OK, so I am not searching for the links but...
Modern 2-stroke dirt bike engines first of all are not regulated for emissions. There is no catalytic converter or other "cleaning" mechanisms. Second, 2-strokes have particle emissions like a diesel; that un-burnt/partially un-burnt fuel and oil escaping out the exhaust. Due to these 2 factors alone make dirt bikes emissions worse than today's cars.
As for comparing it to F1 and again, I am not going to search for the links, that was comparing the entire F1 foot print of a race weekend, not comparing what comes out of the cars. F1 engines are the single most efficient sporting engines on the planet. Yes, they have massive emmisions output, but concidering the amount of power they are creating from such little input, it is amazing. The footprint covers the cars as well as the transporters, the jets, the catering, etc. Considering also that most of the people arrive at an F1 event by plane, unlike motocross which is still predominantly local. So yes, an F1 weekend has a larger footprint than a season of Motocross.
In addition, F1 burns Gasoline, not Ethanol (although I believe it does contain 10% now). Indy Cars are 100% Ethanol. I believe (but again, I'm not looking it up again) that ALMS is E85 for the non diesel cars.
For those that will be in the Houston, TX area or those that were at Indy during the early '00's, the sight of the sky following the event...of all the planes taking off and circling the skys...it is almost worth it to go just to witness it. It is truly a wonder of mankind and kind of resembled Bagdad and Panama during the invasions!
...and Stu, it has gov't involvment has nothing to do with solving pollution problems. The farmers get huge gov't subsidies to grow corn. The oil industry is who makes the ethanol and sells it to us. Those are 2 of the biggest lobbyests...need I say more?
