There is not official tests state that whether Venta airwasher is able to reduce PM2.5 or PM10 effectly, hence, I made some tests with the help of Dylos air particle counter during the good weather, PM2.5 index less than 100 means good or moderate, PM2.5 larger than 100 which means unhealthy or even hazardous. My bedroom's door or window is closed all the time and it's a confined space.
The answer is partially efficient. In centain conditions, it works, other times, no.
When the PM2.5 outside is less than 100, Venta can effectly keep the indoor PM2.5 around 30 or even less.
However, when outside is unhealthy, which means the index is above 100 and beyond, it really can't effectly reduce the particles inside, and the metrics I got from Dylos indoor have positive correlation with outside index, sometimes, Dylos even get 100 or even more which is totally unacceptable for people in the bedroom.
Now, the answer is quite clear, if the weather outside is good, just keep the Venta open and it can handle. When outside is unhealty, you really need to turn on your air filter, and don't rely on it, you need HEPA filter.
What about PM10? Venta seems work all the time, no matter good or bad outside, it can keep the index under 100 or lower, most of time, my bedroom PM10 is around 50, sometimes, after long time filter without opening the door, you can see single digit.