You are pulling numbers from an article that is based on the numbers I posted.
http://www.arb.ca.gov/msei/onroad/onroad.htm That has the explanation of how those numbers were found - they weren't, they were estimated. Since motorcycles are currently NOT required to have emissions tests, where do those numbers come from? They are gathered from specific bikes - then estimated across the board. Now, if you were trying to get legislation passed - what would you use? A bike that has low emissions or high emissions? Either way - THAT isn't defined.
The numbers are found:
http://www.arb.ca.gov/app/emsinv/ems...09&F_AREA=CA#7
Would you like me to draw a better PICTURE?? Since most people deal better with pictures than numbers... let me provide that from the PDF below. This is from THEIR study. Motorcycle is the MC on the right. Clearly, it's a HUGE problem.
http://www.arb.ca.gov/msei/onroad/briefs/emfac7.pdf