Riding faster while commuting increases inhalation of pollutants, UBC study finds

Active commuters beware: Pushing yourself hard while walking orbiking on city streets can dramatically increase the amount ofairborne pollutants you take in, according to a new study from theUniversity of British Columbia.

Cyclists who maintain speeds near 30 kmh may absorb three to four times the toxicants of a cyclistpedalling at a moderate 13 kmh, said lead author Alex Bigazzi, a transportation expert in thedepartment of civil engineering.

Active commuters are exposed to a cocktail of pollutants, which includes carbon monoxide, volatileorganic compounds (VOCs), particulates and soot. But exerting yourself to minimize your time onthe road — and presumably your exposure to toxic pollutants — is a losing strategy, said Bigazzi.

The researchers built a computer model of 10,000 people using census data to find the optimalspeeds pedestrians and cyclists of different ages and sexes should maintain to reduce pollutantintake while enjoying the well-documented benefits of exercise.

“There is a trade-off between the time you spend travelling and how much air you take in,” hesaid. “The faster you move, the harder you breathe and the more pollution you could potentiallyinhale, but you also are exposed to traffic for a shorter period of time.”

“This analysis shows where the sweet spot is and it’s right in the middle,” he said. “You don’t wantto go real slow and you don’t want to power through.”

The optimal speed for cyclists is around 13 kmh on a flat road, but maintaining speeds up to 20 kmhdidn’t make a huge difference in pollutant intake.

“But when you get 10 kilometres per hour above your optimal speed it pretty quickly goes to two,three or four times the total pollution inhaled over a trip,” he said. “The highest risk is to people whoare cycling for exercise on polluted streets.”

The optimal speed for adult walkers is around 4.5 kmh, but the best speed for children is closer tothree kmh, because they have to exert themselves more to keep an adult pace.

“The same principle would apply to families cycling together,” Bigazzi said.

Runners take in about double the pollutants compared with walkers. The optimal speed for joggersis about 10 kmh.

“We don’t know whether the extra exercise is worth the risk, but there are certainly cardiovascularbenefits from running,” he said.

The study, published in the International Journal of Sustainable Transportation, builds on Bigazzi’searlier work, which found that exposure to airborne VOCs was 100 to 200-per-cent higher on high-traffic arterial routes and roads through industrial areas.

Blood levels of toxicants were 40 to 100-per-cent higher than normal in cyclists after riding just sixto nine kilometres on heavily used urban streets. No difference in toxicant levels was detected incyclists that used low-traffic streets.

“When I talk to cyclists, they are worried about air pollution and they want to know what theyshould do to reduce their pollution risk,” said Bigazzi. “This begins to answer that question.”

The next stage of the research will involve taking breath samples from walkers and cyclists usingcity streets to determine the levels of pollutants in their bodies after different levels of exertion.