Tire and brake wear could be the next front of emissions testing, according to Emissions Analytics, an organization that conducts independent emissions tests.

Emissions Analytics found that emissions of particulate matter from tire wear can be 1,000 times worse than from tailpipes.

Because exhaust emissions are becoming more tightly regulated, and more electric cars are on the road, particulate matter from tire and brake wear now make up a larger share of vehicular emissions, according to Emissions Analytics.

According to a press release from the organization, tests involved a “popular family hatchback” with new, correctly-inflated tires. The hatchback’s tires emitted 5.8 grams of particulate matter per kilometer, compared to 4.5 milligrams per kilometer from the exhaust, according to Emissions Analytics.

That means tire-wear particulate emissions were higher than exhaust particulate emissions by a factor of 1,000, the organization noted.

The implication of this test is that electric cars may not be free of particulate emissions after all.

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