#1074 What causes acid rain?

What causes acid rain? Acid rain happens when water molecules in the atmosphere encounter sulfur dioxide or nitrogen oxide. Acid rain was a big problem in the USA and European countries during the 1980s and 1990s, but we don’t hear so much about it anymore. Has the problem been solved, or has it just shifted elsewhere?

Acid rain happens when the water that falls as rain becomes more acidic. The pH scale goes from 0 to 14, with 7 being in the middle. A substance that has a pH of 7 is completely neutral. If the pH goes lower, the substance is acidic and if the pH goes higher, the substance is alkaline. A vulture, for example, has a stomach acid with a pH of 0, which makes it a very strong acid that can dissolve pretty much anything. Bleach has a pH of between 11 and 13, making it very alkaline and able to kill most bacteria and germs. Rain usually has a pH of 5.6, which makes it ever so slightly acidic. This happens because the rain picks up carbon dioxide, which makes a weak acid called carbonic acid. This is one of the reasons why rain is so effective at erosion.

Acid rain is more acidic than regular rain, hence its name. Acid rain has a pH of between 4.2 and 4.4. That doesn’t sound so bad, tomato juice has a pH of about 4, but it is enough acidity to make it highly corrosive to buildings and other structures. It can erode the surface off concrete and stone and it can corrode the metal that bridges are made of. Repairing the damage can cost a lot of money.

So, what causes acid rain? Rain becomes acidic when the water in clouds comes into contact with sulfur dioxide and nitrogen oxide. When sulfur dioxide comes into contact with water and oxygen, it reacts to for sulfuric acid. Nitrogen oxide does the same thing and forms nitric acid. Both of these acids are very strong, but they are diluted in the rain. They are still strong enough to damage buildings, but it is what they do to nature that is more of a worry. Acid rain can destroy habitats, pollute lakes, kill animals and insects, and make the ground too acidic for plants to grow.

So, how does the sulfur dioxide and nitrogen oxide get into the atmosphere in the first place? Both of these compounds are released when fossil fuels, such as oil and coal, are burned. Because of that, coal and oil fired power stations are the largest source of these compounds. Vehicles with combustion engines are another large source, but power stations are far and away the greatest source.

However, acid rain has mostly disappeared from the USA and many European countries because they saw what damage the acid rain was doing and they saw what was causing the acid rain, so they introduced rules to govern how much of certain compounds factories and power stations could release into the atmosphere. It took a few years and a lot of money, but all of the places that produced sulfur dioxide and nitrogen oxide were fitted with filters that caught the compounds. After a few years, acid rain disappeared from the news, but it hasn’t disappeared from the world. There is still a lot of acid rain in developing countries that are burning huge amounts of fossil fuels for their energy and don’t have the ability to enact the laws that the developed countries used to fix the problem. The filters and scrubbers that have to be fitted to the power stations are extremely expensive. Acid rain and air pollution are huge problems in countries like China and India, so they may have to do something about the problem soon, whether they want to or not. And a secondary problem with sulfur dioxide and nitrogen oxide are that they are tiny and they can travel very far in the wind. A lot of countries are getting acid rain, even though they don’t have the power stations that are producing the pollutants. The pollutants can be carried all around the world.

Two things of interest with this. When we decide to fix a problem, we can do it pretty quickly. The hole in the ozone layer and acid rain produced by developed countries were both fixed as soon as there was the will. We must be able to do the same with climate change. The second thing is that we are slowly shifting away from burning fossil fuels, so hopefully acid rain, at least, will go away in the near future. And this is what I learned today.

Photo by Vlad Chețan: https://www.pexels.com/photo/raindrops-1529360/

Sources

https://www.ch.ic.ac.uk/rzepa/mim/environmental/html/sulphuric.htm