Why is Rainwater Slightly Acidic?
Rain is a form of precipitation in the liquid state. Rain is produced when thick layers of the atmosphere have temperatures greater than water’s melting point and above the Earth’s surface. Within the context of the Earth, rain is otherwise known as a condensation process whereby, water vapor turns into heavy drops causing to fall towards the ground, following the rule of gravity. Rain can be formed by either water-saturated air or coalescence. However, there are several factors that cause rain to be formed. Frontal activity, convection, orographic effects, location in the tropical regions and human influences are few of the identified causes of rain formation. The amount of rain can be measured through the use of water gauges and weather radars and can be classified depending on its intensity and frequency.
Among the characteristics of rain, such as pattern, classification and acidity, the one most sought after information is in terms of its acidity or pH level. The acidity or pH of rain is greatly dependent upon its origin. At different continental states, the pH of rain widely varies. But as further studies were conducted, it was discovered that the single most common property of rain water in all countries of the world is its acidic nature. Rain becomes acidic because of the two strong acids that comprise the rain water. As indentified, the strong acids are sulfuric acid and nitric acid. Sulfuric acid naturally comes from volcanoes and wetlands. Anthropogenic sources such as combustion and mining can also contribute to the low pH level of rainwater. Nitric acid on the other hand, also comes from natural and anthropogenic sources similar to how sulfuric acid is produced.
With the components of sulfuric and nitric acid found in rainwater, it is indeed acidic in nature.