Model AE33 Aethalometer
The Aethalometer is the instrument most-used in the world for the real-time measurement of aerosol Black Carbon. The Model AE33 is the culmination of almost 40 years of experience and development. It provides accurate data with aerosol speciation on time-scales as rapid as 1 second, using our patented DualSpot™ technology and multi-wavelength optical analysis.
The Model AE33 ‘Next Generation’ Aethalometer incorporates scientific and technical advances which offer improved measurement performance, user features, networking and communications. The ‘Neutral Density Optics Kit’ provides a validation of the analytical performance that is traceable to fundamental standards. Built-in test programs offer routine checks of performance and stability. These features provide the Quality Assurance that is essential for routine monitoring and research use.
The Aethalometer collects and analyzes aerosol particles continuously. The aerosol-laden air stream is drawn through a spot on a filter tape at a measured flow rate. Simultaneously, the tape is illuminated by light: and sensitive detectors measure the intensities of light transmitted through an un-exposed portion of the tape acting as a reference; versus the collecting spot. As optically-absorbing material accumulates on the spot, the intensity of light transmitted through it, gradually decreases. The decrease in light intensity from one measurement to the next is interpreted as an increase in the amount of collected material. This increase amount is divided by the known air-flow volume to calculate the concentration.
In the new Model AE33 Aethalometer, two sample spots are collected from the same input air stream with different rates of accumulation, and analyzed simultaneously. The two results are combined mathematically to eliminate the “Filter Loading Effect” nonlinearity, and provide an accurate measurement of the aerosol concentration.
Additionally, the analysis is made at 7 optical wavelengths spanning the spectrum from 370 nm to 950 nm. Increases of optical absorption at shorter wavelengths may be interpreted in terms of the presence of so-called “Brown” carbonaceous material, usually an indicator of emissions from biomass combustion.
The Model AE33 Aethalometer has been developed with input from the research and monitoring communities, and is designed for reliable operation under all conditions ranging from state‐of‐the‐art research to routine air-quality monitoring.
The DualSpot™ measurement method
The Model AE33 Aethalometer incorporates the patented DualSpot™ measurement method. This completely solves the loading-dependent nonlinearity which affects the data from any filter-based optical analyzer. The method explicitly does not require any knowledge or assumption about the existence, origin or magnitude of any optical nonlinearity: in fact, the calculation yields the “Loading Compensation Parameter” as an instrumental data output, which may offer insights into the origins and optical properties of the aerosol.
7-WAVELENGHT OPERATION: UV-IR, 1Hz DATA
The analysis is performed at 7 optical wavelengths spanning the range from the near-infrared (950 nm) to the near-ultraviolet (370 nm). The sequencing of illumination and analysis is performed on a 1-Hz timebase. This yields the complete spectrum of aerosol optical absorption with one data line every second.
REAL-TIME SOURCE APPORTIONMENT
An Ångström Exponent model is used in real time to calculate the fraction of BC that may be attributed to biomass combustion.
CALIBRATION AND IN-FIELD VALIDATION
The optical performance of the Model AE33 Aethalometer may be validated by the ‘Neutral Density Optical Filter Kit’, consisting of four precision optical elements whose absorbance is traceable to fundamental standards. Software routines measure the optical intensities at all wavelengths and compare the analysis at the instant with the original reference values. Other built-in test programs offer routine checks of stability and leakage. These features provide the Quality Assurance that is essential both for routine monitoring and research use.
USER AND COMMUNICATIONS INTERFACES
User and communications interfaces permit remote monitoring of operation; data retrieval; performance of internal tests; and reporting of ‘state‐of‐health’ parameters. Networked services offer automated status reports, issuing daily ‘Green’ reports when the instrument is functioning correctly; ‘Yellow’ reports when the instrument detects that it will need routine attention soon; and ‘Red’ reports immediately upon detecting any fault condition.
RUGGED, RELIABLE, AUTOMATIC
The Aethalometer has been developed over almost 40 years to offer rugged, reliable, and automatic operation. The Aethalometer recovers automatically from power interruptions and no operator attention is required for weeks or months, other than replacing the roll of filter tape.
