Air pollution

Air Pollution Study Guide

Reviewing the Atmosphere

• Earth’s atmosphere: the layer of gases that surround the planet

  • Very thin layer, relative to size of planet

Atmospheric Composition

• Atmosphere is composed of:

  • 78% nitrogen

  • 21% oxygen

  • 1% argon

  • Traces of other permanent gases
    and variable small amounts of:

    • Water vapor

    • Carbon dioxide

    • Methane

    • Pollutants, etc.

Layers of the Atmosphere

• Our atmosphere consists of several layers:

  • Troposphere: bottom layer, at Earth’s surface; 11 km high; temperature decreases with altitude

  • Stratosphere: next layer up (11–50 km); temperature increases with altitude; contains 'ozone layer'

  • Mesosphere: third layer up (50–90 km); temperature decreases with altitude

  • Thermosphere: top layer (90–500 km); very thin air; mostly lightweight elements; very hot; ionic radiation

  • Exosphere: the outermost layer

• Temperature and other characteristics vary with altitude. 

• Layers don’t mix! Remember they are different densities due to temperature which makes it harder for them to mix.

Ozone Layer

• Ozone layer is a part of the stratosphere

• It is not really a layer, but a region of higher-than-normal ozone concentrations (which are still very low)

  • About ~17–30 km in altitude

• Absorbs ultraviolet (UV) radiation from sun, protecting organisms on surface from radiation damage

• Any ozone found in troposphere is from burning of fossil fuels and is considered a pollutant- respiratory irritant

Air Pollution

Definitions and Impact

• Air pollution: material added to the atmosphere that can affect climate and harm organisms, including humans

• Air Pollutant: specific molecules and particles that are causing pollution

  • For this Unit and FRQs especially, you need to be specific in the type of pollutant(s) you are discussing as we want more than just general “pollution”

• Government policy and improved technologies have helped diminish outdoor or ambient air pollution substantially in developed but not developing countries.

Pollutants

Primary Pollutants

• Primary pollutants:  polluting compounds that come directly out of the smoke-stack, exhaust pipe, or natural emission source.

  • Examples: CO, CO2, SO2, NOx, and most suspended particulate matter.

  • Notice most of the 6 criteria pollutants belong to this group!

Secondary Pollutants

• Secondary pollutants: pollutants that have undergone transformation in the presence of sunlight, water, oxygen, or other compounds.

  • Examples: tropospheric ozone, sulfuric acid and nitric acid, PANs

  • Only O₃ fits in this group 

The 6 Criteria Air Pollutants

• The Clean Air Act of 1970 set out to identify 6 air pollutants that the EPA is require to set acceptable limits for, monitor, and enforce

  • These pollutants have a direct impact on air quality and impact both the environment and human health

Why is CO₂ not a “criteria air pollutant” according to the clean air act?

• CO₂ we know has a very direct impact on the health of the environment as it does cause global warming due to being a greenhouse gas

  • As of 2011 due to a Supreme Court case, the EPA was given the permission to regulate the emission of CO₂ under the Clean Air Act, but it is still not a criteria pollutant as it does not directly impact the health of humans.

Sources of Air Pollution

Natural Sources of Air Pollution

• Dust storms: main problem is the PM that is involved here as they are able to become lofted in the atmosphere and travel quite a distance from the source

  • Ex: The Saharan Desert generates dust storms that the trade winds can then carry West towards the americas! Texas can be affected by these storms.

• Fires: Similar to burning fossil fuels or biomass this can release CO₂ which affects the climate, CO, PM

• Volcanoes: Release SO₂, CO₂, HF (Hydrogen Fluoride) which is very toxic to organisms.

Anthropogenic Sources of Air Pollution

• These are the human sources of air pollution

• There are 2 types:

  • Point sources: specific spots where large amounts of pollution are discharged (factory smokestacks)

    • You can point to the source! 

  • Non-point sources: diffuse, often made up of many small sources (charcoal fires from thousands of homes)

    • You cannot point to the source as it is a collection of multiple sources that combine together.

Types of Smog

Industrial Smog

• Smog from industrial pollution, fossil-fuel combustion, mainly sulfur rich fuels like COAL and oil.

  • The kind that blanketed London in 1952

  • 'Gray air smog'

  • Contains soot, sulfur, CO, CO2…

• The U.S. had its own 'killer smog' from industrial pollution. Shown is Donora, Pennsylvania, in 1948, at mid-day. 

  • Subsequent demand for legislation against pollution made U.S. air much cleaner.

The Chemistry of Industrial Smog

Photochemical Smog

• Smog from reaction of sunlight with pollutants

• The kind that blankets so many American cities today like LA, California.

• 'Brown air smog'

• Contains tropospheric ozone, NO2, VOCs, 100 more…

• Hot sunny days in urban areas create perfect conditions.

  • Mexico City and many of the world’s cities suffer from the brownish haze of photochemical smog.

• Inversion layers and mountains can trap smog over certain cities.

• Chemistry of photochemical smog:

  • Nitric oxide starts a chain reaction.

  • Reaction with sunlight, water vapor, hydrocarbon, results in over 100 secondary pollutants.

