There are plants that improve air quality - some remove chemicals from the air, formaldehyde for example, but as for removing smells, I can't say I've noticed they're too good at that, though claims are made that some do. There is a list of 19 plants I know about from research done by NASA, but some of those have barbs or thorns, or are very fussy about their growing conditions, or have toxic sap or leaves, or get too large, so the following are ones I would recommend which are worth a try:
- Dracaena fragrans
- English Ivy (Hedera helix varieties)
- Spathiphyllum (though this does require quite frequent watering)
- Golden pothos (Epipremnum varieties)
All these tolerate low light conditions, although golden pothos, if it is variegated, does require some sunlight to keep its colour. Given your grandpa's room faces west, it's likely to get sun in the afternoons, and that should be fine. Spathiphyllum though, does best without direct sun, but likes a bright position.
You should maybe check with his care home that they will allow you to place plants in his room first though - and that they're prepared to water once a week or more if you cannot visit yourself occasionally. Note that plants should not be left standing in water for longer than 30 minutes, so that means someone will need to check and empty any outer pot or tray of water after this time.
UPDATE
In response to a request for a link to the NASA study - I found something else recently which sort of negates that, but here's the NASA results via Wikipedia https://en.m.wikipedia.org/wiki/NASA_Clean_Air_Study. And here's the other thing I found recently regarding how effective (or not) plants actually are at cleaning the air in the average home https://www.gardenmyths.com/garden-myth-born-plants-dont-purify-air/
