UNIT 7 ATMOSPHERIC POLLUTION

AP ENVIRONMENTAL SCIENCE

UNIT 7 ATMOSPHERIC POLLUTION

AIR POLLUTANTS

• Air Pollution

  • The introduction of chemicals, particulate matter, or microorganisms into the atmosphere at concentrations high enough to harm plants, animals, and materials such as buildings,                                                        or to alter ecosystems.

Sources of Air Pollution

• Natural sources

  • volcanoes, lightning, forest fires, plants (both living and dead)

• Anthropogenic Sources

  • on-road vehicles, power plants, industrial processes, waste disposal (incinerator)

Inputs: cars, airplanes Outputs: vegetation, soil

PRIMARY POLLUTANTS

Comes directly out of a smokestack, exhaust pipe, or natural source

1. Carbon monoxide (CO)

2. Carbon dioxide (CO2) 

3. Sulfur dioxide (SO2) 

4. Nitrogen oxide (NOx) 

5. Particulate Matter (PM)

SECONDARY POLLUTANTS

A primary pollutant that has undergone transformation in the presence of sunlight, water, oxygen, or other compounds. 

1. Ozone (O3) 

2. Sulfuric Acid (H2SO4)

3. Nitric Acid (N2O)

NOSCLP (6 big outdoor air pollutants)

1. Nitrogen oxides (NOx)

2. Ozone (Ground-level, tropospheric; not stratospheric)

3. Sulfur dioxide (SO2)

4. Carbon oxides (CO and CO2)

5. Lead (and other toxic metals)

6. Particulate matter

NITROGEN OXIDES (NOx)

• Primary sources: mobile cars and stationary fossil fuel combustion

• An ozone precursor - leads to formation of photochemical smog 

• Respiratory irritant - increases susceptibility to respiratory infection

OZONE

• Ozone = a highly reactive gas that is a major component of photochemical smog

• Causes and aggravates respiratory illness

• Damages plants, rubber tires, fabrics, paints

• Good in the stratosphere              Bad in the troposphere

SULFUR DIOXIDE (SO2)

• A corrosive gas that comes from stationary factories burning coal and oil. (S + O2 → SO2)

• Released during volcanic eruptions and in forest fires.

• SO2 can be converted into sulfuric acid (H2SO4) that returns to Earth as acid rain.

CARBON OXIDES

• Carbon monoxide (CO)

  • common emission in vehicle exhaust and other combustion processes;  can be a significant component of air pollution in urban areas

• Carbon dioxide (CO2)

  • released by burning fossil fuels; appears to be steadily increasing each year

LEAD

• A gasoline additive

• Also found in oil, coal, old paint

• It is a neurotoxin - that impairs the central nervous system  At low concentrations, can have measurable effects on learning and the ability to concentrate

• Does not break down in the environment

PARTICULATE MATTER (PM)

• Solid particles and liquid droplets small and light enough to remain suspended in air

• PM causes 60,000 deaths per year in the U.S.

  • Fine: PM10 (< 10 µm)

  • Ultrafine: PM2.5 (< 2.5 µm) 

Anthropogenic Emissions

• In the U.S., emissions from human activities are monitored, regulated, and controlled. 

• The Clean Air Act requires that the EPA establish standards to control pollutants that are harmful to humans.

• These National Ambient Air Quality Standards (NAAQS) specify concentration limits for each air pollutant. 

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INDOOR AIR POLLUTION

Indoor air pollution is a significant hazard in developing and developed countries

• 90% deaths in developing countries

• More than 50% are children

Four Major Indoor Air Pollutants (CARV)

1. Carbon Monoxide (CO)

   1. Is an asphyxiant

   2. From burning wood for heating and cooking

   3. From tobacco smoke

2. Asbestos

   1. Long thin, fibrous, silicate particulates

   2. Formerly used as insulation in buildings

   3. Can cause lung cancer when inhaled

3. Radon

   1. A naturally occurring radioactive gas produced by the decay of uranium found in rocks and soils.

   2. Seeps into homes through cracks in the foundation, groundwater, or rocks.

   3. Exposure to radon gas can lead to radon-induced lung cancer, which is the second leading cause of lung cancer in America.

• Potential radon exposure in the United States. Depending on the underlying bedrock and soils, the potential for exposure to radon exists in houses in certain parts of the United States.

4. VOCs

   1. Volatile organic compounds used in furniture, paint, and building materials

      1. Ex: Formaldehyde (particle board, glue)

Sick Building Syndrome (SBS)

Affects large office buildings where workers breathe in pollutant gases, which are released from the materials and equipment in the office

• Causes of SBS

  • Inadequate or faulty ventilation

  • Chemical  contamination from indoor and outdoor sources

  • Biological  contamination from outside or inside

• Solutions

  • Cover ceiling tiles & lining of AC ducts to prevent release of mineral fibers

  • Use adjustable fresh air vents for workspaces

  • Increase intake of outside air

  • Ban smoking or limit it to well-ventilated areas

  • Change air more frequently

  • Set stricter formaldehyde emissions standards for carpet, furniture, and building materials

  • Prevent radon infiltration

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OUTDOOR AIR POLLUTION

Two Types of Smog

1. Sulfurous Smog

   1. Smog dominated by sulfur dioxide and sulfate compounds

   2. Emitted by burning oil and coal from stationary sources (factories).

   3. Tall smokestacks transfer pollutants to rural areas. (NIMBY)

   4. In the atmosphere, SO2 reacts with water vapor to form acid rain.

   5. Also known as: Gray smog, industrial smog, London smog 

2. Photochemical Smog

   1. formed when nitrogen oxides (NOx) and volatile organic hydrocarbons (VOCs) react with heat and sunlight to produce ozone (03).

