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NATURAL pH OF RAIN

NATURAL pH OF RAIN. Equilibrium with natural CO 2 (280 ppmv) results in a rain pH of 5.7:. This pH can be modified by natural acids (H 2 SO 4 , HNO 3 , RCOOH…) and bases (NH 3 , CaCO 3 ) e natural rain has a pH in range 5-7. “Acid rain” refers to rain with pH < 5 e damage to ecosystems.

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NATURAL pH OF RAIN

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  1. NATURAL pH OF RAIN • Equilibrium with natural CO2 (280 ppmv) results in a rain pH of 5.7: • This pH can be modified by natural acids (H2SO4, HNO3, RCOOH…) and bases (NH3, CaCO3) e natural rain has a pH in range 5-7 “Acid rain” refers to rain with pH < 5 e damage to ecosystems

  2. PRECIPITATION PH OVER THE UNITED STATES

  3. CHEMICAL COMPOSITION OF PRECIPITATION Neutralization by NH3 is illusory because NH4+g NH3 + H+ in ecosystem

  4. CONTRAST TO THE AEROSOL DISTRIBUTION: Sulfate Nitrate Ammonium Highest concentrations in industrial Midwest (coal-fired power plants) Acidity Park et al. [2006]

  5. LONG-TERM TREND IN US SO2 EMISSIONS

  6. AMMONIUM AND SULFATE TRENDS, 1985-2004 NH4+ SO42- Lehmann et al. [2007]

  7. TREND IN FREQUENCY OF ACID RAIN (pH < 5) 1994-1996 2002-2004 Lehmann et al. [2007]

  8. BUT ECOSYSTEM ACIDIFICATION IS PARTLY A TITRATION PROBLEM FROM ACID INPUT OVER MANY YEARS Acid flux FH+ Acid-neutralizing capacity (ANC) from CaCO3 and other bases

  9. DEPLETION OF BASE CATIONS FROM ACID RAIN(Hubbard Brook Experimental Forest, New Hampshire)

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