Equivalent Effective Stratospheric Chlorine

• little radiation with wavelengths less than ~290 nm makes it down to the troposphere

Solar spectral actinic flux calculated at 50, 40, 30, 20 and 0 km above the surface. From DeMore et al., 1997.

CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE

2

2 3

3 2

3 2

(R1) O O + O ( < 240 nm) (R2) O + O M O M

(R3) O O O ( 320 nm) (R4) O O 2O

h

h

ν λ

ν λ

+ →

+ → +

+ → + <

+ →

O O

O

slow

fast

slow

Odd oxygen family [O_x] = [O₃] + [O]

R2

R3 R4 R1

SOLAR SPECTRUM AND ABSORPTION X- SECTIONS

O₂+hv O₃+hv

Summary of Homogeneous Chemistry

NITROUS OXIDE IN THE STRATOSPHERE

ATMOSPHERIC CYCLING OF NO_x AND NO_y

STRATOSPHERIC OZONE BUDGET FOR MIDLATITUDES CONSTRAINED FROM 1980s SPACE SHUTTLE

OBSERVATIONS

Gas-phase chemistry only

CATALYTIC CYCLE FOR OZONE LOSS:

Chlorine (ClO_x = Cl + ClO) radicals

• Initiation:

CF₂Cl₂ + hν CF₂Cl + Cl

• Propagation:

Cl + O₃ ClO + O₂ ClO + O Cl + O₂ Net: O₃ + O 2O₂

• Termination: Recycling:

Cl + CH₄ HCl + CH₃ HCl + OH Cl + H₂O ClO + NO₂ + M ClNO₃ + M ClNO₃ + hν ClO + NO₂

O₃ loss rate: [O ]³

2[ClO][O]

d

− dt =

ATMOSPHERIC CYCLING OF ClO_x AND Cl_y

Human death due to skin melanoma

Equivalent Effective Stratospheric Chlorine

OBVSERVED CHLORINE PARTITIONING IN

STRATOSPHERE

SOURCE GAS CONTRIBUTIONS TO STRATOSPHERIC CHLORINE (1999)

STRATOSPHERIC DISTRIBUTION OF CF₂Cl₂ (CFC-12)

• In September 1987, Montréal Protocol on Substances that Deplete the Ozone Layer, each signer agreed to reduce the production of CFC-11 ~ CFC-114 and

halons. Consumption of these FCFs was frozen at 1986 level from 1989 and is to be reduced to 80% and then 50% of these values at 1994 and 1999.

• For undeveloped countries, production must not exceed 110% of the 1986 levels.

compound ODP

CFC-11 (CFCl₃) 1.00 CFC-12 (CF₂Cl₂) 0.82 CFC-113 (CFCl₂CF₂Cl) 0.92 CFC-115 (CF₂ClCF₃) 0.40 HCFC-22 (CF₂HCl) 0.04 HFC-225ca (CF₃CF₂CHCL₂) 0.02

SKIN CANCER EPIDEMIOLOGY

PREDICTIONS

VERTICAL STRUCTURE OF THE OZONE HOLE:

near-total depletion in lower stratosphere

OZONE HOLE IS A SPRING PHENOMENON

Timeline of ozone depletion

Figure 19.

Figure 20.

Cl

catalytic

cycles

Sep. 2, 1987

Sep. 16

20 km altitude

Sept. 1987 ER-2 aircraft measurements at 20 km altitude S of Punta Arenas

ASSOCIATION OF ANTARCTIC OZONE HOLE WITH HIGH LEVELS OF CLO

ClO

ClO O₃

O₃

Edge of Polar vortex

Measurements by Jim Anderson’s group (Harvard)

OZONE TREND AT HALLEY BAY, ANTARCTICA (OCTOBER)

Farman et al. paper published in Nature

Tropospheric ozone production

• Note that what the complete cycle has done is to

dissociate molecular oxygen using two photons. One at about 310 nm (4 eV) and one at 400 nm (3 eV).

