That morning commute can be a real killer -- in more ways than one.
Atmospheric science researchers armed with scientific equipment sampled the air on the streets and on the mass rapid transit (MRT) system in Taipei and discovered that commuters were breathing in four to five times more dangerous particles than normal levels.
Levels of particle matter below 2.5 micrometers in diameter -- or PM2.5 -- and carcinogenic polycyclic aromatic hydrocarbons (PAHs) were highest in the morning and scooter riders stuck in traffic were the most exposed.
"A major source of PM2.5 is engine exhaust," said Lung Shih-chun (龍世俊), associate research fellow at Academia Sinica's Center for Environmental Changes.
"The closer you get to traffic, the higher the concentration of fine particular matter and harmful hydrocarbon compounds," Lung said.
The samplings were taken in 2004 and 2005 between two MRT stations in Taipei.
Lung cited the "Six Cities" study conducted in 1993, which showed a strong correlation between exposure to PM2.5 and cardiovascular and lung-related deaths.
"Fine particulate matters are not filtered out by our body but are breathed deep into the lungs," she said.
The study showed that on average scooter drivers were exposed to PM2.5 concentrations of 161 micrograms per cubic meter during their daily commute, substantially more than the 90 micrograms per cubic meter for car drivers and 105 micrograms per cubic meter for people riding on the MRT.
"We could see the concentrations spike at traffic lights, with scooter riders sitting behind the idling engines of the vehicles in front of them," she said.
Scooter riders were also most vulnerable to PAHs, another component of engine exhaust and a highly potent carcinogen.
The study found that scooter riders are exposed to PAH concentrations of 29 nanograms per cubic meter, compared to 8 nanograms per cubic meter for car drivers.
The PAH concentration on the MRT, meanwhile, was below detectable levels, Lung said.
Although the study did not follow bus commuters, Lung said exposure levels were likely to be between that of car drivers and scooter riders because of the frequent opening of bus doors and long waits at bus stops.
Cyclists were likely the worst off as exercising increases the volume of oxygen breathed in, she said.
The levels of fine particulate matter, including PAHs, were consistently more serious in the mornings as there is less air movement, Lung said, adding that sunlight later on helps clear up some pollutants, which tend to be trapped close to the ground.
For people who continue to ride their scooters and bicycles, Lung said face masks were advisable.
"My previous research showed that even the cheap cotton masks block more than a third of fine particulate matter," she said.