Atmosphere

Relative Humidity

• The ratio of water vapor in air to the maximum amount the same air could contain at the same temperature
• Is affected by temperature and location; in general, warm air holds more water.
• When air cools, water vapor may condense to liquid or to ice. Water vapor can only condense on surfaces, such as a petal or a dust particle.

Heat Transfer in the Troposphere

Convection

The transfer of heat by the movement of currents within a fluid (liquid or gas).

Conduction

The transfer of heat directly between two objects that are in contact.

Radiation

The transfer of energy through space, such as heat from the sun to Earth’s atmosphere.

Cooler Atmosphere

Convection Currents

• Warm air is less dense than cool air.
• When air near the surface heats up, it rises; as it rises, it cools and then sinks.
• Rising and sinking fluids generate convection currents.
• Cause wind and heat to move through the atmosphere.

Warmer Surface

Air Masses and Fronts

• Air masses: Large bodies of air with similar properties
• Fronts: Boundaries between air masses of different properties

Warm front

• Boundary along which a mass of warmer, moister air pushes against a mass of cooler, drier air.
• Can produce light precipitation.

Cold front

• Boundary along which a mass of cooler, drier air pushes against a mass of warmer, moister air.
• Can produce heavy precipitation.

Types

• Primary air pollutants: Released directly into the atmosphere; example: soot.
• Secondary air pollutants: Formed when primary pollutants react chemically with other substances; example: sulfuric acid.

Affect on Human Health

• Lung irritation and respiratory illnesses, such as asthma
• Carbon monoxide interferes with body’s ability to use oxygen.
• Trace amounts of some air pollutants, such as benzene or soot, may contribute to cancer.

Smog

• A mix of air pollutants that forms over cities
• “Smog” is a combination of the words smoke and fog.
• Industrial smog (soot, sulfur, and water vapor) comes from industrial sources.
• Photochemical smog is mostly tropospheric ozone created when primary pollutants from vehicle exhaust react to sunlight.

Temperature Inversion

Normal

Temperature Inversion

Acid Deposition

• Sulfur dioxide and nitrogen oxides can react with water, oxygen, and other chemicals to form acids.
• Acid falls as particles or dissolves in precipitation, lowering the pH of rain and snow.
• Acid deposition harms forest and lakes and damages human structures.

Major Accomplishments

• Catalytic converters, present in all cars since 1975, have reduced vehicle emissions.
• Lead has been phased out of gasoline.
• Industries and power plants have reduced releases of pollutants by using scrubbers, which remove or alter chemicals before they leave factory smokestacks.

Ozone Hole

• Ozone is a pollutant in the troposphere, but in the stratosphere it creates a protective barrier against UV radiation.
• Chemicals called chlorofluorocarbons, which used to be found in everything from aerosol cans to refrigerators, have destroyed ozone, causing an “ozone hole” to form over Antarctica.
• An ozone hole allows more UV radiation to reach Earth’s surface, potentially increasing cases of skin cancer.

Recovery of the Ozone

• The Montreal Protocol is an international treaty signed in 1987 that has cut CFC production by 95% since the 1980s.
• Ozone levels in the stratosphere have begun to stabilize, and the ozone hole will likely start to disappear.

2017

1979

2000

Storms

• Tornadoes: Rotating funnels of air that can travel over 400 km (250 mi) per hr
• Hurricanes: Storms that form over tropical oceans, with winds over 119 km (74 mi) per hour
• Thunderstorms: Produce lightning and thunder, usually with heavy rain

• Tropical Depression/Tropical Storm
• less than 73 mph
• Category 1
• 74-95 mph
• Category 2
• 96-110 mph
• Category 3
• 111-129 mph
• Category 4
• 130-156 mph
• Category 5
• 157 mph or higher

https://www.nhc.noaa.gov/aboutsshws.php