Stationary Air Pollution

Stationary Air Pollution

Smog and Acid Rain

The London Smog Disaster of 1952

• The Great Smog, befell London starting on December 5, 1952, and lasted until 5 days.

• This catastrophe caused or advanced the death of 10,000 people and formed an important impetus to the modern environmental movement.

The London Smog Disaster of 1952

• The London Smog was enhanced by a temperature inversion.

• A temperature inversion is a condition in which the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude.

• An inversion, also called a "stable" air layer, acts like a lid, preventing air and pollution from the surface from rising and mixing with the upper air.

Stability of Air

• Whether or not a packet of air will rise depends upon how the temperature in the surrounding air changes with altitude.

• When a packet of air near the Earth’s surface is heated it rises, being lighter than the surrounding air. Think of a hot air balloon.

Unstable Air

• If the temperature of the surrounding air falls more quickly with increasing altitude, the packet of air will continue to rise.

• Hot air is less dense than cold air (at same pressure), and will therefore rise when encapsulated by cooler air.

• The atmosphere in this circumstance is said to be unstable.

Stable Air

• If the temperature of the surrounding air does not fall as quickly with increasing altitude, the air packet will quickly become colder than the surrounding air, lose its buoyancy, and sink back to its original position.

• In this case the atmosphere is said to be stable.

Temperature Inversion

• A temperature inversion is a condition in which the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude.

• An inversion, also called a "stable" air layer, acts like a lid, preventing air and pollution from the surface from rising and mixing with the upper air.

• The London Smog was enhanced by a temperature inversion.

Normal Conditions

• Instability - air pollution rises and mixes in the upper atmosphere

Temperature Inversion

• Stability cap or temperature inversion – pollution trapped at surface

Night Inversions• Clear, calm, cool nights are

perfect for creating inversions near the ground.

• The ground cools much quicker than the air, which cools the air near to the ground. But the air higher up is slower to cool.

• Inversion will last until morning sun heats up the ground.

Pressure Inversions

• When you see an "H" on a surface weather map, it shows the air pressure is higher than in surrounding areas. The high pressure is created by descending air.

• As air descends it is compressed and warmed, which can form some of the strongest inversions

• Since inversions keep air from rising and mixing with cleaner air above, subsidence inversions can cause long-lasting air-pollution episodes.

• This type of inversion occurred in London 1952

Components of Classic SmogParticulate Matter

• Solid or liquid particles with sizes from 0.005 – 100 μm

• General term is aerosols – Dust originates from grinding or crushing– Fumes are solid particles formed when

vapors condense– Smoke describes particles released in

combustion processes– Smog used to describe air pollution particles

Particulate Matter

• PM-2.5 (1997)< 2.5 μm diameter Similar sources, but tend

to be more toxicologically active particles

EPA estimates new standard will save 15,000 lives/yr

• PM-10 (1987)

< 10 μm diameterfuel combustion

(45%)industrial processing

(33%)Transportation

(22%)

Original standards did not account for size – larger particles that were not problematic dominated

Particulate Matter: Health Effects

PM-10 • aggravation of respiratory conditions, such as

asthma.

PM-2.5• increased hospital admissions and emergency

room visits for heart and lung disease• increased respiratory symptoms and disease• decreased lung function• premature death

Particulate Matter: Health Effects

Normal Lung Polluted Lung

Components of Classic SmogSulfur Compounds

• Sulfur dioxide (SO2) is released by burning sulfur-based fossil fuels (coal and oil) and other industrial activities

• Also comes from natural processes (volcanic eruptions, bacterial release of hydrogen sulfide (H2S), sea spray)

• Major component of Classic Smog and Acid Rain

Sulfur Dioxide: Health Effects

Effects of sulfur dioxide pollution on health. The figure shows ranges of concentrations and exposure times in which (a) the number of deaths reported was above expectation (light gray), (b) significant health effects have occurred (dark gray), and (c) health effects are suspected (middle gray).

Acids

• Acids are substances that, when dissolved in water, produce positively charged hydrogen ions (H+)

• Bases are substances that, when dissolved in water, produce negatively charged hydroxide ions (OH-)

• Acidity is measured using the pH scale (potenz hydrogen)

pH Scale

• The value of pure distilled water has a pH value of exactly 7.0

• Acids will have lower pH values

• Bases will have higher pH values

Acid Rain• Note that “clean” rain is naturally acidic

(pH of 5.6) due to carbon dioxide in the atmosphere dissolving in the water to create carbonic acid

H2O + CO2 —> H2CO3

• Other acids are created when pollution aerosols dissolve in water

• Important acids created due to man’s activities are sulfuric acid and nitric acid

Nitric and Sulfuric Acid• Nitric acid is created when nitric oxide

(NO) oxidizes, yielding nitrogen dioxide (NO2). The nitrogen dioxide then dissolves in water creating Nitric acid

2NO2 + H2O—> HNO3

• Sulfur dioxide (SO2) dissolves in water and reacts with oxygen to create sulfuric acid

SO2 + H2O + O2 —> H2SO4

Acid Deposition

Wet Deposition

• Wet deposition of acids occurs when any form of precipitation (rain, snow, etc) removes acids from the atmosphere and delivers it to the Earth's surface.

