Acid Deposition Notes

Acid Deposition

Pollution Reduction & Secondary/Primary Pollutants

  • Primary Pollutants:

    • SO_2 (Sulfur Dioxide)

    • CO (Carbon Monoxide)

    • NO (Nitrogen Oxide)

    • CO_2 (Carbon Dioxide)

    • NO_2 (Nitrogen Dioxide)

    • Most hydrocarbons

    • Suspended particles

  • Sources of primary pollutants include:

    • Mobile sources

    • Stationary sources

    • Natural sources

  • Secondary Pollutants:

    • SO_3 (Sulfur Trioxide)

    • H2SO4 (Sulfuric Acid)

    • HNO_3 (Nitric Acid)

    • O_3 (Ozone)

    • H2O2 (Hydrogen Peroxide)

    • Most NO_3 (Nitrates)

    • SO_4^{-2} (Sulfates)

  • Sources of secondary pollutants include:

    • Mobile sources.

    • Stationary sources.

    • Natural sources.

Methods to Reduce Air Pollutants

  1. Regulatory practices.

  2. Conservation practices.

  3. Alternative fuels.

Additional Ways to Reduce Air Pollution

  1. Scrubbers in Smokestacks:

    • Removes SO_2.

  2. Electrostatic Precipitators:

    • Removes Particulate Matter.

  3. Catalytic Converters:

    • Removes CO, NO_x, and hydrocarbons.

  4. Vapor Recovery Nozzle:

    • Prevents escape of VOCs.

  5. Emissions Trading for SO_2

Scrubbers (Flue Gas Desulfurization – FGD)

  • Scrubbers work by passing the flue gas through a tower in which a water and limestone mixture is sprayed.

  • The SO_2 in the flue gas reacts with the limestone to produce gypsum, a useful additive to concrete or the production of wallboard.

Desulfurization

  • Reduce SO_2 (sulfur dioxide) emissions

  • Burn coal near CaCO_3 (calcium carbonate)

  • Produces CaSO_4 (sheetrock)

Electrostatic Precipitator

  • Device that uses an electrical charge to remove PM from air or other gases in smokestacks and flues.

Catalytic Converters

  • An air pollution abatement device that removes pollutants from motor vehicle exhaust, either by oxidizing them into carbon dioxide and water or reducing them to nitrogen and oxygen.

  • Removes CO, NO_x, and hydrocarbons.

Vapor Recovery Nozzle

  • Prevents fumes from escaping into the atmosphere when fueling a motor vehicle.

  • Special features of Phase II Vapor Recovery nozzle:

    • Holes to suck petrol vapor back to underground storage tank.

    • Vapor guard to prevent vapor release.

Emissions Trading

  • "Cap and trade" concepts—also known as "emissions trading" or "allowance trading"—allow companies to buy and sell "emission allowances" as long as the industry stays under a cap for total emissions of a particular pollutant.

  • Done successfully with SO_2 permits in US.

Acid Deposition (Acid Rain or Acid Precipitation)

  • Commonly called Acid Rain or Acid Precipitation

pH Scale

  • The pH scale is used to rank solutions in terms of acidity or basicity (alkalinity).

  • Since the scale is based on pH values, it is logarithmic, meaning that a change of 1 pH unit corresponds to a ten-fold change in H^+ ion concentration.

What is Deposition?

  • Wet Deposition – acidic rain, snow, fog, and cloud vapor with a pH less than 5.6

  • Dry deposition – acidic gases and aerosol particles

Normal Rainfall

  • Normal Rainfall is Slightly Acidic with a pH of 5.6 – WHY?

  • Rain is naturally acidic as a result of the reaction of water vapor, carbon dioxide, and nitrogen in the atmosphere.

Sources of Acid Deposition

  • Nitrogen Oxides

    • Natural: Lightning, microbes

    • Anthropogenic: Motor vehicles

    • NO, N2O, NO2

  • Sulfur Oxides

    • Natural: Volcanoes

    • Anthropogenic: Coal-burning power plants

    • SO_2, SO

Primary & Secondary Pollutants leading to Acid Precipitation

  • Primary pollutants

    • SO_2: Sulfur dioxide

    • NO_x: Nitrogen oxides

  • Secondary pollutants

    • Oxidants

    • H2SO4: Sulfuric acid (2H^+ + SO_4^{2-})

    • HNO3: Nitric acid (H^+ + NO3)

Acid Formation Equations

  • SO2 + H2O \rightarrow H2SO4 (Sulfuric Acid).

  • NOx + H2O \rightarrow HNO_3 (Nitric Acid).

Acidic Substances in the Atmosphere

  • Acidic substances remain in the atmosphere for 2 – 14 days

  • During this time, the wind will carry the particles downwind

  • The longer the particles are in the air, the more time they have to form secondary pollutants, such as nitric acid and sulfuric acid

The Worst Acid Rain in the U.S.

  • The Eastern United States is downwind from coal-burning power plants, smelters, factories, etc. in the Midwest

Changes in Nitrogen and Sulfur Deposition

  • Nitrogen deposition has changed since the early 2000s (2000-2002 vs. 2017-2019).

  • Sulfur deposition has changed since the early 2000s (2000-2002 vs. 2017-2019).

