ideal design would use maybe two to two-point-five gallons to flush instead of the three or more of the old rim-only toilets, but would have the jet at the bottom of the bowl to get things moving past the u-bend.