Photoacoustic Extinctiometer

The PAX is a sensitive, high-resolution, fast-response instrument for measuring aerosol optical properties relevant for climate change and carbon particle sensing.


Get accurate measurements for both light absorption and scattering in a single instrument. Then correlate the absorption measurement black carbon mass concentration.

Get continuous and autonomous operation, with no filter collection required and no filter data artifacts.

Count on fast response, one-second resolution, and real-time data display on a high-resolution touch screen.

Achieve excellent scattering coefficient sensitivity with reciprocal nephelometry.

Select from three wavelengths (870 nm [standard], optional 405 nm, or 532 nm), and get wide dynamic range suitable for pristine regions to source sampling.

Particle light-scattering and photoacoustic absorption

  • Modulated diode laser simultaneously measures light scattering and absorption.
  • Absorbing particles heat up and quickly transfer heat to the surrounding air. The periodic heating produces pressure waves that can be detected with a sensitive microphone and quantified to determine aerosol light absorption.
  • Wide-angle integrating reciprocal nephelometer measures the light scattering coefficient of all particles.
  • PAX laser wavelength options include:
    • Red (870 nm) ¬– absorption is highly specific for black carbon (soot) particles; scattering best for large particles
    • Green (532 nm) – measures in the visual range, typically what the human eye observes
    • Blue (405 nm) – absorption correlates to the organic, or brown carbon content; efficient scattering for fine and ultrafine particles

Measured Parameters Absorption coefficient, Babs Scattering coefficient, Bscat
Auxiliary Parameters Temperature Pressure Relative Humidity
Derived Parameters Black carbon (BC) mass Extinction coefficient, Bext Single scattering albedo, SSA Dew Point
Measurement Range – Absorption and Scattering < 1 Mm-1 – 10,000 Mm-1 (870 nm, 60 sec. averaging)
Laser 870 nm (1.4 W) Modulation Frequency: 1500 Hz nominal, square wave
Angular Integration for Scattering 6° to 174°
Sample Flow 1 L/min Flow Control: Critical orifice Diaphragm Pump
Response Time < 10 sec; one-second resolution
Data Averaging Time 1, 10 or 60 seconds, user selectable
Zero Check On demand, or automated at user selectable interval at 5, 15, 20, 30, or 60 minutes. Zero check with high-efficiency filtered air sample.
Front Panel Features
  • Graphical color touch-panel display screen
  • Two USB-A ports
  • Power switch
  • User interface via touch screen or standard keyboard
Rear Panel Connections
  • Sample inlet (compression fitting for ¼” tube)
  • Pump exhaust (compression fitting for ¼” tube)
  • AC and DC power connections
  • Serial RS-232 jack
  • Ethernet port
  • Two analog BNC inputs
  • Four analog BNC outputs
Data Storage Capacity > 200 days
Communications Output Ethernet 100/10 Mbps, RS-232 Serial
Power Requirements 90 – 264 V, 47 – 63 Hz (AC Power) or 12 VDC Power Consumption 45 W
Dimensions 18 cm H x 48 cm W x 61 cm D (7" H x 19" W x 24" D); rack mountable
Weight 18 kg (40 lb)
Environmental Operating Conditions Temperature: 0 – 40°C (32 – 104°F) RH: 0 – 90% RH non-condensing
Computer Requirements for PMC Software (Computer not included)
  • Windows XP, Vista, or Windows 7
  • Minimum 1GB RAM

Hard-shell shipping case suitable for frequent travel

PM 1.0 cyclone inlet (1 liter/min) for particle size selection

PM 2.5 cyclone inlet (1 liter/min) for particle size selection

The Lifecycle Care Program ensures PAX integrity and performance vital to your research mission for 3 years or 3 calls (whichever comes first). When conducting complex and time intensive laboratory or field measurements it is critical to avoid down time, and ensure data collection accuracy. The program consists of 3 key deliverables for each year or call:

  • Instrument Logistics
  • Instrument Integrity
  • Instrument Performance

Lifecycle Care Program Includes:


  • Shipping to and from Droplet Measurement Technologies facility
  • Customs handling, including CARNET ATA if required


  • Incoming instrument evaluation and health check


  • Software and firmware validation
  • 100%-unit functionality test
  • Calibration data
  • Calibration report
  • Certificate of calibration

At times, our technician might discover an instrument issue, which might not be covered by the Lifecycle Care Program or by our product warranty. In such case we will reach out to you with a service & repair estimate to allow you to provide us with the next steps of action.