(WKBN) – Yesterday, there was a “controlled release” of vinyl chloride from a tanker that was part of the East Palestine train derailment. There have been many questions about whether this will lead to acid rain across the Valley.

Today, I am going to walk through how acid rain forms, the effects it has on the environment, and the history of acid rain in the United States.

Acid rain typically forms when nitric oxide (NO), nitrogen dioxide (NO2), or sulfur dioxide (SO2) react in the atmosphere to increase the acidity of rainwater. Nitric oxide and nitrogen dioxide are generally grouped into a generic term called nitrogen oxides.

Typically, the creation of acid rain is produced by emissions from vehicles, factories, etc. The reaction occurs in the clouds and then the acidic precipitation falls to the ground and can even leech into the soil and waterways.

Vinyl chloride breaks down into hydrochloric acid, formaldehyde, and carbon dioxide in the atmosphere. Hydrochloric acid and carbon dioxide could theoretically increase the acidity of rainwater, but this would be difficult to measure without the proper equipment.

Image describing the pathway for the creation of acid precipitation courtesy of the Environmental Protection Agency.

The acidity of a substance is measured by the pH scale. The pH scale ranges from 0-14. pHs of less than 7 represent acidic substances while pHs of greater than 7 represent basic substances. A pH of 7 is neutral.

pH scale with common examples. Image courtesy of the United States Geological Survey (USGS).

Common acids include: lemon juice, soda, and coffee. Common bases include most cleaning products. The pH scale is really a measure of the concentration of free hydrogen ions (H+) and hydroxyl (OH) ions in a substance.

An “ion” is an atom or molecule with a net electric charge (positive or negative) due to the loss or gain of an electron. If a substance has more free hydrogen ions than hydroxyl ions, then it is acidic and vice versa.

You might be surprised to know that “normal” rainwater features some acidity. The normal pH of rainwater is about 5.6, and this is because carbon dioxide (CO2) dissolves to form carbonic acid which then increases the acidity in rainwater. Acid rain typically has a pH of less than 4.5.

What effects does acid rain have on the environment?

There are no direct human health issues associated with acid rain. However, acid rain can have many effects on the environment, but they are usually experienced after constant exposure. Acid rain can cause the acidity in soils and water to increase which can be harmful to plants and wildlife.

Another common effect that acid rain has is its contribution to the deterioration of stone and paint. This is probably the most common example you have seen of acid rain.

In fact, this issue became important enough that in 1970, the U.S. Congress imposed acid emission regulations via the Clean Air Act to improve the quality of rainwater. These restrictions were strengthened further in 1990.

Has acid rain improved?

The National Atmospheric Deposition Program (NADP) began monitoring the acidity of precipitation throughout the United States in 1978. One of their sensors is located in Wooster, Ohio about 1.5 hours from Youngstown. The average yearly pH of rainwater has been documented for over 45 years. Let’s see what the trend has been.

pH of rainwater in Wooster, Ohio from 1978 until 2022.

The average pH of rainwater in 1978 was around 4.2, which is considered acid rain. Notice that the improvements in the acidity of rainfall did not really occur until after 1990 (when the restrictions were strengthened). However, the average pH of rainwater in Wooster has gone from 4.2 to 5.6 during the time period, which is a significant improvement.

Hopefully, the acidity of rainfall will continue to improve throughout the rest of the 21st century.