I’m sure I saw a column on the “greenness” of a car compared to a scooter. Can’t seem to find it now, despite several seconds of searching. Can anyone point me to it? Thanks!!! 
Found it!
Here you go. I searched Google for site:straightdope.com scooter car
I’d like to point out that there is a growing trend in the scooter world toward 4-stroke engines. I ride a 2008 Yamaha C3 and it has a 49cc single-cylinder 4-stroke with electronic fuel injection and water cooling.
The difference in pollutants is even more drastic when modern scooters with the latest engine and emissions technology are considered.