Acid Rain

When you get to the end of your rope, tie a knot and hang on.

       - Franklin D. Roosevelt

What is Acid Rain?• "Acid rain" describes how acids fall out of the atmosphere.

• A more precise term is acid deposition, which has two parts: wet and dry.

• Wet deposition refers to acidic rain, fog, and snow.

• It affects a variety of plants and animals.

• The strength of the effects depend on how acidic the water is, the chemistry and buffering capacity of the soils, and the types of fish, trees, and other living things that rely on the water.

Dry Deposition

• Dry deposition is acidic particles.

• Half of the acidity in the air falls to earth through dry deposition.

• The wind blows these acidic particles onto buildings, cars, homes, and trees.

• These particles then are washed from trees and other surfaces by rainstorms.

• Runoff water adds those acids to the acid rain.

• This makes the combination more acidic than the rain alone.

• Prevailing winds blow these compounds over hundreds of miles.

Rain is naturally acidic

• Carbon dioxide in the air reacts with water vapor to produce the mild acid carbonic acid.

• HOH + CO2 H2CO3

• This weak acid lowers the pH of rainfall to about 6.

• So, even in the cleanest environment, rain is naturally slightly acidic.

Causes of Acid Rain• Sulfur dioxide

(SO2) and nitrogen oxides (NOx) are the primary causes of acid rain.

• In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power plants that burn coal.

• These gases react in the atmosphere with water and oxygen to produce HNO3 & H2SO4.

• Sunlight increases the rate of most of these reactions.

How is acid rain measured?

• Acid rain is measured using the pH scale.

• Normal rain has a pH of about 5.5 to 6

• As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.

• The National Atmospheric Deposition Program measures wet deposition.

Dry Deposition • The Clean Air Status and Trends Network (CASTNET) measures dry deposition..

Dry Deposition SO4, 1989-91

Effects of Acid Rain• Acid

deposition causes damage to forests and soils, fish and other living things.

• It also harms materials, and human health.

• It causes acidification of lakes and streams.

• It damages trees at high elevations.

• As the acidity of a lake increases the number of living things that can survive diminishes.

Visible Pollution• Acid rain also reduces

how far and how clearly we can see through the air, an effect called visibility reduction.

• This is Mexico City on a typical day in the summer.

• Acid particles in the air cause the sunlight to be diffracted.

• Mexico City, along with LA, will have many smog alerts during the summer.

• During an alert children will not be allowed outside for recess and seniors will be advised to stay inside..

Damage to Marble

• Acid rain accelerates the decay of building materials and paints.

• The acids react with limestone and marble (CaCO3) to form CO2, HOH and a salt.

• The Marble statue in the upper right picture is from Dresden, Germany.

• The bottom picture is what is left of a marble statue in Rome, Italy.

Acid Rain damage to a statue in Lincolnshire, England

Acid Rain Health Affects• Sulfur dioxide (SO2) and

nitrogen oxides (NOx)) also damage human health.

• These gases interact in the atmosphere to form fine sulfate and nitrate particles that can be transported long distances by winds and inhaled deep into people's lungs.

• Fine particles can also penetrate indoors.

• A relationship exists between elevated levels of fine particles and increased illness and premature death from heart and lung disorders, such as asthma and bronchitis

What Can We Do??

• Use low sulfur coal from the West.

• Wash the coal, and use devices called scrubbers to chemically remove the SO2 from the smokestack.

• Power plants can also switch to natural gas

• (CH4) creates much less SO2 than burning coal.

• This will also have reduce other pollutants such as mercury and carbon dioxide.

• Finally, power plants can use technologies that don't burn fossil fuels.

Smoke stack technology solutions

• NEW scrubber technology incorporates charged water droplets to collect 99.99% of particulates to 0.1µ  using just 600 watts.

• In a Cloud Chamber Scrubber, billions of droplets and particles move continuously in relation to each other. 

• As they approach 10 microns of separation, electrical attraction causes the particulate to enter the droplets.

High Bridge power plant – St. Paul, MNConverted to natural gas which eliminates mercury emmissions Reduced carbon dioxide emissions (by as much as 415,000 tons

The new plant produces twice as much energy and reduces emissions of sulfur dioxide, nitrogen oxides, and particulate matter by more

than 90 percent

Wet Scrubber for NOx• This scrubber system

removes any combination of NO and NO2.

• This scrubber will handle multiple gases, including Cl2, HCl, SO2,

• It can also remove other acids, gases, and caustics.

• It can remove particulates as well.

• This scrubber technology eliminates the visible plume generated by high NO2 loading.

• This scrubber can reduce pollutant loads of 100,000 ppm to below 5 ppm

Acid Rain long term Effects

• Acid deposition affects ecosystems.

• It changes the chemistry of the soil as well as streams and lakes.

• It can narrow, to nothing, the space where certain plants and animals can survive.

• Because there are so many changes, it takes many years for ecosystems to recover.

• Visibility might improve within days.

• Small chemical changes in streams improve within months.

• chronically acidified lakes, streams, forests, and soils can take years to decades or even centuries (in the case of soils) to heal.

Lake and Stream renewal

• There are some things that people do to bring back lakes and streams.

• Limestone (CaCO3) or lime (CaO) can be added to acidic lakes to "cancel out" the acidity.

• This process, called liming, has been used extensively in Norway and Swede.

• Liming tends to be expensive, has to be done repeatedly to keep the water from returning to its acidic condition, and is considered a short-term remedy.

• It does not solve the problems of changes in soil chemistry and forest health in the watershed

• It does nothing to address visibility reductions, materials damage, and risk to human health.

• However, liming often permits fish to remain in a lake.