Many asthmatics blame the Valley's Brown Cloud for their disease. But pollution doesn't cause their asthma, it inflames it. Particulates, microscopic bits of soot and dust, burrow deep in the lungs, swelling airways and constricting already narrow breathing passages.
Ozone sets off similar attacks.
On days with average particulate pollution in 1999, Valley asthma deaths jumped 10 percent compared to clear days, according to an Arizona Department of Health Services study. Asthma attacks increased 9 percent. On the worst pollution day that year, when particulates inched toward unsafe levels, asthma deaths jumped 40 percent and asthma attacks increased 36 percent. Researchers don't know exactly what causes asthma. Even in Phoenix, where people worry increasingly about the Brown Cloud, some air pollutants have declined.