But coal also releases pollutants into the air,like sulfur dioxide,nitrogen oxides,soot,and toxic metals, like mercury.These cause environmental damage,like acid rain,and serious health problems.In fact, in 1952, coal burning caused such heavy smog in London that pedestrians couldn't even see their feet,and thousands of people died from ill health.Since then, many countries have deployed technology to remove most of these pollutants before they reach the air.