Photochemical Smog and Thermal Inversion

Photochemical Smog

O3, HNO3 and PANs
Los Angeles, CA

Thermal Inversion

Thermal inversion = natural occurrence that can exacerbate air pollution locally (in the troposphere)
Inversion layer = band of air in which temperature rises with altitude
“warm blanket” that traps pollution

Urban Climates and Heat Islands

Urban Heat Island Effect

Urban heat island effect – cities often hotter than surrounding countryside
Stone, concrete, asphalt re-emit lots of solar energy
Little surface water to transfer heat
Thermal contribution from combustion (heating buildings)
Buildings block winds
Air pollution absorbs heat to produce local greenhouse warming

Acid Deposition

Definition and Causes

Acid deposition = deposition of acidic or acid-forming pollutants from the atmosphere onto the Earth as acid rain, acid fog, acid snow
One type of atmospheric deposition
Caused by reaction of pollutants like SO2 and NO with water, oxygen, and oxidants resulting in sulfuric acid or nitric acid

Effects of Acid Deposition

Harms plants & soil and alters ecosystems
Lowering the pH of lake water
Decreasing species diversity of aquatic organisms
Mobilizing metals that are found in soils and releasing these into surface waters
Releases aluminum ions
Leaches calcium from red spruce trees
Damaging statues, monuments, and buildings
Acid deposition has killed these conifer trees in the mountains of North Carolina. It also eats away at statues and buildings.

Geographic Variation

Acidity varies geographically. (Orange = more acidic)
Industrialized areas and regions downwind of them suffer most

Check for Understanding

Which of the following would be the strongest evidence in support of a scientist’s contention that a local area was experiencing acid deposition?
a. A sudden die-off of all the fish in a local stream
b. A gradual increase in the temperature of a local lake
c. An increase in the rate of photosynthesis of aquatic plants in a local lake
d. A long-term increase in the pH of a local pond
e. An increase in the concentration of soluble heavy metals in a local pond

Indoor Air Pollution

Major Indoor Air Pollutants

Indoor air pollution usually is a greater threat to human health than outdoor air pollution.
According to the EPA, the four most dangerous indoor air pollutants in developed countries are:

• Tobacco smoke

• Formaldehyde

• Radioactive radon-222 gas

• Very small fine and ultrafine particles

• Chloroform

• Benzo-α-pyrene

• Styrene

• Radon-222

• Methylene Chloride

• Carbon Monoxide

• Asbestos

• Nitrogen Oxides

• 1, 1, 1-Trichloroethane

• Particulates

• Tetrachloroethylene

• Para-dichlorobenzene

Radon-222

Radon-222, a radioactive gas found in some soils and rocks, can seep into some houses and increase the risk of lung cancer.
Can cause lung cancer
Estimated that 7,000 to 30,000 Americans die each year from radon-induced lung cancer
Only smoking causes more lung cancer deaths
Smokers more at risk than non-smokers

Check for Understanding

The major source of radon in houses in the United States is
a. furniture and carpets
b. the underlying bedrock
c. the troposphere
d. nuclear power plants
e. fossil-fuel combustion
The major human health problem related to radon accumulation is
a. lung cancer
b. heart disease
c. pancreatic cancer
d. cataracts
e. malignant melanoma

Health Effects of Air Pollution

Sick Building Syndrome

Developed Nations in temperate zones
Increased insulation to prevent air leaks traps pollutants
Observed in office buildings where workers report nausea, headaches and fatigue
May be due to glues, carpeting, cleaning agents, mold or pollen that build up in high concentrations

Prevention and Regulation of Air Pollution

Ways to Prevent Outdoor Air Pollution

Removing sulfur dioxide from coal emissions with the use of limestone, lime, or magnesium oxide in scrubbers.
Catalytic converters on cars – uses catalysts (catalyzing a redox reaction) to convert harmful pollutants (CO, NO2, HC) into less harmful substances (CO2, N2, and H2O).
Baghouse filters – cloth filtration; removes particulates and gases by filtering through a special cloth.
Electrostatic precipitators – static electricity to remove particulates

Clean Air Act

Law – Clean Air Act
1963 - first passage
1970, 1977 and 1990 - amended
Involves EPA
Sets standards for acceptable levels of sulfur oxides, nitrogen oxides, ozone, carbon monoxide, hydrocarbons, lead, & more
Provides pollution credits for industries that utilize pollution-control devices
Bush administration has relaxed rules
It established NAAQS and AQI

National Ambient Air Quality Standards (NAAQS)

Sets acceptable concentrations for 6 “criteria” pollutants that:

• Threaten public health/the environment over broad areas (non-point)

• Are emitted in large quantities
  CO, Pb, Nitrogen Oxides, Ozone, Particulate Matter and Sulfur Dioxides

Air Quality Index (AQI)

Measures levels of 5 criteria pollutants
Forecast of daily air pollution levels
Purpose to educate and protect public- focuses on health effects
Categories:

• green= good

• yellow= moderate

• orange= unhealthy for sensitive groups

• red= unhealthy

• purple= very unhealthy

Market-Based Solutions to Air Pollution

Emission Trading Program

To help reduce SO2 emissions, the Clean Air Act authorized an emission trading (cap-and-trade) program.
Enables the 110 most polluting power plants to buy and sell SO2 pollution rights.
Between 1990-2002, the emission trading system reduced emissions.
In 2002, the EPA reported the cap-and-trade system produced less emission reductions than were projected.

Air Quality Trends

Air Quality is better in US; EPA estimates since 1970
Particulate Matter (PM)- down 78%
Carbon Dioxide (CO)- down 23%
Nitrogen Dioxide (Nox)- up 14%
Lead (Pb)- down 98%
Sulfur Dioxide (SO2)- down 32%
Air quality is worse in developing countries:

• Mexico City & Beijing: air exceeds WHO standards 350 days/year