What Exactly is Acid Rain?

   Photo Credit: New York Times

             It’s well known that acid rain causes damage to plant and animal life. When acid rain flows through an environment, it can break down aluminum from its surroundings in the soil and carry the metal with it, consequentially, lowering the pH of the water nearby and underground. Both effects can cause a great deal of damage to plant and animal life by making the water intolerable to certain species. Since plants and animals are interconnected by food chains, animals resistant to pH changes are adversely affected when their food supply consumes their own tainted food supply. For example, many plants may die in an area due to acid rain, causing an herbivore that can withstand the pH changes to die as well because its source of food is gone.

            What’s not as well known is how exactly acid rain originates. Most of it comes from harmful pollutants made by humans, especially those from burning fuel in factories or cars. When fuel is burned, it releases energy as well as byproducts including carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxides (NOx). By observation, one can tell that water mixes well with a lot of compounds. The water in the atmosphere is no exception. When water in the atmosphere meets these byproducts, they can mix and create potentially hazardous compounds such as carbonic acid (H2CO3), sulfuric acid (H2SO4), or even nitric acid (HNO3). While these compounds are greatly distilled by the water, they are still harmful to plant and animal life. Additionally, gases from burning fuels don’t even have to mix with rain to reach the ground. They can sink into the ground in their original forms and stick to objects near the surface, adding to the adverse effects from gas pollutants.
           
         Since carbon dioxide is a relatively abundant trace gas in the atmosphere, virtually all rainwater is at least slightly acidic because of the presence of carbonic acid. Thankfully, carbonic acid is a weak acid that doesn’t affect the pH of rainwater to the point of making it harmful. The same could not be said for sulfuric acid or nitric acid. These acids are quite powerful in comparison to carbonic acid. They can cause the pH of water to swing down and create acid rain, which has an average pH of 4.3. For comparison, the pH of pure water is 7 and the pH of regular rain is 5.6. It’s important to note that the pH scale is not linear, but logarithmic. That is, it doesn’t increase and decrease at a constant rate. Instead, it increases and decreases exponentially the farther it gets from the neutral pH of 7. As a result, acid rain is over 10 times more acidic than regular rain on average!

          What can be done to prevent acid rain or decrease its impact? The primary answer is to decrease the number of harmful byproducts coming from factories, since it’s not possible to get the gases out of the atmosphere once they’re up there. Many factories have methods of extracting harmful products out of their emissions and international treaties exist to limit certain types of emissions from factories. It’s essential for those who wish to decrease the prevalence of acid rain to understand where it comes from so the sources of these pollutants can be targeted and limited. By having a full comprehension of how acid rain is formed people can work towards limiting their harmful impacts.
           
            © 2020 Weather Forecaster Cole Bristow