In a German plaza, stands a marble statue of a classic figure. What was a grand sculpture now looks like a grotesque prop from a horror movie, its features are distorted as if melted ... by acid.
Meanwhile, the Statue of Liberty has lost much of its original distinctive green patina.
The statue was initially a shiny brown colour when it was unveiled in 1886 and by 1906, it had turned green with a durable copper sulphate coating.
By 1982, the statue was at serious risk from this and other issues. The surface had deteriorated into a soft black coating that no longer protected the underlying metal.
To avoid major failure, extensive restoration was required, at cost of around $230 million. In some places the copper was reduced from one-half to one-tenth the thickness and some had to be replaced.
Also affected by acid rain are trees, which can suffer severe damage.
In the 1960s, scientists first saw the effect of acid rain and other pollutants on trees in the Black Forest of Germany. They called this "Waldsterben", meaning tree death. By 1990, nearly half of all trees in the Black Forest were damaged.
Soil, lakes and streams can also be made more acidic from deposited particles and gases.
Acid rain is caused by sulphur dioxide or nitrous oxide in the atmosphere. Natural causes include volcanoes, wildfires and decaying plants, but the major sources are vehicles and industries such as manufacturing and oil refineries.
Two thirds of sulphur dioxide and one quarter of nitrous oxide come from fossil fuel electric generators.
While an obvious good start is to reduce the burning of fossil fuels, there are ways of reducing it.
Using several techniques, a coal-burning power station can remove 95 per cent or more of sulphur-containing gases from emissions.
One method is the wet scrubber, which is a reaction tower equipped with a fan that extracts hot smoke from the tower where it is combined with lime or limestone slurry.
That produces pH-neutral calcium sulphate that is physically removed from the scrubber that can then be sold as gypsum or dumped in landfill.
Catalytic converters in vehicles between the intake manifold and the muffler are coated with rare metals such as palladium, rhodium or platinum. The honeycomb or bead shape expose the maximum surface area, converting harmful emissions.
They convert carbon monoxide into carbon dioxide. Hydrocarbons are converted into carbon dioxide and water. Helping to reduce acid rain, nitrogen oxides are converted into nitrogen and oxygen.
Another improvement is stronger fuel emission standards and, while these were strengthened some years ago, Australia's standards remain the worst in the OECD for both sulphur and aromatics content.
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