- Supply voltage: 100-240 V~, 50/60 Hz
- Max power consumption: 90 W. Typical power consumption: 25 W
- Measurement wavelengths: 370, 470, 520, 590, 660, 880 and 950 nm
- Air flow: set-points of 2, 3, 4 and 5 LPM
Environmental operating conditions
- Indoor or sheltered use only: the Aethalometer is not weatherproof.
- Altitude: up to 3000 m with internal pump. Increased flow at very high altitudes possible with external pump on request.
- Temperature range: 0 – 40 degrees Celsius (instrument)
- Relative humidity range: non-condensing. Note that it is essential to prevent condensation of humid outdoor sample air, if the instrument is located in a chilled (air-conditioned) environment.
- Chassis material: sheet metal
- Dimensions: standard 19”/6U, rack mount
- Weight: approx. 20 kg
- Sampling air: inlet / outlet type – ¼” NTPF
- Communication: 3x USB type A, 3x COM, 1x Ethernet
- 8.4” SVGA display with LED backlight
- Basic control: touch-screen
- Optional control: standard PC keyboard and mouse via front-panel USB ports.
- Red, Yellow, Green status LEDs
Magee Scientific Aethalometer® Model AE33 – Stability and Clean air tests
Magee Scientific Aethalometer® Model AE33 – Flow verification procedure
Magee Scientific Aethalometer® Model AE33 – Neutral Density Optical validation procedure
Magee Scientific Aethalometer® Model AE33 – Leakage test
Magee Scientific Aethalometer® Model AE33 – Flow calibration procedure
Magee Scientific Aethalometer® Model AE33 – Installation of a new fiter tape roll
Magee Scientific Aethalometer® Model AE33 – Chamber Sliders greasing
Magee Scientific Aethalometer® Model AE33 – Cleaning the optical Chamber
Magee Scientific Aethalometer® Model AE33 – Installation of a new cartridge filter
Magee Scientific Aethalometer® Model AE33 – Field Installation Retrofit of Tape Drive Grip Spring
Dr. Tony Hansen (Magee Scientific Co.) about Black Carbon
Magee Scientific can provide Aethalometer accessories and routine supplies such as those shown below. Please inquire with our sales team about your specific needs.
SAMPLE STREAM DRYER
Drying the aerosol sample stream is highly recommended to provide accurate measurement data and to protect the equipment from water condensation.
In hot, humid locations, the water vapor content of the ambient sample air may be very large. This can lead to inaccuracies in the BC measurement – but, more seriously, there is the possibility of water condensation inside the instrument which can lead to permanent damage. This issue is solved by the use of our Sample Stream Dryer.
The interaction of water with aerosol species changes their physical properties. Consequently, the World Meteorological Organization has recommended that all aerosol measurements should be performed under conditions where the Relative Humidity is 40% or lower (WMO/GAW 2003; Wiedensohler, 2014).
Many stations in hot, humid locations have air-conditioned interiors. If the indoor air-conditioning temperature Ta is comparable to or lower than the dewpoint (condensation temperature) Td of the outside ambient air, water will condense in the tubing and inside the instrument. This will not only completely in-validate the data, but it can also cause permanent damage to the instrument.
The Magee Scientific Sample Stream Dryer removes water vapor from the inlet flow by means of a semi-permeable Nafion membrane. This membrane selectively absorbs molecules of water vapor from the air-stream and passes them to a space on the other side of the membrane, maintained at a low absolute pressure by means of a vacuum pump.
The Magee Scientific Sample Stream Dryer can reduce the dew point temperature by up to 14 degrees Celsius at a flow rate of 5 LPM. The equipment is self-contained, automatic, and includes a display screen which shows the input and output hygrometric properties. A data cable can connect to the Model AE33 Aethalometer so that the temperature and humidity data are incorporated into the Aethalometer’s data files.
The Magee Scientific Sample Stream Dryer can be used to remove water vapor from the inlet stream to any aerosol instrument, not just an Aethalometer.
NEUTRAL DENSITY OPTICAL VALIDATION KIT
The Neutral Density Optical Filter Kit provides validation of the reproducibility of the photometric detectors.
The optical performance of the Model AE33 Aethalometer may be validated in the field by the ‘Neutral Density Optical Filter Kit’, consisting of four precision optical elements containing precision glass whose absorbance is traceable to primary photometric standards maintained by national organizations such as NIST (USA), NPL (UK), BIPM (EU), etc. Software routines measure the optical intensities at all wavelengths and compare the analysis during the test, with the original reference values. This validates the reproducibility of the Aethalometer’s fundamental measurement of optical Attenuation.
