Approved by the Energy, Environment, and Water Policy Committee on March 3, 2023
Approved by the Public Policy and Practice Committee on May 17, 2023
Adopted by the Board of Direction on July 22, 2023


The American Society of Civil Engineers (ASCE) supports:

  • Continued control and reduction of the emission of sulfur dioxide and nitrogen oxides, the pollutants shown to contribute significantly to acid rain and other forms of acid precipitation.
  • Further research into the control and mitigation of the sources, causes, and consequences of acid rain.


When sulfur dioxide and nitrogen oxides in the atmosphere react with other chemicals, water, and oxygen, they create sulfuric and nitric acids that mix with precipitation. Sulfur dioxide and nitrogen dioxides are mainly emitted into the atmosphere through the burning of fossil fuels. Acid rain is recognized as a contributing factor to environmental problems in aquatic ecosystems, in groundwater systems, in forests, on farmlands, and in the deterioration of buildings, roads, bridges, monuments, and other structures.

Sulfur dioxide and nitrogen oxide emissions have dropped significantly in the United States, in large part due to Clean Air Act amendments passed by Congress in 1990. The Environmental Protection Agency estimates that sulfur dioxide emissions have been reduced by 91 percent, and nitrogen dioxide emissions have been reduced by 54 percent between 1990 and 2021. These emission reductions have led to major decreases in acid rain nation-wide and may be considered by many a success in terms of Federal government regulations. However, acid rain remains a concern as it still occurs (at reduced levels) in North America, and ecosystems continue to experience long term effects of past emissions. In addition, some developing countries are lagging in effectively reducing emissions that cause acid rain. 


There are well-defined and significant environmental problems linked to acid rain, and acid rain can affect all areas, including those far from the source of pollution. The reduction of sulfur dioxide and nitrogen oxides emissions reduces the production of acid rain, which protects both the natural and built environment across the country. Technology is available to control these emissions at the stack or to process the fuel to remove sulfur prior to combustion. Nevertheless, there is a need for additional technological research to develop the most cost-effective controls for these pollutants.

This policy has worldwide applications
ASCE Policy Statement 285
First Approved in 1982