From Reason Magazine:
"Why has air quality improved so dramatically? Part of the answer lies in emissions targets set by federal, state, and local governments. But these need to be understood in the twin contexts of rising wealth and economic efficiency. As a Department of Interior analyst concluded after surveying emissions in 1999, "Cleaner air is a direct consequence of better technologies and the enormous and sustained investments that only a rich nation could have sunk into developing, installing, and operating these technologies." Today, American businesses, consumers, and government agencies spend about $40 billion annually on air pollution controls.
It is now evident that countries undergo various environmental transitions as they become wealthier. Fortune's special "ecology" edition in February 1970 was far more prescient than the doomsters when it noted, "If pollution is the brother of affluence, concern about pollution is affluence's child." In 1992, a World Bank analysis found that concentrations of particulates and sulfur dioxide peak at per capita incomes of $3,280 and $3,670, respectively. Once these income thresholds are crossed, societies start to purchase increased environmental amenities such as clean air and water.
In the U.S., air quality has been improving rapidly since before the first Earth Day--and before the federal Clean Air Act of 1970. In fact, ambient levels of particulates and sulfur dioxide have been declining ever since accurate records have been kept. Between 1960 and 1970, for instance, particulates declined by 25 percent; sulfur dioxide decreased by 35 percent between 1962 and 1970. More concretely, it takes 20 new cars to produce the same emissions that one car produced in the 1960s."