In Los Angeles, the choking smog comes from the tailpipes of cars and trucks. On the Big Island of Hawaii, it comes from the mouth of the Kilauea volcano, and they call it "vog" (volcanic smog).

Sulfur dioxide gas from the volcano has been wafting across the island for weeks, forcing the closure of portions of the Hawaii Volcanoes National Park. It has also begun to sicken residents of the island, who are reporting coughing, choking symptoms. They are also seeing casualties in their gardens.

Here's a satellite view measuring concentrations of sulfur dioxide emissions. Each little square pixel represents a volume about 13 kilometers square, rising 5 kilometers above the surface. Red incidates a concentration of 30 metric tons of sulfur dioxide inside that little volume, or 845 cubic kilometers. 

Here's another view, in visible wavelengths shot from space, showing the sulfur dioxide "vog" plumes blowing across the island and out to sea.