WHEN SMOKE FROM California’s deadliest wildfire blew into downtown Sacramento last November, daylight blurred into dusk and the city’s air became among the world’s most polluted. The Camp Fire has long since been extinguished, but the health effects from the tiny particulate matter in the smoke, which penetrates into the lungs and ultimately into the bloodstream, could linger for years. No one is surprised when smoke brings a surge of emergency room visits for asthma or other breathing problems. More insidiously, people are also inhaling noxious fine particles measuring less than 2.5 microns, or a fifth the size of a particle of dust or pollen. Researchers have had a hard time quantifying exposure to those tiny particles as a smoky plume moves through an area or just how harmful the bursts of such air can be. But recent work suggests that children and babies are particularly vulnerable to long-lasting health effects.