PPT File

1. Air Sampling
Presented to: Mam Hira Dar
Presented by:Amina Haq
Aleena Zafeer
Tooba Firdous

2. Contents
• Air sampling
• Types of contaminant
• Contaminant definition
• Air sampling calculation
• Air sampling method

3. Air sampling
• Capturing the contaminant from a known volume of air, measuring the
amount of contaminant captured and expressing it as a concentration.
• The air passes through a filter medium.
• The volume of air is measured against the amount of contaminant captured.
This gives the concentration.

4. Types of contaminants in air
There are three types of contaminant according to their physical properties:
 Particulates
 Vapors
 Gases
Particulates can be further subdivided into:
o Aerosols
o Dusts
o Fumes
o Smoke
o Mists

5. Contaminant definition
Aerosol: Dispersion of solid particles of microscopic size in air
Dust: Solid particulate capable of temporary suspension in air.
Fumes: Solid particle produced by condensation from the gaseous phase.
Fumes are usually derived from the heating of a solid to its melting point
and the subsequent cooling of gas produced.

6. Smoke: Particle resulting from incomplete combustion of organic matter
consisting predominantly carbon and oxides of carbon.
Mist: Dispersion of liquid droplets in air usually large enought to be seen by
naked eye.
Vapor: Gaseous phase substance that usually exist as a liquid or solid at
room temperature and pressure.
Gas: A substance which does not normally exist as a liquid or solid at
normal room temperature and pressure.

7. Air sampling calculation
An air sample requires three basic measurements:
• Amount of pollutant collected
• Flow of air through the medium
• The run time in minutes.
• Flow rate ×sampling time(in minute) = sample volume
• Concentration in microgram per cubic meter or in ppm

8. Air sampling methods
1.Based on particulate pollutants
Sedimentation
Filtration
Impingement
Precipitation
oThermal precipitation
oElectrostatic precipitation

9. Sedimentation
•Measure the
amount of dust
settles to the
ground as a result
of gravitational
force.

10. Particulate pollutant having size of 10 micro meter can be collected with
99% efficiency.
Sampling period varies from 7-30 days.
The sampler consists of dust fall jar fitted with a funnel.
A liquid is added to collector to prevent the solid blown out from the jar
by air.
Collected dust is evaporated to dryness and weighed in mg.

11. oAir volume: particulate matter collected from how much volume of air.
oDust properties: collection of particulate matter depends on mass and
diffusion of particles.
oMeasures total particulate matter: sedimentation process does not
differentiate between particle size.
oTime consuming
oSimple, inexpensive and requires no electrical power and moving parts.

12. Filtration
• Technique used in the collection of air pollutants of size smaller than 10 micro meter in
diameter.
• The particulates are removed from the air sample by suction apparatus through a porous filter
where particulates are deposited.
• Air passes through a membranes filled with small pores.
• The air can pass through while tiny holes trap the contaminants.
Sampling period: 24 hours
Air volume sucked: 2000 cubic meter
Particulate concentration: micro gram per cubic meter

13. Impingement
• Based on inertial technique in which particles are collected from the high
velocity air directed toward the obstacles placed across the path of air.
• Particulates collide with the obstacle and air changes its direction.
• If the obstacle are adhesive surface then particles are imprinted on it and
this is known as dry impingement.
• If obstacle is wet by any liquid then it is called wet impingement.

14. Precipitation
There are two types of precipitation:
o Thermal precipitation
o Electrostatic precipitation
Thermal precipitation; Particles moves towards the
lower temperature region when subjected to a strong
temperature gradient.
 The temperature gradient are normally in the order of
3000per centimeter.
 This technique is used to collect the particle of size
0.001 micrometer with high efficiency.

15. Electrostatic precipitation
• These precipitators are
electrically charged to
force radioactive
particulates to migrate
out the air steam onto
the collection surface.

16. Air sampling of the gaseous
pollutants
•Absorption sampling
•Adsorption sampling
•Condensation sampling

17. Absorption sampling
• Gaseous pollutants are absorbed in solvent when both the pollutant and
absorbent are in close contact.
• Liquid react with the gaseous pollutant to form a non gaseous pollutant
• Alkaline for acidic gases
• Acidic solution for alkaline gases
• Oils for hydrocarbons

18. Adsorption sampling
• Gaseous pollutants are adsorbed on
the solid surface of;
Activated carbon
Silica gel
Activated alumina
• As the surface area increases
adsorption increases.

19. Condensation
• The conversion of vapor or gas to a liquid.
• Used to collect radioactive gases, hydrocarbons and non reactive
gases.
• As the gaseous pollutant pass through the different temperature
range condensers where temperature is below the boiling point of the
gaseous pollutant will trap in the liquid.