1 / 26

Outline

Outline. Introduction Instruments designed and fabricated at the Desert Research Institute, Reno Emphasis on the Integrating Nephelometer for scattering measurements Compare with Radiance nephelometer during a field study at Ft. Bliss, Texas Summary.

iorwen
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Outline Introduction Instruments designed and fabricated at the Desert Research Institute, Reno Emphasis on the Integrating Nephelometer for scattering measurements Compare with Radiance nephelometer during a field study at Ft. Bliss, Texas Summary

  2. Atmospheric Aerosol Applications and Research • Radiation transfer, light scattering and absorption, emission. • Climate simulation • Visibility at the National Parks • Military applications - sensor performance and plume visibility • Cloud albedo (Twomey effect, more aerosol, more competition for water vapor, smaller droplets, ammonium sulfate aerosol) • Cloud lifetime (Black carbon causes local heating from sunlight absorption, cloud dissipation). • Health effects • PM 2.5 levels are legislated • Likely that PM will be further differentiated into E.C., O.C., etc. • Source Level Combustion • Engine performance • Power plants

  3. Why is light extinction measurement important? • Aerosol Radiative Transfer and Climate impacts • Optical Remote Sensing • Atmospheric Visibility

  4. Visibility: Good for tourism, bad for military when engine plumes become visible. • IMPROVE: (Interagency Monitoring of PROtected Visual Environments) • Aerosols are a dominant influence on man-made visibility impairment. • Aerosol optical properties are very important and are measured. National Park Service, Forest Service, Fish and Wildlife Service, Bureau of Land Management, and Environmental Protection Agency

  5. DRI Instruments for light Extinction Measurements • Photoacoustic absorption instrument • Integrating-Sphere scattering instrument • Cavity Ring-Down (CRD) total extinction instrument

  6. Sketch of the Photoacoustic Instrument • Basic principles: • Laser light is power modulated by the chopper. • Light absorbing aerosols convert light to heat - a sound wave is produced. • Microphone signal is a measure of the light absorption. • Light scattering aerosols don't generate heat.

  7. Aerosol Optical Properties: Absorbing particles. For small optical depths, and D < 0.1 µm: I(L)/I(0) = e(-L L), L(1/m) ≈ S.O.C (m2/g) x r (g/m3), L = path length, r = aerosol concentration by mass. Absorption dominates for D < 0.1 µm (Rayleigh scattering). Aside: For non-absorbing aerosols, Extinction=Scattering. Note the strong dependence of the scattering coefficient on diameter!

  8. Photoacoustic instrument:What it looks like

  9. DRI CRD Extinction Instrument (few 1/Mm to 1000 1/Mm)

  10. DRI CRD Extinction Instrument • A path length of approximately 10 km due to high reflecting mirrors • measures total light extinction

  11. Nephelometers Measure Light Scattering These instruments operate by illuminating a fixed sample volume from the side, and observing the amount of light that is scattered by particles and gas molecules in the direction of a photomultiplier tubes. The instruments integrate over scattering angles of 7-170°

  12. Scattered intensity and forward angle

  13. Scattered intensity and forward angle

  14. DRI Nephelometer with < 1 deg. truncation error.

  15. National Instrument’s Labview is used for data acquisition and signal processing.

  16. National Instrument’s Labview is used for data acquisition and signal processing.

  17. SERDP Field project at Ft. Bliss, TX

  18. DRI nephelometer at Ft. Bliss, TX

  19. Radiance neph at Ft. Bliss, TX Forward angle truncation of 7 deg. DRI neph. Signal over 4 times compared to radiance Dust particles as big as 20 m from the road

  20. Example of Calibration using Rayleigh gases

  21. DRI Nephelometer at Ft. Bliss, TX 20 s time averages Radiance forward angle trunc. of 7 deg. DRI neph. has < 1 deg. DRI neph. Signal over 4 times compared to radiance Dust particles as big as 20 m from the road

  22. Summary The integrating Nephelometer developed at the DRI provides considerable improvements for scattering measurements over the existing instruments Further evaluation of the nephelometer undergoing currently at the Reno Aerosol Optics Experiment A closure experiment ensures reliable measurements from the instruments

  23. Thanks for your attention…

More Related