Stratospheric Ozone

Ozone Type: Tropospheric

Lower atmosphere (0-10 miles)

Ozone Type: Stratospheric

10-30 miles above Earth

Tropospheric Ozone Location

Lower atmosphere (0-10 miles)

Stratospheric Ozone Location

10-30 miles above Earth

Tropospheric Ozone Formation

Secondary pollutant from Nitrogen oxides and VOCs (Volatile Organic Compounds) plus sunlight

Stratospheric Ozone Formation

Natural reaction where Oxygen gas and UV light form Ozone

Tropospheric Ozone Effect

Harmful to humans, causes smog

Stratospheric Ozone Effect

Protective barrier against UV radiation

"Good Ozone"

Stratospheric ozone

"Bad Ozone"

Tropospheric ozone

Stratospheric Ozone Nature

Natural and beneficial, shields life from harmful UV rays

Tropospheric Ozone Nature

Anthropogenic (human-made) and harmful

Stratospheric Ozone's Role

Absorbs 97-99% of UV-B and UV-C radiation

Importance of UV Absorption

Protects DNA from mutation and skin cancer

Importance of UV Absorption

Prevents cataracts and immune suppression in humans

CFCs (Chlorofluorocarbons)

Synthetic compounds used in refrigerants, aerosols, and foam

CFC Destruction Process Step 1

CFCs drift upward into the stratosphere (long-lived gases)

CFC Destruction Process Step 2

UV light breaks CFC molecules and releases chlorine atoms

CFC Destruction Process Step 3

A single chlorine atom reacts with and destroys ozone in a catalytic cycle, then is freed to destroy more

CFC Result

Significant ozone thinning over the poles, especially the Antarctic ozone hole

Montreal Protocol Year

Signed in 1987

Montreal Protocol Key Provision

Phase-out schedule for CFCs, halons, and other Ozone-Depleting Substances (ODS)

Montreal Protocol Key Provision

Created a Multilateral Fund to help developing countries transition

Montreal Protocol Key Provision

Implemented trade restrictions preventing non-signatories from selling ODS

Montreal Protocol Success Rate

97% of ozone-depleting substances phased out globally

Ozone Layer Recovery Projection

Projected to recover to pre-1980 levels by 2050-2075

Benefit of Montreal Protocol

Prevented millions of cases of skin cancer, cataracts, and crop loss

Challenge to Protocol Success

Illegal emissions from some factories (e.g., CFC-11 in China)

Challenge to Protocol Success

Slow natural breakdown of CFCs means full recovery will take decades