Unit-iv unit-iv environmental Hygiene


Methods of air sampling 3. Impingement



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Atmospheric-pollution


Methods of air sampling

3. Impingement

3. Impingement

    • To collect atmospheric particles in a liquid medium
    • The air is sucked through a glass instrument at a defined rate into the fluid
    • The microbial load: determined by examining the fluid
    • 4. Precipitation

    • The precipitation of atmospheric particles in two ways:
    • 1. Thermal precipitation

    • A slowly moving air current (3 lit/min) is directed between heated & cooled surfaces (distance 0.038 cm)
    • The heated wire/surface repulses the particles towards cold surface
    • They get collected in cold surface
    • The organisms are then transferred on to the agar medium
    • 2. Electrostatic precipitation

    • Collects the organisms on the basis of their electric charge
    • It is a highly efficient instrument for collecting the airborne particles

Methods of air sampling

5. Filtration

5. Filtration

    • The microorganisms are trapped on a filter (cotton, glass wool or paper) or membrane filter
    • Membrane filter technique is considered to be better for the purpose
    • Air is filtered through the membrane
    • The particles (with microbes) are impunged on this membrane
    • The membrane is then placed on a paper saturated with an appropriate medium & incubated
    • 6. Sieve (cascade) samplers

    • It is desired to collect samples of air on the basis of the particle size of the pollutant
    • Sieves of varying sizes are arranged in a cascading manner (one upon the other)
    • Larger particles are collected on top
    • Smaller ones towards the bottom sieves
    • Cascade impactor is a highly efficient trap

Methods of air sampling

Control of air pollution

  • Minimize the production & release of pollutants near the animal or human dwellings
  • Control of dust particles: by improving sanitary conditions within the houses
  • Frequent washings of floor & equipment: controlling the dust within the buildings
  • Vacuum cleaners: used effectively
  • Proper ventilation: a prompt clearance of foul gases & particulate pollutants
  • Filters can be installed to check the entry of external contaminants

  • Use of laminar air flow systems for closed compartments/ cabins
  • Allows unidirectional passage of air through cellulose acetate filters


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