@jeremychrysler @mgubrud I've noticed the same. Seeing the dirt on the filters is a selling point. With the commercial air cleaners you only see the dirt when changing the filter and maybe not even then (depends how the filters are packaged).
@jeremychrysler @mgubrud 我也注意到了。看到过滤器上的污垢是一个卖点。使用商用空气净化器时，您只能在更换过滤器时看到污垢，甚至可能看不到（取决于过滤器的包装方式）。