I was walking up the street the other day when a powered bicycle put-putted past me up the hill. The owner was probably secure in the knowledge that he was helping reduce traffic congestion and his environmental impact. If so, he would only be partially right.
Bicycles certainly reduce traffic congestion. And they’re great for your health as long as you don’t use the motor for your whole trip. But power-assisted bicycles aren’t as environmentally friendly as you might think.
Emissions from gasoline-powered engines can be separated into two main types: greenhouse gas (GHG) emissions and criteria air contaminants (CAC). GHG emissions from gasoline engines consist mainly of carbon dioxide. CAC emissions include carbon monoxide, sulfur dioxide, nitrogen oxides, and various substances that result from the partial combustion of the fuel.
The amount of GHG and CAC produced by a gasoline engine is determined by the amount of fuel burned, and the efficiency of the engine. That’s where the similarities end. CAC emissions can have nasty immediate effects on a local scale, creating smog, increasing the incidence of athsma attacks, causing respiratory distress in the elderly, among other effects. The effect of GHG emissions is long-term and global, contributing to climate change.
CAC emissions can be reduced by using devices placed in a vehicle’s exhaust system. For decades now, most engines have had catalytic converters that scrub most of the emissions from the exhaust that leaves the engine. Producing cleaner fuels and making engines run more efficiently also reduce CAC emissions. Unfortunately, there is no ’scrubber’ for carbon dioxide. Carbon dioxide is the simplest substance that can result from burning a carbon-based fuel. In fact, reducing CAC emissions by making engines more efficient increases the amount of carbon dioxide produced.
Therefore, while GHG and CAC emissions both increase with the amount of fuel burned, GHG emissions are greater for larger engines regardless of the emissions controls on the engine. So small engines are always better, right?
Wrong! Small engines can be much, much worse than large engines for short-term local pollution because engines under a certain size are not regulated under laws that require emissions controls (at least in Canada). In fact, the 50cc scooter or power-assisted bicycle you see driving up Main Street tomorrow is probably emitting more than a hundred times as many CAC emissions as the Hummer racing past it.
Being green on the road is not as easy as it seems. Evaluating alternative modes of transportation involves more than just the amount of fuel you burn. If a large number of people traded in their cars for scooters and power-assisted bicycles, traffic congestion and GHG emissions would be reduced drastically, but our cities would become enveloped in deadly smog.
If you want to commute as cleanly as possible, walk, take public transit, ride a muscle-powered bicycle, or ride a motorcycle if you have a longer commute. Drive your car if you have to, but find tips on how to drive as efficiently as possible.
More information about on-and off-road engine emissions is available through the following links:
- Canada Gazette: Off-Road Small Spark-Ignition Engine Emission Regulations
- Canadian Legal Information Institute: On-Road Vehicle and Engine Emission Regulations
- Transport Canada Acts & Regulations: Motor Vehicle Safety Regulations (Short Title, Interpretation)
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