Although heavy-duty diesel vehicles operate in both urban and rural locations, the nearer Vermonters live to urban areas or major transport routes, the more likely they will be exposed to diesel air contaminants.

People living in urban areas, including many poorer neighborhoods where the housing density tends to be higher and residences are closer to major highways, may suffer the most exposure. The density of individual emission sources of air pollution is greatest in our urban centers. Heavy-duty diesel vehicles converge on urban areas from many different directions and traffic is often congested, resulting in almost continuous exposure to vehicle emissions along many urban streets. Although heavy-duty diesel emissions make up only a portion of the total pollution mix, monitoring of urban air pollution has shown that it is a significant portion.

Children and the elderly are generally more at risk from exposure than healthy working-age adults. Studies indicate that children may be at increased risk of pulmonary function changes and increased incidence of symptoms associated with inhaling higher levels of particulate matter exposure. Among adults, studies have shown that lung function declines with age. Other studies suggest that the elderly experience a higher excess risk from exposure to particulate matter air pollution. As we age, more of us are likely to suffer from illnesses which -- whether related to respiratory problems or not -- weaken our resistance to increased air pollution.

Exposure to higher levels of particulate matter in urban areas creates an increased risk of health effects, ranging from mild respiratory difficulties to excess mortality from respiratory and cardiovascular causes. The Vermonters most susceptible to higher ambient levels of particulate matter are seniors with pre-existing respiratory disease who live in urban areas.