The amount of volatile organic compounds and carbon monoxide in the nation's air/water have changed and evolved over time as we can see on quote, “Economist Patrick Weinert notes that, "air pollution was being reduced in the United States decades before any federal regulations were adopted. From 1950 until 1970, the amount of volatile organic compounds and carbon monoxide in the nation's air fell by more than 20 percent, even though total vehicle-miles traveled in the country rose by 120 percent, from 458 billion to 1.1 trillion. The level of sulfur dioxide in the air began falling as far back as 1920, and the total amount of airborne particulate matter has been reduced by 79 percent since 1940." But that record began to drop which prompted the clean water and air acts in the 1970`s.
