Black carbon (BC) is a primary pollutant produced by the incomplete combustion of fuel. Its association with toxic and carcinogenic compounds makes it the pollutant species most associated with adverse health effects. Its absorption of light makes it a major climate forcing agent, second only to CO2. Unlike CO2, emissions of which are directly related to the carbon content of the fuel, the emissions of BC can differ by orders of magnitude from one combustion source to another, depending on the quality of combustion. Consequently, the emission of BC cannot be predicted: it has to be measured.
The Aethalometer collects aerosol particles on a spot on a filter tape. The spot is illuminated from one side, and the transmitted light is measured on the other side. A blank, unloaded 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 amount of material deposited 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, sulphates, 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 light). Some compounds of organic aerosols – such as brown carbon and biomass smoke – may absorb light more strongly at shorter wavelengths. The Aethalometer analyses simultaneously at multiple 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, 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 offers artifact-free measurements (DualSpot), detailed aerosol characterization (multi-wavelength analysis), and reliable operation, making it the preferred choice for both research and long-term BC/BrC monitoring studies. Its design directly addresses issues such as filter-loading errors and environmental instability, which commonly plague other BC instruments.
Further details:
The Aethalometer uses patented DualSpot technology to automatically correct for filter-loading effects in real time. This delivers precise black carbon (BC) data even at high concentrations without the need for post-processing. High-quality data is essential for accurate source apportionment.
With seven or nine optical wavelengths (from 340 to 950 nm), the Aethalometer can distinguish between different sources of carbonaceous aerosols in real time - – such as BC from diesel exhaust and BrC from biomass burning.
The Aethalometer is built for field use, with low power requirements and proven durability in all conditions. Some instruments have been in service for decades.
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 have been used in more than 10,000 scientific studies (Google Scholar) in a wide variety of applications. With five decades of experience, we know more about black carbon than anyone else: we’re able to answer any question our users may have, from practical setup to advanced scientific support.
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