Humans have affected this rate of acid rain through the huge amounts of pollutants that we dispose of every year. Cars are the most obvious and are also the most damaging problem. Every year tonnes of harmful gases are exposed from exhaust pipes of cars and into the atmosphere. The exhaust fumes from cars contain gases such as sulphur dioxide (SO2) and nitrogen oxide (NOX). When these substances are released into the atmosphere, they can be carried over long distances by prevailing winds before returning to earth as acidic rain, snow, fog or dust. The acidity of rain is determined by the concentration of hydrogen ions, and this concentration depends on two things: the presence of acid-forming substances such as sulphates, and the availability of acid-neutralizing substances such as calcium and magnesium salts. Clean rain has a pH value of about 5.6. By comparison, vinegar has a pH of 3.
These gases passing through cars every year are causing massive problems in the world through depletion of soils and consequently exposure of tree roots and so many forest areas are being affected so dramatically that they are in a constant threat of destruction. Another way that humans cause these problems is because of massive industrialisation the world around. Huge factories are throwing away waste and spewing gases out into the atmosphere, containing the same hazardous properties of those from car emissions. They cause the same problems and are just as bad.
Secondly humans also affect the rates of weathering through mass removal of vegetation. Vegetation around the world is constantly being uprooted, especially in rainforest areas where logging goes on every day. Deforestation and removal of many types of vegetation can cause dramatic changes to the environments they were taken from. Deforestation plays a major problem in today’s society because we would be fools if we were to say we did not know it was going on. We buy wood all the time for home uses; it must have come from somewhere, but we just do not think about it.
Removing trees and vegetation exposes soils to high levels of rainfall and run off and leaves areas open to wind and chemical weathering in terms of acid rain. Soils get depleted of all their nutrients due to excessive amounts of run off from rain on the top layers of soil. As well as soils being exposed we find that rock faces previously covered by vegetation become exposed when it is removed. Rocks are then open to all types of physical weathering including chemical acid rain weathering and biological weathering. These break down and then rocks that could have been used for building or even shielding an area which is for example, very windy, are lost as they slowly wear away.
When the environment cannot naturally neutralize the acid being deposited, damage occurs. The impact of acid rain on trees ranges from minimal to severe, depending on the region of the country and on intensity and type of air pollutant. Acid rain, acid fog and acid vapour damage the surfaces of leaves and needles, reduce a tree's ability to withstand cold, and inhibit plant germination and reproduction. Consequently, tree vitality and regenerative capability are reduced. Prolonged exposure to acid rain also causes forest soils to lose valuable nutrients. It also increases the concentration of aluminium in the soil, which interferes with the uptake of nutrients by the trees. Lack of nutrients causes trees to grow more slowly or to stop growing altogether. More visible damage, such as defoliation, may show up later. Trees exposed to acid rain may also have more difficulty withstanding other stresses, such as drought, disease, insect pests and cold weather.
The ability of forests to withstand acidification depends on the ability of the forest soils to neutralize the acids. This is determined by much the same geological conditions that affect the acidification of lakes. Consequently, the threat to forests is largest in those areas where lakes are also seriously threatened - in central Ontario, southern Quebec, and the Atlantic provinces. These areas receive about twice the level of acid rain that forests can tolerate without long-term damage. Forests in upland areas may also experience damage from acid fog that often forms at higher elevations.
