Two separate questions here, bud: 1. Which vehicle pollutes
more? 2. Which leaves a smaller carbon footprint? You get a
different answer depending on which one you ask. The serious
vehicle pollutants these days are carbon monoxide (CO), nitrogen
oxides (NOx), and unburned hydrocarbons. (Sulfur and lead
emissions, once problematic, are now largely a thing of the
past.) Here are the federal standards for four wheels versus
two: Cars and light-duty trucks (including SU Vs). Maximum CO
emissions: 7.5 pounds per thousand miles. Unburned hydrocarbons:
0.154 pounds. NOx: 0.154 pounds. Scooters and small motorcycles.
Maximum CO: 42.57 pounds. Unburned hydrocarbons: 3.55 pounds.
NOx: no limit. In other words, scooters can legally emit about
5.7 times more CO than cars, nearly 24 times more unburned
hydrocarbons, and infinitely more NOx—and realworld testing
suggests they do run pretty dirty. One reason for the looser
restrictions is that it’s tougher and costlier to put emissions
controls on a scooter than on a car. S