Atmospheric Science: Structure, Circulation, Climate & Pollution

Atmosphere

The layer of gases held by a planet's gravity, surrounding the planet.

Troposphere

The lowest layer of Earth's atmosphere (0-12 km) where weather occurs, temperature decreases with altitude, and contains approximately 80% of the atmosphere's mass.

Stratosphere

The second layer of Earth's atmosphere (12-50 km) where temperature increases with altitude due to the ozone layer.

Mesosphere

The atmospheric layer above the stratosphere (50-80 km) where temperature decreases with altitude due to rapidly decreasing air density.

Thermosphere

The outermost layer of Earth's atmosphere (80-500 km) where temperature increases with altitude due to the absorption of intense solar radiation.

Ozone Layer

A region in the stratosphere with a high concentration of ozone ($O_3$), which absorbs UV radiation from the sun, protecting life on Earth.

Greenhouse Effect

The process by which greenhouse gases in the atmosphere trap infrared radiation emitted by Earth, warming the planet's surface.

Greenhouse Gases

Gases that absorb and emit infrared radiation, including water vapor, carbon dioxide, methane, nitrous oxide, and ozone.

Radiosonde

An unmanned balloon with instruments that collects atmospheric data and transmits it via radio as it ascends through the atmosphere.

Infrared Radiation

Long-wavelength radiation emitted by Earth's surface after absorbing solar energy.

Electromagnetic Spectrum

The range of all types of electromagnetic radiation, from gamma rays to radio waves, including visible light.

Wien's Law

Formula that relates the peak wavelength of radiation emitted by an object to its temperature ($\lambda = 2898 / \text{Temperature}$).

Nitrogen ($N_2$) Concentration

~78% (Consists of molecules containing two atoms with a triple bond, making it extremely inert and difficult to break).

Oxygen ($O_2$) Concentration

~21% (Very reactive: causes things to burn, makes metal rust, and is breathed by living organisms).

Argon (Ar) Concentration

~0.93% (A fairly abundant noble gas that is extremely unreactive).

Steps of the Natural Greenhouse Effect

1. Incoming Sunlight passes through; 2. Surface Absorption by Earth; 3. Re-radiation outward as infrared radiation; 4. Infrared Absorption by greenhouse gases; 5. Warming Effect keeping Earth's surface ~33°C warmer.

Atmospheric Circulation

The world-wide system of winds by which the necessary transport of heat from tropical to polar latitudes is accomplished.

Hadley Cell

A large-scale atmospheric circulation cell in which air rises at the equator and sinks at medium latitudes, typically about $30^\circ$ north or south.

Ferrel Cell

A mid-latitude atmospheric circulation cell between the Hadley and Polar cells where air flows poleward and eastward near the surface and equatorward at higher levels.

Polar Cell

An atmospheric circulation cell located at the poles where cold, dense air descends and flows toward lower latitudes at the surface.

Intertropical Convergence Zone (ITCZ)

The area near the equator where the northeast and southeast trade winds converge, characterized by ascending air, low pressure, and abundant precipitation.

Trade Winds

The prevailing pattern of easterly surface winds found in the tropics, blowing from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere ($0^\circ$ to $30^\circ$ N/S).

Prevailing Westerlies

The dominant west-to-east winds in the middle latitudes between $30^\circ$ and $60^\circ$ latitude in both hemispheres.

Polar Easterlies

Cold, dry winds that blow away from high-pressure poles toward lower latitudes ($60^\circ$ to $90^\circ$ N/S).

Coriolis Effect

The apparent deflection: a curved path of long-distance objects—such as air currents, ocean currents, aircrafts—caused by the rotation of the Earth beneath them. (Deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere).

Jet Stream

A narrow, fast-flowing air current found in the upper atmosphere, primarily the polar front jet stream and subtropical jet stream.

Air Mass

A large body of air with generally uniform temperature, humidity, and density characteristics, covering thousands of square miles.

Front

The boundary between two air masses of different densities, often associated with significant weather events.

Subtropical High

A semi-permanent high pressure system in the subtropical regions that contributes to the formation of deserts at approximately $30^\circ$ latitude.

Low-Pressure System (Depression)

Ground warms up, causing moist warm air to expand, become less dense, and rise, cooling down to form clouds/rain. Associated with storms, clouds, and wet weather.

High-Pressure System (Anticyclone)

Dry and cold air declines extensively and warms up as it descends, preventing condensation. Associated with nice weather, clear skies, and stable conditions.

Tropical Cyclone Naming by Region

Hurricane: North Atlantic, Northeast Pacific, and Caribbean. Cyclone: South Pacific and Indian Ocean. Typhoon: Northwest Pacific Ocean.

Air Pollution

Contaminants in the atmosphere that can harm human health, damage ecosystems, and affect climate.

Aerosols

Tiny solid and liquid particles suspended in the atmosphere (natural: sea salt, dust, volcanic ash; anthropogenic: smoke, industrial pollution).

Particulate Matter (PM)

Solid and liquid particles found in the air, classified by size ($PM_{10}$, $PM_{2.5}$) where the number indicates maximum diameter in micrometers. Smaller particles penetrate deeper into lungs.

Tropospheric Ozone ($O_3$)

"Bad down low"—a harmful pollutant created via photochemical reactions between $NO_x$ and VOCs in the presence of sunlight.

Stratospheric Ozone ($O_3$)

"Good up high"—protects Earth from harmful UV radiation.

Ozone Hole

A region of exceptionally depleted ozone in the stratosphere over Antarctica that forms during Southern Hemisphere spring (August-October).

Chlorofluorocarbons (CFCs)

Human-made chemicals once widely used in refrigeration and propellants that break down in the stratosphere, releasing chlorine atoms that destroy ozone.

Montreal Protocol

International agreement created in 1987 to phase out ozone-depleting substances. Expected to allow the ozone hole to close completely by the 2060s.

Air Quality Index (AQI)

A measure combining concentrations of major pollutants into a single value related to health impacts.

Volatile Organic Compounds (VOCs)

Carbon-containing chemicals that readily evaporate at room temperature (natural from pine trees, human from gasoline/paints). Contribute to ground-level ozone formation.

Nitrogen Oxides ($NO_x$)

Gases produced during fossil fuel combustion, fires, and by bacteria. Important in tropospheric ozone formation.

Polar Stratospheric Clouds

Clouds that form in the extremely cold stratosphere over polar regions, providing surfaces for chemical reactions that accelerate ozone destruction.

Dobson Unit

A unit of measurement for total ozone in a column of air from the Earth's surface to the top of the atmosphere.

Tropospheric Ozone Formation Equation

$$\text{VOCs} + \text{NO}_x + \text{light} + \text{heat} = \text{Ozone}$$