atmosphere: structure and composition

ATMOSPHERE- COMPOSITION AND STRUCTURE

Dr. Basharat Mushtaq

ATMOSPHERE- COMPOSITION & STRUCTURE DR. BASHARAT MUSHTAQ

The present condition and properties of earth’s atmosphere are one of the main reasons for earth to support life

The atmosphere is the blanket of gases or vapours that surrounds the earth, and held together by the force of gravity.


Extends from a few meters below the earth’s surfaces or water’s surface to a height of about 60,000 km. About

90% of the atmosphere is within few km from the ground.

Most of the mass of the atmosphere is near planetary surface, as the gravity

pulls them towards the earth’s centre.

The atmosphere is a complex system in which physical and chemical

reactions are constantly taking place and many atmospheric

processes take place in a state of dynamic balance

for example; there is an average balance between the heat input to, and output from, the atmosphere.

Earth's climate system maintains a dynamic balance between solar energy entering

and radiant energy leaving the atmosphere


GENERAL CHARECTERISTICS OF THE ATMOSPHERE

Air has weight and the pressure it exerts is known as atmospheric pressure. Atmospheric pressure is a climatic element. At sea level the pressure is 1034 gram per square cms. (14.7pound per square inch.)

Air is colourless, odourless, and tasteless.

It is mobile, elastic, and compressible

We cannot feel its presence unless there is horizontal motion in it…….WIND


The atmosphere is special because it contains life-sustaining oxygen in large quantities (about 21% by volume). It is amazing to know that how perfectly, all the natural processes on earth are functioning harmoniously.

It nurtures life on earth, providing carbon dioxide to plants to make food through photosynthesis and oxygen to organisms for respiration and releasing energy from their food

Importance of atmosphere


Nitrogen : essential to make living matter, nitrogen fixing

bacteria and ammonia manufacturing plants produce

chemically bound nitrogen, which is also available to the

animals

Atmosphere transfers water from the oceans due to evaporation and transpiration.

Atmosphere constantly exchange energy and matter with other components of the earth – lithosphere, hydrosphere

and biosphere

Atmosphere maintains the level of water

and radiation in the Earth system


Constant gases are the ones, whose concentrations do not change over time, and their concentrations almost remain same.

COMPOSITION OF ATMOSPHEREThe composition of the atmosphere are gases present in large amounts, water vapour and solid particles in considerably less amounts.

Gases

constant gases

variable gases

Variable gases are present in different concentrations at different places and times.


COMPOSITION OF ATMOSPHERE

Gaseous composition of the atmosphere is usually expressed by percentage

volume, that is, each gas’s relative part of the total mixture

Major gaseous

composition

78% nitrogen (N2), 21% oxygen (O2), and 0.9% argon (Ar). These three gases together

make up 99.9% of the atmosphere

Trace gases

water vapor (H2o), Carbon Dioxide (CO2), Neon (Ne),

Helium (He), Methane (CH4), Krypton (Kr), and

Hydrogen (H2)The concentration of gases in the atmosphere is measured in parts per thousand (ppt), parts per million (ppm) and parts per billion (ppb).


Full Name Formula % Volume # Of Parts Unit Variable? Cumulative Volume

Nitrogen N2 78.1% 78 parts per Hundred 78.10%Oxygen O2 20.9% 21 parts per Hundred 99.00%Argon Ar 0.934% 9 parts per Thousand 99.93%Water Vapor H20 0.04% 400 parts per million variable 99.97%Carbon Dioxide CO2 0.0369% 370 parts per million 99.99%Neon Ne 0.00182% 18 parts per Million 100.00%Helium He 0.000524% 5 parts per Million 100.00%Methane CH4 0.0001842% 2 parts per Million 100.00%Krypton Kr 0.000114% 1 part per Million 100.00%Hydrogen H2 0.0001% 1 part per million variable 100.00%Nitrous Oxide N20 0.0000315% 315 parts per billion 100.00%Carbon Monoxide CO 0.00002% 200 parts per billion variable 100.00%Xenon Xe 0.0000087% 87 parts per billion 100.00%Ozone O3 0.000005% 34 parts per billion variable 100.00%Sulphur Dioxide SO2 0.000002% 20 parts per billion variable 100.00%Ammonia NH3 0.000002% 20 parts per billion variable 100.00%Formaldehyde CH20 0.000001% 10 parts per billion variable 100.00%Nitrogen Dioxide NO2 0.0000003% 3 parts per billion variable 100.00%Nitric Oxide NO 0.0000003% 3 parts per billion variable 100.00%Hydrogen Sulfide H2S 0.0000002% 2 parts per billion variable 100.00%Hydrochloric Acid HCl 0.00000015% 2 parts per billion variable 100.00%Nitric Acid HNO3 0.0000001% 1 part per billion variable 100.00%


Methyl Chloride CH3Cl 0.00000006% 600 parts per trillion 100.00%

Freon-12 CF2Cl2 0.0000000544% 546 parts per trillion 100.00%

Carbonyl Sulfide COS 0.00000005% 500 parts per trillion 100.00%

Freon-11 CFCl3F 0.0000000263% 263 parts per trillion 100.00%

Carbon Tetrachloride

CCl4 0.000000098% 97 parts per trillion 100.00%

Freon-113 C2F3Cl3 0.000000082% 82 parts per trillion 100.00%

Methyl Chloroform CH3CCl3 0.000000056% 47 parts per trillion 100.00%

HCFC-22 CHClF2 0.0000001525% 153 parts per trillion 100.00%

HFC-23 CHF3 0.0000000011% 23 parts per trillion 100.00%

Sulphur Hexaflouride

SF6 0.000000004% 5 parts per trillion 100.00%

Perfluoroethane C2F6 0.000000004% 4 parts per trillion 100.00%

Triflouromethyl Sulphur Pentaflouride

SF5CF3 0.00000000012% .12 parts per trillion 100.00%

Sources 1. McGraw-Hill Encyclopedia of Science and Technology, 1987, McGraw-Hill, Inc.

