Back in the 70’s and 80’s acid rain was one of the most well-known environmental problems in Europe and North America, appearing frequently in news reports. The answers below discuss why we never hear about acid rain anymore.
Acid rain was caused by SO2 emissions from coal plants, which have been cut by >90% since 1990.The 1990 Clean Air Act Amendments kicked off a cap-and-trade scheme that incentivized coal plants to install scrubbers and/or switch to low-sulfur coal, then low-cost natural gas took ~50% of coal’s market share since 2008.
Bottom line: coal is somewhat cleaner than it used to be, and we’re burning far less of it.
The reduction in the prevalence of acid rain in the US is largely been attributed to the success of the EPAs Acid Rain Program.
All rain is somewhat acidic from rainwater forming carbonic acid from rainwater reacting with carbon dioxide, but acid rain is particularly lower in pH. This is due to the reaction of rainwater with nitrogen and sulfur oxides to form the much stronger Nitric and Sulfuric acids, respectively. The primary source of these nitrogen and sulfur oxides is power plant emissions, particularly those burning coal. The Ohio River Valley contains a large concentration of these power plants, and acid rain issues in the US were largely concentrated around this region and points downwind (the Atlantic Coast).
The Acid Rain Program was begun in 1990 based under the Clean Air Act. It established a market-based (cap and trade) system of regulation upon which emitters of sulfur and nitrogen oxides were granted pollution allowances. Polluters were incentivized to voluntary undertake measures to reduce the volume of their emissions as they could sell unused allowances for profit.
By most estimates, the Acid Rain Program has been largely successful. The Pacific Research Institute has estimated that this program has reduced total acid rain levels by 65% from 1976 levels while the EPA estimates the program cost businesses only a quarter of what was originally estimated. Savings in property damage and human health costs, such as lowered incidences of heart and lung problems exacerbated by acid rain, most likely have resulted in the Acid Rain Program actually saving money, overall.
It is still there, albeit most data shows a decline in the prevalence due to consistent progress in reducing emissions. The pH of rain is decreased (made more acidic) primarily through the action of sulfur dioxide and nitrogen oxides. One of the biggest changes has been the result of a significant decrease in sulfur dioxide generation by China. Parts of the US has seen some change, however other regions showed almost no improvement, if any at all regarding the pH of its rainwater in this timeframe.
The other aspect of this is that acid rain isn’t nearly as harmful as people thought it was in the 90’s, at least in terms of the public perception. Acid rain is typically in the 5.0-5.5 pH range, with parts of the US seeing as low as 4.5 pH. On one hand, when compared to something like a can of Coca-Cola which has a pH of ~2.3 this seems like it is nothing, but on the other hand, the effects of acid rain cover such a large surface area that it is not appropriate to compare it simply in terms of acidity. There is a little bit of controversy as to just how harmful acid rain actually is, but most experts agree the most affected part of the environment are the various bodies of water, which are more susceptible to pH changes. The amount and acidity of acid rain isn’t enough to kill off wildlife outright in most cases, however it does cause the water to leech aluminum from the soil.
As pointed out below, when we take issues seriously we can solve them and even create products which are profitable(Sulfuric Acid), but companies don’t do these thing without some sort of imposed government regulation. Another example is the Ozone layer…which has also been addressed…Air Pollution and Pollution of many of our rivers and lakes(check out Lake Erie).
The problem is when we can’t see the problem/pollution and science naysayers deny, (groundwater pollution, air born toxins), then we need intelligent world leaders to rely on science to recognize and address problems.