Environmental science Unit 2

Atmosphere

The layer of gases that envelops our planet

What does the atmosphere do?

• Moderates our climate

• Provides oxygen

• Shields us from meteors and hazardous solar radiation

• Transports and recycles water and nutrients

Atmospheric composition of gases

• Nitrogen

• Oxygen

• Trace gases

• Water vapor

Why is nitrogen important for the atmosphere?

It provides us with proteins

Why is oxygen important?

It helps us breathe

What is air pollution?

Any gas or particulate matter that can affect climate or harm people or other organisms

Air pollution primary causes

• Anthropogenic

• Natural

Human exposure to pollutants

90% of the global population are exposed to unsafe air pollution

NAAQS

National Ambient Air Quality Standards

What does NAAQS do?

It monitors pollutants in countries

Long-term exposure to air pollutants

Has been linked to:

• Cancer

• Immune damage

• Neurological

• Reproductive

• Respiratory

• Death

Improving air quality

Translates to better health outcomes (asthma in children decreased over decades)

Types of atmospheric pollution

• Primary

• Secondary

Primary pollutants

Compounds emitted directly into the air

Examples of primary pollutants

• Sulfur dioxide

• Nitrogen dioxide

• Suspended particulate matter

• Lead

• Carbon monoxide

Point source (Stationary)

• Industrial smokestack

• Coal burning power plant

Secondary pollutant (Created in the atmosphere)

Ozone (O3)

Non-point source (Mobile)

Motor vehicles

Clean Air Act (1970)

Requires Environmental Protection Agency (EPA) to set NAAQS for pollutants considered harmful to public health and the environment

Primary standards

Sets limits on pollutants in order to protect public health especially children and elderly

Secondary standards

Limits to protect public welfare; protection against decreased visibility and damage crops and vegetation

Nitrogen Oxide (NOx)

Group of gases that contain Nitrogen and oxygen in varying amounts

How is Nitrogen Oxide made?

When fuel is burned at a high temperature (vehicles and power plants)

How is Sulfur Oxide made

When fuel containing sulfur is burned (coal and oil), dissolves in water to form an acid (power plants)

How is lead made?

Used to be from vehicles but now that gasoline is unleaded, it comes from metal manufacturing.

How is lead particulate matter made?

Small particles and liquid droplets (Ash, soil, or dust)

How does particulate matter move through the body?

10 microns or smaller can enter the lungs and blood stream which can lead to decreased lung function and increased risk of heart attack and stroke.

How is Carbon Monoxide formed?

When carbon in fuel is incompletely burned; from vehicle emission, forest fires, and combustion of fuel in homes

Why is carbon monoxide dangerous?

It is colorless and odorless

How is Ozone formed?

NOx and VOC react in the atmosphere in the presence radiation of the sun

Stratospheric Ozone

Critical to life on Earth because it screens our harmful radiation from the sun

Tropospheric Ozone

A pollutant with significant consequences for human health

Major sources of chemicals

• Vehicles

• Industrial emissions

• Gasoline vapors

• Chemical solvents

Primary components of smog

Tropospheric ozone

Smog

Made of ground-level ozone, other gases, and particulate matter

Air Quality Index (AQi)

EPA monitors and records concentration of the major pollutants at more than a thousand locations across the country

Air Quality Index above 100

Unhealthy for sensitive groups and as it rises, more groups will be impacted

Why is the Air Quality Index good for citizens

It is an acessable way for the general public to understand air quality

Results of Clean Air Act (1990)

• Averted 230,000 premature deaths a year

• Prevented 17million lost work days

Lead as a gasoline additive in the U.S

Banned in 1996

Scrubbers

Air pollution control device in a coal power plant that use a chemical reaction to reduce SO2 by 90%

Air Quality Trends

• Enforcement actins

• Tougher state laws

Global Air Quality

Other countries are far less optimistic than in the U.S

90% of the global populatio

Live in areas where air quality indices far exceed healthy limits

Most harmful chemical

Particulate matter

Factors that contribute to poor air quality

• Fossil fuels

• Private motor vehicles in crowded cities

• Biomass for cooking and heating

Dirty air

• Kills 7 million people each year

• Drain global economy $5 trillion annually

Worlds largest environmental health threat

Air pollution

Acid rain

Received most press in the 80’s and 90’s and generated a lot of controversy

Climate change took over the acid rain controversy

Along with biodiversity loss and other environmental concerns

Acid rain composition

Transformation of SO2 and NOx into secondary pollutants such as sulfuric acid and nitric acid

