Acid Deposition

Measuring Acidity

• pH scale (log scale)

• 0-6: acid,

7: neutral,

8-14: base

Each step is a power of 10

Ex: pH 4 is 100x’s stronger than

pH 6

Normal Rain Water•pH of 5-6

•Due to CO2

+ H2O

H2CO3

(carbonic

acid)

Acid Rain pH

•pH is a 3-4

Acid Dep. from SO2

• SO2: Coal combustion from power utilities.

• SO2 + H2O --->H2SO4

(Sulfuric acid)

• NO2: Gasoline combustion and

fertilizer application

• NO2 + H2O --->HNO3- (Nitric acid)

Acid Dep. from NO2

Effects of Acid

Deposition

Destroys Limestone!Before

After

An

extra

hole…

Fish Deaths• Acid in lakes declining fish

pops

• Can only tolerate certain pH

ranges.

Hmm…

Dinner!

Plant Deaths• Acid in soils declining agricultural

productivity

• Plants can only tolerate certain pH

ranges too!

External damage to bark & leaves

Little resistance to pests

Lower rate of photosynthesis

Tree Damage

• Metals become ionic at lower pH

taken up via ion channels of fish gills

(Hg+2 /K+)

Metal accumulation in food web

metal toxicity in fish

In Rivers and Oceans

Plant Metal Toxicity

• If metals sit in ground taken up by plants (plant

metal toxicity)

Soil Leaching• If it rains after acid breaks up metals

into ions, then metals leave soil (soil leaching). Loss of nutrients

Changes

in Rain

pH

Why

East

Coast?

Controlling Acid Deposition

Reduce SO2 and NO2

emissions Switch to alternative energies (solar,

hydroelectric)

• Legislation: Clean Air Act

Set standards on how much NO2

and SO2 are allowed to be emitted

(NAAQS).