Composition and Layers of the Atmosphere

Air

The homogeneous mixture of gases that makes life on Earth sustainable due to its dioxygen molecule component.

Atmosphere

The thin air made up of a low-density fluid that extends a few hundred kilometers from the surface of the Earth, surrounding the planet.

Main Components

Nitrogen (78 percent) and Oxygen (21 percent) are the main components of the atmosphere, with Oxygen's abundance making life possible.

Troposphere

Ground level to 1-15 km. Lowest part of the atmosphere; where the planet Earth's weather and air pollution take place. Lapse rate decreases at 5-6 K/km.

Thermal Inversion

Occurs in the Troposphere. An unwanted phenomenon where the lapse rate becomes positive, resulting in cold air at the surface overlaid by warmer air. Traps air pollutants near the surface.

Tropopause

Between Troposphere and Stratosphere. Layer of constant temperature.

Stratosphere

Up to about 50 km. Temperature profile increases with altitude up to about 273 K. This profile suppresses vertical air motions. The Ozone layer is found here.

Stratopause

Between Stratosphere and Mesosphere. Layer of constant temperature.

Mesosphere

Up to 85 km. Temperature profile is similar to the troposphere (temperature decreases as altitude increases). Gases are thick enough to slow down and burn up meteors.

Mesopause

Between Mesosphere and Thermosphere. Layer of constant temperature.

Thermosphere

Above Mesopause Has a lapse rate of 5 K/km.

Thermopause

Between Thermosphere and Exosphere. Layer of constant temperature.

Exosphere

Outermost layer, up to 10,000 km. Satellites orbit the Earth in this layer.

Primary Pollutants

Those that are directly emitted to the atmosphere. Examples: Carbon Monoxide, Nitrogen Oxides, Sulfur Dioxide, Volatile Organic Compounds (VOCs) from internal combustion.

Secondary Pollutants

Those that are products of various chemical reactions in the atmosphere. Examples: Photochemical oxidants (Ozone, Peroxyacyl Nitrate (PAN), Nitrogen Dioxide.

Aerosols

Solid and liquid particulates that alter the Earth's radiative processes and impact atmospheric temperature and climate. Example: Soot from burning fossil fuels.

Carbon Dioxide

Complete combustion, metabolic processes.

Carbon Monoxide

Incomplete combustion, photochemical transformation of VOCs (e.g., Methane) by hydroxyl radical.

Nitric Oxide

Combustion (oxidation of air nitrogen at high temperature), lightning.

Nitrogen Dioxide

Oxidation of Nitric Oxide.

Dinitrogen Oxide

Released by soil bacteria.

Sulfur Oxides

Oxidation of sulfur-containing fuels and dihydrogen sulfide.

Dihydrogen Sulfide

is from biological decay and geothermal/industrial processes.Natural sources: Volcanic eruptions. Top anthropogenic source: Combustion processes.

Photochemical Oxidants

Secondary pollutants, products of chemical reactions from other pollutants. Common oxidants: Ozone, Peroxyacyl Nitrate (PAN), Hydroxyl radicals.

Particulates & Aerosols

Mixture of small particles/liquid droplets (salt, soil, minerals, soot). Sources: Wild fires, volcanic eruptions, incomplete combustion. PM2.5 (particles smaller than or equal to 2.5 micrometers): Considered dangerous/carcinogenic as the body cannot release them; active in smog formation. PM10 (2.5 micrometers to 10 micrometers).

Metal/Metalloid Vapors

Vapors of metals (Lead, Mercury, Arsenic, Nickel, Beryllium, Copper). Generated by combustion/incineration, engine wear, lamp wastes.

Polycyclic Aromatic Hydrocarbons (PAHs)

Aromatic compounds of three or more fused aromatic rings. Products of incomplete combustion of fossil fuels and vegetable matter. Hazardous.

Volatile Organic Compounds (VOCs)

Light and unsaturated hydrocarbons. Precursors to smog formation and organic aerosols. Sources: Incomplete combustion, industrial processes, solvent-intensive processes (e.g., painting).

Halogenated Hydrocarbons

Volatile chlorinated hydrocarbons, dioxins, and furans. Includes the ozone layer destructing CFCs. Sources: Incineration processes, car emission.

Radionuclides

From natural deposits of uranium where radon is liberated, nuclear reactors, and fuel-reprocessing wastes.

Natural Process

Earth maintains surface heat to make life sustainable. Solar radiation is absorbed by the Earth's surface, and some outgoing infrared radiation is trapped by greenhouse gases, keeping the planet warm.

Global Warming

The gradual increase in greenhouse gas concentration traps more heat, causing the Earth's temperature to rise.

Climate Change

Refers to the effect of global warming on winds and ocean currents, which can cool some areas and warm others.

Water Vapor

Largest contributor; absorbs infrared radiation and maintains temperature at night.

Carbon Dioxide

Second major contributor; generation is faster than it is absorbed by oceans or used by plants.

Methane

Produced in rice pads and intensive livestock breeding.

Photochemical Smog

Consequence of photochemical reactions where Nitrogen Oxides and hydrocarbons (VOCs) react in the presence of sunlight and oxygen to produce Nitrogen Dioxide and Ozone.

Acid Rain

Rain pH is below 5.7 due to the dissolution of oxides of sulfur and nitrogen in rain droplets. Causes deterioration of marble and oxidation of materials like copper and iron.