For those of you who can remember back to year 8 science or for those unfortunate enough to occasionally teach it (it’s not that bad, it’s actually lots of fun), you might remember the water cycle. This global phenomena is incredibly important as it is essential for the distribution and recycling of water throughout the biome that we call Earth. There is one aspect of this phenomena that can be quite hazardous when it does occur with it having a higher chance of occurring thanks to human input; acid rain.
The water cycle is a description of how water moves through its different states (solid, liquid and gas) and how it moves through the environment in these forms. Let’s start with when it rains. This is a process called precipitation and also involves forms like hail and snow. As the water vapour in the air starts to cool, it condenses becoming heavier and falls. For the sake of being able to continue the story, lets say it lands on a mountain range. The water hits the mountain range and the simple friction between the rain and earth, and slight chemical reactions (will look at more later), the rock and earth starts to weather (breakdown into smaller particles). As the water passively moves from high to low ground, the weathering process continues and the rock erodes (moves rock sediment from one place to another). Similar things occur with the runoff from snow, ice and glaciers. The water can continue to rundown above the earth, collecting into larger bodies of moving and stagnant water, or below where it becomes groundwater and can collect to rejoin the larger bodies of water later.
As water moves towards the ocean (main collection points of water), some is consumed by animals (fauna) and is returned to the cycle as water vapor when they exhale or as waste. It can also be consumed by plants (flora) through their root system and used in a process called photosynthesis. This is a process in which carbon dioxide and water react due to energy from the sun to produce glucose and oxygen. Humans do the opposite of this within their bodies in a process called respiration. Plants can also ‘exhale’ water vapor in a process called evapotranspiration where it rises to join with the rest of the condensed water vapor in clouds. The water left then continues to move, collecting more and more then becomes part of the largest body of water; oceans.
Throughout the life of water being in liquid form, whether it be runoff or when collected in oceans, evaporation is always occurring. This is the process in which water is heated, mainly by the sun but sometimes the Earth (geothermic activity), turning it from a liquid to a gas. As the vapor cools, it condenses to form clouds and the process starts all over again. Now, we’ve all heard of acid rain but what is it actually and how are we contributing to the increased susceptibility of this event occurring.
When it rains, the pH of the water is usually around 6 meaning that it is slightly acidic. As it starts to make its way into a pH of 5 and even 4, this is when it is classified as acid rain. Acid rain is actually a natural phenomena that can occur as rain collects around ash and smog (sulfur dioxide and types of nitrogen oxide) that is emitted from volcanoes. There is also man-made acid rain that is due to the emissions of cars and from coal and oil power plants (sulfur dioxide). When these gases start to dissolve in the condensed water in clouds, it creates nitric acid and sulfuric acid where it then falls to Earth as acid rain (precipitation).
Most of the time, the earth is slightly basic (pH of 8) which allows for the acid rain to be made harmless by neutralization. But in rocky areas, there isn’t much earth and the acidic rain results in an increase in weathering and erosion. This is also seen in densely populated areas. If you have a look at some of the statues, depending on what they are made of, you can determine their age by the amount of weathering that has occurred to them. Some plants are damaged by the acid rain as well as a number of aquatic animals that can have issues with reproduction if the water is too acidic. One of the most acidic rainfalls on record is one that occurred in West Virginia where a pH of 1.5 was recorded which not only tastes bad but is incredibly dangerous as it burns the skin.
There are somethings that can be done to limit the effects of this once natural phenomena that man seems to have taken over. Many companies have been trying to minimise the amount of sulfur and nitrogen gases being emitted with some pretty good results with the average acidity of rain in a variety of areas decreasing. This includes making the ground more alkaline (basic) by spreading limestone (expensive), making smoke stacks taller to increase dispersion (still polluting) and by moving towards renewable energy like solar and wind. I am definitely in agreement for the last option. Looks prettier anyway.