NO₂ + hν → NO + O O + O₂ + M→ O₃ + M OH + CO → H + CO₂ H + O₂ + M → HO₂ + M HO₂ + NO → OH + NO₂ CO + 2O₂ + hν → CO₂ +O₃

• Similar chain reactions can be written for RO₂

O₃-NO-NO₂ photochemical steady state

• consider the two reactions just seen

NO₂ + hv (+O₂) ≡ NO + O₃ J₁ NO + O₃ ≡ NO₂ K₁

• ignoring other reactions, during daylight this forms a fast cycle in steady-state

d[NO₂]/dt = Prod - Loss = 0 K₁[NO][O₃] = J₁[NO₂]

[NO]/[NO₂] = J₁/K₁[O₃]

• partioning of NO_x between NO and NO₂ has important implications for removal of NO_x

from the atmosphere

Chemistry of the troposphere

NO_x EMISSIONS (Tg N yr^-1) TO THE TROPOSPHERE

FOSSIL FUEL 23.1

AIRCRAFT 0.5

BIOFUEL 2.2

BIOMASS BURNING

5.2

SOILS 5.1

LIGHTNING 5.8

STRATOSPHERE 0.2

NO_x is the limiting precursor for tropospheric ozone formation

• presence of peroxy radicals, from the

oxidation of hydrocarbons, disturbs O₃-NO- NO₂ cycle

NO + HO₂· ≡ NO₂ + OH·

NO + RO₂· ≡ NO₂ + RO·

– leads to net production of ozone

Oxidation of CO - production of ozone

CO + OH· ≡ CO₂ + H·

H· + O₂ + M ≡ HO₂· + M NO + HO₂· ≡ NO₂ + OH·

NO₂ + hv ≡ NO + O O + O₂ + M ≡ O₃

CO + 2 O₂ + hv ≡ CO₂ + O₃

CH₄ + OH· ≡ CH₃· + H₂O CH₃· + O₂ + M ≡ CH₃O₂· + M CH₃O₂· + NO ≡ CH₃O· + NO₂

CH₃O· +O₂ ≡ HCHO + HO₂· HO₂· + NO ≡ OH· + NO₂ 2{NO₂ + hv (+O₂) ≡ NO + O₃}

CH₄ + 4 O₂ + 2 hv ≡ HCHO + 2O₃ + H₂O

• HCHO will also undergo further reaction

HCHO + hv ≡ H₂ + CO

≡ H· + HCO HCHO + OH ≡ HCO + H₂O HCO + O₂ ≡ HO₂· + CO

H· + O₂ ≡ HO₂·

Oxidation of a VOC - daytime

© 2003 John Wiley and Sons Publishers

Weather effects on pollution levels

Air Pollution I

Air Pollution I

An active adult inhales 10,000 to 20,000 liters of An active adult inhales 10,000 to 20,000 liters of

air each day, or 7 to 14 liters every minute.

air each day, or 7 to 14 liters every minute.

The Role of Climate and

Geography on Air Quality

Temperature Inversion

Figure 3.9

Photochemical Smog

London

London

Smog 1952

Smog 1952

London

London

Smog 1952

Smog 1952

Los Los

Angeles

Angeles

Houston

Houston

Ozone Creation by Time-of- Day

Ozone Nitric oxide NO₂

6 am 9 am 12 pm 3 pm 6 pm 8 pm

10 20 30 40

ppm

Photochemical Smog /

To fully appreciate

photochemical smog formation, one must first recognize that

nitrogen is transformed between many different substances in the

atmosphere.

Automobile exhausts release nitrous oxide (NO) along with small amounts of nitrogen dioxide (NO₂). These two substances form the starting materials for a vast array of

chemical reactions that lead to products with higher oxidation

© 2003 John Wiley and Sons Publishers

Daily cycles in photochemical smog

Contrary to popular belief, death as a result of a Contrary to popular belief, death as a result of a

smog siege is often not a result of air pollutant smog siege is often not a result of air pollutant

poisoning, but rather, a result of increasing poisoning, but rather, a result of increasing

susceptibility to diseases.

susceptibility to diseases.

By and large, children, asthmatics, people with By and large, children, asthmatics, people with

chronic respiratory or pulmonary and heart disease, chronic respiratory or pulmonary and heart disease,

and the elderly are the most susceptible to air and the elderly are the most susceptible to air

pollutants.

pollutants.

Effects of Air Pollution on Human Health

Effects of Air Pollution on Human Health

Effects of Air Pollution on Human Health Effects of Air Pollution on Human Health

Because the lungs of children are not yet fully Because the lungs of children are not yet fully

developed and because children inhale more air per developed and because children inhale more air per

unit of body weight than adults, they are prone to unit of body weight than adults, they are prone to

greater health effects as well as long

greater health effects as well as long--term damage to term damage to the lungs.

the lungs.

Similarly, because asthmatics and those suffering Similarly, because asthmatics and those suffering

from chronic diseases are already in a weakened state, from chronic diseases are already in a weakened state,

smog adds stress to their bodies. For the elderly, smog adds stress to their bodies. For the elderly,

smog increases their susceptibility to viral and smog increases their susceptibility to viral and

bacterial attacks, as both lung and immune system bacterial attacks, as both lung and immune system

functions decrease with age.

functions decrease with age.

