Environmental chemistry

Sergey Cheskis cheskis@post.tau.ac.il

If mankind is to survive, we shall require a substantially new manner of thinking

Albert Einstein

Europe population (est.)

World population

Fritz Haber, 1918N2 + 3 H2 → 2 NH3   (ΔH = −92.22 kJ·mol−1)

Fertilizer generated from ammonia produced by the Haber process is estimated to be responsible for sustaining one-third of the Earth's population.

The course structure

• Atmospheric chemistry and air pollution

• Stratospheric chemistry, the ozone holes

• The chemistry of ground-level air pollution

• The detail free radical chemistry of atmosphere

• Combustion as source of air pollution

• Chemical kinetics of combustion

• Mechanisms of NOx formation

• Sulfur chemistry in combustion

• Energy and climate change

• The greenhouse effect, global climate change

• Biofuels and other alternative fuels

If we will have time

• Water chemistry and water pollution

Recommended literature

• Colin Baird and Michael Cann, Environmental chemistry, 5th edition, W.H.Freeman and Co. NY, 2012

Atmospheric chemistryChemistry of stratosphere

Subscript bHeight above sea level Static pressure Standard temperature!

(K)

Temperature lapse rate

(m) (ft) (pascals) (inHg) (K/m) (K/ft)

0 0 0 101325.00 29.92126 288.15 -0.0065 -0.0019812

1 11,000 36,089 22632.10 6.683245 216.65 0.0 0.0

2 20,000 65,617 5474.89 1.616734 216.65 0.001 0.0003048

3 32,000 104,987 868.02 0.2563258 228.65 0.0028 0.00085344

4 47,000 154,199 110.91 0.0327506 270.65 0.0 0.0

5 51,000 167,323 66.94 0.01976704 270.65 -0.0028 -0.00085344

6 71,000 232,940 3.96 0.00116833 214.65 -0.002 -0.0006096

P = P0e−µghRTBarometric formula

Absolute and relative concentration in the atmosphere

For Absolute concentrations, the most common scale is the number of molecules per cubic centimetre of air. !!Absolute concentrations are also sometimes expressed in terms of the partial pressure of the gas (kPa, bars)

Relative concentration are usually based on molecule fraction as a part per … value!percent (%) part per 100!ppm part per millon 1/106!ppb part per billion 1/109!ppt part per trillion 1/1012

Chemical thermodynamics and!chemical kinetics

Ozone layer - Earth’s natural sunscreen

Structure of ozone layer

CHAPTER 01: Figure 1.2

! © 2012 W. H. Freeman & Co.

The Beer–Lambert law can be derived from an approximation for the absorption coefficient for a molecule by approximating the molecule by an opaque disk whose cross-sectional area σ represents the effective area seen by a photon of frequency ν.

Oxygen and ozone absorption spectra

CHAPTER 01: Figure 1.5

! © 2012 W. H. Freeman & Co.

Propagation of UV radiation in the atmosphere

CHAPTER 01: Figure 1.8

! © 2012 W. H. Freeman & Co.

The Chapman mechanism of ozone formation

Dobson units (DU) for overhead ozone

One Dobson unit is equivalent to 10 μm (0.001 cm) thickness of

pure ozone at the density it would possess if it was brought to ground

level (1 atm) pressure and 0 oC temperature

In atmosphere about 350 DU of ozone tropics - 250 DU, subpolar -450DU

For above the stratosphere, the air is very thin and the concentration of molecules is so low that most oxygen exists in atomic form, having been dissociated from O2 molecules by UV-C photons from sunlight. The main

mechanism at this altitude is O2 +UV −C→ 2OO + O → O2

In the stratosphere itself, the intensity of the UV-C light is much less since much of it is filtered by the diatomic

oxygen that lies above. In addition, since the air is denser than it is higher up, the molecular oxygen concentration is much higher in the stratosphere. For this combination of reasons, most stratospheric oxygen exists as O2 rather

than an atomic oxygen

Oxygen atoms are more likely to collide with molecular oxygen than with atomic oxygen:

O + O2 → O3 + heatThe release of heat by this reaction results in the

temperature of the stratosphere as a whole being higher than the air that lies below or above it.

At bottom of the stratosphere, the abundance of O2 is much greater than that at the top. However, relatively little of the oxygen is dissociated and thus little ozone is formed,

because almost all the high energy UV has been filtered from sunlight before it descends to this altitude. For this

reason the ozone layer does not extend below the stratosphere.

The Sun heats the ground, and hence the air in contact with it. It is this reason that the air temperature falls with

increasing the altitude in the troposphere. In the stratosphere, after the tropopause (boundary between troposphere and stratosphere) the temperature grows

with increasing the altitude, because of the reaction between oxygen atoms and molecular oxygen with

releasing the heat.

Ozone absorption in absolute units

Ozon absorption in visual range

Structure of ozone layer

Image of a man's face with sunscreen on the left, in visible (left) and UV light, demonstrating how sunscreen protects against UV exposure. The side of the face with sunscreen is darker, showing that the sunscreen absorbs the UV light.

Damage DNA by UV-B

CHAPTER 01: Figure 1.6

! © 2012 W. H. Freeman & Co.

CHAPTER 01: Figure 1.7

! © 2012 W. H. Freeman & Co.