[copperx]

Post append: According to [1], a simple activated charcoal cabin air filter is better than the stock one in removing diesel exhaust particles.

[1]: https://www.ncbi.nlm.nih.gov/pubmed/24621126

[kaybe]

Thanks, I didn't know this paper. We just measure the NO2.

edit: Seriously, how did they get that through the ethics committee.. I'm astonished and a little bit appalled. There is a second study too.