What is an atom?
proton
electron
neutron
The kind of atom is determined by the number of
protons and neutrons.
Nomenclature:
symbol protons
H
1
He
2
N
7
C
6
O
8
neutrons
0
2
7
6
8
name
hydrogen
helium
nitrogen
carbon
oxygen
Periodic table of elements
Atomic number = # of protons
1
What is a molecule?
Two or more atoms that are bound together forming
one unit.
Nomenclature:
hydrogen oxygen
H
H2O
water
H
O
number of H atoms
in molecule
Other Examples
O
O
O
O
O
C
Oxygen molecule: O2
O
Ozone molecule: O3
O
Carbon dioxide molecule: CO2
2
Chemical Reactions
O3 + NO → NO2 + O2
we say:
O3 (ozone) reacts with NO
(nitric oxide) to form NO2
(nitrogen dioxide) and O2
(oxygen)
What happens: (not every collision leads to a reaction)
O
O
N
O
O
O
N
O
O
O
Nomenclature of Chemical Reactions
direction of reaction
O3 + NO → NO2 + O2
reactants
products
4 O atoms + 1 N atom = 4 O atoms and 1 N atom
Rules:
• the number of specific atoms, for example O, N,
etc. are always the same on both sides.
• in air reaction only occur with 2 reactants
• whether a reaction occurs depends on many
things, that we will not discuss in this class
3
1m
Concentration
C=
Amount of substance
Volume
1m
Volume = 1m × 1m × 1m = 1m 3
1m
20 balls
balls
=
20
1m 3
m3
Gas: molecules in Volume
⇒ unit: molec.
cm 3
C=
20 Tennis Balls
in the cube
Mixing Ratio (M.R.)
1m
M.R. =
Amount of one substance
Amount of all substances
1m
1m
M.R. =
2 red balls
= 0.1
20 balls
no unit
20 tennis balls
in the cube
2 of those red balls
4
Mixing Ratios
name
symbol ratio
One percent
1%
10-2 one out of each 100
One part per million 1ppm 10-6 one out of each million
One part per billion 1ppb
10-9 one out of each billion
One part per trillion 1ppt
10-12 one out of each trillion
Mass
Volume / Number
M.R. =
Amount of one substance
Amount of all substances
M.R. =
Mass of one substance
Mass of all substances
ppmv
ppbv
ppmm
ppbm
1m
expand
1m
10 cm
10
cm
10 cm
Concentration vs. Mixing Ratio
1m
C=
20 balls
balls
= 20000 3
3
0.001m
m
2 red balls / 0.001m3
= 0.1
M.R. =
20 balls / 0.001m 3
C=
20 balls
balls
= 20 3
3
1m
m
M.R. =
2 red balls / 1m 3
= 0.1
20 balls / 1m 3
Concentration changes, M.R. not!
5
How can we quantify the amount of a
pollutant that comes out of a smoke stack?
How do we quantify the amount of pollutant
a person breaths in?
Question
One car emits 1012 molecules of carbon
monoxide (CO) in 1 hour, another car
emits 1012 molecules CO in 30 minutes.
Which car is the worse polluter?
A third car emits 1013 molecules per day.
Is it better or worse than the other
two?
6
Some of the more abundant “variable”
trace gases:
Species
Mixing ratio
Water vapor (H2O)
4% (tropics) - 0.00001% (South
Pole)
Carbon dioxide (CO2)
380 ppmv (increasing ~0.4%
per year due to fossil fuel
burning)
Methane (CH4)
2 ppmv
Hydrogen (H2)
0.6 ppmv
Ozone (O3)
0.4 ppmv
Nitrous oxide (N2O)
0.3 ppmv
Carbon monixide (CO)
0.09 ppmv (90 ppbv)
Fluorocarbon-12 (CF2C12)
0.0005 ppbv (0.5 pptv)
CO
CO2(g)2 mixing ratio (ppmv)
Carbon Dioxide Mixing
Ratio
380
370
360
350
340
330
320
310
1960
1970
1980
Year
1990
2000
Figure 3.11
7
Main sources of methane (CH4)
Termites
Biomass burning
Rice Paddies
Wetlands
Ruminants
Natural Gas Leakage
CH
CH4 4(g) mixing ratio (ppmv)
Change in CH4(g) Mixing Ratio
2
1.8
1.6
1.4
1.2
1
0.8
0.6
1840
1880
1920
Year
1960
2000
Figure 12.7
8
Ozone (O3) non-attainment areas
Federal 8-hour ozone standard: 0.08 ppmv averaged over 8 hours
(recently changed to 0.075 ppmv)
Chloroflourocarbons (CFCs)
Refrigeration
Propellant
Trends in atmospheric CFC concentrations
9
Thomas Midgley (1889-1944)
Edgar Fahs Smith Collection, U. Penn. Library
Invented leaded gasoline and CFCs
Thomas Midgley
•
•
•
•
•
1916: Joined Dayton Eng. Laboratory Companies (DELCO)
1919: DELCO main research lab for General Motors (GM)
1921: Invented leaded gasoline, which he named Ethyl
Lead reduced knock, increased power to vehicles
1923: VP of Ethyl Gas. Co., a GM and Standard Oil subsidiary
1923: Midgley suffered lead poisoning, but he defended lead:
"The exhaust does not contain enough lead to worry about, but
no one knows what legislation might come into existence
fostered by competition and fanatical health cranks.”
