E11: Acid Deposition (UNMODIFIED)

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Formation of Hydroxyl Free Radicals (OH•)

Hydroxyl free radicals = important in the mechanisms that produce sulfuric acid and nitric acid

Produced by 2 reactions of atomic oxygen (O•)

H2O + O• --> 2OH•

H2O + O3 --> 2•OH + O2

Formation of Nitrous and Nitric Acid

Acids form when OH• react with NOx

OH• + NO --> HNO2

OH• + NO2 --> HNO3

Formation of Sulfuric Acid

OH• + SO2 --> HOSO2•

HOSO2• + O2 --> HO2• + SO3

SO3 + H2O --> H2SO4

First 2 steps - Formation of SO3

Last Step - Formation of H2SO4

Background Information:

Source = Assorted Processes in Ecosystems

Ammonia is a weak base

It can neutralize acids to form ammonium salts

NH3 + HNO3 --> NH4NO3

2NH3 + H2SO4 --> (NH4)2SO4

When it falls as precipitation, they enter the soil and dissolve to give free ammonium ions (NH4+)

NH4NO3/ (NH4)2SO4 --> NH4+ + anions

Ammonium Ions make the soil more acidic

Ammonium Ions are weakly acidic (NH4+ --> H+ + NH3)

Ammonium ions react with oxygen to form nitrate ions (H+ ions and water) aka nitrification (NH4+ + 2 O2 --> 2 H+ + NO3- + H2O)

Important because it produces nitrates that plants need as nutrients

HOWEVER: still adds H+ (making soil more acidic)

Free Radical Mechanisms for the Formation of Acid Rain

Role of Ammonia in Acid Depostion