E10: Smog (UNMODIFIED)

Seite 1

Word

Word Form: SMoke + fOG

2

2 Main Types:

Pea Soup Smog (reducing smog)

Source = fog + SOx + soot +ash

Cold and wet weather conditions

Combustion of sulfur containing coal (industry, power plants, homes)

Photochemical Smog (oxidizing smog)

Source: VOCs + NOx + Sunlight (create many secondary pollutants such as O3 and PANS)

Sunny and Dry Weather Conditions

Vehicle Exhausts

Conditions to the Formation of Photochemical Smog

Temperature/ Thermal Inversions

- Warm layer of air forms between 2 cool layers

- Cool air in lower atmosphere cannot flow upwards

- Pollutants remain in the lower atmosphere

Bowl Shaped Cities

- Surrounded or bordered by mountains

- Promote formation of temperature inversions

- Night time ground cooling

- Movement of warm air masses over mountains

Windless Conditions (and many coastal communities)

- No horizontal movement of air away from cities

- Pollutants build up in the lower layer

Ultraviolet Radiation from the Sun

- Promotes the existence of free radicals within the atmosphere (which can react with other substances to make photochemical smog)

NO

Formula: N2 + O2 --> 2NO

Source:

High temperature conditions in internal combustion engines in road vehicles

VOCs

Example: Unburned Hydrocarbons

Source:

Incomplete combustion in internal combustion engines in road vehicles

NO2

Where it came from:

Oxidizing of NO

Properties:

Reddish brown in color (gas)

Formula: NO + 1/2 O2 --> NO2

Another method: Free Radicals Production

UV light from sun starts photochemical reactions

NO2 absorbs UV light (produce NO and O•)

O• = very reactive (will react with other chemicals in the atmosphere)

O3

Where it came from:

Reaction between O• and O2 at ground level

Formula:

O• + O2 --> O3

Effects:

Very harmful and damaging pollutant

Cause eye, nose and throat irritation

Damage plants and many materials (e.g. rubbers and metals)

OH•

Formula: O• + H2O --> 2 OH•

Effects:

React with other free radicals in atmosphere to make more photochemical smog

HNO3

Where it came from:

Hydroxyl free radicals react with NO2 to form Nitric Acid

Formula: •OH + NO2 --> HNO3

R•

Where it came from:

Hydroxyl free radicals react with hydrocarbon VOC (RH) to produce reactive hydrocarbon free radicals

Formula: •OH + RH --> R• +H2O

ROO•

Where it came from:

Hydrocarbon Free Radicals react with O2 to form extremely reactive peroxides

Formula: R• + O2 --> ROO•

RCHO

RCHO

Where it came from:Peroxides lead to the formation of aldehydes and ketones

Effects:

Aldehydes and ketones contribute to the formation of aerosols, which reduce visibility

PAN

Where it came from:

Smorgasbord of reaction - terminated when perxode free radicals react with a free radical of NO2 to form PAN

Formula: ROO• + •NO2 --> ROONO2

Properties and Effects:

Relatively stable

Very powerful lachrymators (eye irritants)

Respiratory Irritants

Introduction

Primary Pollutants and Source (of Photochemical Smog)

Secondary Pollutants (of Photochemical Smog)