Air Pollution - Chapter 10 Chemistry of the environment

Primary air pollutants

Primary air pollutants

emitted directly to the atmosphere

Secondary air pollutants

formed by atmospheric chemical processes \n - from primary air pollutants and water \n - from sunlight

\n Industrial smog

smog that is generally associated with coal burning

Smog

smoke + fog

smoke

comes from incomplete combustion of carbonaceous fuel; very fine particles

fog

high level of water droplets

soot

small particles of unburned coal known

requirements of photochemical smog

1. Air containing a mixture of gases \n 2. Sunlight \n 3. Temperatures above 65°F (18°C)

*4. An inversion layer along with calm or an inversion layer in a mountain valley

Peracetyl nitrate (PAN)

• produced when acetaldehyde reacts with oxygen and nitrogen dioxide in the presence of sunlight: \n CH3CHO + hv + NO2 + O2 → PAN

• causes tearing and burning in the eyes

• has damaging effects on plants and animals

• is more toxic to plants than any other photochemical pollutants

• is present in the lowest concentration of any of the major components of smog

acid rain

any rainwater with a pH of < 5

acid rain effects on lakes

• Underlying most lakes is some type of bedrock, most commonly either limestone or granite.

• Acid reacts with limestone to produce products that are not acids, so acid is removed by reaction with the limestone as soon as it enters the lake.

• For most lakes, a “normal” pH would be \n 6.5 - 7

acid rain effects on vegetation

• acid precipitation can wash away many necessary nutrients out of the soil

• Plants and trees can also take up toxins released by the soil

acid rain effects on human health

Acid precipitation itself has very little \n direct effect on human health

Clean Air Act

• separates air pollutants into two categories:

  • Criteria air pollutants

  • Hazardous air pollutants (HAPs, also known as air toxics)

Primary standards

pollution limits based on human health effects

Secondary standards

pollution limits based on environmental and property effects

three categories of air pollution reduction

1. Change the energy source

2. Change the process so the pollutant is not \n produced

3. Remove the pollutant before it enters the air

2C + O2 → 2CO

Incomplete combustion of coal:

carbon normally combines with two atoms of \n oxygen, but lack of oxygen causes one atom of carbon to combine with one atom of oxygen

N2 + O2 → 2NO

• Forcing air in to give more complete combustion causes the fuel to burn hotter and consume fuel faster

• At high temperatures nitrogen and oxygen react to form nitric oxide

dilemma of industrial smog

• At higher temperatures, more NO is produced and less CO.

• At lower temperatures, NO production is minimized, but CO production increases

2NO + O2 → 2NO2

NO pollutants produce secondary pollutants

3NO2 + H2O → 2HNO3 + NO

NO2 is more dangerous and toxic than NO and \n reacts with water in air to form nitric acid

S + O2 → SO2

Sulfur is an impurity in coal and burns when coal burns.

2SO2 + O2 → 2SO3

SO2 is poisonous and forms secondary pollutants.

SO3 + H2O → H2SO4

SO3 is toxic, corrosive, and reacts with water to form sulfuric acid.

gasoline

a mixture of low-boiling compounds, mostly hydrocarbons, obtained from petroleum.

main problem with photochemical smog

ozone is continuously produced

C6H14 + O or O3 → aldehydes

• Hydrocarbons in the air are subject to attack by very reactive chemical species produced in the air such as atomic oxygen or ozone to give aldehydes

• aldehydes produce oxidants