The Global Problem of Acid Rain

  • Acid rain and polluted air emissions leading to acid rain exist worldwide.

  • Sensitive soils indicate potential problems.

Effects of Acid Deposition on Aquatic Ecosystems

  • Loss of biodiversity – most species cannot survive below a pH of 5

  • Release of aluminum ions from nearby soil can kill fish by stimulating excess mucus formation

Effects on Organisms

  • Organisms vary in their tolerance of acid rain, with some species unable to survive in water with a pH less than 6.0.

  • Effects of losing some organisms from acidified lakes can cascade through food webs and reduce water quality.

Acidity Examples

  • Baby Trout:

    • Normal pH: Above pH 5.5

    • Abnormal pH: Below pH 5.0

  • Salamander Eggs:

    • Many amphibians begin to have developmental or reproductive problems when a lake acidifies to pH 6.0 or 5.5. In water below pH 5.0, most salamander species won’t survive.

pH Values and Environmental Effects

  • ACIDIC

    • pH = 0: Battery acid

    • pH = 1: Sulfuric acid

    • pH = 2: Lemon juice, Vinegar

    • pH = 3: Orange juice, Soda

    • All fish die (4.2) pH=4

    • Frog eggs, tadpoles, crayfish, and mayflies die (5.5) pH=5

    • Acid rain (4.2-4.4)

    • Acidic lake (4.5)

    • Bananas (5.0-5.3)

    • Clean rain (5.6)

  • NEUTRAL

    • Rainbow trout begin to die (6.0)

    • Healthy lake (6.5)

    • pH = 6: Milk (6.5-6.8)

    • pH = 7: Pure water

  • BASIC

    • pH=8: Sea water, Eggs

    • pH = 9: Baking soda

    • pH=10: Milk of Magnesia.

    • pH 11: Ammonia.

    • pH 12: Soapy water

    • pH 13: Bleach

    • pH = 14: Liquid drain cleaner

Acid Rain Effects on Food Webs

  • Acid Rain Can Cause Serious Problems for Many Different Plants and Animals

  • Acid rain can cause phytoplankton in lakes to die.

  • This process continues up the entire food web.

  • Acid rain can affect the entire food web by limiting the amount of food available.

Effects on Nitrogen Pollution

  • 10 – 45% of the nitrogen produced by human activities reaches estuaries and coastal ecosystems by acid rain

  • Contributes to eutrophication

Effects on Human Health

  • Contributes to human respiratory diseases such as asthma and bronchitis

  • Increases premature death from heart and lung disorders

  • Can leach toxic metals from water pipes into drinking water

Effects on Economy

  • Lower profits and job losses because of lower productivity in fisheries, forests, and farms

Effects on Visibility

  • Sulfate particles account for 50 - 70% of visibility reduction in the Eastern U.S.

Effects on Materials

  • Damages statues, buildings, metals, and car finishes

  • Limestone and marble dissolve even in weak acid solutions, making many monuments and statues especially vulnerable

Effects on Plants and Soils

  • Extensive harm to forests and crops when soil pH drops below 5.1

  • Damages leaves and needles directly

  • Releases aluminum ions that prevent the uptake of nutrients and water

  • Leaching of nutrients

Effects on Plants and Soils (Detailed)

  • Acidic deposition effects on trees, specifically:

    • Red Spruce: Calcium leached from needle membranes, decreased cold tolerance, increased freezing injury.

    • Sugar Maple: Calcium & magnesium leached from soil, aluminum mobilized & taken up by tree.

What Can be Done About Acid Rain?

  • Prevention:

    • Reduce air pollution by improving energy efficiency and increasing renewable resources

    • Use natural gas/low sulfur coal

  • Cleanup

    • Add lime to neutralize acidified lakes and soils

Buffering Capacity

  • The ability of a water body and/or forest soils to resist large changes in pH when an acidic or alkaline solution is added to it.

  • Once buffering capacity is exhausted, the pH of the system will begin to drop

Reducing Effects

  • Add lime or limestone to acidified lakes and/or soil

  • Crushed limestone is sometimes added to soils, lakes, ponds, and other aquatic areas to help neutralize the effects of acid rain.

  • Crushed limestone is easily obtained from local lawn and garden stores or nurseries.

Limestone

  • A sedimentary rock composed mainly of calcium carbonate (CaCO_3)

  • When present in the geologic substrate, it can absorb the excess hydrogen ions

  • Areas high in limestone experience less impacts from acid precipitation

Prevention

  • PREVENTION IS BEST

  • "BE A PART OF THE SOLUTION Not PART OF THE Pollution"

  • PREVENTION BEATS REMEDIATION EVERY TIME!

Summary: Causes and Effects of Acid Deposition

  • Nitrogen dioxide emitted from fossil fuels dissolves in water vapor and is carried by wind, falling as acid rain.

  • Heavy particles damage stonework and cause irritations.

  • Acid rain damages leaves, impacting crops.

  • Aluminum is washed into water bodies, harming aquatic life.

  • Soil nutrients are depleted, harming trees.

Summary: Acid Deposition Management Strategies

  • Strategies include reducing demand for private cars, promoting cleaner fuels, using alternative energy, monitoring emissions, using limestone scrubbers, liming soil, and captive breeding of endangered species.