The indoor air needed to be cleaned

I didn’t realize it until I stepped into my friend’s house but he needed to clean his indoor air quality! But how am I supposed to bring this up to somebody without offending them.

It’s not like I can go up and say “Hey man your air conditioning system is terrible and your indoor air quality is horrendous, you need to do something about it.” I mean I suppose you could say that but it wouldn’t be the nice thing to do now would it? So I needed to tell him that he should take care of his indoor air quality in another way, but how was I going to do that? I decided to sort of hint at it lightly, hoping that I wouldn’t offend him. So I told him that his air conditioning system was very interesting, that it made his indoor air quality unlike any other that I had experienced. He asked what I meant and that’s what I told him, and I told him that the indoor air quality in his home is really bad. He didn’t get offended at all and thanked me for telling him because he wasn’t aware of it. He said he’d gone nose blind to the smells. He said that he would try to get in a HEPA filter and hope that fixed it. A week later I visited him again and I noticed that his indoor air quality was much better this time. Not only have you gotten the HEPA filled over here, also got a few standing in the air purifier and put one in each room. I was happy for him and he was happy too and he said that his home was much more comfortable to be in there with his indoor air quality having been taken care of.
air purification system