Fireworks on Bonfire Night can send air pollution to high levels.
Scientists looked at the cities of Newcastle and Gateshead last year and found that as bonfires and fireworks were lit at night, the levels of pollution in the air tripled.
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Professor Phil James, from Newcastle University said it shows a "striking picture of the impact the fireworks and bonfires are having on air quality."
But government officials have said that pollution levels are not expected to stay high around Bonfire Night this year.
That's because the weather conditions will be different with more winds that will blow away the pollution particles in the air.