 
Sulphur dioxide is a colourless gas with a pungent odour. It dissolves in water easily. SO2 in the air comes from the burning of coal and oil at power plants, or from copper ore smelting. In nature, sulphur dioxide can be released to the air from volcanic eruptions.Sulphur itself is a nonmetallic element, and one of the most reactive. It's a tasteless, odourless, pale yellow solid. Sulphur dioxide is a covalent compound where each oxygen atom is covalently double bonded to sulphur; each oxygen atom is sharing two pairs of electrons with the sulphur atom. NOTE: While both spellings, sulphur and sulfur, are correct, the International Union of Pure and Applied Chemistry (IUPAC) decided that the single spelling 'sulfur' was prefered. We will use that convention from this point. SO2 in the air can be oxidized to sulphur trioxide, which in the presence of water vapour is quickly transformed to sulphuric acid mist. Sulphuric acid is battery acid, and is highly corrosive. It is the main component of acid rain, which has caused untold damage around the world. Health effects caused by exposure to high levels of SO2 include breathing problems, respiratory illness, changes in the lung's defences, and worsening respiratory and cardiovascular disease. People with asthma or chronic lung or heart disease are the most sensitive to SO2. It also damages trees and crops. SO2, along with nitrogen oxides, are the main precursors of acid rain. This contributes to the acidification of lakes and streams, accelerated corrosion of buildings and vehicles, and reduced visibility. SO2 also causes the formation of microscopic acid aerosols, which have serious health implications as well as contributing to climate change. 
On a personal note, I grew up in a small town in Ontario called Copper Cliff. Copper Cliff was a mining town. Ore was dug out of the ground and sent first to a huge complex of buildings where it was melted (called 'smelting') and the valuable minerals separated out. Gases from the smelting process, mostly sulfur dioxide, were extracted and sent up into the atmosphere through three tall smokestacks.  On days when the wind was blowing the wrong way, those gases would settle like a blanket over the town, making the air hazy. It made breathing difficult and downright painful. School was never cancelled, and no warnings were ever issued, and I remember days when the lung-burning air was so thick it was difficult to see the end of the street. I don't know what the medical effects of breathing those concentrations of sulfur dioxide for decades were, but I'm sure there were a lot of chronic illnesses that resulted. The effects on the town and surrounding regions were catastrophic. Trees and other vegetation that wasn't cared for died; the hilly terrain became a vast landscape of bare rock and hills of slag, waste from the smelting process. Nothing would grow. Later, the mining company replaced the three chimneys with a much larger and taller one. It was billed as the 'super stack', and at that time was the second tallest chimney in the world. It was hoped it would disperse the toxic gases into the upper atmosphere, where they would dissipate. This certainly solved the problem for the Copper Cliff and Sudbury regions. However, what no-one anticipated was that the noxious gases would not dissipate. That super stack released the gases at a high altitude where the winds picked them up and sent them south to the rest of Ontario. Too rarefied to cause breathing problems, they were still sufficiently concentrated to cause acid rain that killed most of the lakes in southern Ontario. Where fishing used to be good, there was nothing left. 
However, with the sulfur dioxide no longer periodically settling over the town, Copper Cliff and the Sudbury region is now, after an incredible effort to replace topsoil and plant trees, one of the greenest places in Ontario. Planting trees and grass has transformed the slag heaps into a sea of green. The region is now compltely healthy. But the lakes of southern Ontario have never recovered. |