10
Thomas Midgley
•
•
•
1923-5: 17 workers died, 149 injured due to lead poisoning
1924: 5 of the workers became suddenly insane from poisoning
1925: Despite working on ethanol/benzene blends, iron carbonyl alternatives,
Midgley countered,
"...tetraethyl lead is the only material available which can bring about these
(antiknock) results, which are of vital importance to the continued economic use by
the general public of all automotive equipment, and unless a grave and inescapable
hazard exists in the manufacture of tetraethyl lead, its abandonment cannot be
justified"
•
•
•
1924: Forced to step down as VP due to managerial problems
1924: Returned to research on synthetic rubber in Dayton for GM
1925: U.S. Surgeon General organized committee to investigate lead
Observed drivers/garage workers did not experience poisoning
--> “no grounds for prohibiting the use of Ethyl gasoline.”
though cautioned that further studies should be carried out (they weren’t)
Leaded Gasoline
•
•
1930s: 90 percent of vehicles leaded
1936: Federal Trade Commission issued a restraining order forbidding commercial
criticism of tetraethyl lead:
"...entirely safe to the health of (motorists) and to the public in general when used
as a motor fuel, and is not a narcotic in its effect, a poisonous dope, or dangerous to
the life or health of a customer, purchaser, user or the general public."
•
1959: U.S. Public Health Service
"...regrettable that the investigations recommended by the Surgeon General's
Committee in 1926 were not carried out by the Public Health Service."
•
•
•
•
1975: Catalytic converter invented; lead deactivates catalyst
1976: Lead regulated as criteria air pollutant in the U.S.
Between 1970 and 1997, total lead emissions in the U.S. decreased from 219,000
to 4,000 tons per year.
Today, largest sources of lead in the U.S. are from lead-ore crushing, lead-ore
smelting, and battery manufacturing.
11
How did it start?
Big Bang
Rotating disk of
collisions
dust grains and gases
accretes into meter sized
“planetesimals” around sun
15 billion
years ago
Planets form
Our Solar System
4.5 billion years ago
12
1. Prebiotic atmosphere – 1st Stage
H, He
4.5 billion years ago
Atmosphere initially contains
light gases, such as
Hydrogen (H) and Helium
(He), that can
escape the atmosphere due
to the solar wind and
gravitational escape.
Earth looses its primordial atmosphere.
1. Prebiotic atmosphere – 2nd Stage
After a few hundred million years
Densest elements
(iron, nickel) form the
core.
Atmosphere formed
by outgassing of the
interior (volcanoes)
as well as
bombardment by
planetoids and
meteorites.
13
1. Prebiotic atmosphere – 2nd Stage
4.5 billion years ago
Earth cools down…
• Condensation of H2O → rain → oceans form
• CO2 forms carbonates in the ocean
→ sedimentary rocks
• N2 left as most abundant
component in the atmosphere
H2 O
CO2
N2
No Oxygen!