Effects of Air Pollution on Plants Effects of Air Pollution on Plants

Air pollution commonly leads to oxidation damage of Air pollution commonly leads to oxidation damage of

both crop plants and wild species.

both crop plants and wild species.

Effects of Air Pollution on Plants Effects of Air Pollution on Plants

Air pollution weakens plants by damaging their Air pollution weakens plants by damaging their

leaves, limiting the nutrients available to them, or leaves, limiting the nutrients available to them, or exposing them to toxic substances slowly released exposing them to toxic substances slowly released

from the soil. Quite often, injury or death of plants is from the soil. Quite often, injury or death of plants is

a result of these a result of these

effects of acid rain effects of acid rain

in combination with in combination with

one or more one or more

additional threats.

additional threats.

Effects of Pollution on Buildings Effects of Pollution on Buildings

For limestone, the acidic water reacts with the calcium to For limestone, the acidic water reacts with the calcium to

form calcium sulfate:

form calcium sulfate:

CaCOCaCO₃₃ + H+ H₂₂SOSO₄₄ CaSOCaSO₄₄ + 2H+ 2H⁺⁺ + CO+ CO₃₃^22--

The calcium sulfate is soluble so it is easily washed away The calcium sulfate is soluble so it is easily washed away

during the next rain storm.

during the next rain storm.

Statue carved in 1702 Statue carved in 1702 photographed in 1908 photographed in 1908 (left) and 1969 (right).

(left) and 1969 (right).

Costs of Pollution Costs of Pollution

Health

Health:: $36 billion in sickness annually -$36 billion in sickness annually - health care and health care and lost work.

lost work.

Agriculture

Agriculture:: up to 10% of nation's crops lost to all forms up to 10% of nation's crops lost to all forms of pollution.

of pollution.

Materials

Materials:: corrosion corrosion -- $5.5 billion annually.$5.5 billion annually.

Types of Smog Types of Smog

Photochemical smog

Photochemical smog = brown and smelly, found in = brown and smelly, found in large cities in warm climates.

large cities in warm climates.

Most are the result of gases from auto exhaust.

Most are the result of gases from auto exhaust.

This is the type of smog that hangs over Los This is the type of smog that hangs over Los

Angeles or Houston and causes air quality warnings Angeles or Houston and causes air quality warnings

many days each year.

many days each year.

Photochemical Smog

Photochemical Smog

Industrial Smog

Industrial Smog

Ground level ozone

• Not emitted directly into air

• Created by UV

reactions with NOx and VOCs

• Sources:

– Vehicle exhaust – Gasoline vapors – Dry cleaners

Photochemical Smog

• Formation of brown haze (NOx and VOCs) from combustion

• Exposed to UV

• Creates: O₃, PANs, nitric

acid, aldehydes

Solar radiation

Ultraviolet radiation

NO Nitric oxide

Photochemical smog H₂O

Water

NO₂ Nitrogen

dioxide

Hydrocarbons

O₂ Molecular

oxygen

HNO₃ Nitric acid

PANs Peroxyacyl

nitrates

Aldehydes (e.g., formaldehyde)

O₃ Ozone O

Atomic oxygen

Health Impacts of Ozone

• Trigger chest pain, coughing, throat irritations, congestion

• Worsen existing bronchitis, asthma, other chronic conditions

• Reduce lung function, inflame linings

• Repeated exposure-permanently scars

lungs

Good vs. Bad Ozone…

Thermosphere Exosphere

Troposphere Mesosphere Stratosphere

10 km 40 km 50 km 300 km 400 km

Ecological Effects of Ozone

• Damages vegetation

• Reduced agricultural crops, forests yields

• Reduces growth, seedling

development

• Agriculture alone:

US estimates $500 million lost annually

• Landscape and aesthetic losses

Chemical Reactions of Smog

A few important reactions:

(1) NO₂ + hν Æ NO + O (hν represents a photon)

fast (2) O + O₂ + M Æ O₃ + M (M represents a neutral molecule)

(3) O₃ + NO Æ NO₂ + O₂

(4) O + HC (hydrocarbon)Æ stable product + F.R. (free radical)

slow (5) O₃ + HC Æ S.P. + F.R.

(6) F.R. + HC Æ S.P. + F.R.

(Being a stable product doesn’t mean it is pleasant! It can be irritating to our body.)

(7) F.R. + NO Æ F.R. + NO₂

fast (8) F.R. + NO₂ Æ Stable Product (PAN-Type, Peroxyacetyl Nitrate ) (9) F.R. + F.R. Æ Stable product

• The most important reactions are (1)-(3).

Anthropogenic Pollution Sources

Figure 3.10