Tricolor Absorption Photometer (TAP)

Model 2901


Perform real-time light absorption and black carbon measurements using light transmission through a filter with the Tricolor Absorption Photometer (TAP). Based on a decades-proven design that is simple to use and maintain, the TAP measures light absorption at three wavelengths by particles deposited on a filter. By assuming a mass extinction efficiency, the ambient mass loadings of black carbon can also be determined. The TAP has been deployed at Global Aerosol Watch sites around the world for many years, demonstrating good agreement with other simultaneously deployed filter-based light absorption methods.

  • Eight sample channels and two reference channels
  • Easy to operate and install (external pump required)
  • Multiple-wavelength light source (Red, Green and Blue)
  • Data logging software included


  • Fully characterized and field tested
  • Low maintenance
  • Up to 84 days of unattended operation at a PM2.5 loading of 10ug/m3 and an aerosol single scatter albedo of 0.95
  • Extremely compact – fits inside a 6.3 inch (16 cm) cube!
  • Only 5 minutes required to change filter

Technical Specs

TAP Tech Specs

parameter value
Sample flow rate (volumetric) 2 lpm
Wavelengths 467, 528, 652 nm (365 nm UV option)
Filter media Glass fiber, 47 mm diameter
Noise (standard deviation of 60 sec averages on filtered air) +/- 0.2 Mm-1 (0.02 μg/m3 black carbon mass)
Number of sample spots 8
Number of reference spots 2
Power consumption 36 W
Supply voltage 100-230 VAC
Operating temperature range 15-35°C
Dimensions 6.3 x 4.3 x 4.5 in/16 x 11 x 11.5 cm
Weight 3.6 lbs/1.6 kg
Mounting holes x4, 6-32 tapped holes on bottom 3.375"x 4.375"/(8.57 x 11.11 cm apart

Copyright ©2017 All specifications are subject to change without notice. BMI assumes no responsibility for inaccuracies in this document or for any obligation to update information in this document. BMI reserves the right to change, modify, transfer or otherwise revise this publication without prior notice.

*Some products may be shown with optional accessories, which are sold separately. Items shown may not be to scale.

Applications and Solutions

  • Continuous monitoring of ambient aerosol light absorption and black carbon
  • Laboratory smog chamber studies
  • Visibility reduction studies
  • Aerosol health impacts
  • Long-term climate and air quality monitoring

What’s Included

The TAP includes the following items:

  • Tricolor Absorption Photometer
  • Control software for Windows™ PC
  • Package of 20 spare filters
  • Zero-air filter for white filter check
  • External power supply with chord
  • USB-RS232 converter cable
  • Operating manual


The TAP comes with a Graphical User Interface (GUI) for Windows™ PC (not included) to allow easy configuration and operation of the instrument. The GUI allows you to set the sampling average time, a wait time between averages, start and end filter spots as well as the transmittance threshold values to switch to a new spot. Published corrections are applied internally by the software and all raw and processed data are written to a data file on the PC.

The GUI also automatically allows white filter checks to be performed when new filters are installed. Timelines of transmittance, absorption coefficients, temperatures and sample flow are provided to easily monitor instrument performance. Indicators are provided of expected spot and filter life so you can plan for an upcoming filter change. The TAP has built-in firmware that supplies a constant output stream of serial data if you would like to read the data directly without use of the GUI.


The following optional accessories are available:

TAP Accessories

Part Number Description
TAP-FIL100 Package of 100 sample filters
TAP-P115 External vacuum pump, 115 V
TAP-P230 External vacuum pump, 230 V
TAP-PC Computer with TAP control software
3105 Thermodenuder
TAP-Kit Maintenance kit for 2901 TAP


TAP Brochure

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