Chapter 20

AIR POLLUTION

THE ATMOSPHERE

We live in a thin layer of gases that surround the Earth called the atmosphere.

The atmosphere is divided into sub layers that have changes in temperature that result in absorbing solar energy.

As gravity pulls molecules closer to the surface, the density of gases increases. If we were to climb Mt. Everest we would need oxygen masks as there is limited oxygen near the top.

LAYERS OF THE ATMOSPHERE

The troposphere is closest to the Earth’s surface.

It’s components are mainly nitrogen (78%) and oxygen (21%).

The other 1% is water vapour, argon, carbon dioxide, and traces of other gases.

This is where all the geochemical cycles that we studied occur and the air currents that are found here are responsible for the weather patterns and the climate found on Earth.

LAYERS OF THE ATMOSPHERE

The stratosphere, which is above the troposphere, has less matter but is similar in composition

There are only two changes:

1/ 1,000th of the water vapour

Ozone (O3)concentration is much higher!

Ozone is produced when the oxygen molecules interact with the UV radiation.

3 O2 + UV radiation 2 O3

THE ROLE OF THE OZONE

Ozone is considered the ‘global sunscreen’

It filters almost 95% of the sun’s harmful UV radiation

This protects us from sunburn, skin and eye cancer, cataracts, and damage to our immune system!

By interacting with UV in the stratosphere, the oxygen in the troposphere is less likely to be converted to photochemical smog on the surface – a harmful air pollutant!

WHAT ARE THE POLLUTANTS?

Primary pollutants are released directly into the troposphere

CO, CO2, NO, NO2, SO2, hydrocarbons, and suspended particles (dust, debris, soot) They come from mobile sources, stationary sources,

and natural sources.

Secondary pollutants are byproducts of the primary products reacting with one another and producing new compounds

HNO3, SO3, H3SO4, H2O2

HOW MUCH POLLUTION IS THERE?

The World Health Organization says that 1/6 people on this planet, or 1.1 billion people, live in urban areas where the outdoor air quality is unhealthy to breathe!

In Canada, we have government mandated standards that set maximum allowable concentrations of conventional air pollutants found outside.

This regulation has helped reduce the levels in most developed areas.

CLASSIFYING CO2 AS AN AIR POLLUTANT

Many regulatory agencies feel that CO2 should not be considered an air pollutant.

However, many scientists do because

Any chemical in the air in a great quantity can be a pollutant

We have been increasing the concentrations by burning fossil fuels and deforestation

Global warming is occurring and there is significant evidence to state that CO2 (a greenhouse gas) by human activities has played a huge role!

WHY WORRY ABOUT THE EARTH WARMING?

The Earth is warm due to the greenhouse effect.

Gases in the atmosphere helped trap in heat to keep us warm. If they didn’t we would freeze to death!

However, increasing the concentrations of these gases has led to an increase in temperature

With an increase in temperature we alter how much precipitation occurs, where food can grow, floods around the world.

Therefore, people, economies, and ecosystems, may be harmed greatly which makes CO2 an important air pollutant to be monitored

PHOTOCHEMICAL SMOG

Any photochemical reaction is a chemical reaction that is activated by light.

Photochemical smog is an air pollutant that forms when nitrogen oxides (NO or NO2 – Nox) and volatile organic compounds (VOCs) react chemically under UV radiation to produce a mixture of 100 primary and secondary pollutants!

Essentially:

VOCs + Nox + heat + sunlight ground level ozone

+ other oxidants

+ aldehydes

+ secondary air pollutants

PRODUCTION OF SMOG

It begins in automobiles and coal-burning power and industrial plants.

Nitrogen + oxygen react to produce 2 molecules of NO.

The NO in the atmosphere can be converted to NO2 and will be a brownish color. This is why in come large cities the overcast is sometimes a brown color – known as brown-air smog.

In the air the NO2 reacts with hydrocarbons in the atmosphere to produce ozone, nitric acid, aldehydes, and other secondary pollutants.

EFFECTS OF SMOG

Smog can cause or aggravate health problems such as asthma, emphysema, chronic bronchitis and other respiratory problems as well as eye irritation and reduced resistance to colds and lung infections.

The ozone in smog also inhibits plant growth and can cause widespread damage to crops and forests.

SMOG ELSEWHERE!?

The grasshopper effect is created when air currents move the pollution from one air on Earth to another.

Essentially, in warm temperate areas near the equator the volatile compounds will rise and travel with air currents to the poles where it can settle in the oceans or on land

In polar regions, many polar bears, whales, sharks, and other carnivores (as well as Native peoples) have had high levels of DDT and other toxic substances accumulating in their systems even though there are no industrial facilities in the area.

AIR POLLUTION FROM ACID DEPOSITION

Sulphur dioxide, nitrogen oxides, and particulates can react in the atmosphere with water to form acidic compounds that can travel long distances before coming back to the surface.

Acid precipitation

Coal burning power plants, ore smelters, and other industrial plants use tall smokestacks to reduce the amount of local air pollution.

However, this generates an SEP – somebody else’s problem!

They can travel up to 1000km by winds and then react in the atmosphere to form these harmful acids.

OCCURS IN TWO FORMS

Wet deposition is acidic rain, snow, fog, and cloud vapour with pH less than 5.6

Dry deposition is the particles in the air that can settle – dust, debris, etc. that has been turned acidic in a chemical reaction.

This is called acid deposition when they land on a given area.

AREAS AROUND THE WORLD

Eastern Canada and U.S. are downwind of major coal-burning and industrial cities (Hamilton, ON and Ohio Valley)

We commonly have smog alerts as well as precipitation that can range from a pH of 4.4-4.8.

About 10 times higher than regular precipitation!

Some mountain tops in the eastern US have fog and dew on the plants that is acidic as lemon juice (pH 2.3) – 1000 TIMES STRONGER THAN REGULAR PRECIPITATION!

REGIONS WHERE ACID DEPOSITION IS A MAJOR PROBLEM

EFFECTS OF ACID DEPOSITION

Respiratory diseases – bronchitis and asthma

Corrosive to metal pipes that can leach heavy metals in the water systems

Damages statues and monuments

Limestone is ruined – eaten away!

Decreases atmospheric visibility

Fish kills

Aluminum ions are leached into water and cause mucus to form in gills and cause asphyxiation

Lakes lose many fish from water runoff

In Canada, 7000 lakes in the Canadian Shield have been acidified!

EFFECTS ON PLANT AND SOILS

Reduces plant productivity over time

Soils lose the capacity to buffer acids

Calcium deficient plants (from acid leaching calcium from soil) pass on to herbivores – eggs, weaker bones, weaker exoskeletons

Weakens trees and makes susceptible to disease.

PREVENTION AND CLEAN UP

ASSIGNMENT FOR AIR POLLUTION

Do questions on Page 487 – 2, 3, & 6

Describe photochemical smog and how it is formed.

List five factors that can reduce air pollution and five that worsen it.

On page 488, generate a one paragraph response to the critical thinking questions: 1, 3, 4, & 6

Please hand in these questions by the end of class or tomorrow… along with any other worksheets and assignments that you have not already handed in!!