our atmosphere: a chemical perspective lecture 1

AY 2010–2011, Semester I

Ms. Prabha Janardhana,

Instructor, Department of Chemistry

email : [email protected]

GEK1535Our Atmosphere:

A Chemical Perspective

Our Atmosphere: A Chemical Perspective

•The ‘Ozone Hole’

•Global Warming

•Air Pollution

•The Gaia Hypothesis

•How Life Began?

Course Highlights


To understand:

•The past, present and future chemistry of the atmosphere;

•The relationship between the biota and the composition of the atmosphere; and,

•The way scientists think — The Scientific Method

Aims and Objectives


1.A brief history of atmospheric science

2.The birth and evolution of our atmosphere

3.The physical structure of the atmosphere

4.Biogeochemical cycles

5.Elementary photochemistry and kinetics

Syllabus


6.Stratospheric ozone

7.Tropospheric air pollution

8.Greenhouse gases and global warming

9.The Gaia hypothesis

10.Eco-philosophy and environmental politics


Read not to contradict and confute, nor to believe and take for granted, nor to find talk and discourse, but to weigh and consider.

— Of Studies, Essays (1597)Francis Bacon, Baron Verulam

•All course texts have been placed in RBR collections at either the Central Library or Science Library

•The main course text, The Earth System by Lee Kump, James Kasting and Robert Crane, can be purchased from the Science Cooperative Bookstore

Reading Lists


In the words of the respected geneticist, J. B. S. Haldane:

Teaching Objectives

“It is the whole business of the university teacher to induce people to think.”

The philosopher, A. N. Whitehead, wrote:

“It should be the chief aim of the university professor to exhibit himself in his true character—that is as an ignorant man thinking.”


noun: A method of procedure that has characterised natural science since the 17th century, consisting in scientific observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.

— Oxford English Dictionary

The Scientific Method

Schematic Diagram of the Scientific Method

Source : Environmental Science,

Sixth EditionBotkin and KellerChapter 2, Page22


How does Beer Froth Decay with Time?

•Three years ago, a very interesting communication to the scientific literature was published:

Demonstration of the exponential decay law using beer froth, A. Leike, Eur. J. Phys., 23, 21–26, 2002.

•It addressed a question of such great concern that the author, Arnd Leike, won an Ig Nobel Award in that very same year


The Hypothesis

•The volume of beer froth decays exponentially with time

•A reasonable explanation for such a hypothesis might be that the rate at which froth disappears is proportional to the weight of froth

When half the froth has gone, the weight of froth left is halved and so the rate at which froth disappears at this stage will also be halved

•If we use a cylindrical beaker, then because

we can simply measure the height of the beer froth as a function of time and see if it decays exponentially


Testing the Hypothesis

areaheightvolume

thth t exp)( 0

•Thus, our mathematical model for the decay of the beer froth becomes:

where h is the height of the froth, t is the time and τ is the decay constant

•Early history of atmospheric chemistry

•What is the nature of ‘air’?

•Vegetable staticks

•Dr. Joseph Black (1728–1799)

•The problem of combustion

1. A Brief History of Atmospheric Science

•Henry Cavendish (1731–1810)

•The discovery of oxygen

•Joseph Priestley (1733–1804)

•Antoine-Laurent Lavoisier (1743–1794)


•Astrometeorology developed by the Babylonians and Chinese and still in use today

The superstitious linking of astronomical and astrological events to

predict the weather

•The four universal elements — fire, air, water, and earth — proposed by Empedocles (c.493–c.433 BC)

Taught that these elements mingle and separate under the influence of the opposing forces of Love and Strife

According to legend, he leapt into Mount Etna in order that he might be thought of a god

Early History of Atmospheric Science


•Meteorologica written by Aristotle (384–322 BC)First written attempt to explain weather phenomena based on

visual observations and speculation

Recognised water as a distinct component of air, and realised that this element was continuously recycled between the atmosphere and the ocean

Remained the basis of all meteorology until the scientific revolution some 2000 years later

A translation of the full text can be found at http://classics.mit.edu/Aristotle/meteorology.html


•After the Greek period, little progress was made until the Renaissance

•First, Leonardo da Vinci (1452–1519) and then later John Mayow (1641–1679) suggested that air is composed of two distinct components:

‘Fire-air’ that supports combustion and life; and,

‘Foul-air’ that does not

What is the Nature of ‘Air’?