AMBIENT METEOROLOGICAL SENSOR
The Ambient Meteorological Sensor is a non-aspirated unit which measures air temperature, relative humidity and barometric pressure. It uses a Pt100 element for Temperature; a compensated solid-state capacitive sensor for Relative Humidity; and a piezo-resistive pressure transducer for Pressure. The sensing elements are protected by a UV-resistant polymer shield. A data cable (supplied in 10-m. or 20-m. lengths) connects the sensor to the AE33, and its data is automatically imported and merged with the Black Carbon measurements.
The Model AE33 Aethalometer collects its samples on a proprietary filter tape made of glass fibers coated with PTFE/PET, and supported on a mechanical backing for transport in the instrument. When the spot reaches a pre-set loading density, the tape is advanced to create a new spot. Each roll of tape is 10 m. in length and will last from a few weeks to a few months, depending on the average concentration of BC in the sampled atmosphere and the operational flow-rate that is chosen.
Ambient atmospheres include suspended particles of large aerodynamic size such as pollen, dust, etc. These particles are not strongly optically absorbing and therefore do not interfere with the Aethalometer® analysis: however, after lengthy use a deposit of dust in the internal optics will degrade performance. To exclude large particles, and to provide analysis of a known respirable size fraction, we recommend use of size-selective inlets designed to exclude particles of aerodynamic size greater than a specified cut point at a specified sample air flow rate. We offer the ‘Sharp-Cut Cyclones’ designed by BGI (USA) and now manufactured by Mesa Labs (USA). These inlets are usually attached directly to the sample inlet tube at the point of entry, but may also be installed in-line closer to the Aethalometer..
BGI model SCC-1.828. Provides a cut point of 2.5µm at a sample flow rate of 5 LPM.
BGI model SCC-1.197. Provides a cut point of 2.5µm at a sample flow rate of 2 LPM, or 1µm at a sample flow rate of 5 LPM.
BGI model SCC-0.732. Provides a cut point of 1µm at a sample flow rate of 2 LPM.
BGI ‘Mini-PM’ Inlet Kit
The BGI ‘Mini-PM’ Inlet Kit offers impaction jet inserts to provide size selective capabilities of TSP, PM-4, PM-2.5, and PM-1, when operated at a flow rate of 5 LPM.
For situations where the Aethalometer® must be shipped or transported frequently, we recommend the use of Pelican® transit cases. These provide internal padding; a sturdy waterproof exterior; and integrated retractable handle and roller wheels.
GENERAL QUESTIONS ABOUT THE AETHALOMETER
WHAT IS BLACK CARBON? WHY SHOULD WE MEASURE IT?
Black Carbon 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 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.
HOW DOES THE AETHALOMETER WORK?
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, un-loaded portion of the filter is used as a reference. The ‘optical attenuation’, “ATN”, is a measure of the absorption of light, 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.
HOW DOES THE AETHALOMETER MEASURE ONLY BC, WHILE THE AMBIENT AIR IS A MIXTURE OF MANY POLLUTANTS SUCH AS GHGS, 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 are associated with ‘brown Carbon’ and biomass smoke – may absorb more strongly at shorter wavelengths. The Aethalometer analyzes at 7 wavelengths and is able to discriminate “diesel” emissions from “wood smoke”.
WHY DON’T WE NEED TO CALIBRATE THE LIGHT SOURCE INTENSITY?
The Aethalometer measures the Attenuation of the light transmitted through the sample-collecting spot, relative to the intensity of light transmitted through a blank portion of the tape acting as a Reference. This ratio is independent of .the absolute intensity of the source. Therefore, changes in the optical source intensity are irrelevant, and the source intensity never needs to be adjusted or calibrated.
DOES THE LIGHT SOURCE INTENSITY EVER FAIL?
Even if the output intensity of the light source changes, the ATN measurement is not affected, since it is the ratio of two signals. The optical source in the Aethalometer is an array of LED chips which are operated at much less than their maximum rated power. Consequently, these LED sources are expected to last almost indefinitely.
AE 33 software – latest release and other important documents
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