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Category: Applied and Industrial Microbiology
Indoor and Outdoor Air Sampling, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817473/9781555814502_Chap06-1.gif /docserver/preview/fulltext/10.1128/9781555817473/9781555814502_Chap06-2.gifAbstract:
This chapter aims to provide information on the selection and deployment of air sampling systems for detecting biological agents in both indoor and outdoor settings. In the first half of the chapter, the most widely used collection techniques and classes of currently available instrumentation are presented along with a discussion of the advantages and disadvantages of each. The second half of the chapter addresses field deployment and use of aerosol collection systems, including methods of choosing appropriate sites and ensuring proper sampler placement. Air sampling is performed to document the concentration and composition of airborne biocontaminants. The most important property of aerosol-dispersed biocontaminants to be considered in air sampling is their tendency to settle onto surfaces and be redispersed as a result of air movement and physical disturbance. The process of settling and reaerosolizing continues until the airborne microorganisms are removed from the environment. A wide variety of aerosol samplers and methods have been used to collect airborne biological materials in indoor and outdoor environments. Impaction is the process of forcing particles from the air onto a solid or semisolid surface. Impaction samplers are widely used for the collection of culturable airborne microorganisms. Ideally, air samplers should collect all airborne microorganisms without affecting their ability to be detected. The sampler should be well separated from nearby structures such as walls or pillars. A general rule of thumb is that the sampler should be placed at a distance of twice the height of an obstruction away from the obstruction.
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An impactor collector, the Quartz Crystal Microbalance Cascade Impactor, model PC-2, made by California Measurements, Inc.
An impactor collector, the Quartz Crystal Microbalance Cascade Impactor, model PC-2, made by California Measurements, Inc.
An Andersen cascade impactor.
An Andersen cascade impactor.
An all-glass impinger.
An all-glass impinger.
A Dry Filter Unit collector.
A Dry Filter Unit collector.
An electrostatic collector, the Aerosol-to-Liquid Particle Extraction System (ALPES), made by the Savannah River National Laboratory.
An electrostatic collector, the Aerosol-to-Liquid Particle Extraction System (ALPES), made by the Savannah River National Laboratory.
Samplers may be placed in the mixing chamber of an HVAC system.
Samplers may be placed in the mixing chamber of an HVAC system.
Urban canyon effects cause particles to become either more or less spatially dispersed than might be predicted. The picture on the left shows a particle plume calculated based on wind from the southeast, with no buildings in the path of the plume. The release location is indicated by the black dot. The picture on the right shows a plume calculated using the same quantity of particles and wind direction. In this picture, the path of the plume is significantly affected by the presence of buildings, which are indicated in black. For purposes of comparison, the same buildings are represented in outline in the picture on the left.
Urban canyon effects cause particles to become either more or less spatially dispersed than might be predicted. The picture on the left shows a particle plume calculated based on wind from the southeast, with no buildings in the path of the plume. The release location is indicated by the black dot. The picture on the right shows a plume calculated using the same quantity of particles and wind direction. In this picture, the path of the plume is significantly affected by the presence of buildings, which are indicated in black. For purposes of comparison, the same buildings are represented in outline in the picture on the left.
Samplers should be positioned with the air intake near breathing height.
Samplers should be positioned with the air intake near breathing height.
Ideally, there should be no airflow obstructions in a 360° arc around the sampler. If this is not possible, a 270° arc is acceptable.
Ideally, there should be no airflow obstructions in a 360° arc around the sampler. If this is not possible, a 270° arc is acceptable.
Samplers should be positioned at least 20 m from nearby trees.
Samplers should be positioned at least 20 m from nearby trees.
Samplers should be separated from buildings by a distance of at least twice the height of the building.
Samplers should be separated from buildings by a distance of at least twice the height of the building.
A sampler with a partially obstructed monitoring path. In this case, the sampler placement is acceptable because the prevailing wind directions are toward the building.
A sampler with a partially obstructed monitoring path. In this case, the sampler placement is acceptable because the prevailing wind directions are toward the building.
Example showing cumulative dosage in the subway system and above ground 30 min after a biological-agent release in a two-line hypothetical subway.
Example showing cumulative dosage in the subway system and above ground 30 min after a biological-agent release in a two-line hypothetical subway.
Some commercially available samplers
Some commercially available samplers