Business was brisk at Teddy’s Cocina in Pasadena as wildfire evacuees ate lunch and passersby ducked indoors to escape from the brown, smoky air blanketing the city.

“It’s not breathable,” said Dulce Perez, a cook at the restaurant, as an eye-watering haze hung overhead on Thursday about two miles (3.2 km) away from one of the multiple fires burning around Los Angeles. “We just try to stay indoors.”

This week, as the wildfires raged and smoke billowed across Los Angeles, officials issued air quality alerts, schools canceled classes and scientists warned about the dangerous – even fatal – consequences of wildfire smoke.

All around the United States’ second-largest city, residents worried about air that has, at times, turned lung-burning from the ash, soot and smoke emanating from fires that have destroyed 10,000 structures.

Air purifiers were sold out at some big-box stores, according to interviews with employees at four businesses. Some residents were taping windows to keep the smoke out of their homes. And Los Angeles officials urged people to stay indoors in areas where smoke was visible.

While conditions improved on Friday, an air quality alert remained in effect until the evening and dangerous particulate matter remained around four times World Health Organization guidelines.

At the Pasadena Convention Center, which has been converted to a temporary shelter, aid workers from Sean Penn’s global humanitarian organization, CORE, were handing out N95 masks on Friday.

Emergency response programs manager Sunny Lee said the homeless were particularly vulnerable to bad air.

“There was no place for them to go inside, and so they were suffering even more outside with the poor air quality, without any kind of masks,” said Lee. “So, we pushed out N95 to our partners that reached those communities. We’re distributing as many as we can.”