A tapered element oscillating microbalance (TEOM) is an instrument used for real-time detection of aerosol particles by measuring their mass concentration. It makes use of a small vibrating glass tube whose oscillation frequency changes when aerosol particles are deposited on it increasing its

inertia Inertia is the natural tendency of objects in motion to stay in motion and objects at rest to stay at rest, unless a force causes the velocity to change. It is one of the fundamental principles in classical physics, and described by Isaac Newto ...

. TEOM-based devices have been approved by the

U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

for environmental air quality monitoring, and by the U.S.

Mine Safety and Health Administration The Mine Safety and Health Administration (MSHA) () is a small agency of the United States Department of Labor which administers the provisions of the Federal Mine Safety and Health Act of 1977 (Mine Act) to enforce compliance with mandatory sa ...

for monitoring

coal dust Coal dust is a fine-powdered form of coal which is created by the crushing, grinding, or pulverizer, pulverization of coal rock. Because of the brittle nature of coal, coal dust can be created by mining, transporting, or mechanically handling it. ...

exposure for miners to prevent several respiratory diseases.

Operation

Tapered element oscillating microbalance diagram static

The TEOM uses a hollow glass tube as a

microbalance A microbalance is an instrument capable of making precise measurements of weight of objects of relatively small mass: of the order of a million parts of a gram. In comparison, a standard analytical balance is 100 times less sensitive; i.e. it i ...

. Incoming particles are deposited on a filter at the tip of the tube, and the added mass causes a change in its oscillation frequency which is detected electronically. The element is periodically cycled to return it to its natural frequency. The inlet to the device only allows particles of the desired size range to enter. TEOM devices operate continuously and do not need filter changes as frequently as high-volume air samplers. Mechanical noise and dramatic temperature fluctuations can interfere with the operation of a TEOM device. In addition, water droplets cannot be distinguished from particle mass, so the device must adjust the incoming air temperature to cause water droplets to evaporate, or contain a dryer or humidity sensor to adjust the readings. Under ideal conditions, TEOM is just as accurate as the standard reference method, but its sensitivity presents complications for use for environmental monitoring in urban areas. A filter dynamic measurement system (FDMS) can be used to adjust for the volatile component of the mass. TEOM has poor sensitivity to semi-volatile particles due to the temperature and humidity conditions used. TEOM instruments with FDMS alternate between a base cycle and a reference cycle, the latter of which measures the mass loss of the filter when clean air is passed through it, allowing the mass loss during the base cycle to be estimated. It is important that the air conditioning system not cycle over the same period as the TEOM instrument, because this can cause

aliasing In signal processing and related disciplines, aliasing is a phenomenon that a reconstructed signal from samples of the original signal contains low frequency components that are not present in the original one. This is caused when, in the ori ...

Applications

Instruments using TEOM have been designated as Federal Equivalent Methods by the

for environmental air quality monitoring of both coarse and fine

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

(PM₁₀, PM_2.5, and PMc). TEOM instruments are faster than and avoid difficulties with beta attenuation and

quartz crystal microbalance A quartz crystal microbalance (QCM), also known as quartz microbalance (QMB) and sometimes also as quartz crystal nanobalance (QCN), measures a mass variation per unit area by measuring the change in frequency of a quartz crystal resonator. The res ...

(QCM) methods. TEOM is the basis for a continuous personal dust monitor (CPDM) for

in mines, to protect workers from exposure to coal mine dust which leads to

black lung disease Black lung disease (BLD), also known as coal workers' pneumoconiosis, or simply black lung, is an occupational type of pneumoconiosis caused by long-term inhalation and deposition of coal dust in the lungs and the consequent lung tissue's react ...

and

progressive massive fibrosis Progressive massive fibrosis (PMF), characterized by the development of large conglomerate masses of dense fibrosis (usually in the upper lung zones), can complicate silicosis and coal worker's pneumoconiosis. Conglomerate masses may also occur in ...

. Prior to the introduction of CPDMs, dust particles collected on a filter needed to be analyzed in a laboratory, leading to a delay of weeks in obtaining results. Continuous monitoring allows miners to take corrective action such as moving to another area or changing their activities if dust levels exceed exposure limits. In one study this led to a 90% reduction in samples exceeding the dust exposure limit. In February 2016, the U.S.

(MSHA) mandated the use of CPDMs on working sections of underground coal mines, and for workers who have evidence of the development of

pneumoconiosis Pneumoconiosis is the general term for a class of interstitial lung disease where inhalation of dust (for example, ash dust, lead particles, pollen grains etc) has caused interstitial fibrosis. The three most common types are asbestosis, silico ...

. As of 2017, the only CPDM instrument approved by MSHA uses a TEOM. As of 2013, TEOM was not considered suitable for workplace monitoring of

nanomaterials Nanomaterials describe, in principle, chemical substances or materials of which a single unit is sized (in at least one dimension) between 1 and 100 nm (the usual definition of nanoscale). Nanomaterials research takes a materials science ...

due to its cut-off particle sizes of 10, 2.5, or 1 μm, and the physical size of the instrument.

History

TEOM is a proprietary technology developed by Rupprecht and Patashnick Co., Inc. of

Albany, New York Albany ( ) is the List of capitals in the United States, capital city of the U.S. state of New York (state), New York. It is located on the west bank of the Hudson River, about south of its confluence with the Mohawk River. Albany is the oldes ...

, whose successor company (as of 2005) is

Thermo Fisher Scientific Thermo Fisher Scientific Inc. is an American life science and clinical research company. It is a global supplier of analytical instruments, clinical development solutions, specialty diagnostics, laboratory, pharmaceutical and biotechnology s ...

. "TEOM" is a registered trademark. It was originally developed as a fixed-site environmental particulate mass monitor, and TEOM aerosol detectors were available in 1981. Development of the continuous personal dust monitor was originally performed by Rupprecht and Patashnick Co., Inc. and continued by Thermo Fisher under contract from the U.S.

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the List of United States federal agencies, United States federal agency responsible for conducting research and making recommendations for the prevention of work-related occ ...

with input from other government, labor, and industry organizations. Machine-mounted continuous dust monitors have been available since 1997.

Operation

Applications

History

References

Further reading