I like the take of System Science researchers on this matter -- they say that air/water quality monitoring works exactly because it introduces a feedback loop in the existing system.

Here is a relevant anecodote from Prof. Donella Meadows (who was a major proponent of environemental quality watches):

  During the oil embargo and energy crisis of the early 1970s, the Dutch began to pay close attention to their energy use. It was discovered that some of the houses in this subdivision used one-third less electricity than the other houses. No one could explain this. All houses were charged the same price for electricity, all contained similar families.

  The difference, it turned out, was in the position of the electric meter. The families with high electricity use were the ones with the meter in the basement, where people rarely saw it. The ones with low use had the meter in the front hall where people passed, the little wheel turning around, adding up the monthly electricity bill many times a day.

Adding a quick, tight feedback loop is often a high-ROI way to change the behavior of goverments (or people in general).