Collection Techniques:Collection techniques are determined by particulate involved indicates these particulate sampling devices and a summary of the samples of particulates is listed in Gravity Technique:The gravity technique is used to collect settle able particulates that settle out of the atmosphere as a result of the force of gravitational pull. Devices that use this technique are referred to as dust fall sampling instruments. Dust fall sampling may be done with a dust fall brush or cellophane tape coated with a material that captures dust or its sticky surface, but is most often done with a dust fall bucket.
Dust is rinsed from the bucket, evaporated to dryness, and, then, weighed in milligrams. The amount of air sampled is based on the measurement of the area of the bucket. The standard collection period is 30 days. The results are reported in milligrams per square cm per 30 days (mg. /cm2/ month).
Filtration Technique:This technique is used to collect suspended particulates that do not settle out of the air. Particulates are removed from air sample by a suction apparatus, e.g., vacuum pump and are deposited on a porous filter. The high-volume sampler is most frequently used when sampling for suspended particulates. The paper tape sample is another filtration instrument used for suspended particulates.
It is most suitably adopted to collect fine or soiling materials. In the inertial technique, total particulates are collected. In this technique, a polluted air stream containing particulates is drawn into a sampler where obstacles are placed across the path of the airstream. The obstacle causes the airstream to change direction but particles continue to travel in the initial direction and collide with the obstacle. If the obstacle has an adhesive surface, the particulates are impacted on it.
If the obstacle is immersed in a fluid, the particulates are collected by impingement in the liquid. Precipitation Techniques:These techniques are divided into thermal and electrostatic precipitation. Thermal precipitation uses a heated wire to drive radioactive particulates by thermal convection and molecular bombardment out of gaseous stream into a cold collecting surface.
Particles 0.01m to 10m adhere best to a collecting surface.