By: Chhavi, Kimanie, Tarn, Youkees, Victor


  • Acid rain is any precipitation of pH less than of 5.6
  • Wet Deposition: Rain, Snow, Fog, Dew
  • Dry Deposition: Dust, Smoke, Gas


  • Oxides of Sulphur (SO2), Nitrogen (NOX) and Carbon (CO2) combine with moisture in the air to form Sulphuric acid, Nitric acid and Carbonic acid. These strong acids readily dissociate to release the H+ ion, which decreases the pH.
  • Biogenic Sources: Bushfires, volcanic eruptions, microbial processes, lightning.
  • Anthropogenic Sources: Burning of fossil fuels for power generation, transportation, Industrial processes, residential heaters.


  • Human Health: Pollutants that cause acid rain increase fine particle levels in the atmosphere. Inhalation can lead to increased illness and premature death from heart and lung disorders, such as asthma and bronchitis. Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions contribute to visibility impairment.
  • Materials: Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals and the deterioration of paint and stone. These effects significantly reduce the societal value of buildings, bridges, cultural objects and cars.
Image: The effect of acid rain on Leshan Giant Buddha of China.

Terrestrial Ecosystems

Nutrient Leaching: Acid deposition dissociates into hydrogen ions, which are positively charged. Magnesium, potassium, and calcium are essential nutrients to many plants, and exist as cations in soil. Hydrogen ions from acid precipitation displace these nutrient cations, starving plants.

Nutrient leaching by acid deposition

Aluminum Mobilization: Aluminum naturally exists in soil in a non-toxic form: Al(OH)3. Acid deposition causes non-toxic aluminum to be converted into a soluble, toxic form: Al2(SO4). Toxic aluminum is absorbed by plants and causes damage

Al(OH)3 + H2SO4 --> Al2(SO4)3 + H2CO3

Microbial Death: Plants depend on microbes to break down organic matter into nutrients. Acid deposition decreases pH of soil. Lower pH causes decreased metabolic activity and death of essential microbes, and plant life suffers due to less organic matter being broken down.

Direct Damage: Acid deposition may burn leaves and create lesions, negatively affecting photosynthetic ability. Acid fog or clouds are mainly responsible for causing burns.

Conifer branches damaged by acid deposition (left) and undamaged (right)

Pests and Diseases: Soil effects + direct damage = weakened plants. In consequence, plants' abilities to defend against pests and diseases are compromised. This can lead to the mass death of plant life.

Aquatic Ecosystems

Effects of acid deposition are very serious on freshwater aquatic ecosystems


  • Natural aquatic ecosystems have a pH between 6 – 8
  • Normal deposition (rain) is slightly acidic (pH = 5.0 – 5.6)

Acid deposition:

  • Ranges from a pH of 2.1 – 5.0

Chemical Effects of Acid Deposition of Aquatic Ecosystems

  • Increases acidity (by the introduction of hydrogen ions)
  • Leaches metals (aluminium)  
  • Removes important minerals (calcium)
pH scale showing the acidity ranges of normal aquatic levels and acid rain levels.

Aquatic ecosystems that have carbonate-containing compounds (limestone and calcite) can buffer acids. The Canadian Shield gives us beautiful scenery and plenty of minerals but contain few limestone-type materials and thus the a large portion (46%) of Canada is very sensitive to acid deposition.

The vulnerability of Canada's ecosystems to acid rain (red means non-carbonate bedrock that cannot buffer acid deposition).

Effects of Acid Deposition on Phytoplankton

  1. Promote the formation of toxic algal blooms
  2. Decreased the abundance of other necessary primary producers
Formation of toxic algae bloom on Lake Erie in 2011. They block off sunlight, produce toxins and reduce oxygen levels in freshwater lakes.

Effects of Acid Deposition on Fish

  • Negatively affects fish physiology by reducing oxygen uptake, causing mineral/salt imbalances and reducing reproduction ability
  • Causes aluminum toxicity
  • Reduces biodiversity by acting as a natural selection pressure and eliminating acid-sensitive species
pH ranges that various aquatic species can tolerate.

CASE STUDY: Lake 223 Acidification

Design: From 1976 to 1983, a group of scientists at ELA (Environmental Lakes Area) added sulfuric acid to Lake 223 to decrease the pH level from 6.8 to 5.0 in 8 years.


  • Change in phytoplankton species from small edible to large protected species
  • The condition of the fish population greatly declined (due to direct toxicity, reproductive failure, and disrupted food chains)
  • Benthic crustaceans disappeared (due to reduced calcium).
Change in phytoplankton species from small edible species to large non-edible well-protected species
Decline in the lake trout condition. (A) Represents the condition in 1979 (pH = 5.4). (B) Represents the condition in 1982 (pH =5.1)

CASE STUDY: Canadian “Jelly Lakes”


  • Acid rain causes aquatic osteoporosis which when acids combine with calcium and remove it from the water column.
  • Daphnia is a keystone water flea that uses high amount of calcium to make their shells (high calcium requirement). They are a keystone species because they are a major food source for many aquatic species in the food chain.
  • Holopedium has a lower requirement for calcium and can outcompete Daphnia in lakes that have reduced calcium levels.

Design: Sampled sediments to date back around 150 years from 84 Canadian lakes.


  • Increase in Holopedium is a result of the decline in Daphnia
  • Decrease in calcium concentration leads to an increase in Holopedium abundance
Canadian 'Jelly' Lakes. Reduced calcium Increases abundance of Holopedium and a sheer number produces a jelly-like consistency.

Inco Superstack in Greater Sudbury, Ontario Drone View!

  • Superstack disperses sulphur gases and other byproducts of the smelting process away from the city of Sudbury.
  • It did this by placing the gases high in the air where they normally blew right past the city on the prevailing winds.
  • The Superstack helped Sudbury locally with its local S02 problem but not thinking globally caused acid rain across the Northeastern portion of US and Canada (Dillon, 1994).
  • Program AER = Atmospheric Emissions Reduction was established by Vale  Canada Limited (formerly known at Vale Inco) to capture sulfur-bearing gases from the smelter converter aisle and reduce dust and metal emissions
    (Vale, 2014).

Policies, Laws and Activities

  • Canadian Acid Rain Program (1985): Joint venture by the federal and provincial governments and industry to reduce SO2 in eastern Canada.
  • The Canada-U.S. Air Quality Agreement (1991): Scheduled reduction of nitrogen oxide emissions over a 10 year period. Tighter emission standards for new motor vehicles, the monitoring of sulphur dioxide and nitrogen oxide emissions, and specific actions to protect both countries’ pristine wilderness areas.
  • Activities/Future Actions: Acid Rain Assessment (2004).

What Can we Do?

  • Turn off lights, computers, and other appliances when you're not using them.
  • Use energy-efficient appliances.
  • Carpool, use public transportation, or better yet, walk or bicycle whenever possible.
  • Use Alternate Energy Sources.
  • Reduce Reuse Recycle.
  • Stay Informed.


Comment Stream

3 years ago

very good! Clear and well organized. Could have some sources for the case studies mentioned though. I like it