   2. Also known as: Los Angeles–type smog, Brown smog

   3. Photochemical smog often forms in urban areas (large number of motor vehicles).

   4. Photochemical smog = cars + sun 

   5. Photochemical smog is most common in cities with warm, dry, sunny climate (e.g. Mexico City, Los Angeles, Beijing). 

1. Nitrogen oxides (NOx)

   1. NOx refers to NO and NO2.

   2. The combustion of fossil fuels releases nitrogen oxides into the atmosphere.

2. Volatile Organic Compounds (VOCs)

   1. Organic compounds (fuels, solvents, paints, and incomplete combustion of gasoline) evaporate (sublimate) at typical atmospheric temperatures

   2. VOCs are precursors to ozone.

Thermal Inversion

A weather event when a relatively warm layer of air at mid- altitude covers a layer of cold, dense air below

• Thermal inversions that create pollution events are particularly common in cities where vehicle exhaust and industrial emissions are easily trapped by the inversion layer.

Outdoor air pollution can increase by:

1. Urban buildings (slow wind dispersal of pollutants)

2. Mountains (promote thermal inversions)

3. High temperatures (promote photochemical reactions)

• Photochemical smog can harm human health (respiratory problems and eye irritation).

• Photochemical smog can be reduced through the reduction of NOx and VOCs.

Smog Check

1. Emissions measured include:

   1. Carbon monoxide (CO)

   2. Carbon dioxide (CO2)

   3. Oxides of nitrogen (NOx)

2. Vehicles in California are required to pass a smog check every two years for registration renewal.

Noise Pollution

• Noise pollution is sound at levels high enough to cause physiological stress and hearing loss.

• Sources of noise pollution in urban areas include transportation and construction.

• Effects:

  • stress, the masking of sounds used to communicate or hunt, damaged hearing, and causing migratory routes to change.

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ACID RAIN

Layers of the atmosphere

1. Thermosphere

2. Mesosphere

3. Stratosphere

4. Troposphere

• Density of air increases closer to the earth. 

• Atmospheric pressure decreases with altitude.

• Acid Deposition

  • nitrogen oxides and sulfur oxides are released into the air and combine with oxygen and water. 

  • Nitric Oxides (NOx)

    • comes from motor vehicles and coal-burning power plants.

  • Sulfur Dioxide

    • comes from coal-burning power plants.

• Nitric oxides and sulfur oxide form secondary pollutants nitric acid and sulfuric acid.

  • These acids further break down into nitrate sulfate, and hydrogen ions (H+) which cause acid deposition.

• Acid rain is rainwater with a pH of less than 5.6.

Harmful effects of Acid Deposition

1. Lowering the pH of lake water

2. Decreasing species diversity of aquatic organisms

3. Mobilizing metals that are found in soils and releasing them into surface waters

4. Damaging structures: statues, monuments, and buildings

Variables

• Regional differences in soil and bedrock affect the impact that acid deposition has on the region.

• Ex: limestone in bedrock can neutralize the effect of acid rain on lakes and ponds.

SOLUTIONS

1. Produce energy without using fossil fuels → use renewable energy sources, such as solar and wind power

2. Reduce vehicle use → use public transportation, walking, riding a bike, or carpooling

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POLLUTION CONTROL

Outdoor air pollution

Air pollutants may be natural:

• Dust blown by the wind

• Soot from wildfires

• Chemicals from volcanic eruptions or released by plants.

Air pollutants may be anthropogenic:

• Industrial (stationary sources)

• Vehicles (mobile sources)

• Often the result of burning fossil fuels

• Carbon dioxide, sulfur dioxide, toxic metals, and particulates are released during coal combustion.

• Burning fossil fuels (mainly gasoline) release NOx.

INPUT and OUTPUT approaches in solving air pollution

INPUT

1. Coal Gasification

   1. The process of producing syngas – a mixture consisting CO, H2, CO2, CH4, and H2O from coal, water, air and/or O2.

   2. Clean-burning coal with little to no carbon emissions

   3. A part of “clean coal” technology

2. Fluidized-bed Combustion

   1. Can burn any type of fuel at high efficiency.

   2. Steam is pumped into a boiler to burn a mixture of powdered coal and crushed limestone (neutralizes sulfur emissions).

3. Regulations

   1. Can burn any type of fuel at high efficiency.

   2. Steam is pumped into a boiler to burn a mixture of powdered coal and crushed limestone (neutralizes sulfur emissions).

OUTPUT

1. Vapor Recovery Nozzle

   1. A vapor recovery nozzle is an air pollution control device on a gasoline pump that prevents fumes from escaping into the atmosphere when fueling a motor vehicle.

2. Catalytic Converter

   1. A catalytic converter is an air pollution control device for engines that converts pollutants (CO, NOx, and hydrocarbons) in exhaust into less harmful molecules (CO2, N2, O2, and H2O).

3. Wet Scrubber

   1. Particles are “scrubbed” from the exhaust stream by water droplets. A water-particle “sludge” is collected and processed for disposal.

4. Electrostatic Precipitator

   1. Can remove 99% of particulate matter

   2. Does not remove hazardous ultrafine particles

   3. Produces toxic dust that must be safely disposed of

   4. Uses large amounts of electricity

Innovative control measures:

Municipalities have tried a number of strategies:

1. Reduce gasoline spilled at the pump

2. Restrict evaporation of dry-cleaning fluids

3. Restrict the use of lighter fluid

4. Reduce use of wood-burning stoves and fireplaces

5. Limit automobiles to every other day-use

6. Charge user fees for roads during heavy commute times

• Currently, the popular approach of controlling pollution seems to be focused on the output (clean-up) approach rather than the input  (prevention) approach.