SAMPLING METHODS

PRESENTED BY

AJITH KUMARmohamed sathak engineering college

Ramanatha puram

Sampling

In order to control and remove the air pollutants from air. It is necessary to know the sources of air pollutants and to collect the sample of emission of gases at sources.

The collection of sample at various sources is called stack sampling

Objectives of sampling

To measure quality and quantity of pollutant produced by the source.

To determine the effect of emission througout the year and monthly variation in the year

To determine the effect of emission in different zones/area of the country.

To know the nature of the pollutant source. To estimate the single or mutiple pollutant sources.

To determine the method of control of air pollutants. To implement the local air pollution- control system.

Objectives of sampling

Selection of sampling location

The sampling point should be as far as possible from any disturbing influence, such as elbows, bends, transition pieces, baffles.

The sampling point, wherever possible should be at a distance of 5-10 diameters down-stream from any obstruction and 3-5 diameters up-stream from similar disturbance.

The size of the sampling point may be made in the range of 7-10 cm, in diameter.

Number of stations• Minimum number is three.

The location is dependent upon the wind rose diagram that

gives predominant wind directions and speed. One station must be at upstream of predominant wind

direction and other two must at downstream pre dominant wind direction.

More than three stations can also be established depending upon the area of coverage.

Monitoring of Air pollutants

Source Ambient

As per WHO ambient monitoring protocol

SOxEssential NOx SPM HC CO Additional O3

PointSOX

NOX

COPM

LineCONOxHCRPM

Basic components of sampling

Amount of pollutant collected Flow of air through the medium The run time in minutes.

Flow×time(in minute)=volume through filter in cubic meter

Concentration in microgram per cubic meter or in ppm

AIR SAMPLING METHODS

particulate pollutant

Gaseous and vapour pollutant

particulate pollutant

Air sampling techniques for particulate

pollutants SEDIMENTATION FILTRATION IMPINGEMENT PERCIPITATION 1) THERMAL PRECIPITAION

2) ELECTROSTATIC PRECIPITATION

SEDIMENTATION Used to collect settle able particulate that settle out of the atmosphere as a result of the gravitation forceParticulate pollutant having size of 10 mirco meter can be collected with 99% efficiencyThe sampler consists of simple dust jar fitted with a funnel A liquid is added to collector to prevent the solids blown out from the jar by airCollected dust is evaporated to dryness and then weighed in mgSampling period is 30 days

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

The glass fiber filter of porous size less than 0.1 micro meter is used in high volume sampler

Sampling period: 24 hours Air volume sucked: 2000 cubic meter Particulate concentration: micro gram per cubic

meter

IMPINGEMENT

Based on the inertial technique in which particles are collected from the high velocity air steam directed toward the obstacles placed across the path of air stream

Particulates collide with the obstacle and air changes its direction

If the obstacle are adhesive surface then particles are impacted on it and this is known as dry impingement

If obstacle is wet by any liquid then it is called wet impingement

PRECIPITATION

THERMAL PRECIPITATION :-

Thermal precipitation is based on the principle that the particles move towards the lower temperature region when subjected to a strong temperature gradient

The temperature gradients are normally of the order of 3000 C per centimeter

This technique is used to collect the particle of size 0.001 micrometer with high efficiency

ELECTROSTATIC PRECIPITATION:- Theses precipitators are an electrically charged to

force radioactive particulates to migrate out the air steam onto a collection surface

In this precipitators two electrodes are used positive and negative

When the air stream with particulates pass through the electrodes particles pick up negative charge and migrate towards inner post of the precipitators where got discharged and deposited on the positive electrodes

gaseous pollutants

Air sampling techniques for gaseous pollutants

ABSORPTION SAMPLING ADSORPTION SAMPLING CONDENSATION SAMPLING

ABSORPTION SAMPLING

Gaseous pollutants are absorbed in a 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 GASESACIDIC SOLUTION FOR ALKALINE GASES OILS FOR HYDROCARBONS

ADSORPTION SAMPLING

Gaseous pollutants are adsorbed on the solid surface of activated carbon, silica gel, activated alumina and molecular sieve

As the surface area increases the adsorption increases

CONDENSATION SAMPLING

The conversion of a vapour or gas to a liquid Method used to collect the radioactive gases,

hydrocarbons and non reactive vapors Air pollutant can be trapped by condensation

reaction As the gaseous pollutant pass through the different

temperature range of condensers where the temperature is below the boiling point the gaseous pollutant will trap in the liquid

SOME NEW METHODS OF AIR SAMPLING

Bubble Sampling Air drawn into the impinger is forced through a nozzle,

which is covered by a liquid such as high purity water. The pollutant dissolves in the liquid and is subsequently

analysed, usually by colorimetric techniques.Sorbent Sampling Sorbents are normally contained in a small glass tube with

sealed ends. Air is drawn through the sorbent, which captures molecules

of the gas or vapour to be sampled. The trapped contaminants are released using solvent

washing or heat to a gas chromatograph (GC) for analysis. One of the best known sorbents is charcoal.

THANK YOU