Interstate 95, the major truck route from Florida to Maine, cuts straight through the Bronx, where it becomes the Cross Bronx Expressway and merges with a snarl of other full-throttle routes. As the trucks idle, they churn out diesel fumes, which meld with the fumes from incoming traffic into a smog that blankets Hunts Point and the bordering low-income communities of Port Morris and Longwood. What the Bronx gets out of this is dirt and noise. Schroeder can't be sure that the diesel fumes spewing from those eighteen-wheelers are in any way responsible for the poor health of his patients. But he thinks they are, and so do other clinicians I spoke with.
Scientists are equivocal.
Studies done in the 1990s found that the former East Germany, with its heavy pollution from industry and domestic coal burning, had far less asthma than the ostensibly cleaner West Germany. Likewise, asthma is more common on the pristine, factory-free Isle of Skye, off the west coast of Scotland, than in Cardiff, the relatively gritty capital city of Wales. Douglas Dockery, a professor of environmental epidemiology at the Harvard School of Public Health, says that even if air pollution does not cause asthma, it can and does provoke symptoms in asthmatics. This makes us think that there must be environmental characteristics involved. Some scientists believe that diesel fumes are particularly potent asthma irritants, but most seem to agree with Dockery that symptoms are provoked by any number of pollutants, and that substances found indoors are often more irritating than auto and truck emissions.