Im with Zombie in that they are more polluting in general since they do give out more ppm's but given that they use less fuel and oil i assume that ove the year it would work out greener overall. I think
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One reason that your V8 Suburban, that gets 12 mpg, TESTS out cleaner than your scooter is because they inject air into the exhaust to aid in after-combustion burning of hydrocarbons and to dilute the discharge so it looks like it is cleaner in exhaust gas analysis. Put an air pump on your scooter to blow air into the exhaust port and mount a Cat then test.
Counter intuitive or not, given the choice of being locked in a garage with a running scooter or a running Suburban for 20 minutes..........
EVEN with scoots and bikes being less clean, they still make up about 2% of the measurable, not calculated, pollutants in the USA.
Taiwan has scooter lanes because they would rather trade the less efficient combustion by-products from 50cc scooters for the massive pollutants, congestion, grid lock and landfill gorging from cars and trucks also carrying one person.
My Stella scooter is a 150cc 2T that is EPA approved and there are new DIRECT GAS INJECTION systems that make 2T engines EPA compliant. Austria has recently approved a 2T outboard for use in their pristine alpine lakes.
It is curious that a post on an opinion about warming up an engine gets hijacked by environmentalism.