Pollution drops rapidly after household income (or was it GDPPC) rises above $5000, because people have more acute problems taken care of and start to care more about clean air, water, etc. Essentially poor countries use "pollution acceptance" as an asset to grow richer, until they earn enough to spend buy pollution acceptance from someone else.

But pollution per marginal dollar of GDP per capita is lower. That could just be an artifact of the rich world relatively de-industrializing: as the US gets more Facebooks and Starbuckses, China gets more steel mills. But it also seems that one luxury rich countries pay for is lower pollution relative to GDP.