Chapter 8 Air Pollution & Energy Use

Lecture 13

• Properties and Motion of the Atmosphere

• Air Pollutants and Sources– Acid rain– Particulates– Aerosols– VOCs– Indoor Air Pollution– Air Quality Standards– Automobile Emissions– Emission Control Devices

The Ocean That We Live In

• We live in an ocean of air 20 miles deep• Air pressure exerted on us is 14.7 psia (100,000

Pa) at sea level• As a comparison, air pressure at the top of Mt.

Everest is ~5 psia at a height of 29,035 ft• Measured with a Barometer at 76 cm of Mercury

at sea level• Measured with Water column Barometer at

39.959 feet

Table 8-1, p. 244

Effects of Atmospheric Pressure

Mercury Barometer

Aneroid barometers

More info: http://www.bom.gov.au/info/aneroid/aneroid.shtml

Buoyancy Forces

Archimedes’ Principle – the buoyant force on an object is equal to the weight of the fluid displaced by that object

– Allows concrete and steel battleships to float– Balloons to float

Fig. 8-3, p. 247

What are we measuring here?

Body density = W/[(W - WW)/c.f. - LV]

– W: weight in air (kg) – WW: weight in water (kg) – c.f.: water correction factor (equal to 1 at

39.2oF because one gram of water occupies exactly one cm3 at this temperature, equal to .997 at 76-78oF)

– LV: residual lung volume (liters)

Air Currents & Temperature Inversions

• Air rises from the surface as bubbles of hot air called “Thermals”

• Thermals continue to rise and cool until their temperature matches the temperature at that level

• When the thermal temperature reaches an equilibrium temperature level, it stops vertical motion and creates an “inversion layer”. Rising air reaches an overriding layer of warmer air

• Air Temp decreases ~3.5oF/1000 ft.

Fig. 8-4, p. 248

Houston, TX

Lochcarron, Scotland

• Definition and history of acid rain

• How acid rain is formed– Industries– Natural processes

• The effects of acid rain

• Ways to reduce acid rain

Definition of Acid Rain

• Any type of precipitation with a pH that is unusually low (acidic)– pH = 7 is neutral (not acid or base)

• Natural dissociation of CO2 gives rain a pH = 5.6– In areas with natural sources of acidity the rain has

acidity between 4.5 < pH < 5.6

• Generally any precipitation with pH < 5 is considered “acid rain”

• Acid rain can be in the form of snow, dew, or dry particles

pH Scale

acid rain affects aquatic life and reproductive ability

History of Acid RainIn 1852 Robert Angus Smith in Manchester, England found the relationship between acid rain and atmospheric pollution

– Manchester was an ‘industrial revolution’ city– He used the term “acid rain” in 1872

Acid rain began to be widely researched in and after the late 1960’s

– Harold Harvey researched a “dead” lake in Canada• Dead = fish used to live there and no longer do

– In 1990’s the New York Times reported on a forest in New Hampshire that was greatly affected by acid rain

p. 263

Effect on forests

How Acid Rain is Formed

• Industries burn fuels that contain sulfur (e.g., coal; oil and natural gas to a lesser extent)

• The sulfur forms SO2 (sulfur dioxide) when it burns

• In the atmosphere the SO2 first reacts to form SO3 (sulfur trioxide) and reacts with water to form H2SO4 (sulfuric acid)

• The sulfuric acid comes down with rain and affects buildings, forests, rivers, and lakes

Human Caused SOx Emissions

• Most SOx is caused from coal since it has much more sulfur in it compared to gasoline

• Since 2006 China is largest contributor, 25.49 million tons

How Acid Rain is Formed• Sulfur has the biggest effect but nitrogen can also

make acid rain• Monatomic nitrogen (N) can come from:

– Fuel (such as coal)

– Air; dissociation of diatomic nitrogen (N2) used in burning coal, gasoline, or natural gas

• Nitrogen forms NOx (nitrogen oxides)

– Transportation is largest contributor of NOx

• In the atmosphere NOx reacts to form HNO3 (nitric acid)

• Nitric acid has the same effects as sulfuric acid

Human Caused NOx Emissions

Transportation has greater effect on NOx than SOx

– Nitrogen comes from air

– Transportation has fewer devices to clean up NOx

(because devices are large & heavy)

How Acid Rain is Formed from Natural Processes

• Biggest natural source of acid rain is from emissions from volcanoes that contain sulfur– 3% - 20% Carbon Dioxide– 46% - 87% Sulfur Dioxide

• Other areas of geothermal activity (besides volcanoes) also have sulfur, such as Yellowstone

• Some wetlands have a source of sulfur

Natural Sources:

hydrogen sulfide (H2S)

carbon disulfide (CS2)

carbonyl sulfide (COS)

methyl mercaptan (CH3SH)

dimethyl sulfide (DMS) (CH3SCH3)

dimethyl disulfide (DMDS) (CH3SSCH3)

The Effects of Acid Rain

• Rivers and Lakes

• Forests

• Visibility

• Manmade Outdoor Objects– Buildings, monuments, cars

• People’s health

The Effects of Polluted Air – Acid Rain Being One Part of This

• Greater medical costs

• Greater food costs

• Decrease in visual appearances