+1 on the question above me too, is there an improvement with charcoal and where did you guys get it?
Dust Filter
Nearly all dust particles and pollen are filtered out before
outside air enters the passenger compartment through
the air distribution system.
That is the only mention of the filter on page 116 of 04 owners manual. Thats it..... no mention of how to clean or how to access. Service manual has no hits for "dust filter" or "cabin filter" either. How odd.