Motorycle Podcast produce their own podcasts (in german only) where they talk about motorcycle tests and other related stuff.

Study: pollution caused by motorcycles

The Swiss EMPA Institute (Materials Science and Technology) which is a branch of the Swiss Federal Institutes of Technology in Zurich (ETH) published their results on some research related to pollution caused by motorcycles. You can get the summary which was sent to the press in German. The detailed report was published in "Environmental Science and Technology" and could be downloaded from here as PDF (English only).