SAN JUAN, Puerto Rico — Shortly after he turned 2, Yadriel Hernandez started struggling to breathe. His doctor prescribed an inhaler and an allergy pill for asthma, and his symptoms were mostly under control. Then Hurricane Maria devastated Puerto Rico, strewing mold-producing wreckage across the island and forcing many to use fume-spewing generators for power. The boy, now 8, started having twice-monthly attacks and needing nearly four times the amount of medicine he used to take. His mother said weekly power outages in their coastal town of Aguadilla also feed his anxiety, which can make symptoms worse.