Abstract:Abstract. The multi-pass photoacoustic spectrometer (PAS) is an important tool for the direct measurement of light absorption by atmospheric aerosol. Accurate PAS measurements heavily rely on accurate calibration of their signal. Ozone is often used for calibrating PAS instruments by relating the photoacoustic signal to the absorption coefficient measured by an independent method such as cavity ring down spectroscopy (CRD-S), cavity-enhanced spectroscopy (CES) or an ozone monitor. We report here a calibration … Show more
“…Despite the fact that this photodissociation pathway is well established, ozone has been used to calibrate aerosol PAS instruments with a dearth of discussion on the impact of photodissociation until very recently. Significantly, Davies et al (2018) find good agreement 10 between an ozone calibration and one performed with nigrosin particles, while Bluvshtein et al (2017) measured an ozone calibration half that of the one obtained with nigrosin particles with no obvious explanation for the disparity. Here, we expand on this work by systematically investigating the dependence of the ozone sensitivity on O 2 concentration and performing kinetic modeling suggesting that N 2 as a bath gas results in efficient deactivation of O 3 * .…”
Section: Discussionmentioning
confidence: 96%
“…We chose to take an alternate approach to calibrating with ozone compared to prior studies (Bluvshtein et al, 2017;Davies et al, 2018). Instead of using the flow directly out of an ozone generator, we trapped ozone on a silica gel trap prior to analysis.…”
Section: Resultsmentioning
confidence: 99%
“…Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols for PAS (Lack et al, 2006(Lack et al, , 2012, recent works exploring its validity have come to contradictory conclusions: Bluvshtein et al (2017) saw a discrepancy between ozone calibrations and particle-based calibrations, while Davies et al (2018) found this not to be the case. Concurrent to these publications, we have been exploring the use of ozone as a PAS calibrant for multipass, multi-wavelength, aerosol photoacoustic spectrometers; our observations are presented here to add to the discussion on the topic.…”
Section: Introductionmentioning
confidence: 97%
“…All lasers were operated simultaneously. The refractive index from Bluvshtein et al (2017) was used to calculate nigrosin absorption cross sections using Mie theory assuming a geometric standard deviation of 1.05. Mie theory calculations were performed in MATLAB.…”
Section: Ozone Measurementsmentioning
confidence: 99%
“…As noted above, Bluvshtein et al (2017) conducted a systematic study of calibrants for a multipass photoacoustic spectrometer. They measured light absorbing aerosols, including nigrosin, Suwannee River fulvic acid, and Pahokee peat fulvic 25 acid.…”
Abstract. Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols in both the laboratory and in field campaigns. It has low detection limits, measures suspended aerosols, and is insensitive to scattering. But PAS requires rigorous calibration to be applied quantitatively. Often, a PAS instrument is either filled with a gas of known concentration and absorption cross section, such that the absorption in the cell can be calculated from the product of the two, or the absorption is measured independently with a technique such as cavity ringdown spectroscopy. Then, 5 the PAS signal can be regressed upon the known absorption to determine a calibration slope that reflects the sensitivity constant of the cell and microphone. Ozone has been used for calibrating PAS instruments due to its well-known UV-visible absorption spectrum and the ease with which it can be generated. However, it is known to photodissociate up to approximately 1120 nmpathway, which is likely to lead to inaccuracies in aerosol measurements. Two recent studies have investigated the use of O 3 for PAS calibration but have reached seemingly contradictory conclusions 10 with one finding that it results in a sensitivity that is a factor of two low and the other concluding that it is accurate. The present work is meant to add to this discussion by exploring the extent to which O 3 photodissociates in the PAS cell and the role that the identity of the bath gas plays in determining the PAS sensitivity. We find a 5% loss in PAS signal attributable to photodissociation at 532 nm in N 2 but no loss in a 5% mixture of O 2 in N 2 . Furthermore, we discovered a dramatic increase of more than a factor of two in the PAS sensitivity as we increased the O 2 fraction in the bath gas, which reached an asymptote near 15 100% O 2 that nearly matched the sensitivity measured with both NO 2 and nigrosin particles. We interpret this dependence with a kinetic model that suggests the reason for the observed results is a more efficient transfer of energy from excited O 3 to O 2 than to N 2 by a factor of 22-55 depending on excitation wavelength.
