Key Point:

The increase in carbon dioxide–related air pollution is posing a serious health threat to residents of inner-city communities, especially children.

BOSTON—What is the impact of air pollution—specifically carbon dioxide (CO2)—on allergies and asthma? According to a report recently released by Harvard University’s Center for Health and the Global Environment, CO2 is responsible not only for poor air quality in urban areas but also for increased pollen production and allergenicity of certain plants.[1]

The report posits that rising CO2 levels are changing the climate and, in doing so, are affecting the prevalence of respiratory diseases. The pollen season arrives earlier in cities each year, and plants are releasing more pollen. There has also been an increase in the amount of ground-level smog that forms in hot weather to create ozone. Ozone, in turn, can cause asthma and trigger asthma attacks in those with existing disease. In recent years, the incidence of asthma has increased 160% among preschool-aged children, and the estimated annual cost for treating asthma in children is $3.2 billion in the United States alone.

TRACKING THE ENVIRONMENTAL CULPRITS

“CO2 is a problem in cities and a particular problem for those who are poor and living in the inner city,” said Paul R. Epstein, MD, MPH, Associate Director of the Center for Health and the Global Environment. Thus, the increase in CO2 levels may help explain the asthma epidemic in inner cities.

Mainly a product of fossil fuels, coal, oil, and natural gas, CO2 tends to be present at particularly high levels in areas where there are frequent bus stops and idling of trucks. In fact, noted Dr. Epstein, nearly one quarter of children living in Harlem have asthma—and the incidence is highest along bus routes.

“There is a confluence of factors assaulting the inner-city populations,” Dr. Epstein said. In cities, especially in warm weather, domes of air form that are higher in temperature than the surrounding air and have elevated CO2 levels. Added to these domes are diesel particles and ozone from tailpipe emissions. Diesel particles, when small enough to bypass the lungs’ defenses, not only clog airways and exacerbate respiratory illness, remarked Dr. Epstein, but they are also a highly effective system for delivery of pollens and molds deep into the lungs.

The rapid increase in asthma cases among children is likely the result of changes in the environment. Dr. Epstein noted that air pollution, increased outdoor allergens, and climate change act synergistically to produce an enhanced allergic response and, in children with asthma, a higher incidence of asthma exacerbations.

POLLEN ON THE RISE

“As a result of increasing temperature and CO2, plants are showing greater levels of photosynthesis, biomass, water use efficiency, and an enhanced reproductive effort,” commented Christine Rogers, PhD, Senior Research Scientist at the Harvard School of Public Health. Under normal conditions, these changes in plant growth and reproduction are positive. However, they also affect the timing, production, and distribution of aeroallergens, which are implicated in the escalation of allergic disease.

Early pollen seasons are evidence that plants are responding to CO2-driven warming trends, explained Dr. Rogers. “In controlled environment studies of ragweed, when we doubled the amount of CO2 that the plants were exposed to, we saw 40% to 60% more pollen produced.” This phenomenon, she said, has also been observed in field studies of ragweed in both urban and rural areas. Interestingly, the allergen content was higher in the rural (low CO2) areas.

Dr. Rogers said that children in the inner city not only have the greatest incidence of asthma but are also at high risk of suffering the ill effects of CO2-generated increases in pollen allergens. “These children get hit with a powerful one-two punch,” she observed. “They are exposed to the worst air pollution, and they also have increased exposure to allergenic pollens.”

The allergy implications of runaway CO2 mean that millions of Americans living in urban and suburban areas have a real stake in seeing that some kind of action is taken, Dr. Rogers said.

CO2 SPELLS TROUBLE FOR CHILDREN

Georges Benjamin, MD, Executive Director of the American Public Health Association, agreed with Dr. Rogers, adding that inner-city communities already bear a disproportionate amount of the asthma burden. To make matters worse, residents of low-income communities tend to receive less treatment for environment-related diseases because they usually have less access to health care. Yet, said Dr. Benjamin, they are often at much greater risk of health problems.

“Human health is strongly linked to our environment,” he added. Dr. Benjamin explained why children in the inner city have such a high risk for asthma. “Children are not little adults,” he pointed out. “They breathe faster and pull in more air. If the air is dirty, they pull in more soot and ozone.” He added that unhealthy air masses in the inner city are trapping high levels of CO2. “When you look at CO2 levels going from the suburbs to the city, you see levels of 400, 500, and 600 parts per million in the air over cities.” A CO2 level of 379 parts per million is the current atmospheric level globally. Dr. Benjamin expressed the need for policies that can be put into practice today to ensure better air quality.

ENVIRONMENTAL “TO DO” LIST

Dr. Epstein remarked that although the situation is grave, “we already have the answers.” Initiatives on individual, organizational, city, state, and regional levels can go a long way towards improving air quality. Some of the actions he proposed include:
• Convert from fossil fuel use to alternative energy sources when possible.
• Develop hybrid vehicles that use less gas.
• Construct energy-efficient buildings, with rooftop gardens and light-colored pavement and roofing.
• Improve public transport so that fewer people need cars to commute.
• Implement tree-planting programs to maximize shade.

“The issue of asthma is something that comes home to all of us,” said Dr. Epstein. “Gasping for breath is frightening—for patients, their parents, and certainly for clinicians.”

—Gale Jurasek

Reference
1. Epstein PR, Rogers C, eds. Inside the Greenhouse: The Impacts of CO2 and Climate Change on Public Health in the Inner City. Boston, Mass: Center for Health and the Global Environment; 2004.

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