environmental chemistry

1. Atmospheric Chemistry
Composition ,Pressure & Temp, profile of Atmosphere

2. • Environment:
• Environment means the surrounding in which we live or environment is
taken to mean all those which are physical, chemical, organic or non-organic
components of atmosphere, lithosphere and oceans.
• Environmental Chemistry:
• Environmental chemistry is the science pertaining to the study of different
chemical processes occurring in the environment and it includes the study of
sources and their adverse effects of chemical species or substance formed
either by natural sources or by human activity or alteration on air, soil and
water environment.

3. • Pollution:
❖Substances having adverse effects on human beings, plants and animals
when they are present in the environment (air, water and soil) are termed as
pollution.
• Environmental Pollution:
❖Any substance or parameter or factor in environment which has adverse
effects on life of humans, plants and animals either directly or indirectly are
categorized as environmental pollution.

4. • Pollutants:
❖A pollutant has been defined as any solid, liquid or gaseous substance
present in such a concentration as it may be or tend to be injurious to the
environment.
• Air Pollution:
According to WHO, air pollution is defined as
“Substance put into the air by the activity of mankind upto such a
concentration sufficient to cause harmful effects to his health, vegetables,
property or interfere with the enjoyment of his property.

5. Atmosphere:
❖The atmosphere refers to the protective blanket of gases which are surrounding the
earth and protects it from the hostile environment of outer space. This thin gaseous
envelope forms the basis for the maintenance of life on earth. Transmits only near
ultraviolet, visible, near infrared radiation (300-500nm) and radio waves while
filtering out tissue, damaging ultraviolet radiation below about 300nm.
❖Plays a major role in maintaining the heat balance of the earth, through adsorption
of infrared radiations emitted from the sun and re-emitted from the earth.
• The composition of the atmosphere is predominately determined by biological
processes acting in concert with physical and chemical change

6. Composition of the Atmosphere:
❖ The components of the atmospheremay be divided somewhat into major, minor & trace constituents.
1. Major Components:
Nitrogen……….. 78.08% Oxygen…………20.95%
2. Minor Components:
Argon……………..9.34 × 10-1 (0.934%) Carbon dioxide…… 3.14 × 10-2 (0.0314%)
3. Trace Components:
Neon, Helium, Methane, nitrous oxide, hydrogen, sulphur dioxide, ozone, nitrogendioxide,
ammonia, carbon monoxide.
In addition to these, air may be having 0.1- 0.5 % water. Although the concentrations of the major atmospheric
components remain the same, howeverthe concentrations of trace species, which play key role to many
atmospheric processes,are changing. It is becoming apparent that man’s activities are beginning to change the
composition of the atmosphere overa range of scales, leading to, for example, increased acid deposition,
stratospheric ozoneloss and potentially climate change.

7. ❖Density Profile :
Density of the atmosphere decreases sharply with increase in altitude. Over
99% of the total mass of the atmosphere is found to be present within 30 km
of earth surface. The characteristics of the atmosphere have been found to
vary greatly particularly with altitude or other factors like season, latitude, time
and even solar energy.

8. ❖Mean Free Path:
The mean free path of the species in the atmosphere increases over many
orders of magnitude with increasing altitude. Mean free path mean the average
distance travelled by a particle before collision with another particle
❖Temperature & Pressure profile:
Temperature and pressure in the atmosphere may vary with a wide range.
Temperature may be as low as 13°C and as high as 1700°C.Atmospheric pressure
drops from 1atm at sea level to 3.0×10-7 atm at height of 100km from sea level.

9. ❖ Pressure Profile of the Atmosphere:
Atmospheric pressure tends to decrease as an approximately exponential function of altitude.
The pressure at any given height is given by exponential equation
𝑃ℎ = 𝑃° 𝑒Mgh ⁄ RT
Here
Ph = Pressure at a given height P° = Pressure at zero altitude
M = Average gram molecular weight of air g = acceleration due to gravity
h = altitude in cm R = Gas constant
At an altitude of about 8km is only about 39% of the sea level pressure. Actual atmospheric
pressure deviates from ideal expectation of pressure fall because of mixing of air masses and
non- uniform temperature distribution with altitude. The actual pressure is somewhat higher
upto 15km than expected and somewhat lower at altitude above 15km. The pressure decreases
by a factor of 10 for each approximately 20km increase in altitude.

10. Regions of the atmosphere:
• Atmosphere can be divided into different regions depending upon the system of classification followed.
➢ Generally it is classified as
❖ Upper atmosphere….Theregion of the atmosphereabove 50km of the earths surface. It is heterogenous in
its composition and species present in this part are quite different than those found in lower atmosphere.
❖ Lower atmosphere…..This region of atmosphereextends upto 50km of the earth,s surface. This region is
homogenous in its composition.
➢ Anothersystem divides as
❖ Homo-sphere……Theregion of atmosphere having little variation in its composition. It refers to lower
layers.
❖ Hetero-sphere…..The region of the atmosphere having wide variation in its composition.