What is the pink powder sprayed over the California wildfires?

The powdered substance sprayed over the California wildfires is called Phos-Chek. It contains ammonium phosphate — an ingredient commonly found in fertilizer.

As the wildfires in Southern California continue to burn, streaks of bright pink fire retardant have become a familiar sight.

Fanned by strong Santa Ana winds, the fires have killed at least 25 people and burned around 40,000 acres in the greater Los Angeles area. More than a week after it ignited, the area's largest blaze, the Palisades Fire, was 19% contained as of Wednesday. Los Angeles County has declared a public health emergency because of the smoke.

The powdered substance being sprayed over the wildfires is called Phos-Chek. It can be dropped from the air or applied via trucks on the ground. It's primarily made up of water, ammonium phosphate — an ingredient commonly found in fertilizer — and pink coloring, though it's thickened with gum to improve accuracy for aerial drops.

“Phos-Chek is a fertilizer-based retardant product. It’s the same ingredients that are used on your fertilizer for lawn care,” said Shannon Horn, chief operating officer at Perimeter Solutions, the maker of Phos-Chek.

When used in fire retardant, ammonium phosphate can change the way the cellulose in plants reacts to heat. Ordinarily, plants exposed to a fire's heat begin to decompose and become fuel, but Phos-Chek acts as a coating, creating a barrier that consumes the heat energy. The reaction produces a nonflammable carbon material, thereby slowing a blaze to buy firefighters time.

https://www.nbcnews.com/weather/wildfires/pink-powder-fire-retardant-california-wildfires-rcna187620

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