Commuters' Exposure to Air Pollution More than Previously Believed

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HONOLULU (April 13) – Air pollution and commuters' exposure to the same is a well known fact and a growing health concern in urban areas worldwide, more so in Asian cities.  But a recent study conducted in Hanoi under the direction of Sumeet Saksena, a research fellow at the East-West Center in Honolulu, and a team of colleagues from Vietnam and the University of Hawaii-Manoa, found that the exposure problem may be bigger than previously thought.

"Most studies of air pollution in cities," Saksena says, "have concentrated on urban background air quality and its effects on people away from roads." But he notes, "Scientific evidence (now) suggests that road users of all kinds are exposed to higher levels of air pollution."

Part of the problem is that the traditional measurement of pollutants is taken far above ground level, usually on building rooftops along busy thoroughfares. Saksena and his team hit the road, as it were, with sophisticated measuring instruments and found that pedestrians were not alone. Commuters in cars, buses, motorcycles, and bicycles are also risking their health, to one degree or another, on their way to work. In fact, motorcyclists are the most exposed road-user group.

The research team was in a sense starting from scratch. Saksena says many studies have been done in the United States and Europe but they are "not easily adaptable to Asia." According to Saksena, that is because of "the unique modes of transportation in Asia, such as two-wheelers and highly used bus systems." He also notes, "In Asian cities the use of diesel is much higher than in the west and the implications of this for actual human exposure to air pollution is not known."

Concentrating on estimates of personal exposure to particulate matter (PM 10), diesel being the main culprit in this category, and carbon monoxide (CO), Saksena and his team targeted four major roads in Hanoi. Not surprisingly, they found that air pollution in the Vietnamese capital is at its worst along traffic thoroughfares where people live and work. 

Hanoi is a city that has seen its population jump from 300,000 in 1954 to 1.8 million in 2003, with a major leap in vehicular activity and those numbers are expected to grow. Most of the motor vehicles in the Vietnamese capital are, as Saksena puts it are "old cars and trucks emitting harmful air pollutants." To that you may add large numbers of motorcycles. He notes that the city has a well-developed street system within its central districts, but they too "contribute to high ambient dust concentrations, often above the allowable limit," due mainly to new construction and repairs. He adds "at the traffic intersections," where vehicles are forced to wait and idle, "concentrations of air pollutants exceed Vietnam's standards of ambient air quality."

The study found that all using the roadways, no matter what the means of transport, were at risk. Pedestrians certainly, but Saksena and his colleagues found that people in cars, and buses, and those making their way via motorcycles and bicycles were being exposed to levels of pollution not considered before. The research team also found that people living and working along the thoroughfares were not immune to the problem. Startlingly, road-level pollution was found to be more than twice the background level usually measured on roof-tops.

And, it is a problem … not the pollution alone, but the lack of comprehensive scientific study, as well.

Saksena says, "Studies of human exposure are needed to quantify the impact of air pollution on public health." He underscores the need by pointing out, "fine particles are responsible for cases of respiratory disease and premature death every year," and are concentrated along traffic thoroughfares where people live and work. He adds, "most particle pollution originates from combustion operations and from vehicles."

Quantifying that impact can be difficult, Saksena acknowledges "because large numbers of people may be exposed to relatively low levels over long periods of time … exposures (that can) result in rare health problems that are difficult to value or even attribute to air pollution." On the other side of the coin, he points out, "a substantial number of people can be exposed to relatively high levels of air pollution for short periods of time due to the nature of their daily activities or occupations."  Therefore, Saksena says, "it becomes important to measure air pollutant exposures as people perform their daily activities."

Following that suggestion,  Saksena says the recent survey, "has clearly provided evidence of the extremely high levels of pollution experienced by commuters," and "highlights the need to consider comprehensive assessments of exposures within buildings, such as cafes, shops, offices and homes which are very near the road."

To do that, Saksena and his team recommend, among other things, that governments rely on actual exposure estimates to spread awareness on the twin benefits of switching to modes of transportation such as buses. This leads, they say, to "an immediate and direct reduction in an individual's exposure, something very critical in the case of vulnerable groups like children, elderly and asthmatics." It also reduces the ambient background pollution. The study's authors also suggest that "long-term periodic evaluation using exposure estimates may improve the benefit-to-cost ratio of government interventions."


Sumeet Saksena is a research fellow at the East-West Center specializing in environmental health impacts of energy use. He can be contacted at (808) 944-7249 or via email at


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