Effect of Impairment on ROA

I don’t understand why the following is correct: “If an asset is impaired the ROA decreases.”

When an asset is impaired, Net Income drops and also Assets drop. So how do I know what caused the bigger effect on the ROA ratio since both numerator and denominator go down at the same time?
Thanks

Pick a publicly traded company. Any company.

Look at their income statement and balance sheet. In the US, you can get that information from Edgarscan.

Compare the magnitudes of their net income and their total assets.

Then you can answer your own question.