2. Biotic atmosphere before O2
Life develops
3.5 billion yrs ago
• No oxygen → no ozone layer → life not possible
on surface
• Life can only develop in the ocean
water protects from sun’s ultraviolet radiation
• Early microbes did not
require oxygen (anaerobic)
14
One theory on how life began…
H2O, CH4, NH3, H2
Miller and Urey,
1953
Life without oxygen
Anaerobic respiration
Fermentation
C6H12O6 Æ …Æ 2 C2H5OH + 2 CO2
Sugar
Æ alcohol + carbon dioxide
15
Life without oxygen
Anaerobic respiration
Methanogenic bacteria converted hydrogen
gas (H2) into methane (CH4)
CO2 + 4H2 Æ CH4 + 2H2O
Source of CH4 in the atmosphere
Today: cows+wetlands
Life without oxygen
Autotrophic photosynthesis
2-3 billion yrs ago
Microscopic bacteria use sunlight as energy source
(purple bacteria)
sunlight
CO2 + H2S Æ “CH2O” + SO42Organic matter
Currently live near volcanic vents rich in CO2 and H2S
16
3. Oxygen Age
2-3 billion yrs ago
Oxygen producing photosynthesis develops
Microscopic algae (cyanobacteria, blue-green algae)
Organic matter
CO2 + H2O Æ “CH2O” + O2
Hot Spring in Yellowstone National Park
Different colored photosynthetic
cyanobacteria grow at in hot spring
due to different temperatures.
How was the ozone layer formed?
→ illuminate Oxygen (O2) with UV-Radiation
O2 + ultraviolet (UV) light → O + O
O2 + O → O3
The stratospheric ozone layer formed,
protecting the Earth’s surface from harmful
UV radiation, and allowing life on land to
develop.
17
Coevolution of life and the
atmosphere
Figure 4.6
The Atmosphere
Circumference
~40,000 km
Depth of Atmosphere: ~100 km
Depth of Habitable Part: ~5 km
Diameter: ~12,750 km
(~8,000mi)
18
Exosphere (lighter, faster molecules such as H
that are moving in the right direction can
escape the Earth’s gravitational pull)
Mean free path in exosphere > 10 km
Thermosphere (collisions infrequent, heavier
atoms and molecules settle to bottom of layer)
Mean free path in thermosphere > 1 km
Homosphere (well mixed because collisions
are frequent: 78% N2, 21% O2)
Mean free path at surface = 1/10,000,000 = 10-7 km
Vertical Temperature Profile
Stratosphere:
T↑ as alt. ↑
Troposphere:
T↓ as alt. ↑
Figure 2.6 Turco
19
Density
ρ=
20 × 100 g
g
kg
= 2 × 10 6 3 = 2 × 103 3
−3 3
10 m
m
m
10 cm
20 × 100 g
g
kg
= 2000 3 = 2 3
3
1m
m
m
cm
1m
ρ=
Mass (i.e. g, kg)
M
=
Volume (i.e. cm 3 , m 3 ) V
10 cm
10
Density : ρ =
1m
Density of air at surface:
1.3 kg/m3 = 1.3 mg/cm3
1m
Each Tennis Ball: 100g
ρ(water) = 1000 kg/m3
Pressure
Force / Weight
Weight
air
Surface Area
Pressure (P) =
Force
Area
More Force / Weight
⇒ higher pressure
Surface
Surface
at the earth surface:
P = 1013 mbar (millibar)
P ~ 10 tonne / m2
P ~ 10,000 kg/ m2
P ~ 14.7 pound/in2
Æ Enough to crush a can!
20
Boyle’s Law
As the volume decreases
the pressure increases
(constant temperature)
P0×V0 = P1×V1 = P2×V2
V0
P
V1
0
V2
P
P2
1
P
increases
V
decreases
ρ
increases
Charles’ Law
V1/T1 = V2/T2
As temperature increases,
volume increases
(constant pressure)
P = 1 atm
P = 1 atm
Heat
V1
T1
V2
T2
T
increases
V
increases
ρ
decreases
21
Change of Pressure with Altitude
Pressure decreases by a factor of 10 every 10 km
altitude:
• ~1% every 80m
Altitude
• ~3-5% up elevator in tall
building
• ~40% climbing top of Mt.
Rainier (1013 mbar Æ 600
mbar)
Pressure
Æ Plumes of air expand as they rise (decreasing pressure)
Pressure and Density
Versus Altitude
100
100
80
80
Altitude (km)
Altitude (km)
Pressure halves every: 5.5 km
1 mb (above 99.9%)
60
10 mb (above 99%)
40
100 mb (above 90%)
20
500 mb (above 50%)
40
20
0
0
60
200 400 600 800 1000
Air pressure (mb)
0
0
0.4
0.8
1.2
Air density (kg m-3)
Figure 3.2
22
Vertical Temperature Profile
Stratosphere:
T↑ as alt. ↑
Troposphere:
T↓ as alt. ↑
Figure 2.6 Turco
The Can Experiment
P
P
high temp
water vapor
air cools
water
condenses
lower
pressure
than outside
pressure from inside
and outside balance
each other when can
open
heating
atmospheric
pressure crushes
can
23