In the U.S., ambient air concentrations of which of the following have declined the most since 1980 compared to its health and safety standard?
A) lead
B) SO2
C) CO
D) ozone
E) NO2

Question

Quizplus · Accepted Answer

Lead has seen the most significant decline in ambient air concentrations since 1980 compared to its health and safety standard, largely due to the phase-out of leaded gasoline and tighter industrial emission standards.

In the US, Ambient Air Concentrations of Which of the Following Have