Black carbon (BC) is a primary pollutant produced by the incomplete combustion of fuel. Its association with toxic and carcinogenic compounds makes it the Number-1 pollutant species most associated with adverse health effects. Its absorption of light makes it the Number-2 climate forcing agent, second only to CO2. Unlike CO2, whose emissions are directly related to the carbon content of the fuel, the emission of BC can differ by orders of magnitude from one combustion source to another. Consequently, the emission of BC cannot be predicted and has to be measured.
The Aethalometer collects aerosol particles on the spot on a filter tape. The spot is illuminated from one side, and the transmitted light is measured on the other side. A blank, un-loaded portion of the filter is used as a reference. The optical attenuation, ATN, is a measure of light absorption and is directly proportional to the density of absorbing material on the spot. The rate at which ATN increases is proportional to the rate of accumulation of absorbing material. Knowing the sample air flow rate, the concentration in the air stream is calculated. This analysis is performed at multiple optical wavelengths since some aerosol species may have enhanced optical absorption at shorter wavelengths.
Great question - How does the Aethalometer measure only black carbon, while the ambient air is a mixture of many pollutants such as greenhouse gases, sulfates, nitrates, CO2, etc.?
The Aethalometer collects aerosols on a filter tape – but gases pass through it. Aerosol black carbon is the only species with a very strong optical absorption at 880 nm (infra-red). Some compounds of organic aerosols – such as brown carbon and biomass smoke – may absorb more strongly at shorter wavelengths. The Aethalometer analyzes at several wavelengths and can discriminate diesel emissions from wood smoke.
The filter loading effect refers to the progressive reduction in measurement sensitivity as aerosol particles accumulate on the filter. As the filter darkens, the optical path is altered, leading to a non-linear underestimation of black carbon (BC) concentrations over time.
To address this, the Aethalometer employs a patented DualSpot technology developed by Aerosol Magee Scientific. This method uses two parallel filter spots exposed to different flow rates. By continuously comparing the optical attenuation rates between the two spots, the instrument can dynamically quantify and correct for the loading effect in real time.
This correction is further refined through embedded software algorithms that calculate a compensation parameter (commonly referred to as k), which reflects the degree of non-linearity introduced by particle accumulation. This approach ensures more precise, stable, and reliable black carbon measurements, even during long-term unattended operation or in environments with high particulate concentrations.
Accurate correction of the loading effect is essential not only for reliable black carbon quantification but also for correct source apportionment, especially when distinguishing between fossil fuel and biomass burning emissions.
In summary:
The Aethalometer outperforms alternatives through its almost artifact-free measurements (DualSpot), detailed aerosol characterization (multi-wavelength), and autonomous operation, making it the preferred choice for long-term BC/BrC monitoring in research, compliance, and climate studies. Its design directly addresses pitfalls like filter-loading errors and environmental instability, which commonly plague other BC instruments.
In few more details:
The Aethalometer uses patented DualSpot technology to automatically correct for filter-loading effects in real time. This means you get precise black carbon (BC) readings even at high concentrations without the need for complicated post-processing, which is also important for source apportionment algorithm to perform optimally.
With seven or nine optical wavelengths (form 340 or 370 to 950 nm), the Aethalometer can distinguish between different sources of BC - such as diesel exhaust and biomass burning, and can also analyse brown carbon (BrC) data.
It’s built for field use, with low power requirements and proven durability in all conditions. We have been servicing instruments even 15 years old that worked perfectly, apart from minor glitches.
The Aethalometer provides real-time data with time resolution as fast as one second. This allows users to monitor rapid changes in air quality or to use the instrument for specific applications, such as emission factors, mobile measurements, monitoring wildfire smoke, etc.
Features like automatic QA/QC, built-in diagnostics, and remote operation make the Aethalometer simple to deploy and maintain, whether in the lab or the field.
Aethalometer data are used in more than 10.000 scientific studies (source Google Scholar) in a variety of applications. With decades of experience, we know more about black carbon than anyone else, and we’re ready to answer any question our customers may have, from practical setup to advanced scientific support.
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