# What is a Micro-Aethalometer; how do portable Black Carbon (BC) Monitors work?

The screenshot below is from MIT's Erik Velasco's presentation Particle exposure and dosage on public transport. My question is about the small, portable Black Carbon (BC) monitor.

From my reading, Black Carbon refers to mostly carbon particles, mostly produced in natural and anthropogenic combustion processes (e.g. forest fires, vehicles...). Unlike most of the particles that fall into the PM10 and PM2.5 classifications, it seems that a very important fraction of BC comes from very small particles of the order 0.1 microns since they are formed during a short time during combustion.

0.1 micron particles are hard to detect using laser scatterometry since they scatter very weakly compared to the larger particles, and the size of the portable meter shown seems quite small for an advanced scatterometer.

Question: How do small, portable Black Carbon (BC) Monitors work? I believe this one is called a Micro-Aethalometer in the presentation; what basic principles do they use to quantify BC in the air that fits in such a small form factor?

From Particle exposure and dosage on public transport, open image in new window for full size.

From The Aeroflex: A Bicycle for Mobile Air Quality Measurements, Bart Elen et al. Sensors 2013, 13, 221-240; doi:10.3390/s130100221 open image in new window for full size.

• I would expect they work like other black carbon monitors, A filter strip is drawn across the air stream for a set time them the reflectance or transmission of light through the filter material is compared to the calibrated value. The site here gives a good description. aethlabs.com/faq – user824 Apr 9 '19 at 15:39
• @Friddy I've written a short answer based on your suggestion, thanks! – uhoh Apr 12 '19 at 8:24

Following @ Friddy's comment, I started reading Aethlabs AE51 FAQ and was quite surprised!

While a conventional aethalometer use a long tape and move it to the new position after each measurement (which could be as fast as one measurement per minute), the compact device shown in the image in question uses a single filter position, and just keeps measuring as it gets darker and darker as black carbon collects.

Q: Do all the microAeth use the same filters?

A: No. The microAeth AE51 uses a T60 Teflon-coated borosilicate glass fiber filter strip which has 1 sampling location and must be manually replaced. The microAeth MA200 uses a roll of Polytetrafluoroethylene (PTFE) filter material housed in a filter tape cartridge which has 15 sampling locations that can automatically advance. The microAeth MA300 and MA350 use a roll of Polytetrafluoroethylene (PTFE) filter material that is housed in a filter tape cartridge which has 85 sampling locations that can automatically advance. Filter tape cartridges have to be manually replaced much less often than a single use filter strip.

Also:

[...] A guide for measurement limits regarding saturation can be found on the AE51 Specifications Sheet. For example, filters need to be changed according to the following BC concentration/flow rate ranges:

 - Avg.   5 µg BC/m3   for 24 hours    @ 100 ml/min
- Avg. 100 µg BC/m3   for  3 hours    @ 50 ml/min
- Avg.   1 mg BC/m3   for 15 minutes  @ 50 ml/min


Compare this to a conventional aethalometer:

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