2. Carbon Dioxide Information Analysis Center


The gaseous area surrounding the planet is divided into several concentric strata or layers. About 99% of the total atmospheric mass is concentrated in the first 20 miles (32 km) above Earth’s surface.

There are two types of atmospheric structures such as: 1. Thermal structure 2. Magneto-electronic structure.

Structure of Atmosphere


Atmospheric layers are characterized by variations in temperature resulting primarily from the absorption of solar radiation;

• visible light at the surface, • near ultraviolet radiation in the

middle atmosphere, and • far ultraviolet radiation in the

upper atmosphere.

THERMAL STRUCTURE


THERMAL STRUCTURE OR Vertical structure of Atmosphere

Exosphere

Thermosphere

Mesosphere

StratosphereTroposphere


Bottom layer of the atmosphere

70% mass of the atmosphere

Extends to an average height of 5-20 km

Thickness varies with latitude: poles about 8 km; about 16 km above the equator

Temperature decreases with height in this layer

The rate of decrease of temperature with altitude is called, lapse rate. Average lapse rate in troposphere is -6.4 °C / km

Troposphere ends at tropopause. Tropopause is just like a lid over the troposphere, where temperature stops decreasing with height

Troposphere


Second lowest layer of atmosphere. Very little weather occurs

Extends above the tropopause to an altitude of about 30 miles (50 km) above the planet’s surface.

Temperature inversion occurs in Stratosphere, Temperature increases as a result of interactions between high energy UV radiation and ozone (O3)

Ozone absorbs the bulk of solar ultraviolet radiation in wavelengths from 290 nm – 320 nm (UV-B radiation)

Stratopause Where the temperature reaches a maximum of 10 OC

Stratosphere



On the average, the temperature decreases about 6.5OC/1,000 km, which is known as the observed lapse rate.

An inversion is a layer of air in which the temperature increases with height.



The mesosphere a layer extending from approximately 30 to 50 miles (50 to 85 km) above the surface

Characterized by decreasing temperatures

The coldest temperatures in Earth’s atmosphere occur at the top of this layer, the mesopause

The stratosphere and mesosphere together are sometimes referred to as the middle atmosphere.

Mesosphere


The thermosphere is located above 80 km from earth

The temperature in the thermosphere generally increases with altitude reaching 600 to 3000 F (600-2000 K) depending on solar activity.

Above 60 miles (100 km) from Earth’s surface the chemical composition of air becomes strongly dependent on altitude and the atmosphere becomes enriched with lighter gases (atomic oxygen, helium and hydrogen).

Very little energy transfers, however, due to the lack of molecules (very few molecules to collide with objects)

Thermosphere


The exosphere is the most distant atmospheric region from Earth’s surface

The altitude of its lower boundary, known as the thermopause or exobase, ranges from about 150 to 300 miles (250-500 km) depending on solar activity

The exosphere is a transitional zone between Earth’s atmosphere and interplanetary space

Exosphere


The upper atmosphere is also divided into regions based on the behaviour and number of free electrons and other charged particles

MAGNETO-ELECTRONIC STRUCTURE

Ionosphere Plasmasphere Magnetosphere


The ionosphere is defined by atmospheric effects on radiowave propagation as a result of the presence and variation in concentration of free electrons in the atmosphere

Ionosphere

D-region is about 35 to 55 miles (60 - 90 km) in altitude but disappears at night.

E-region is about 55 to 90 miles (90 - 140 km) in altitude.

F-region is above 90 miles (140 km) in atitude. During the day it has two regions known as the:

o F1-region from about 90 to 115 miles (140 to 180 km) altitude

o F2-region in which the concentration of electrons peaks in the altitude range of 150 to 300 miles (around 250 to 500 km).


image: regions of ionosphere)


The plasmasphere is not really spherical but a doughnut-shaped region (a torus) with the hole aligned with Earth’s magnetic axis.

The Earth’s plasmasphere is made of just that, a plasma, the fourth state of matter. This plasma is composed mostly of hydrogen ions (protons) and electrons. It has a very sharp edge called the plasmapause

The plasmasphere is essentially an extension of the ionosphere. Inside of the plasmapause, geomagnetic field lines rotate with the Earth.

Plasmasphere



Extension of plasmasphere)


Magnetosphere

The magnetosphere is a cavity (also not spherical) in which the Earth’s magnetic field is constrained by the solar wind and interplanetary magnetic field (IMF).

The outer boundary of the magnetosphere is called the magnetopause. The magnetosphere is shaped like an elongated teardrop (like a Christmas Tree ornament) with the tail pointing away from the Sun



The magnetopause is typically located at about 10 Earth radii or some 35,000 miles (about 56,000 km) above the Earth’s surface on the day side and stretches into a long tail, the magnetotail, a few million miles long (about 1000 Earth radii)

Beyond the magnetopause are the magnetosheath and bow shock which are regions in the solar wind disturbed by the

presence of Earth and its magnetic field


Environment

atmosphere: structure and composition