Science Man and His Environment/Air Quality

Atmospheric layers
The atmosphere is composed of layers as shown in the diagrams below:





A spectacular aspect of the ionosphere are the auroras





Atmospheric composition


The numbers in the diagram consider a dry atmosphere. Water vapor accounts for 0-4%.

Air Pollution

 * Primary air pollutants : pollutants emitted directly


 * Secondary air pollutants : pollutants created from reactions between primary air pollutants


 * Criteria air pollutants : 6 pollutants regulated by the US Environmental Protection Agency (USEPA)
 * carbon monoxide
 * particulate matter
 * sulfur dioxide
 * nitrogen dioxide
 * ozone
 * lead

Carbon Monoxide (CO)
Source: incomplete burning of organic materials


 * complete combustion:	CH4 + 2O2 &rarr; CO2 + 2H2O


 * incomplete combustion:	CH4 + 1.5O2 &rarr; CO + 2H2O

Effects: binds with hemoglobin to form carboxyhemoglobin. This carboxyhemoglobin cannot transfer oxygen to the cells.

Particulate matter (PM)
Small solid and liquid particles which remain suspended in the atmosphere.

Sizes are up to 10 micrometers in diameter.

Sources:


 * dust from construction, agriculture, and roads
 * forest fires
 * burning of solid and liquids -- especially from coal, wood, and diesel fuel
 * clearing of land for agriculture

Effects:


 * The small particles can get trapped in the lining of the lung causing irritation, inflammation, or cancer


 * Inflammation


 * Silicosis (silica dust)


 * Black Lung disease (coal dust)


 * Cancer


 * Asbestos


 * Polynuclear aromatic hydrocarbons (PAH))

Sulfur Dioxide
Source:


 * burning of sulfur-containing compounds including coal and oil


 * S + O2 &rarr; SO2


 * smelting of metal ores


 * Cu2S + O2 &rarr; 2Cu + SO2 (metal ore)

Health Effects:


 * Absorbed by moist respiratory tissue causing restriction of airway


 * - especialy severe in people with asthma

Environment Effect:


 * Acid deposition

Nitrogen Dioxide
One of the nitrogen oxides (NOx).

Source:


 * high temperature combustion


 * low temperature combustion: CH4 + O2 + N2 &rarr; CO2 + H2O +  N2


 * high temperature combustion: CH4 + O2 + N2 &rarr; CO2 + H2O + NO2

Health Effects:


 * lung irritation


 * increases susceptibility to lung disease

Environment Effects:


 * smog


 * acid deposition

Ozone
Note: In this section we are talking about ozone generated in the troposphere, not the stratospheric ozone layer

Source:


 * secondary pollutant from photochemical smog

Health Effects:


 * lung problems


 * eye irritation

Environment Effects:


 * damage to plants and trees

Lead
Sources:


 * paint
 * smelters
 * batteries
 * leaded gasoline

Effects:
 * memory loss
 * learning difficulties
 * nervous system damage
 * damage to bones and kidneys
 * accumulative poison

Mercury
Sources:


 * burning of coal
 * small-scale gold mining

Effects:


 * mental effects ("mad-hatter's" disease)
 * kidney disease

Radon
Source:


 * Naturally radioactive gas. A decay product of radium (which is a decay product of uranium). Uranium and radium can be found naturally in some rocks especially granite. Radon can then enter houses built on such rocks.

Effects:


 * lung cancer (due to alpha radiation)

Volatile Organic Compounds (VOC's)
Definition:


 * Organic compounds which rapidly evaporate.

Examples:


 * benzene
 * acetone
 * solvents
 * formaladehyde (from building materials)

Effects:

varies widely depending on substance


 * eye, nose, and throat irritation
 * dizziness and headaches
 * damage to liver, kidney, and nervous system
 * actual toxicity varies widely

Photochemical Smog
This is created when sunlight hits nitrogen dioxide it reacts to form nitric oxide (NO) and atomic oxygen. The oxygen then reacts very quickly with molecular oxygen to form ozone. Ozone can then react with nitric oxide to regenerate nitrogen dioxide.

NO2 + h&nu; &rarr; NO + O

O + O2 &rarr; O3

O3 + NO &rarr; NO2 + O2

The ozone created by this mechanism can react with organic molecules to create free radicals. These free radicals then react to form peroxyacyl nitrates (PAN), aldehydes, VOC's and other organics. This results in a toxic soup of hundreds of different chemicals.

Thermal inversions
Under certain conditions a layer of warm air can occur above cold air. This causes any pollutants to be trapped and not dispersed.





Acid Deposition
Sulfur dioxide in the atmosphere gets oxidized to sulfur trioxide. Sulfur trioxide then combines with water to form sulfuric acid. Some sulfuric acid will also adhere to particles in the form of sulfates.

2SO2 + O2 &rarr; 2SO3

SO3 + H2O &rarr; H2SO4

The fallout of either is called acid deposition or, commonly, acid rain.

Effects:
 * Destruction of concrete and stone structures




 * Acidification of forests, rivers, and lakes


 * Some lakes have natural buffering, but many do not. Acidified water causes death of fish and other organisms. This can eventually lead to dead lakes.



Ozone Depletion
The stratosphere contains a layer of ozone. This ozone protects the Earth from dangerous ultraviolet radiation. If it wasn't for this layer life could not exist -- too much radiation would reach the surface.

O3 + h&nu; &rarr; O2 + O &rarr; O3

Chlorinated and brominated hydrocarbons can travel unreacted up to the stratosphere. The most important of these are the chlorofluorocarbons (CFC's).

CCl3F + h&nu; &rarr; CCl2F + Cl

This free chlorine then reacts with the ozone.

Cl + O3 &rarr; ClO + O2

ClO + O &rarr; Cl + O2

net O3 + O &rarr; O2 + O2

This depletes the amount of ozone present.

Montreal Protocol


In the 1980's, it was found the ozone layer was thinning. In 1987 a treaty called the Montreal Protocol was signed.

It bans the use of chlorofluorocarbons (CFCs). This has stabilized the ozone layer.