• This can result from the deposition of acids produced in the raindrops or by the precipitation removing the acids either in clouds or below clouds.

Dry Deposition• Acid deposition also occurs via dry

deposition in the absence of precipitation.

• This can be responsible for as much as 60% of total acid deposition.

• This occurs when particles and gases stick to the ground, plants or other surfaces. There particles react with water to form the acids directly on the surface.

• Much more damaging than wet deposition.

Acid Deposition in the U.S.

2/3 sulfuric1/3 nitric

Coal burningpower plants

Regional Acid Rain

• The northeastern United States has the worst acid rain problem– Midwestern industry located along the Great

Lakes– Prevailing winds blowing eastward

• The southwestern United States has an enhanced acidity due to Mexico

• pH values have improved overall in recent decades, especially in the northeast

• pH values have worsened slightly in the southwest

Acid Rain Consequences

• Fish affected at pH of 6 and less

• Building/Monuments affected at pH of 5 and less

• Trees/Plants affected at pH of 4 and less

Fish Populations

Fish from Normal Lake

Fish from Acidified Lake

Damage to Buildings/Monuments

• Building and Monuments made of limestone or marble are especially prone to decay due to acid rain

• Marble and Limestone are is made of calcium carbonate (CaCO3), and it weathers in sulfuric acid to produce gypsum, carbon dioxide gas, and water – CaCO3 + H2SO4 -> CaSO4 + H2O + CO2

• Repairing the damage caused by acid rain to buildings and monuments costs millions of dollars per year.

Cleopatra’s Needle stood for 3000 years in Egypt, but has experienced significant erosion in New

York over 100 years (symbols barely visible now)

Egypt New York

Forest Damage

• Fears that forests would die worldwide were prevalent in the 80s

• Further studies have shown that the trees in most regions are growing better, and studies have supported the fact that trees can see an increase in growth

• Areas where tree deaths have been observed are a result of smoke falling directly on the trees from the source

Forest Damage

Stationary Source Pollution Control Systems

• First Pollution Control systems

• Build tall smokestacks to release hot pollution into the upper atmosphere

• $$$$ and hard to maintain

Stationary Source Pollution Control Systems

• Particulate Matter

– Cyclone

– Fabric Filter (Baghouse)

– Electrostatic Precipitator

• Sulfur Dioxide

– Scrubber

Cyclone Collector

• Most Common and Cheapest

• “Dirty” Air Enters The Side.

• The Air Swirls Around The Cylinder And Velocity Is Reduced.

• Particulate Falls Out Of The Air To The Bottom Cone And Out.

Fabric Filter (Baghouse)

• Same Principle As Home Vacuum Cleaner

• Air Can Be Blown Through Or Pulled Through

• Bag Material Varies According To Exhaust Character

• Can Capture Smaller Particles Than A Cyclone

• More Complex, Cost More To Maintain Than Cyclones

Fabric Filter (Baghouse)

Baghouse contains

~15,000 bags

Electrostatic Precipitator

• High-Voltage Charges Wires

• Gases Are Ionized

• Particles Become Charged

• Collection Plates (Opposite Charge) Attract Particles

• Rapper Knocks Plates So That The Collected Dust Layer Falls Into Hoppers

Fly ash accumulation hoppers beneath electrostatic precipitators

Before-and-after sequence showing the effect of an electrostatic precipitator on stack gas emissions from a coal-fired power plant.

Scrubber• Sulfur oxides can be

controlled by the installation of scrubbers at coal-fired power plants.

• Scrubbers allow high-sulfur coals to be used because they remove sulfur dioxides out of the gas stream in the stacks (a process called desulfurization).

Scrubber

• Scrubbers work by spraying limestone slurry directly in the path of the materials leaving the boiler chamber.

• The limestone reacts with the sulfur in the gases within the stacks. The combination of carbonate (limestone) and sulfur forms the mineral gypsum.

• Gypsum (CaSO4)is a solid, which falls out of the gas to the bottom of the stacks, where it can be collected. The by-product gypsum created in this process can be used to make drywall

Pollution Control Systems

Removes Particulate Matter

Removes SO2

Effectiveness of Scubbers

1990 2004