Hi Matthew,

I was reading messages on the clean air group.

I don't know whether you still live in the same location or not and whether your air filters are as black as they were when you posted your message a few years back. 

I was wondering whether the colour of your filters may be due to neighbours using wood stoves in your neighbourhood, or it could just be that it's down to pollution generated by cars, of course. 

Kind regards,

Amandine