1. Sulfur Cycle
Ch 7 Part 6

2. Sulfur Cycle
Describes the routes that sulfur atoms take though the environment
“Sedimentary Cycle”
Much of the sulfur is tied up in underground rocks & is primarily released through geological activity
Its then used by plants (& subsequently animals)
Sulfur is mostly taken up by plants as sulfate (SO42-) & used for amino acids.
It is eventually redeposited into the ground.
Has a gaseous phase
b/c it is a non-metal
So, it is faster than those cycles without a gaseous phase (ex. phosphorous)

3. Much of Earth’s sulfur is stored underground in rocks & minerals
including sulfate
(SO42-) salts
buried deep under ocean sediments

4. Sulfur Cycle: How Does Sulfur Enter the Atmosphere?
As hydrogen sulfide (H2S)
Colorless, highly poisonous gas
Rotten-egg smell
During:
volcanic eruptions
(& hydrothermal vents)
decomposition
Anaerobic
in swamps, bogs, tidal flats
As sulfur dioxide (SO2)
Colorless, suffocating gas
Volcanic eruptions
Burning fossil fuels
As sulfate (SO42-) salts
From sea-spray

5. The Sulfur Cycle
Certain marine algae produce large amounts of volatile dimethyl sulfide (DMS or CH3SCH3)
Serve as condensation nuclei for water droplets
Can affect cloud cover & climate

6. Sulfur Dioxide in the Atmosphere
Sulfur dioxide (SO2) reacts with oxygen to produce sulfur trioxide (SO3) gas
Reacts with water vapor to make H2SO4 (a weak sulfuric acid)
which is then carried to Earth in rainfall (acid deposition)
Harms trees & aquatic life

7. Human Effects on the Sulfur Cycle
1/3 of all sulfur released is due to human activity
Add sulfur dioxide to atmosphere by:
Burning coal and oil
Produces sulfuric acid
Refining sulfur-containing petroleum
Mining & converting sulfur-containing metallic ores into free metals
copper, lead, & zinc

8. Acidic fog and precipitation
The Sulfur Cycle
Water
Ammonia
Sulfur trioxide
Sulfuric acid
Acidic fog and precipitation
Ammonium sulfate
Oxygen
Sulfur dioxide
Hydrogen sulfide
Plants
Volcano
Dimethyl sulfide
Animals
Industries
Ocean
Sulfate salts
Metallic
Sulfide
deposits
Decaying matter
Sulfur
Hydrogen sulfide
Fig. 3-30, p. 60