I recently found this blog post about an effective DIY air filter - explicitly filters pm2.5
https://chillphysicsenjoyer.substack.com/p/measuring-my-diy-...
I built one (< $50) and I'm pretty happy with the results. As someone with a life long sensitivity to air quality, the air definitely feels cleaner.
You really don't need to DIY unless you really want to. My non-DIY mass produced air filter from Home Depot can filter PM2.5 too.
Different strokes. I've been disappointed by every commercial air purifier I've ever bought - expensive and unreliable.
The blog is persuasive and provides a full air quality analysis. It's cheap and effective, a potent combination.