File name: EarthDay_3CleanAirAct_large.png Original Resolution: 3000 × 2008 File Size: 4807 KB (MIME Type: image/png) Date Published: April 22, 2016 Download file View image caption Industrial smog blacks out homes adjacent to North Birmingham Pipe Plant. This was the most heavily polluted area of the city. 1972. Photo: LeRoy Woodson, Courtesy: U.S. National Archives via Wikimedia Commons.