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  • Abnormally acidic (low pH) precipitation (or dry deposition) resulting from emissions of sulfur and nitrogen compounds that transform during chemical processes in the atmosphere. Acid deposition can affect the chemistry of soils and acidify lakes, adversely affecting forests and fish. It does not adversely affect cropland. The Clean Air Act includes a program focused on controlling precursor emissions of acid deposition—primarily sulfur oxides from coal-fired electric utilities.
  • Acidified particulate matter in the atmosphere that is deposited by precipitation onto a surface, often eroding the surface away. This precipitation generally has a pH less than 5 and sometimes much lower depending on the concentration of acidic components. [Nature; v367; page 321; 1994.] [Canadian Geographic; v114n5; pages 10-14; 1994.] Source: Atmospheric Chemistry Glossary