Pollution might not be the best word here, better to use the chart word environment worsens. Either way it doesn’t sound right to me that environment naturally worsens with a rise in per capita income but I am listening.
One has only to look at the Eastern Block and Communist countries where per capita income fell.
Just horrendous environmental impacts. Worst in the world.
The environment would initially worsen as people move from subsistence survival to farming and then dirty industry — but then as wealth increases industry becomes cleaner and the degradation curve turns downward.