Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Air Pollution Chapter 18.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

Air Pollution

Chapter 18


Outline:

• Natural Sources• Human-Caused Air Pollution

Conventional Pollutants Unconventional Pollutants Indoor Air Pollution

• Climate and Topography• Effects of Air Pollution• Air Pollution Control• Clean Air Legislation


THE AIR AROUND US

• Approximately 14 million metric tons of air pollution are released annually into the atmosphere in the US by human activities. Worldwide emissions total around 2 billion

metric tons.• Developed countries have been improving air

quality, while air quality in developing world is getting worse.


NATURAL SOURCES OF AIR POLLUTION

• Natural Fires - Smoke• Volcanoes - Ash and Acid components• Sea Spray - Sulfur• Vegetation - Volatile organic compounds • Bacterial Metabolism - Methane• Dust

Pollen• Viruses and Bacteria


HUMAN-CAUSED AIR POLLUTION

• Primary Pollutants - Released directly from the source.

• Secondary Pollutants - Modified to a hazardous form after entering the air and mixing with other environmental components. Fugitive Emissions - Do not go through

smokestack.- Dust from human-activities.


Conventional Pollutants

• US Clean Air Act designated seven major (conventional or criteria) pollutants for which maximum ambient air levels are mandated. Sulfur Dioxide Carbon Monoxide Particulates Hydrocarbons Nitrogen Oxides Photochemical Oxidants Lead



• Sulfur Compounds Natural sources of sulfur in the atmosphere

include evaporation from sea spray, volcanic fumes, and organic compounds.

Predominant form of anthropogenic sulfur is sulfur-dioxide from fossil-fuel combustion.

- Annual Emissions: 114 million metric tons


Sulfur Compounds



• Nitrogen Compounds Nitrogen oxides are reactive gases formed

when nitrogen is heated above 650o C in the presence of oxygen, or when nitrogen compounds are oxidized.

- Annual Emissions: 230 million metric tons


Nitrogen Compounds



• Carbon Oxides Predominant form of carbon in the air is

carbon dioxide. - Increasing levels due to human activities.- Annual Emissions: 8-10 billion metric tons

Carbon monoxide is a colorless, odorless, toxic gas produced by incomplete fuel combustion.

- Annual Emissions: 1 billion metric tons



• Metals Many toxic metals occur as trace elements

in fuel.- Lead Emissions: 2 million metric tons.

Mercury- Bioaccumulation in aquatic ecosystems.

Nickel, beryllium, cadmiuym, arsenic…• Halogens (Fluorine, Chlorine, Bromine)

CFC’s



• Particulate Matter Atmospheric aerosols (solid or liquid)

- Respirable particles smaller than 2.5 micrometers are among most dangerous.

• Volatile Organic Compounds Organic chemicals

- Generally oxidized to CO and CO2. Of 188 air toxics listed in Clean Air Act,

two-thirds are VOC’s.



• Photochemical Oxidants Products of secondary atmospheric

reactions driven by solar energy.- Ozone formed by splitting nitrogen

dioxide.


Unconventional Pollutants

• EPA sets emissions standards for unconventional or non-criteria pollutants that are considered especially hazardous. Asbestos, benzene, beryllium, etc.

- Most have no natural source in the environment.

Aesthetic Degradation- Noise, odor, light pollution.

Reduce quality of life.


Indoor Air Pollution

• EPA found indoor concentrations of toxic air pollutants are often higher than outdoor. People generally spend more time indoors. Smoking is the most important air pollutant

in the US.- 400,000 die annually from a disease

related to smoking. Associated costs are estimated at

$100 billion annually.


Indoor Air Pollution

• Less Developed Countries also suffer from indoor air pollution. Organic fuels make up majority of

household energy.- Often burned in smoky, poorly ventilated

heating and cooking fires.


CLIMATE AND TOPOGRAPHY

• Inversions Temperature inversions occur when a

stable layer of warm air overlays cooler air, reversing the normal temperature decline with increasing height, and preventing convection currents from dispersing pollutants.

- Cold front slides under warm air mass.- Cool air subsides down slope.

Rapid nighttime cooling in a basin.


Inversions


Dust Domes and Heat Islands

• Sparse vegetation and large amounts of concrete and glass create warm, stable air masses, heat islands, over large cities. Concentrates pollutants in a “dust dome”.

- Rural areas downwind from major industrial areas often have significantly decreased visibility and increased rainfall.


Long-Range Transport

• Fine aerosols can be carried great distances by the wind. Increasingly, sensitive monitoring

equipment has begun to reveal industrial contaminants in places usually considered among the cleanest in the world.

- Contaminants trapped by winds at the north pole, concentrate at high latitudes and eventually fall out as snow and ice and enter the food chain.


