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• 1. [Article] Third-generation FAGE instrument for tropospheric hydroxyl radical measurement

  The authors have constructed a single-stage, frequency-doubled, copper vapor laser-pumped dye laser to be used in the measurement of atmospheric hydroxyl radical concentrations. This laser can be tuned ...

  Citation × Citation Citation Abstract Copy Title: Third-generation FAGE instrument for tropospheric hydroxyl radical measurement Author: Chan, C. Y., Hard, Thomas M., Mehrabzadeh, A. A., O'Brien, Robert J. Year: 1990 The authors have constructed a single-stage, frequency-doubled, copper vapor laser-pumped dye laser to be used in the measurement of atmospheric hydroxyl radical concentrations. This laser can be tuned to either the 1← 0 or 0← 0 vibrational transition in the electronic transition ²Sigmalarr²Pi. A new photon counting instrument is used for HO fluorescence detection. Theoretical and experimental studies of instrument performance show better sensitivities and reduced photolytic interferences than have been possible with previous systems based upon Nd:YAG pumping. Title: Third-generation FAGE instrument for tropospheric hydroxyl radical measurement Author: Chan, C. Y., Hard, Thomas M., Mehrabzadeh, A. A., O'Brien, Robert J. Year: 1990 The authors have constructed a single-stage, frequency-doubled, copper vapor laser-pumped dye laser to be used in the measurement of atmospheric hydroxyl radical concentrations. This laser can be tuned to either the 1← 0 or 0← 0 vibrational transition in the electronic transition ²Sigmalarr²Pi. A new photon counting instrument is used for HO fluorescence detection. Theoretical and experimental studies of instrument performance show better sensitivities and reduced photolytic interferences than have been possible with previous systems based upon Nd:YAG pumping. Close

• 2. [Article] Intercomparison of Local Hydroxyl Measurements by Radiocarbon and FAGE Techniques

  A direct intercomparison of near-surface tropospheric HO concentration measurements by two different techniques was made in October–November 1992 at a rural site near Pullman, Washington. The atmosphere ...

  Citation × Citation Citation Abstract Copy Title: Intercomparison of Local Hydroxyl Measurements by Radiocarbon and FAGE Techniques Author: Campbell, Malcolm J., Hall, Brad D., Sheppard, John C., Utley, Philip L., O'Brien, Robert J., Hard, Thomas M., George, Linda Acha Year: 1995 A direct intercomparison of near-surface tropospheric HO concentration measurements by two different techniques was made in October–November 1992 at a rural site near Pullman, Washington. The atmosphere at the site is believed to contain low levels of anthropogenic pollution. The instruments' inlets were located at the same height (3.5 m) above the ground and were separated by 10 m along a line normal to the prevailing wind. Readings of the FAGE3 and radiocarbon instruments showed a high correlation (r² = 0.74) despite HO concentrations that were frequently near the detection limit of the instruments. An unweighted least squares regression shows a slope significantly different from unity, indicating different calibration scales of the two instruments Title: Intercomparison of Local Hydroxyl Measurements by Radiocarbon and FAGE Techniques Author: Campbell, Malcolm J., Hall, Brad D., Sheppard, John C., Utley, Philip L., O'Brien, Robert J., Hard, Thomas M., George, Linda Acha Year: 1995 A direct intercomparison of near-surface tropospheric HO concentration measurements by two different techniques was made in October–November 1992 at a rural site near Pullman, Washington. The atmosphere at the site is believed to contain low levels of anthropogenic pollution. The instruments' inlets were located at the same height (3.5 m) above the ground and were separated by 10 m along a line normal to the prevailing wind. Readings of the FAGE3 and radiocarbon instruments showed a high correlation (r² = 0.74) despite HO concentrations that were frequently near the detection limit of the instruments. An unweighted least squares regression shows a slope significantly different from unity, indicating different calibration scales of the two instruments Close

• 3. [Article] FAGE determination of tropospheric HO and HO₂

  FAGE (fluorescence assay with gas expansion) was developed as a sensitive technique for the detection of low-concentration free radicals in the atmosphere. The application of FAGE to tropospheric hydroxyl ...

  Citation × Citation Citation Abstract Copy Title: FAGE determination of tropospheric HO and HO₂ Author: George, Linda Acha, Hard, Thomas M., O'Brien, Robert J. Year: 1995 FAGE (fluorescence assay with gas expansion) was developed as a sensitive technique for the detection of low-concentration free radicals in the atmosphere. The application of FAGE to tropospheric hydroxyl (H0) and hydroperoxyl (H0₂) radicals has yielded calibrated measurements of both species in both clean air and highly polluted urban air. For HO calibration, a continuously stirred tank reactor provides a uniform external HO concentration, which can be measured by gas chromatography of an HO-reactive hydrocarbon. The aerodynamics of the air-sampling process has been modeled computationally, with results that agree with empirical observations of the effects of nozzle diameter on HO loss during sampling. The authors have also modeled airborne fluid dynamics of a FAGE probe. They have recently obtained FAGE sensitivity as high as ± 1 × 10⁶ cm-³ for a 6-minute averaging period, during field studies in highly polluted Los Angeles air, yielding a 7:1 signal-to-noise ratio near midday. Multipass excitation can further improve this sensitivity. The authors summarize their recent field studies of HO and HO², current work on improved calibration methods, other improvements, and future plans. Title: FAGE determination of tropospheric HO and HO₂ Author: George, Linda Acha, Hard, Thomas M., O'Brien, Robert J. Year: 1995 FAGE (fluorescence assay with gas expansion) was developed as a sensitive technique for the detection of low-concentration free radicals in the atmosphere. The application of FAGE to tropospheric hydroxyl (H0) and hydroperoxyl (H0₂) radicals has yielded calibrated measurements of both species in both clean air and highly polluted urban air. For HO calibration, a continuously stirred tank reactor provides a uniform external HO concentration, which can be measured by gas chromatography of an HO-reactive hydrocarbon. The aerodynamics of the air-sampling process has been modeled computationally, with results that agree with empirical observations of the effects of nozzle diameter on HO loss during sampling. The authors have also modeled airborne fluid dynamics of a FAGE probe. They have recently obtained FAGE sensitivity as high as ± 1 × 10⁶ cm-³ for a 6-minute averaging period, during field studies in highly polluted Los Angeles air, yielding a 7:1 signal-to-noise ratio near midday. Multipass excitation can further improve this sensitivity. The authors summarize their recent field studies of HO and HO², current work on improved calibration methods, other improvements, and future plans. Close