“…Despite the fact that this photodissociation pathway is well established, ozone has been used to calibrate aerosol PAS instruments with a dearth of discussion on the impact of photodissociation until very recently. Significantly, Davies et al (2018) find good agreement 10 between an ozone calibration and one performed with nigrosin particles, while Bluvshtein et al (2017) measured an ozone calibration half that of the one obtained with nigrosin particles with no obvious explanation for the disparity. Here, we expand on this work by systematically investigating the dependence of the ozone sensitivity on O 2 concentration and performing kinetic modeling suggesting that N 2 as a bath gas results in efficient deactivation of O 3 * .…”
Section: Discussionmentioning
confidence: 96%
“…We chose to take an alternate approach to calibrating with ozone compared to prior studies (Bluvshtein et al, 2017;Davies et al, 2018). Instead of using the flow directly out of an ozone generator, we trapped ozone on a silica gel trap prior to analysis.…”
Section: Resultsmentioning
confidence: 99%
“…Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols for PAS (Lack et al, 2006(Lack et al, , 2012, recent works exploring its validity have come to contradictory conclusions: Bluvshtein et al (2017) saw a discrepancy between ozone calibrations and particle-based calibrations, while Davies et al (2018) found this not to be the case. Concurrent to these publications, we have been exploring the use of ozone as a PAS calibrant for multipass, multi-wavelength, aerosol photoacoustic spectrometers; our observations are presented here to add to the discussion on the topic.…”
Section: Introductionmentioning
confidence: 97%
“…All lasers were operated simultaneously. The refractive index from Bluvshtein et al (2017) was used to calculate nigrosin absorption cross sections using Mie theory assuming a geometric standard deviation of 1.05. Mie theory calculations were performed in MATLAB.…”
Section: Ozone Measurementsmentioning
confidence: 99%
“…As noted above, Bluvshtein et al (2017) conducted a systematic study of calibrants for a multipass photoacoustic spectrometer. They measured light absorbing aerosols, including nigrosin, Suwannee River fulvic acid, and Pahokee peat fulvic 25 acid.…”
Abstract. Photoacoustic spectroscopy (PAS) has become a popular technique for measuring absorption of light by atmospheric aerosols in both the laboratory and in field campaigns. It has low detection limits, measures suspended aerosols, and is insensitive to scattering. But PAS requires rigorous calibration to be applied quantitatively. Often, a PAS instrument is either filled with a gas of known concentration and absorption cross section, such that the absorption in the cell can be calculated from the product of the two, or the absorption is measured independently with a technique such as cavity ringdown spectroscopy. Then, 5 the PAS signal can be regressed upon the known absorption to determine a calibration slope that reflects the sensitivity constant of the cell and microphone. Ozone has been used for calibrating PAS instruments due to its well-known UV-visible absorption spectrum and the ease with which it can be generated. However, it is known to photodissociate up to approximately 1120 nmpathway, which is likely to lead to inaccuracies in aerosol measurements. Two recent studies have investigated the use of O 3 for PAS calibration but have reached seemingly contradictory conclusions 10 with one finding that it results in a sensitivity that is a factor of two low and the other concluding that it is accurate. The present work is meant to add to this discussion by exploring the extent to which O 3 photodissociates in the PAS cell and the role that the identity of the bath gas plays in determining the PAS sensitivity. We find a 5% loss in PAS signal attributable to photodissociation at 532 nm in N 2 but no loss in a 5% mixture of O 2 in N 2 . Furthermore, we discovered a dramatic increase of more than a factor of two in the PAS sensitivity as we increased the O 2 fraction in the bath gas, which reached an asymptote near 15 100% O 2 that nearly matched the sensitivity measured with both NO 2 and nigrosin particles. We interpret this dependence with a kinetic model that suggests the reason for the observed results is a more efficient transfer of energy from excited O 3 to O 2 than to N 2 by a factor of 22-55 depending on excitation wavelength.
The radiative effects of biomass‐burning aerosols on regional and global scales can be substantial. Accurate modeling of the radiative effects of smoke aerosols requires wavelength‐dependent measurements and parameterizations of their optical properties in the UV and visible spectral ranges along with improved description of their chemical composition. To address this issue, we used a recently developed approach to retrieve the time‐ and spectral‐dependent optical properties of ambient biomass‐burning aerosols from 300 to 650 nm wavelengths during a regional nighttime bonfire festival in Israel. During the biomass burning event, the overall absorption at 400 nm increased by about 2 orders of magnitude, changing the single scattering albedo from a background level of 0.95 to 0.7. Based on the new retrieval method, we provide parameterizations of the wavelength‐dependent effective complex refractive index from 350 to 650 nm for freshly emitted and slightly aged biomass‐burning aerosols. In addition, PM2.5 filter samples were collected for detailed offline chemical analysis of the water‐soluble organics that contribute to light absorption. Nitroaromatics were identified as major organic species responsible for the increased absorption at 400 to 500 nm. Typical chromophores include 4‐nitrocatechol, 4‐nitrophenol, nitrosyringol, and nitroguaiacol; oxidation‐nitration products of methoxyphenols; and known products of lignin pyrolysis. Our findings emphasize the importance of both primary and secondary organic aerosols from biomass burning in absorption of solar radiation and in effective radiative forcing.
Structural color fabrication attracting significant interest for science and art is usually restricted by costly and time‐consuming structuring processes or inerasable characteristics of structures. Herein, by developing a universal, low‐cost technical solution—the nanosecond laser irradiation of ink (Solvent Black 7) layers coated on metal—laser‐induced heterogeneous permanent/erasable nanostructures (LIHPEN) are produced successfully on multiple metals, especially noble metals, without ablation damage to intrinsic surfaces. LIHPEN consist of uniform laser‐induced periodic surface structures produced by surface plasmon polariton excitation of metals and can be extended into 2D hybrid micro/nanostructures by introducing the direct laser interference patterning technique. LIHPEN technology operated under a large processing parameter window can realize space‐selective erasability of prepared structures by controlling processing parameters, which determine the ink‐layer carbonization degree and thus the permanent or erasable characteristic. Because ink layers can be coated manually, in addition to realizing digital scanning patterns, LIHPEN technology can be integrated with traditional artistic techniques to solidify and color artworks without risk of information loss and leakage in digital copying. LIHPEN with good durability can exhibit vivid structural colors on metals, demonstrating its great potential in fields of artwork iridescent coloring, encryption, and anti‐counterfeiting, particularly those requiring customization, personalization, and rewritability.
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