Class Notes (1,100,000)
CA (630,000)
UOttawa (30,000)
ENV (80)
Lecture

Class 10 - Air Pollution & Global Climate Change.docx


Department
Environmental Studies
Course Code
ENV 1101
Professor
Sonia Wesche

This preview shows pages 1-2. to view the full 8 pages of the document.
Air Pollution & Global Climate Change
Mount Everest
Is the highest elevation on Earth (8.85km above sea level)
Name in Tibetan is Chomolungma, in Nepalese Sagarmantha
Conditions of Summit
Wind blows at about 250km/h for much of the year die to the jet stream
There is only 1/3 the concentration of oxygen per unit air at sea level
The temperature is virtually always well below freezing, can go to -75C
Everest Climbs
First successful climb to summit and return: 1953, Hillary and Norgay
First female to summit: 1975, Tabei
First clime without oxygen: 1978, Habeler and Messner
Most summits: 10, Ang Rita Sherpa (all without oxygen)
Composition of the Atmosphere
Nitrogen: 78.08%
Oxygen: 20.95%
Troposphere
Where we live (and everything else on Earth)
Precipitation cycle occurs here
Temperature gets colder the higher you go (dry air cools at ~loC/100m; moist air
at a typically lower rate
Lots of mixing of the air
Means that airborne pollution can make its way up to the tropopause fairly
quickly
Stratosphere
15-50km above the surface
Air is thin, does not move around much
Contains ozone (O3) which absorbs some radiation, causing the stratosphere to
warm
Higher up are the mesosphere, thermosphere and transition to outer space
Energy Balance
Energy passing through the atmosphere drives ecological systems
The amount of energy arriving at the Earth from solar radiation is balanced by a
similar amount of radiation leaving the Earth’s atmosphere
Human Modification of the Stratosphere

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Global Environmental Challenge: Protecting the Ozone Layer
Why is the ozone layer important?
The ozone layer screen out incoming solar radiation in the ultra-violet ranger (10-
400nm)
(A nanometre = one-billionth of a metre)
Ultra-Violet Radiation
A little UV is good for you, stimulates vitamin D production
Too much UV damages the DNA and proteins contained in living tissues
If all UV radiation reaches the Earth’s surface, few organisms would survive
>99% of UV radiation fails to penetrate the stratosphere
Stratosphere Processes
When oxygen molecules (O2) encounter UV radiation, they tend to split apart into
two O atoms
Some free O atoms tend to quickly recombine with other O molecules to form
ozone O3
Ozone molecules may also combine with free oxygen atoms, creating two new O2
molecules
When an ozone molecule encounters UV radiation, it splits into O2 and O
Stratospheric Processes
In other words…
Dynamic interactions between oxygen and UV radiation are continually occurring
in the stratosphere
O2 + UVB O + O
O + O2 O3
O + O3 O2 + O2
O3 + UVB O + O2
Stratospheric Ozone
Continually forming and being destroyed
This dynamic process consumes most of the UV radiation that enters the
stratosphere
Concentrations of ozone are highest at equator, where incoming radiation is
highest
Concentrations vary seasonally as well; over Canada concentration is lowest
during winter, highest during summer
Human Interference with Stratospheric Ozone
You're Reading a Preview

Unlock to view full version

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

In 20th century, chemists invented choloroflurorocarbons (CFCs)
These are non-natural combinations of Chlorine (Cl), fluorine (F) and carbon (C)
These chemicals had numerous useful applications
Refrigeration, air conditioning, plastic foam, aerosol cans, cleaning computer
parts
In 1970’s it was discovered that when CFCs make their way into the stratosphere
they react with UV radiation
The UV causes the CFC atom to realease chlorine, which in turn attacks ozone
CFCl3 + UV Cl + CFCl2
Cl + O3 ClO + O2
ClO + ClO 2 Cl + O2
Chlorine (Cl) ordinarily does not leave the troposphere
CFCs transport it to the stratosphere
Because Cl lasts for decades in the stratosphere, a single Cl atom can break down
100,000 ozone molecules
In 1985, a “hole” in the ozone layer was observed over the southern hemisphere
Panic Ensues
Why hadn’t scientists noticed the ozone hole sooner?
Ozone depletion is a non-linear phenomenon
Incorrect Assumption by Scientists
1970s scientists assumed that ozone depletion would be a gradual process, and
occur uniformly across the stratosphere (ex. Linear change)
Observational systems were calibrated to reject data showing drops of ozone
concentration greater than 30%
The actual decrease over Antarctica was >50% by the time the error was realized
Montreal Protocol
You're Reading a Preview

Unlock to view full version