Sustainability

The problem of acid rain

Whenever substances are released by industrial stacks or vehicles, they mix up in the atmosphere with water vapour and generate new acid compounds. These compounds fall back on the ground during precipitations, causing serious damage to the flora, the soil and the water. The problem of acid rains can be solved by reducing the emissions of nitrogen oxides and sulphur oxides in the atmosphere. To reduce these emissions, the use of fossil fuels with a high sulphur content (such as coal), the use of cars and the traffic of our cities need to be reduced. A number of technologies have been developed over the last few years that can remarkably reduce the sulphur content of the raw materials used to produce electric energy from fossil sources (coal reclamation, desulphurisation systems and others). In addition, the stacks of power plants and industries have been fitted with filters that collect the sulphur compounds contained in the exhaust fumes, so that they will not disperse in the atmosphere. The emissions of nitrogen oxides, mainly from cars, can be reduced by installing catalytic exhaust pipes. In particular, the cars of a country (i.e. the cars driven by its people) need to be new, since last-generation cars are equipped with devices that can reduce the emissions of nitrogen oxides much better than in the past. It takes many years for an ecosystem damaged by acid rains, such as a lake or a river or a forest, to go back to its original balance. But man can help by speeding up this process through some specific measures: for instance, by adding lime to acidified lakes or rivers to bring their pH back to neutral (‘calcification’). But these techniques are expensive and have a limited life. In these cases, prevention is certainly better than the cure and the alleviation of the damage.