Manual Analyses

Manual analyses for air quality measurements are those that require the sample first be collected and then analyzed in the laboratory. Manual instruments provide no automatic indication of pollution levels.

The manual air sampling instrument in widest use is the high-volume sampler. With this method, ambient air is drawn through a preweighed filter at a rate of approximately 50 atmospheric cubic feet per minute (acfm) for a period of 24 hr. The filter is then removed from the sampler, returned to the laboratory, and weighed. The weight gain, combined with the measured air volume through the sampler, allows the particulate mass concentration, expressed in micrograms per cubic meter, to be calculated.

Reference methods for nearly all gaseous air pollutants involve the use of a wet sampling train in which air is drawn through a collecting medium for a period of time. The exposed collecting medium is then returned to the laboratory for chemical analysis. Sampling trains have been developed that allow sampling of five or more gases simultaneously into separate bubblers. Sequential samplers, which automatically divert the airflow from one bubbler to another at preset time intervals, are also available.

These sampling methods can be accomplished with a modest initial investment; however, the manpower required to set out and pick up the samples, combined with the laboratory analysis, raises the total cost to a point where automated systems can be more economical for long-term studies.

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