No haze? You may still be inhaling even smaller pollutant particles while waiting for the bus

Dr Erik Velasco with his instruments used to quantify pollution at VivoCity's bus stop.
Dr Erik Velasco with his instruments used to quantify pollution at VivoCity's bus stop.PHOTO: SMART
Commuters wait to board bus service 972 at Jelapang Road
Commuters wait to board bus service 972 at Jelapang RoadPHOTO: ST FILE

SINGAPORE - It is not just during hazy periods that people inhale tiny pollutant particles. Commuters could be breathing in such particles even while waiting for a bus.

A new study by an air pollution expert from the Singapore-MIT Alliance for Research and Technology (Smart) has found that a commuter who makes a two-way bus journey five days a week could inhale an average of 3.5 times more tiny pollutant particles than at an ambient level.

And according to the study led by research scientist Dr Erik Velasco, these particles are smaller - and more toxic - than the PM2.5 pollutant particles dominant during periods of haze. Tiny particles are toxic as they can dissolve into the blood stream where they are carried to organs around the body, such as the brain.

PM2.5 refer to pollutant particles less than 2.5 microns in diameter - about a 30th the diameter of a strand of human hair.

But the particles that commuters breathe in while waiting at a bus stop are much smaller. They measure 27 nanometres in diameter - about 100 times smaller than PM2.5.

Due to the large content of sulphur in fuel, catalytic converters in cars do not remove all the particles and gases. The toxic, ultrafine particles are formed when gases and particles from vehicle exhaust pipes react with each other in the air after they are discharged.

"Waiting at the bus stop for only 10 minutes each time may seem innocuous. But these short exposures all add up," said Dr Velasco at a media briefing on his latest work on Tuesday (Sept 20).

"A commuter who takes a two-way trip by bus to work for five days per week is actually exposed to these participles for nearly seven hours per month and over three full days per year. This exposure can affect people with existing pulmonary and cardiovascular diseases, among others."

Dr Velasco worked with Ms Tan Sok Huang, a former master's student from the National University of Singapore (NUS), on the study which sought to quantify pollution at five bus stops in Singapore - at VivoCity, Little India, Bugis, One Raffles Quay and NUS.

These were selected for the different properties of the roads nearby. The bus stop at NUS, for instance, was next to the Ayer Rajah Expressway, on which many heavy vehicles travel. The bus stop at One Raffles Quay, on the other hand, enjoyed windy conditions and had less traffic.

Dr Velasco also shared some possible solutions to this on Tuesday. For instance, installing fans at bus stops could not only make waiting in the heat more comfortable, but the wind could also disperse pollutant particles, he said.

He also said Singapore's move to install arrival time information at some bus stops is a good move, but said the Republic could consider getting buses to arrive at the same time every hour, as is the practice in other countries. This way, commuters could ensure they reach the bus stop at a specific time, say, 7.16am every morning, minimising the waiting time at the bus stop.