SMOG

Ch. 18

Smog• Localized air pollution in urban

areas, mixture of pollutants that form with interaction with sunlight

TYPES:1. Brown2. Gray

Photochemical (Brown) Smog

• Brown haze• Light initiates complex chemical

reactions

Photochemical Smog in Santiago, Chile

Photochemical Smog Reaction

• VOCs + NOx + Heat + Sunlight yields– Ground level O3 and other photochemical

oxidants– Aldehydes– Other secondary pollutants

Fig. 18-11, p. 475

PANS and other pollutantsVolatile organic compounds (VOCs)

Ozone (O3)

Oxygen (O2)

Nitric oxide (NO) + Oxygen atom (O)

Water vapor (H2O)

Hydrocarbons UV radiationPeroxyacyl nitrates (PANs) Nitrogen dioxide (NO2)

Oxygen (O2)Nitric oxide (NO)

Oxygen (O2) Burning fossil fuels

Nitrogen (N) in fossil fuel

SimplifiedModel

HOW? (Nitric Acid AKA Acid Rain)

NO2 +UV NO + O

2NO + O2 2NO2

3NO2 + H2O 2HNO3 + NO

N2 & O2 in air react @ high temps nitrogen monoxide

Stinky, yellowish brown gas, haze above cities (Nitrogen dioxide)

Forms nitric acid & Nitrogen monoxide

HOW? Tropospheric Ozone (BAD!)

NO2 +UV NO + O

O + O2 O3

Produces free oxygen

Tropospheric ozone

O2 + hydrocarbons + NO PANS (peroxyacyl nitrates)

Photochemical Smog ReactionFig. 17-6 p. 424

Photochemical Oxidants• NO2, O3, PANS • Able to react with & oxidize

compounds in atm. or our lungs • Respiratory health issues• Damaging to vegetation

Smog• Hotter days = O3 & other

components

What’s location got to do with it?

• Cities with sunny, warm & dry climates

• Greater number of motor vehicles EX: LA; Salt Lake City, Utah; Syndey, Australia; Sao Paulo, Brazil; Bangkok, Thailand; Mexico City, Mexico and Santiago, Chile

Industrial (Gray) Smog• Smoke pollution• Sulfur oxides• Particulates from burning

coal/oil,• Problems in China/India/Russia

due to lack of pollution controls on smokestacks

Industrial Smog Reaction • When burned, most carbon in

coal and oil converted to CO & CO2

• Soot = unburned coal (suspended particulates)

• Sulfur dioxide & sulfuric acid created

Fig. 18-9, p. 474

Ammonium sulfate [(NH 4 )2SO4]

Ammonia (NH3)

Sulfuric acid (H2SO4)

Water vapor (H2O) Carbon monoxide (CO) and carbon

dioxide (CO2)Sulfur trioxide (SO3)

Oxygen (O2)

Sulfur dioxide (SO2)

Burning coal and oil

Oxygen (O2)

Sulfur (S) in coal and oil Carbon (C) in coal and oil

How? (Carbon) C + O2 CO2 + Soot (gray color)2C + O2 2CO + Soot

How? (Sulfur) S + O2 SO2 (suffocating gas)

2SO2 + O2 2SO3

SO3 + H2O H2SO4 (sulfuric acid, acid rain)

2NH3 + H2SO4 (NH4)2SO4 (Ammonium Sulfate – GRAY COLOR)

Smog also creates greenhouse gases

• Methane (CH4)• Nitrous Oxide (N2O

What’s Location Got to Do With It?

• Temperature differences help to disperse air pollutants preventing harmful buildup of air toxins

• Ground air is warmed, rises, then cools = CONVECTION

Temperature Inversions• Ground air colder than

upper air – trap harmful pollutants near ground

• Cooler air is denser than warmer air above it

• Pollutants concentrate in stagnant cool layer

• NO mixing due to density

Types of Temperature Inversions

• Subsidence - Warmer mass enters high altitude region and floats atop a colder air mass. Prevents vertical mixing.

Types of Temperature Inversions

• Subsidence

Types of Temperature Inversions• Radiation – Occurs at night as ground air

cools faster than air above. Sun rises and warms surface – dispersing pollutants that were trapped during night

Inversion layer

Mountainrange

Sea breeze

Descending warm air mass

Decreasing temperature

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Types of Temperature Inversions*

Where does this occur? • Valleys surrounded by mountains

Where does this occur? • Near coastlines with sunny

climage, and surrounded by mountains

EX: Los Angeles, CA

Where does this occur? • Leeward side of mountains