One-quarter of the sulfur in the atmosphere is natural, the rest is caused by human activity. Nature releases sulfur through decomposing marine algae and erupting volcanoes. Industry releases sulfur dioxide when fossil fuels are burnt and sulfide ores smelted. Sulfur dioxide readily forms sulfuric acid in the air or when it reaches the ground. In the year 1900, global sulfur dioxide emissions were approximately 15 million tonnes.
Annual emissions are now close to six times that amount.
Nitrogen oxides are generated by lightning and microbes, and by burning of fossil fuel and biomass. In the atmosphere the oxides are often transformed into nitric acid. Victoria's Latrobe Valley, and the Hunter Valley and Western Coalfields of New South Wales. Greg's team needed some way of reliably monitoring and collecting daily rainfall at each site. After some thought, they came up with an automatic sampler containing eight polyethylene bottles mounted on a carousel.