[donutreceipt]

From the FAQ:

You can! We have links on our Particle Counting blog. We're more committed to spreading the knowledge that HEPA filters are a cheap way to effectively combat air pollution than we are to making money, so we'd never discourage anyone from buying the same parts elsewhere.

We just try to make the parts easier to get for people who don't want to scour Taobao for the cheapest filters. People have also emailed us saying that some stores stop carrying fans in the winter and that some HEPA manufacturers don’t sell in small orders. We buy in bulk so we can offer a low, flat rate (200RMB) that includes shipping anywhere in Mainland China. By buying with us, you also know that you’re getting HEPAs that we tested personally for effectiveness.

[drivingmissm]

The irony is that running all of these filters is consuming electricity, which in turn means more coal-fired power plants and even dirtier air for everyone. Beijing should move to clean up the environment.

[ericd]

The irony's not very strong, since these can clean a lot more than they contribute via electricity consumption.