The real world is a complicated place. It is often exceedingly difficult to disentangle the causes of phenomena, such as the increasing rate of childhood asthma, from the spaghetti-like mass of possible contributors. Was a new pollutant or irritant added to our air? Did something disappear from our air? Are children today exposed to more allergens at an earlier age than their parents were? Or less exposed? Do these exposures affect susceptibility to asthma?
For years, scientists speculated that there was a link between increasing asthma rates and the pollution generated by burning gasoline in cars and trucks. A primary suspect was ground-level ozone, a substance formed by a chemical reaction between sunlight and certain tailpipe emissions–volatile organic compounds and oxides of nitrogen. Although there was good evidence for this link, it was nonetheless challenging to prove. One obvious way to test the link would be to simply reduce traffic-related pollution levels in a city, and record the corresponding effects, if any, on the rate and severity of asthma attacks. Of course, researchers are unlikely to get permission to do this kind of testing.
Prior to the 1996 Olympics in Atlanta, quick-thinking scientists at the Centers for Disease Control (CDC) realized the upcoming Games provided them with a unique research opportunity. City officials, worried about Atlanta’s notorious traffic congestion, initiated an ambitious traffic reduction program in the city center for the 17 days of the Olympic Games. They added 1,000 buses to the city’s fleet, provided 24-hour public transportation, closed downtown streets to private vehicles, and asked local businesses to stagger work hours and delivery times. It was the perfect chance to observe first-hand the effects of decreased traffic pollution on asthma in the city’s children.
For the four weeks prior to the Olympic Games, and for the 17-day duration of the Games, the CDC monitored the number of asthma-related visits among one- to 16-year old children in five downtown clinics and hospitals. They compared this information to traffic and air quality data collected over the same period.
The city’s traffic reduction programs were very successful. During the Olympics, Atlanta’s morning rush hour averaged 22 percent fewer vehicles than during the four previous weeks. The lighter traffic lead to a 28 percent decrease in peak ground-level ozone, as well as decreases in all but one of the other traffic-related pollutants studied.
The apparent health effects were startling. Asthma-related visits by children to the five study centers dropped by 11 to 44 percent during the Olympics, as compared to the prior four weeks. (Only one of these decreases was statistically significant; however, decreases at the other four centers all approached significance). Importantly, non-asthma related visits among children during the Olympics showed no change from the prior month. Thus, the results could not be explained by parents with children leaving the city during the Games. Because sunlight and wind patterns play an important role in the formation of ground-level ozone, the researchers also ruled out changes in weather than may have explained the findings. These data are compelling indeed.
The pollution problems of a large metropolitan area of nearly 4 million people, such as Atlanta, may not seem relevant to those of us lucky enough to live in the sparsely populated state of Maine. However, Maine consistently reports childhood asthma levels among the highest in the nation. Statistics from state offices indicate that over two thirds of Mainers live in areas with ozone levels exceeding the state’s recommended concentrations. While some of the ozone and other pollutants in Maine’s air are clearly brought in on winds from the west, we are also responsible for a significant proportion. Estimates for the size of this proportion vary drastically. My quick perusal found a range of 10-70 percent!
It is interesting to note that while Atlanta reduced its morning rush hour traffic by nearly 25 percent during the Games, its 24-hour traffic counts were only suppressed about 3 percent below normal. This suggests that people changed the timing of their trips more than they reduced their absolute amount of driving. Pollutants emitted during morning rush hours are known to be primary contributors to high afternoon ozone counts. It is therefore not surprising that a 22 percent drop in peak ozone could be achieved with only a 3 percent drop in daily traffic counts. Driving outside of busy times as well as reducing our amount of driving both have the potential to substantially reduce the severity of asthma among our children.
Sarah Walpow can be contacted at [email protected].