Why should it be any more costly to clean up the last 10 percent of polluted air than to clean up the first 90 percent?

Because the 90% that's left is more available to clean

HEy!

Explanation:

Thermal energy makes the rocks of the lithosphere more elastic. Tectonic activity is responsible for some of Earth's most dramatic geologic events: earthquakes, volcanoes, orogeny (mountain-building), and deep ocean trenches can all be formed by tectonic activity in the lithosphere.