The term 'acid rain' is commonly used to mean thedeposition of acid component in rain, snow, fog, dew, or dry particles. Theyare the result of air pollution. When any type of fuel is burnt, lots ofdifferent chemicals are produced. The smoke that comes from a fire or the fumesthat come out of a car exhaust don't just contain the sooty grey particles thatyou can see - they also contains lots of invisible gases. Some of these gases (especiallynitrogen oxides and sulphur dioxide) react with the tiny droplets of water inclouds to form sulphuric and nitric acids. The rain from these clouds thenfalls as very weak acid - which is why it is known as "acid rain".

Acid rain has an adverse effect on forest,freshwater and soil, killing off insects and aquatic life forms as well ascausing damage to building and having possible impact on human health.

It is thought that acid rain can cause tree togrow more slowly or even to die. As it falls on a forest it trickles throughthe leaves of the trees and run down into the soil below. Some of it find itsway into streams and then on into the river and lakes, thus effecting itscreatures.

On other hand acid rain can affect trees bydissolving and washing way the nutrients and minerals in the soil which help intheir growth. It is one of the major causes of the release of harmfulsubstances such as aluminum into the soil. Somewhere, acid rain wear away thewaxy protective coating of leaves, damaging them and preventing them from beingable to photosynthesize properly.

On lakes and river water, acid rain has a diverseeffect. Both the lower Ph and higher aluminum concentration in the surfacewater that occur as a result of the acid rain can cause damage to fish andother aquatic animals. At pHs lower than 5 most fish eggs will not hatch andlower pHs can kill adult fish. As lakes become more acidic biodiversity isreduced. Acid rain has eliminated insect life and some fish species. 

Soil biology can also be seriously damaged byacid rain. Some tropical microbes can quickly consume acids but other microbesare unable to tolerate low pHs and are killed. The hydronium ions of acid rainalso mobilize toxins and leach away essential nutrients and minerals of thesoil. The effects of acid rain can last for generations, as the effects of pHlevel change can stimulate the continued leaching of undesirable chemicals intootherwise pristine water sources, killing off vulnerable insect and fishspecies and blocking efforts to restore native life.

On human health, acid rain havebeen shown to cause illness and premature deaths. Acid rain can also causedamage to certain building materials and historical monuments. Acid rain cancause weathering on ancient and valuable statues and has caused considerabledamage. This is because the sulfuric acid in the rain chemically reacts withthe calcium compounds in the stones (limestone, sandstone, marble and granite)to create gypsum, which then flakes off. This is also commonly seen on oldgravestones where the acid rain can cause the inscription to become completelyillegible. Acid rain also causes an increased rate of oxidation for iron.Visibility is also reduced by sulfate and nitrate in the atmosphere.

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