Aethalometer

An aethalometer is an instrument for measuring the concentration of optically absorbing (‘black’) suspended particulates in a gas colloid stream; commonly visualized as smoke or haze, often seen in ambient air under polluted conditions.

The aethalometer, a device used for measuring black carbon in atmospheric aerosols, was initially deployed in 1980 and was first commercialized by Magee Scientific.

The gas stream (frequently ambient air) passes through a filter material which traps the suspended particulates, creating a deposit of increasing density.

[3] Improvements in optical and electronic technology permitted the measurement of very small increases in attenuation, such as would occur during the passage of typical ambient air through a filter on a 5- or 10-minute timebase.

The first-ever aethalometer was developed at the Lawrence Berkeley National Laboratory by Anthony D. A. Hansen (who would later found Magee Scientific), Hal Rosen and Tihomir Novakov, and was utilised in an EPA visibility study[4] at Houston in September 1980,[5] with the first real-time data chart of black carbon concentrations in ambient air published in 1981.

A comprehensive summary of black carbon (including a review of aethalometer data) was submitted to the U.S. Congress by the U.S. Environmental Protection Agency in 2012.

[11] The aethalometer has been developed into rack-mounted instruments for use in stationary air quality monitoring installations; transportable instruments which are often used at off-grid locations, operating from batteries or photovoltaic panels in order to make measurements at remote locations; and hand-held portable versions for measurements of personal exposure to combustion emissions.

The attenuation of light transmitted through a deposit of these particles increases linearly with the frequency of the electromagnetic radiation, i.e. inversely with respect to wavelength.

In the absence of aromatic components, the aethalometer data for black carbon concentration is identical at all wavelengths, after factoring in the standard λ−1 response for ‘resistive’ gray materials.

Real-time aethalometer measurements at multiple wavelengths are claimed to separate these different contributions and can apportion the total impact to different categories of sources.

Its only consumable is a filter which needs to be replaced every one or two days in portable models, but larger units have a roll of filtration tape which usually lasts from months to years.