Long-Range Transport


Stratospheric Ozone

• Discovered in 1985 that stratospheric ozone levels were dropping rapidly during September and October. Occurring since at least 1960.

• At ground-level, ozone is a pollutant, but in the stratosphere it screens UV radiation. A 1% decrease in ozone results in a 2%

increase in UV rays reaching the earth.


Stratospheric Ozone

• Circumpolar vortex isolates Antarctic air and allows stratospheric temperatures to drop and create ice crystals at high altitudes. Absorb ozone and chlorine molecules.

- When sun returns in the spring, energy liberates the chlorine allowing the depletion process to proceed rapidly.

CFC’s believed to be main culprit. Persist for decades. Production eliminated in 1996.


CFC Production


EFFECTS OF AIR POLLUTION

• Human Health EPA estimates each year 50,000 people

die prematurely from illnesses related to air pollution.

- Likelihood of suffering ill health is related to intensity and duration of exposure.

Inhalation is the most common route, but absorption through the skin and consumption via food can also occur.


Human Health

• Bronchitis Persistent inflammation of airways in the

lung that causes mucus build-up and muscle spasms constricting airways.

- Can lead to emphysema - irreversible obstructive lung disease in which airways become permanently constricted and alveoli are damaged or destroyed.


Plant Pathology

• Chemical pollutants can directly damage plants, or can cause indirect damage by disrupting normal growth and development patterns. Certain environmental factors have

synergistic effects in which the injury caused by the combination is more than the sum of the individual exposures.

- Pollutant levels too low to cause visible effects may still be damaging.


Acid Deposition

• pH and Atmospheric Acidity pH scale ranges from 0-14.

- 7 = Neutral; <7 = Acidic; >7 = Basic Unpolluted rain generally has ph of 5.6.

- Carbonic acid from atmospheric CO2. In industrialized areas, anthropogenic

acids in the air often outweigh natural sources of acid.


Acid Deposition


Acid Deposition

• Aquatic Effects Thin, acidic soils and oligotrophic lakes of

southern Norway and Sweden have been severely affected by acid deposition.

- Generally, reproduction is the most sensitive stage in fish life cycles.

In early 1970’s, evidence began to accumulate suggesting air pollutants are acidifying many NA lakes.


Acid Deposition

• Forest Damage Air pollution and depositions of

atmospheric acids are believed to be important causes of forest destruction in many areas.

• Buildings and Monuments Limestone and marble are destroyed by air

pollution at an alarming rate. Corroding steel in reinforced concrete

weakens buildings, roads, and bridges.


AIR POLLUTION CONTROL

• Particulate Removal Remove particles physically by trapping

them in a porous mesh which allows air to pass through but holds back solids.

Electrostatic Precipitators - Fly ash particles pick up electrostatic charge as they pass between large electrodes in waste stream, and accumulate on collecting plate.


Sulfur Removal

• Fuel Switching Switch from soft coal with a high sulfur

content to low sulfur coal. Change to another fuel (natural gas).

• Limestone Injection Can reduce sulfur emissions by 90% by

mixing crushed limestone with coal before it is fed into a boiler.


Sulfur Removal

• Flue Gas Desulfurization Inject crushed limestone into stack gas

stream to remove sulfur after combustion.- Dry Alkali Injection

• Sulfur Recovery Process Use catalytic converters to oxidize or

reduce sulfur and create chemical compounds that can be collected and sold.


Air Pollution Control

• Nitrogen Oxide Control Best method is to prevent creation.

- Staged Burners- Selective Catalysts

• Hydrocarbon Control Use closed systems to prevent escape of

fugitive emissions.


CLEAN AIR LEGISLATION

• Clean Air Act (1963) - First national air pollution control.

• Clean Air Act (1970) rewrote original Act. Identified critical pollutants. Established ambient air quality standards.

- Primary Standards - Human health- Secondary Standards - Materials,

environment, aesthetic and comfort.


Clean Air Act

• Revision (1990) - Included provision for: Acid Rain Urban Smog Toxic Air Pollutants Ozone Protection Marketing Pollution Rights Volatile Organic Compounds Lead

• Revision (1997) - Stricter standards


CURRENT AND FUTURE CONDITIONS

• In the United States, air quality has improved dramatically in the last decade in terms of major large-volume pollutants. Cities where pollution is largely from traffic

still have serious air quality problems.• Major metropolitan areas of many developing

countries are growing at explosive rates, and environmental quality is very poor.


Summary:

• Natural Sources• Human-Caused Air Pollution

Conventional Pollutants Unconventional Pollutants Indoor Air Pollution

• Climate and Topography• Effects of Air Pollution• Air Pollution Control• Clean Air Legislation

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Air Pollution Chapter 18.

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Transcript of Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Air Pollution Chapter 18.