The Aethalometer: Real-Time Measurement of Aerosol Black Carbon

Aerosol black carbon ("BC" or "EC" [for elemental carbon]) is a ubiquitous component of combustion emissions. It is most obvious in diesel exhaust. However, all combustion sources emit BC (along with other toxic species, and BC can be found in every sample of air.

The Aethalometer uses continuous filtration and optical transmission to measure the concentration of BC in near real time. Tony Hansen* developed the basis for the instrument in the late 1970s. More than a hundred instruments were distributed in the first few years following initial manufacture of the instrument in the mid-1980s—primarily to research laboratories and research stations at remote locations.

Applications
The speciation of inhalable aerosol particulates (PM2.5) in real time is a current topic of considerable interest to the U.S. EPA and government air-quality-management organizations in the states of the USA. A standard for allowable BC concentrations has been legislated by the German government.

In urban locations, Aethalometers monitor combustion-derived particulates where the are high concentrations due to traffic and other emissions. They are being installed across Germany as well as other European countries.

The recent Model AE1x series is designed for automatic, unattended monitoring operation. Its rapid response allows data to be collected on a (typical) three- to five-minute interval, providing immediate identification of source strength and dispersion patterns. In occupational health studies, the Aethalometer can be used to monitor the exposure of workers to exhaust emissions and fumes arising from fuel combustion. Examples include the underground mining environment, railroad and truck drivers, vehicle repair garage technicians, and others.

In the indoor environment, the Aethalometer can be used to monitor the infiltration and trapping of emissions in a building as well as the production and circulation of internal emissions. (The "classic" example of its use is for a building whose air intake is next to the truck unloading dock.)

At remote sites, the presence of BC in the atmosphere is an indicator of the long-range distribution of combustion-derived pollution. The high sensitivity of the Aethalometer allows useful data to be acquired at 1-hr intervals even for the cleanest atmospheres. Aethalometers have been installed in the Arctic, on remote islands and wind-swept ocean coasts, on the periphery of the Antarctic and even at the South Pole.

Operation
The Aethalometer is fully automatic and completely self-contained. Its construction consists of a standard 19-in. enclosed chassis. The chassis includes:

• the filtration and analysis chamber with automatically advancing quartz fiber tape;
• the sample aspiration pump and air mass flow meter or controller (typical flow rates are 2 to 6 L/min); and
• temperature-stabilized optics and electronics.

The instrument's operation is managed by an embedded computer. There are a display screen and keypad that allow for:

• the control of all instrument functions,
• recording the data to a built-in 3.5-in. floppy diskette,
• outputting a digital data stream through a COM-port, and
• outputting an analog voltage terminal that can be programmed either to represent the measured concentration or to function as an on/off alarm.

The Aethalometer operates automatically upon power-up and can be unattended for long periods of time. Power consumption is approximately 100 W at either 115 or 230 VAC. Weight is approximately 35 lbs. Its dimensions are 19-in. rack width, 11-in. height and 12-in. depth.

*Tony Hansen founded Magee Scientific Company in 1986 to manufacture the instrument and promote its use in a wide range of research applications.

Contact: Magee Scientific Company, 1829 Francisco Street, Berkeley, CA 94703 USA. Tel: 510-845-2801; fax: 510-845-7137.

Edited by Paul Hersch