Four times each day, Emma Allen runs through a careful regimen of prescriptions, marking each one down in a notebook as she takes them: steroid pills, an inhaler, two solutions mixed in a power nebulizer, misted through a thin plastic tube. Shields and her brother both have sinus infections, she said, and their parents were hospitalized with respiratory problems and pneumonia. The same story is repeated around the neighborhood - symptoms that make daily tasks difficult, exacerbate illnesses, drive up expenses for doctors' visits, prescriptions and over-the-counter medications, and have neighbors worried about how much longer they can bear it. From 9 a.m.