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Photoacoustic Extinctiometer (PAX)
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COMING SOON...
The Photoacoustic Extinctiometer (PAX) is a sensitive, high-resolution, fast-response instrument for measuring optical aerosol properties relevant for climate radiative forcing and carbon particle sensing. The instrument directly measures in-situ light absorption and scattering of aerosol particles, from which it derives extinction, single scattering albedo and black carbon (soot) mass concentration. With no filter collection required, and therefore no filter-media artifacts, the PAX provides a highly accurate measure of absorption from black carbon.
Advantages:
Direct in-situ measurement of light absorption and scattering in a single instrument Ensemble measurement correlates to black carbon mass concentration Reciprocal nephelometry provides excellent scattering coefficient sensitivity Choice of wavelengths: 870 nm (standard); other optional wavelengths (future) Real-time, fast response, one-second resolution Wide dynamic range suitable for pristine regions to source sampling Continuous and autonomous operation High-resolution touch screen display for real-time data and instrument status No filter collection required - no filter data artifacts
Research Applications:
Air quality and visibility Atmosphere and climate Health effects Combustion source emissions Biomass burning
Suitable for fixed site, mobile or airborne sampling
What is Scattering, Absorption, Extinction and Single Scattering Albedo?
The scattering coefficient is a measure of the ability of particles to scatter light photons, while the absorption coefficient is a measure of how many photons are absorbed. The coefficients are expressed as a number proportional to the amount of photons scattered or absorbed per unit distance.
The extinction coefficient is the sum of the scattering and absorption coefficients. In climate models, the extinction coefficient is used to help determine the amount of solar radiation that is blocked from reaching the surface of the earth. Single scattering albedo (SSA) is a measure of the reflectivity of a particle and is a key optical characteristic in assessing the radiative effects of aerosols. SSA is the dimensionless ratio of the scattering relative to extinction. Albedo is one for a perfectly white object and zero for a perfectly black object. SSA helps determine whether aerosols have a heating or cooling effect on climate in their interaction with solar radiation.
How Does the Instrument Operate?
The PAX uses a single modulated diode laser to measure light scattering and absorption in parallel. The standard 870-nm wavelength has strong sensitivity to black carbon particles, and relative lack of cross sensitivity from gases and other aerosol species.
A 1 L/min aerosol sample flow is drawn into the PAX using an internal vacuum pump controlled by a critical orifice. The flow is split between the nephelometer and photoacoustic resonator for simultaneous measurement of light scattering and absorption.
The absorption measurement uses in-situ photoacoustic technology as follows. A laser beam directed through the aerosol stream is modulated at the resonant frequency of the acoustical resonator. 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. An integral speaker is used to determine the resonator quality factor and resonance frequency, both of which are needed to quantitatively determine aerosol light absorption. Phase sensitive detection is used for all sensors.
The PAX uses a wide-angle integrating reciprocal nephelometer to measure the light scattering coefficient. The scattering measurement responds to all particle types regardless of chemical makeup, mixing state, or morphology.
What are the specifications for the PAX, and how can I order it?
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