Wet acid rain deposition

Acid rain, fog, and snow

Dry acid rain deposition

SO2 and NOx particles are deposited onto surfaces, driven by gravity and wind

Ultraviolet radiation

Destructive to genetic cellular material in all organisms; biologically harmful to plants, animals, and human

Ozone does not have an actual layer

It is a gas that is dispersed over 20km of altitude

Greatest Ozone concern

Antarctic ozone hole that thins out each spring (august, september, october)

Arctic Ozone depletion

Not as significant as Antarctic ozone hole

Thinning of Stratospheric ozone

Caused by humans, even in Antarctica

Where is the Stratospheric Ozone formed

Formed naturally in stratosphere of the tropics

The Tropics

Receives ample extreme UV radiation from the sun which is essential for ozone production

Splitting Ozone process

O2 is split into 2 O molecules by incoming UV radiation

Combination Ozone process

Single O molecules with O2 to form O3

Step 3 of Ozone process

O3 absorbs UV radiation, which breaks down into O2 and O

How are Ozone levels measured?

Dobson Units (DU)

Dobson Units

Named after pioneering scientists in atmospheric Ozone research

Less total Ozone

Means more UV light penetration, leading to quicker sunburns and greater potential to mutate DNA

300 Dobson Units (2 stacked pennies)

Enough thickness to protect us from UV radiation

100 Dobson Units (1 dime)

Not enough Ozone to protect us

What is the thickness of the Ozone layer in Antarctica?

100 Dobson Units

Ozone is a selective gas

Only absorbs and emits radiation only at specific wavelengths

What does Ozone absorb?

• UV-C (The most hazardous)

• UV-B (Only absorbs some)

Increased exposure to UV-B

Raises the risk of skin cancer, cataracts, and a weakened immune system

Excessive UV-B exposure

Harms plants, single celled organisms, and aquatic ecosystems

UV-A radiation

Can lead to premature skin aging

Broad spectrum protection sunscreen

Shields against both UV-A and UV-B

SPF minimum

30

Dobson units in the 1960’s

300-320

Dobson units in the 1990’s

100 </=

Initial step in ozone depletion

Ozone depleting gases are released; chlorine and bromine

Chlorofluorocarbons (CFC)

• Non-toxic alternative to dangerous substances for use in spray can propellants and refrigeration

• Does not break a part and can drift 10-15 miles above Earth into the Stratosphere

CFC’s in Stratosphere

UV radiation breaks apart the original CFC molecule, leading to Ozone destruction

Reservoir gases

Transported. by wind currents to North or South poles

Polar darkness in Antarctica

Hardly any daylight hours and temperatures plummet to extremely low levels

Polar vortex

-108F (-78C) threshold, polar Stratospheric clouds form

Polar Stratospheric Clouds

Reservoir gases mix and will eventually destroy the Ozone layer

Molecular Chlorine (CL2)

Does not destroy the Ozone

What is Molecular Chlorine?

When polar stratospheric clouds form, CL2 from reservoir gases builds up in the stratosphere

What destroys the Ozone

Free Chlorine

Free Chlorine

Only available when sunlight is present to break down Cl2

When sunlight returns to the polar region, onset of spring

Cl2 is rapidly split by the sunlight into free chlorine atoms that quickly attack and destroy Ozone molecules

Ozone minimum (Ozone at its thinnest)

Occurs towards the end of september/october when the sun is fully above the horizon even at the south pole

Artic temperatures

Much higher than in Antarctica

Winter temperatures in Antarctica

Low enough for PSC’s to form for the entire winter (5 months)

The Arctic

PSC conditions only exist for limited periods (10-60 days), but they don’t reach necessary temperatures to form PSC

No PSC =

More stratospheric ozone

A single chlorine atom

Can destroy tens of thousands of ozone molecules

Chlorine

Is a catalyst for ozone destruction

Catalyst

Promotes significant change

What does chlorine do?

Speeds up the chemical reactions without getting broken down in the process

When does the ozone hole expand

Throughout Antarctic spring until temperatures rise and polar vortex weakens