Unit I

STRUCTURE AND COMPOSITION OF ATMOSPHERE: Environment - definition, scope and importance of environmental study - composition of atmosphere. ECOSYSTEM: Concept, Structure and Function, Energy flow. Biodiversity

BookBenny Joseph, “Environmental Science and Engineering”, Tata McGraw-Hill, New Delhi, 2010.

ENVIRONMENT

DEFINITION: Surrounding and everything that affect an organism during its lifetime SCOPE

Conservation of nature and natural resources. Conservation of biological diversity. Control of environmental pollution. Stabilization of human population and environment. Social issues in relation to development and

environment. Development of non-polluting renewable energy

system and providing new dimension to nation’s security.

IMPORTANCE OF ENVIRONMENTAL SCIENCE

Brings in us the awareness of environmental issues like

Global warming, depletion of ozone layer, dwindling forest, energy resources, loss of global biodiversity etc.

Deals with the analysis of the processes in Water, air, land, soil and organisms which leads to

pollute or degrade environment

Helps us for establishing standard for safe, clean and healthy natural ecosystem

Deals with important issues like Safe and clean drinking water, hygienic living

conditions and clean and fresh air, fertility of land, healthy food and development

Composition of the Atmosphere

i) Permanent Gases

Gas Symbol Percent (by Volume) Dry Air

Nitrogen N2 78.08

Oxygen O2 20.95

Argon Ar 0.93 Neon Ne 0.0018 Helium He 0.0005 Hydrogen H2 0.00006

Xenon Xe 0.000009

ii) Variable GasesGas (and Particles) Symbol Percent (by

Volume) Water vapor H2O 0 to 4 Carbon dioxide CO2 0.038 Methane CH4 0.00017 Nitrous oxide N2O 0.00003 Ozone O3 0.000004 Particles (dust, soot, etc.)

0.000001

Chlorofluorocarbons (CFCs)

0.00000002

For CO2, 380 parts per million means that out of every million air molecules, 380 are CO2 molecules+Stratospheric values at altitudes between 11 km and 50 km are about 5 to 12 ppm.

Permanent Gases 78% Nitrogen (N2) 21% Oxygen (O2) <1% Argon (Ar)

Relative percentages of the permanent gases remain constant up to 80-100km high (~ 60 miles!)

This layer is referred to as the Homosphere (implies gases are relatively homogeneous)

Homosphere: Turbulent mixing causes atmospheric composition to be fairly homogenous from surface to ~80-100 km (i.e., 78% N2, 21% O2)

Heterosphere: Above ~80-100km, much lower density, molecular collisions much less, heavier molecules (e.g., N2, O2) settle lower, lighter molecules (e.g., H2, He) float to top

Structure of the Atmosphere

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Atmosphere is divided into four major layers Troposphere, Stratosphere, Mesosphere and Thermosphere

Troposphere Extents up to 8 km at the poles and 16 km at the

equator 3/4th of the atmospheric mass Clouds, Storms and convective motions Greater height of troposphere in summer than in

winter Plays major role in pollution control Fairly uniform decrease in temperature (6 °C/min) to a

minimum of about – 60 °C

Stratosphere Temperature is constant upward to about 20 km, then

increases to 0 °C near its outer limit This is due to absorption of UV radiation by ozone Mean altitude is about 50 km

Mesosphere Tempearature decreases slowly but then sharply

to a minimum of about -75°C at 80 km Most meteorites burn and disintegrate due to

increasing friction in this layer

Thermosphere The temperaterue again rises to very high values at

times it approaches 2,000°C and even more at about 500 km depending on solar activity

However as the gas molecules are too sparse to transfer the energy and hence the heat is not realized

Hydrosphere Describes the combined mass of water found on,

under, and over the surface of a planet This includes water in liquid and frozen forms in

groundwaters, glaciers, oceans, lakes and streams

Saline water account for 97.5% of this amount. Fresh water accounts for only 2.5%. o Of this fresh water 68.7% is in the "form of ice and

permanent snow cover in the Arctic, the Antarctic, and in the mountainous regions.

o Next, 29.9% exists as fresh groundwaters. o Only 0.26% of the total amount of fresh waters on

the Earth is concentrated in lakes, reservoirs and river systems

Biosphere

Global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere

The life sustaining resources (air, water, food) are withdrawn from the biosphere and cycled through the biosphere only

ECOSYSTEMThe ecological unit consisting of biotic factors (living) and abiotic factors (non-living) in a specific area. For example forest, grassland, desert, aquatic etc.

STRUCTURE AND FUNCTION OF AN ECOSYSTEMAn ecosystem has the following two components—1. Abiotic2. Biotic3. Decomposer

1. Abiotic component includes—(A) Physical

(1) Sunlight (for photosynthesis)(2) Water (essential for living beings)(3) Temperature (necessary to get survive)(4) Soil (provide base and nutrients)

(B) Chemical(1) Proteins(2) Carbohydrates(3) Fats(4) Minerals etc.

2. Biotic component(1) Producers /Autotrophs(2) Consumer/ heterotrophs(3) Decomposers

Producers: They are chlorophyll bearing, self nourishing organisms, which prepare organic compounds from inorganic raw materials, through the processes of photosynthesis e.g. all green plants.

Consumers: They depend on the energy, produced by the producer. Different categories of consumer are herbivores, carnivores and omnivores.

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Decomposers: They attack on dead animals, producers etc. and convert the complex organic compounds, locked in to them in to, simpler compounds (by the process of decomposition and disintegration) and then recycle all the nutrients back. For example bacteria and fungi.

Atmosphere Thick blanket of mixture of permanent and variable

gases and suspended liquids and solids that entirely envelops the earth.

Density of air 1.225 kg/m3 at 15⁰C at sea level Density of water 1 g /cc Atmospheric pressure – 1 cm2 of a column from sea

level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N.

Mass – 500000 tonnes (one millionth of earth mass) 50% lies below 5.5 km 49% lies between 5.5 km to 30 km altitude Atmosphere is bound to earth by gravity. Acts as a great Canopy to protect the earth’s suface

from the full range of solar effects Under water for every 1 cm a pressure of 1 gram/cm2

would be increased.

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