Take a look at Figure 31-2. Suppose that initially, society experiences a degree of air cleanliness that is lower than Q0. What would be true of the marginal benefit in relation to the marginal cost, and why would this fact induce society to increase the degree of air cleanliness toward Q0?

The socially ideal level is given where the marginal cost is equivalent to the marginal benefit of contamination reduction. Anytime lower than the social ideal, the marginal benefit from contamination decrease will be more prominent than the marginal cost of contamination reduction.

Expanding the level of air neatness will be useful till the fact of the matter is its marginal cost is equivalent to the marginal benefit. To focus more prominent than $Q_o$, marginal cost of contamination reduction (cleaning the air) is more noteworthy than the marginal benefit from clean air. Consequently, the general public will decrease the level of clean air to where the marginal benefit from the perfect air is equivalent to the marginal cost of clean air.