Get rid of leaf blowers: they pollute and their purpose is dubious

 

The most infuriating feature of my walk up to my office every morning is neither the distance nor the steep hill; it is the daily presence of a leaf blower. Never has a machine been so pointless, wasteful and widely disliked, and yet so widely used.

There are many reasons to hate leaf blowers. They are loud and their sole purpose is to over-manicure nature. They disperse debris rather than gathering it, and they kick dust and small particles up into the air.

The world is not worse off if the leaves are left unblown.

But perhaps the worst thing about most leaf blowers is that the majority of them use two-stroke petrol engines.

Despite being far less economical with fuel than the more common four-stroke engine designs, two-stroke engines were for many years prized for their high power-to-weight ratio. It makes them appealing for applications where weight is a severe constraint. This is the case for leafblowers, which are typically carried around manually. It is also the case for a handful of other applications such as outboard boat motors, jet-skis, and chainsaws.

Two-stroke engines are also mechanically simpler, which makes them cheaper to make and easier to repair. These are all appealing characteristics for devices that users don’t necessarily want to spend much money on purchasing. These applications also don’t generally represent a high fuel spend, so the financial trade-offs often outweigh the lower fuel economy. As a result, two-stroke engines, despite having been largely discontinued in car engines, have retained certain niches where they are still prevalent.

Unfortunately, the fundamental design of small two-stroke engines means that the extra fuel-spend is the least of their drawbacks, for two reasons. The first of these is that they exhaust gases at the same time as they inject fuel, which results in unburnt and partially-burnt fuel leaving with the exhaust gases, discharging petrol fumes and carbon monoxide into the air.

The second problem is that small two-stroke engines cannot be lubricated repeatedly from a reservoir like conventional four-stroke engines, which means that instead, the fuel they burn is a mix of petrol and oil. This means that oil is usually used once and discarded and, worse, it results in the release of extremely high quantities of small particulate matter. In one study it was found that small vehicles with two-stroke engines released roughly ten times the quantity of fine particulate pollution as comparable four-stroke vehicles.

These pollutants pose a general environmental hazard. They are also toxic to people receiving close exposure. Two-stroke engines have been associated with severely elevated rates of respiratory illness and also with early markers of lung cancer, presumably from the long list of known carcinogens in petrol.

One common “use” of leaf-blowers is a particular problem. A private person using a leaf-blower in their yard will typically have little trouble using an electric one, where standard extension cords offer enough range to cover the area. Two-stroke petrol leaf-blowers are, however, quite commonly used by employees on larger premises such as housing complexes, estates and schools, and may be used on a daily basis.

The health effects of regularly using a two-stroke engine leaf-blower arguably contravene the Basic Conditions of Employment Act, which guarantees a safe working environment for employees. A number of the pollutants emitted by two-stroke engines shorten lifespan. Taking these effects together, it is likely that requiring a person to operate a leaf-blower on a daily basis compromises their health. There is, as far as I am able to find, no comprehensive study on the individual health effects of daily leaf-blower use, but given the number of toxic compounds emitted, the burden of proof should be to prove them safe, rather than to prove them dangerous.

The risk may be reduced by using personal protective equipment, but this is tougher than it seems. The particulate matter exposure can be handled by a filtration mask (along with ear-plugs for the noise), but that will not handle either the carcinogenic volatile organic compounds nor the carbon monoxide. Highly specialised respirators with appropriate adsorption media could handle the organic compounds, but carbon monoxide is a light gas that is not that easily adsorbed, so safe operation in its presence generally requires self-contained breathing apparatus (typically, an oxygen tank).

I’ve never seen a person using a leaf blower wearing an oxygen tank.

If the leaves truly need to be blown, the responsible option is to use an electric or four-stroke (within weight allowances) or, better yet, a rake.

 

The environmental problems with two-stroke engines

In each cycle of an internal combustion engine, four steps must occur.

1. Fuel and air must be brought into the cylinder.

2. The mixture of fuel and air must be compressed

3. That compressed fuel and air mixture must be combusted to drive the piston

4. The exhaust gas produced by combustion must be discharged.

In a four-stroke engine, such as those found in the vast majority of modern vehicles, these four things take place in four separate steps. The piston moves down and sucks fuel and air in during a down-stroke with intake valves open. That mixture is then compressed during an up-stroke with all valves closed. With the valves still closed, the fuel-air mixture is then combusted, forcefully driving a down-stroke – it is only in this phase that power is produced. Finally, the exhaust valves are opened and an up-stroke of the piston drives out all of the exhaust gases.

In a two-stroke engine, there are only two phases instead of four, meaning there is just an up-stroke and a down-stroke. Power is produced during the down-stroke, and compression happens during the up-stroke, and intake of new fuel-air mixture and discharge of exhaust gases occur simultaneously during the end of the down-stroke and the start of the up-stroke, while the piston is near the bottom of its range.

Because fuel intake occurs at the same time as gas is exhausted, some of the fuel is inevitably lost with the exhaust. Another feature of this cycle is that the valves are open for a portion of the power stroke, which means that a portion of the energy from gas expansion is lost without providing power.

These features tend to make two-stroke engines far less fuel efficient than four-stroke engines, which in turn also gives them high CO2 emissions.

More concerning is that the unburnt fuel poses health and environmental hazards; petrol contains a number of known human carcinogens. Another problem is that incomplete combustion in small two-stroke engines tends to produce carbon monoxide, a toxic gas that interferes with the body’s ability to absorb oxygen.

The problem of unburnt or partially-combusted fuel is less severe, but not eliminated, in a modern type of two-stroke engines referred to as direct injection. These designs are more complex, requiring that fuel be injected separately.

Another characteristic of most two-stroke engines is that their mechanical design, in which both sides of the piston head are functioning components, means that they can’t be lubricated in the same way as four-stroke engines. Instead, they must burn a mixture of petrol and oil so as to be constantly lubricated. This results in additional hydrocarbon and particulate emissions, which also harm respiratory health. Small two-stroke engines have been implicated in widespread respiratory illness and cancer risk in areas where they are commonly used.