About 75-80% of the earth's air mass is found here.

The atmospheric layer closest to the earth's surface.

atmosphere's second layer above the earth's surface

extends from about 17 to 48 kilometers

Although it contains less matter than the troposphere, its composition is similar

volume of water vapor is about 1/1,000 as much

its concentration of ozone is much higher

a colorless, odorless, and highly toxic gas that forms during the incomplete combustion of carbon-containing materials

Major sources are motor vehicle exhaust, clearing and burning of forests and grasslands, tobacco smoke, and cooking with open fires and inefficient stoves

a colorless gas that forms when gases in air react at the high-combustion temperatures in automobile engines and coal-burning plants

lightning and certain bacteria in soil and water also produce this as part of the cycle

irritate the eyes, nose, throat, and lungs

a colorless gas with an irritating odor

About 1/3 of it in the troposphere comes from natural resources as part of the cycle

The other 2/3 comes from human sources, mostly combustion of coal in electric power and industrial plants and from oil refining and smelting of ores

a variety of solid particles and liquid droplets small and light enough to remain suspended in the air for short to long periods

About 62% of it in outdoor air comes from natural sources such as dust, wild fires, and sea salt nuclei.

The remaining 38% comes from human sources such as plowing fields, road construction, unpaved roads, tobacco smoke, coal-butning electric power and industrial plants, and motor vehicles

a naturally occurring colorless and odorless radioactive gas found in some types of soil and rock

It can seep into homes and buildings sitting above such deposits.

Long-term exposure can cause lung cancer, especially among smokers.

Exist as gases in the air

Most are hydrocarbons such as isoprene and terpenes emitted by the leaves of many plants and methane.

About 1/3 of global methane emissions come from natural sources, mostly plants, wetlands, and termites.

The NO is converted to red NO2, explaining why photochemical smog is sometimes called this.

When exposed to ultraviolet radiation from the sun, some of the NO2 engages in a complex series of reactions with VOCs released by certain trees, motor vehicles, and businesses such as bakeries and dry cleaners.

When coal and oil are burned the sulfur compounds they contain react with oxygen to produce sulfur dioxide gas, some of which is converted to tiny suspended droplets of sulfuric acid.

Some of these droplets react with ammonia in the atmosphere to form solid particles of ammonium sulfate.

a mixture of primary and secondary pollutants formed under the influence of UV radiation from the sun.

The formation of this begins when exhaust from morning commuter trafic releases large amounts of NO and VOCs into the air over a city.

Occurs when volatile air pollutants are transported from the tropical and temperate areas toward the earth's poles, especially during winter.

This explains why pilots have reported seeing dense layers of reddish-brown haze over the Arctic.

It also explains why polar bears, whales, sharks, and other top carnivores and native peoples in the Arctic have high levels of DDT and other long-lived pesticides, toxic metals, and polychlorinated byphenyls in their bodies even though there are no concentrations of industrial facilities and cats in these remote areas.

Can cause buildup of high levels of air pollutants

Under certain atmospheric conditions, a layer of warm air can lie atop a layer of cooler air nearer the ground.

Because the cooler air is denser than the warmer air above it, the air near the surface does not rise and mix with the air above it.

In some areas, soils contain basic compounds such as calcium carbonate or limestone that can react with and neutralize some inputs of acids.

The areas most sensitive to acid deposition are those with thin acidic soils, which provide no such natural this, and those where this capacity of soils has been depleted by decades of acid deposition.

source: pipe insulation, vinyl ceiling and floor tiles

threat: lung disease, lung cancer

source: furniture stuffing, paneling, particleboard, foam insulation

threat: irritation of eyes, throat, skin, and lungs; nausea; dizziness

To help reduce SO2 emissions, the Clean Air Act of 1990 authorizes this.

Enables the 110 most polluting power plants in 21 states to buy and sell SO2 pollution rights

After particulates in smokestack gas are given a negative charge, they are attracted to a positively charged precipitator wall and fall off the wall into a collector.

Simple to maintain and can remove up to 99% of the particulate matter.

Use a large amounf of electricity and are not very effective in removing hazardous ultrafine particles

fine mists of water vapor trap particulates.

SO2 passing through a watery mixture of lime or limeestone is converted to a calcium sulfite sludge that is collected and usually disposed of in a landfill.

Modern these remove 98% of the SO2 and 98% of the particulate matter in smockstack emissions.