The assumption remains, however, that ‘air’ is a single substance as envisaged by the early Greek thinkers


Vegetable Staticks

•In 1727, the Reverend Stephen Hales (1671–1769) published his Vegetable Staticks, a report on plant respiration and transpiration that laid the groundwork for photosynthesis

•Hales noted that in his experiments ‘air’ could be released from solids through the application of heat


Dr. Joseph Black (1728–1799)

•In searching for a method that would dissolve gallstones, Black discovered that a new ‘air’ was given off when magnesium carbonate was heated

•This ‘air’ turned lime water milky and did not support life

•Black gave it the name ‘fixed air’ — now known as carbon dioxide

It was now finally realised that air was not one substance, and the search was on to find more ‘airs’


•Combustion was completely misunderstood by the alchemists and early chemists

It was known that air was needed to sustain combustion and to sustain life

Also known that when a metal was heated in air it changed and gained weight

•Two Germans called Becher and Stahl developed the Phlogiston theory

It was suggested that during burning some part of the substance was given off and this substance was called phlogiston

If something gave off a lot of heat, it was thought to be rich in phlogiston

The Problem of Combustion


Henry Cavendish (1731–1810)

•Cavendish was the first to suggest that air is a complex mixture of different ‘airs’ and did himself discover a new ‘air’

•This ‘air’ burns explosively and is much less dense than air

•Cavendish gave it the name ‘inflammable air’ — now known as hydrogen

•It was thought that ‘inflammable air’ might be pure phlogiston


•Three so-called Pneumatic Chemists ‘independently’ discovered oxygen in the 1770s

The Discovery of Oxygen

Carl Wilhelm Scheelein 1773

Joseph Priestleyin 1774

Antoine-Laurent Lavoisierin 1779


•Perhaps foremost amongst the Pneumatic Chemists, Priestley was the great investigator of various ‘airs’

In his investigations of how the solubility of ‘fixed air’ varies with pressure, Priestley discovered Soda Water

•Heated Mercury Oxide and isolated the ‘air’ releasedNoted that it supported combustion and was totally consumed and

so called it ‘dephlogisticated air’

Priestley visited the Lavoisiers in Paris in 1774 and related his studies into this new type of ‘air’

Joseph Priestley (1733–1804)

Priestley never recognised what he had discovered and for all his useful and interesting experiments, he never produced a new system of chemistry


•Lavoisier understood the importance of the new ‘air’ and his studies led to a chemical revolution

Named the new ‘air’ oxygen

Stated that combustion is always and only to do with oxygen, which combines with other substances during combustion

In collaboration with Pierre-Simon de Laplace, showed that animal respiration was a slow form of combustion with the consumption of oxygen and the release of carbon dioxide

In noting that the weight gained by a substance in combustion is lost by the air, he established the Law of Conservation of Mass upon which all modern chemistry is founded

•Published the first modern chemistry textbook — Traité élémentaire de chimie

Antoine-Laurent Lavoisier (1743–1794)


It is thus that the birth of atmospheric science is linked inextricably to the emergence of chemistry as a distinct and rational science

•His theory of combustion explained the observation by Cavendish that water was released when hydrogen is burnt, i.e. that water is a molecule

•Introduced the word ‘gas’ to mean any chemical substance in the vaporous state, and thus reserved the word ‘air’ to mean only the atmosphere

•Rightly regarded as the Father of Modern Chemistry

our atmosphere: a chemical perspective lecture 1

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