By: Elizabeth Miyasaka

Acid Deposition

Acid Deposition: The process by which acid leaves the atmosphere and fall on earth in the form of dry (gases, dry particles) or wet deposition (snow, rain, fog..).

Though rain and snow are naturally acidic, if their pH is less than 5, it's considered too acidic.

Why does it happen?
Chemicals such as Sulfur dioxide (SO2) and Nitrogen oxides (NOx) are released into the atmosphere. These chemicals react with other particles, oxygen, water, and carbon dioxide to form acidic compounds, nitric acid (HNO3) and Sulfuric acid (H2SO4).

Sulfur dioxide and Nitrogen oxide can come from 2 main sources:
1) Natural emission such as:
- Volcano emissions
- Lightning
- Decomposition

2) Human Emissions:
- Combustion of fossil fuels
- Transportation
- Electric utilities
(Human emissions are approximately twice as much as natural ones)
external image acid-rain-1a.jpg
Picture 1
What are the effects of acid deposition?
Mostly bad effects.
- Deterioration of historic marble buildings and statues (that cannot be reconstructed)
- Lowers the pH (makes it more acidic) of bodies of water (i.e. lakes, rivers), making it very hard for organisms such as fish to survive and reproduce.
This then affects the rest of the food chain linked to organisms living in water. It can also affect people who live off fish.
- Acid deposition also affects trees by damaging its leaves, reducing its ability to stand cold weather and germinating seeds for reproduction.
- Leaching in soils can occur. This is when the acid reacts with the soil replacing nutrients such as calcium, magnesium and potassium.
These nutrients are then taken deeper into the soil or out of the soil completely, leaving the soil infertile for healthy plant growth. These ions can
also be carried into drinking water supplies, making it toxic.
- Destroying these natural resources will naturally impact us in many ways.
external image moz-screenshot-5.pngexternal image acid-raid-vegetation.jpgPicture 2
Leaf destroyed by acid deposition
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Left taken in 1908. Right taken in 1968.
Statue deteriorated by acid deposition

How to prevent/ control it:
*Reduce amount of SO2 going into the atmosphere by:
- Before releasing the produced SO2 in burning coal industries, add CaCO3 (powdered limestone) to react with the SO2, to form CaSO3 instead.
(Though this reaction produces CO2 in the process)
- Producing sulfuric acid (which is the most produced chemical in the world) with the SO2
- Washing the coal before combustion to remove sulfur
- Using low-sulfur coals

*Adding lime-based fertilizers to water supplies can serve as buffers against the effects of acid deposition, avoiding low pH.

*Reducing usage of vehicles such as car which produces nitrogen oxides.

- Ecological Society of America. 2000. Acid Deposition. Retrieved March 15, 2011, from Esa:
- Picture 1:
- Demand Media. 2010. Acid Deposition- Causes, Effects, and Resolutions. Retrieved March 20, 2011, from Essortment:
- Book: 'Environmental Chemistry'
- Picture 2:
- Picture 3: