University of Illinois Extension
Environmental Awareness: Knowing Your World

Acid Preparation - Are Things getting better?

Acid precipitation has been an important environmental topic for many years, not only in the United States, but in Europe as well. What is acid precipitation?

Acids are an important group of chemicals. All acids contain chemicals that are combined with hydrogen in a specific way. Acids are present in aspirin, carbonated drinks, and your stomach.

Another group of chemicals is called bases. They contain oxygen and hydrogen that arecombined with other chemicals. Chemicals containing basesare called alkaline. Examples of alkaline substancesare deodorants, ammonia cleaners, and the mortar aroundbricks.

Liquids are sometimes measured in termsof acidity or alkalinity. A scale called the pH scale is used for this measurement. The scaleranges from zero to 14. Anything with a pH below 7 is consideredacidic. The lower the pH, the more acidic it is. Substancesabove 7 are alkaline. The higher the pH, the more alkalineit is. Liquids that are very acidic or alkaline are dangerousto handle. A substance that is neither acidic or alkalinewould have a pH of 7. Absolutely pure water would have apH of 7.

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Normal rainwater has a pH of around5.6. This is because some carbon dioxide in the atmospherecombines with atmospheric water to form a weak acid. Theterm acid rain is used when rainwater becomes moreacidic.

Acid precipitation occurs when water(rain, snow, sleet and fog) combines with pollutants containingsulfur or nitrogen. This may bring the pH down to between4 and 5.

Many laws and regulations have beencreated in United States and other countries to cut downthe amount of sulfur and nitrogen that is released intothe air by human activity. This seems to already be helpingto raise the pH of precipitation back to normal. An IllinoisState Water Survey study has shown that the amount of sulfurin precipitation has decreased the last few years over Illinoisand much of the Northeastern United States.


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