Seasonal fires and a slew of air pollutants are obscuring skies across northern India, registering “very unhealthy” air quality in New Delhi and causing schools to shut down. Advisories recommend residents avoid spending time outside in the city, which has experienced toxic smog from around the beginning of November

The smoke has gone all over to the Bay of Bengal,” said Hiren Jethva, an aerosol scientist at Morgan State University and NASA. So far, the fire activity is lagging behind other years, but he said “this many fires are still sufficient to create the air quality issue in the vicinity of the burning region.”

The thick plume of smoke pollution, sprawled across northern India, was visible on NASA satellite imagery.

The air quality index in New Delhi for PM2.5 — a particularly hazardous pollutant known as particulate matter 2.5 — reached 285 or “very unhealthy” on Thursday, which is the second most severe level, according to data from the U.S. Embassy. These tiny pollutants, spanning one-thirtieth of the width of a human hair, can travel into our lungs and bloodstream to cause heart disease or lung cancer.