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Mopeds Cause Significantly More Air Pollution Than Cars In Some Places

While some may just offhand assume that, owing to the relatively small size of mopeds, there’s no way that they produce more air pollution than a car (during an equivalent trip), that’s not always true, according to new research from the Paul Scherrer Institute.

Despite making up just a fraction of total traffic-volume in most regions, mopeds with two-stroke engines are, apparently, at the top of the list of air polluters in many regions of Africa, Asia, and southern Europe.

There’s been talk in recent years suggesting as much, but this new work is some of the first to put hard data behind that idea — while utilizing innovative measurement techniques. The reason for the relatively high contribution to air pollution is mostly down to the fact that the popular two-wheelers aren’t held to the same strict emissions requirements that most other vehicles are.

The press release from the Paul Scherrer Institute provides more:

The scientists used a smog chamber developed at PSI to measure the emission of organic aerosols and aromatic hydrocarbons from mopeds in the laboratory and in standard driving cycles. Organic aerosols are small particles which are suspended in air. They account for a major share of fine particles from traffic. By contrast, after being emitted as gaseous substances aromatic hydrocarbons (arenes) can be converted through chemical reactions in the atmosphere in part into secondary organic aerosols and, by extension, into fine particles. In fact, these secondary organic aerosols often account for the main proportion of fine particles. In their original gaseous form some arenes are harmful, too. Benzene, for instance, which is added to petrol is carcinogenic.

The new study shows that during the conversion of exhaust gas from two-stroke mopeds other worrying products are formed. Using chemical analyses the scientists discovered that during the conversion of arenes from moped exhaust gases into aerosols, harmful reactive oxygen species are also formed which can reach the lungs.

Both when standing still and in motion mopeds with two-stroke engines emit amounts of arenes which are several orders of magnitude higher than the limit values admissible in Europe and the USA. According to the study authors, waiting behind a two-stroke moped in traffic may, therefore, constitute a considerable health risk.

The researchers note that there are several different possible reasons for these elevated emissions — incomplete combustion (common to the engine type), the high ratio of fuel to air in the fuel mixture, or the need to add the lubricating oil directly to the fuel. These issues are far less present in four-stroke engines.

Some of the other interesting findings/notes of the work:

  • In the city of Bangkok, two-stroke mopeds generate as much as 60% of emissions of primary organic aerosols — while only accounting for 10% of total fuel consumption by traffic in the city. Given the fact that the calculations are based on the average emission factor of the European mopeds used in the study, the actual emissions are actually probably considerably higher.
  • “Field measurements in China confirm the image of these rampant polluters on two wheels. In the city of Guangzhou the concentrations of arenes in the air fell by more than 80% in 2005 after a ban on two-stroke mopeds. Just 60 kilometers away in the city of Dongguan with its comparatively strict traffic restrictions, higher aromatic concentrations are measured today than in Guangzhou.”
  • The concentration of specific air contaminants in many Southern European cities could be significantly reduced if two-stroke mopeds were slowly phased-out.

Regardless of health issues, if the idea of a moped or scooter that doesn’t stink and isn’t irritatingly loud appeals to you, then you can, of course, now get an electric one. While the pricing on many EV mopeds and scooters are typically higher, the pay-offs are significant (fuel costs, health-wise, etc), as this new research reinforces.

On that note — series production of BMW’s C Evolution electric scooter recently began at BMW’s Berlin plant. The electric scooter represents BMW’s first entry into the market. For those wondering about the tag of “scooter,” the C Evolution can reach speeds of 75+mph. 🙂


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Written By

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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