top 14 photochemical smog (part 2) (1)

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TOPIC 14(part 2)

SMOG & OZONE DEPLETION

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SMOG

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Introduction

It is a general term first used in 1905 for a mixture of smoke and fog.

A kind of urban air pollution.

2 major types:Photochemical smogSulfurous smog (Classical smog)

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Photochemical Smog

Solar radiation is important for formation of photochemical smog.

The reactions that occur is complex and involve nitrogen oxides (NOx) and hydrocarbons.

It is directly related to automobile use.

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Formation of Photochemical Smog

Sun

Nitrogen oxides (NOx) + Hydrocarbons

Photochemical Smog

Solar radiation

Pollutants are trapped in an inversion layer.

Source: Botkin&Keller.2003. Environmental Science, 4th ed.

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Example: Photochemical Fog Formation over Los Angeles Area

Source: Botkin&Keller, 2003. Environmental Science. 4 th ed. Chapter 23.

CHEM115 Envrionmental Chemistry 7Source: Botkin&Keller, 2003. Environmental Science. 4 th ed. Chapter 23.

The city of Los Angeles, on a clear day (left) and a smoggy day (right)

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Sulfurous Smog (Classical Smog)

It is mainly due to burning of coal or oil at large power plants.

Sulfur oxides and particulates combine to produce sulfurous smog.

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Formation of Sulfurous SmogBurning of coal or oil

Sulfur oxides + particulates

releases

Concentrated sulfurous smog

•stagnant and stable air•sufficient relative humidity•cloud cover •formation of inversion layer

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What are the consequences?

• Reduce visual range and atmospheric clarity• Damage plant tissues• Increase lung disease and respiratory system

disease such as bronchitis• Aggravate chronic disease such as asthma and

emphysema

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Control of Smog

• Stricter emission control for automobiles• Requirement for more making fuel cleaner• Improvement in public transportation and

incentives for people to use it• Enforcing mandatory carpooling• Increase control on industrial and household

activities

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Relevant Regulations and Guidelines

Clean Air ActNational Ambient Air Quality Standards (NAAQS)Air Quality IndexClean Air RegulationsAir Pollution Index

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OZONE DEPLETION

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Introduction

Ozone is a triatomic form of oxygen.

In the lower atmosphere, ozone is a pollutant produced by photochemical reactions which involve sunlight, nitrogen oxides, hydrocarbons, and oxygen.

In the upper atmosphere, ozone acts as a sunscreen against UV radiation.

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Formation of Stratospheric Ozone

Source: Botkin&Keller, 2003. Environmental Science. 4 th ed. Chapter 25.

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Ozone Depletion

CFCs are considered responsible for most of the ozone depletion.

CFCs, unlike other pollutants cannot be broken down by sunlight, rain-out and oxidation. CFCs are transparent to sunlight, insoluble in water, and non-reactive in oxygen-rich at lower atmosphere.

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When CFCs wander to the upper atmosphere, the highly energetic UV splits up the CFCs, releasing chlorine. Then, ozone depletion occurs.

Cl + O3 -> ClO + O2

ClO + O -> Cl + O2

The series of reactions is known as catalytic chain reaction.

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Formation and Destruction of Ozone

Source: Botkin&Keller, 2003. Environmental Science. 4 th ed. Chapter 25.

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What are the consequences?

• Damage on food chain• Increase in skin cancer, cataracts and

suppression of immune system

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Control

• Montreal Protocol, 1987• Substitutes for CFC.

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