M. Segal-rosenheimer - Academia.edu (original) (raw)
Papers by M. Segal-rosenheimer
Phys. Chem. Chem. Phys., 2011
Evaluation of pesticides' fate in the atmosphere is important in terms of environmental effects o... more Evaluation of pesticides' fate in the atmosphere is important in terms of environmental effects on non-target areas and risk assessments analysis. This evaluation is usually done in the laboratory using analytical grade materials and is then extrapolated to more realistic conditions. To assess the effect of the pesticide purity level (i.e. analytical vs. technical) and state (i.e. sorbed film vs. airborne particles), we have investigated the oxidation rates and products of technical grade cypermethrin as thin film and in its airborne form, and compared it with our former results for analytical grade material. Technical grade thin film kinetics for both ozone and OH radicals revealed reaction rates similar to the analytical material, implying that for these processes, the analytical grade can be used as a good proxy. Oxidation products, however, were slightly different with two additional condensed phase products: formanilide, N-phenyl and 2-biphenyl carboxylic acid, which were seen with the technical grade material only. OH experiments revealed spectral changes that suggest the immediate formation of surface products containing OH functionalities. For the ozonolysis studies of airborne material, a novel setup was used, which included a long-path FTIR cell in conjugation with a Scanning Mobility Particle Sizer (SMPS) system. This setup allowed monitoring of real-time reaction kinetics and product formation (gas and condensed phases) together with aerosol size distribution measurements. Similar condensed phase products were observed for airborne and thin film technical grade cypermethrin after ozonolysis. Additionally, CO, CO 2 and possibly acetaldehyde were identified as gaseous oxidation products in the aerosols experiments only. A kinetic model fitted to our experimental system enabled the identification of both primary and secondary products as well as extraction of a formation rate constant. Kinetic calculations (based on gaseous products formation rate) have revealed values similar to that of the thin film experiments. Interestingly, heterogeneous oxidation of cypermethrin was also found to generate ultra fine secondary organic aerosols. Again, no significant difference was observed between analytical and technical grade materials. However, particle size distribution was much broader when films were exposed to OH and ozone than to ozone alone.
Optical Sensors and Sensing Congress (ES, FTS, HISE, Sensors), 2019
To realize the potential of spectrometers for airborne sunphotometry, a hybrid instrument incorpo... more To realize the potential of spectrometers for airborne sunphotometry, a hybrid instrument incorporating radiometers and miniature spectrometers is being built. This brings with it several challenges in amplifier design, thermal management and stray-light control.
The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements ... more The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements of spectral aerosol optical depth (AOD), precipitable water and spectral sky radiance, which can be inverted to retrieve aerosol microphysical properties that are critical to assessments of aerosol-climate interactions. Because of data quality criteria and sampling constraints, there are significant limitations to the temporal and spatial coverage of AERONET data and their representativeness for global aerosol conditions.The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument, jointly developed by NASA Ames and PNNL (Pacific Northwest National Laboratory) with NASA Goddard collaboration, combines airborne sun tracking and AERONET-like sky scanning with spectroscopic detection. Being an airborne instrument, 4STAR has the potential to fill gaps in the AERONET data set. The 4STAR instrument operated successfully in the SEAC4RS (Studies of Emissions and Atmosp...
Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles... more Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for global climate change scenarios. Our understanding of aerosol-cloud interactions in the SE Atlantic is hindered both by the lack of knowledge on aerosol and cloud properties, as well as the lack of knowledge about detailed physical pro...
The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements ... more The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements of spectral aerosol optical depth (AOD), precipitable water and spectral sky radiance, which can be inverted to retrieve aerosol microphysical properties that are critical to assessments of aerosol-climate interactions. Because of data quality criteria and sampling constraints, there are significant limitations to the temporal and spatial coverage of AERONET data and their representativeness for global aerosol conditions. The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument, jointly developed by NASA Ames and PNNL with NASA Goddard collaboration, combines airborne sun tracking and AERONET-like sky scanning with spectroscopic detection. Being an airborne instrument, 4STAR has the potential to fill gaps in the AERONET data set. Dunagan et al. [2013] present results establishing the performance of the instrument, along with calibration, engineering flight ...
To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate th... more To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate that daytime aerosol optical depth over low-level clouds is similar to that in neighboring clear skies at the same heights. Based on recent airborne lidar and sun photometer observations above the southeast Atlantic, the mean aerosol optical depth (AOD) difference at 532 nm is between 0 and −0.01, when comparing the cloudy and clear sides, each up to 20 km wide, of cloud edges. The difference is not statistically significant according to a paired t test. Systematic differences in the wavelength dependence of AOD and in situ single scattering albedo are also minuscule. These results hold regardless of the vertical distance between cloud top and aerosol layer bottom. AOD aggregated over ∼ 2 • grid boxes for each of September 2016, August 2017 and October 2018 also shows little correlation with the presence of low-level clouds. We posit that a satellite retrieval artifact is entirely responsible for a previous finding of generally smaller AOD over clouds (Chung et al., 2016), at least for the region and time of our study. Our results also suggest that the same values can be assumed for the intensive properties of free-tropospheric biomass-burning aerosol regardless of whether clouds are present below.
Atmospheric Chemistry and Physics Discussions, 2019
The SouthEast Atlantic (SEA) is host to a climatologically significant biomass burning aerosol la... more The SouthEast Atlantic (SEA) is host to a climatologically significant biomass burning aerosol layer overlying marine stratocumulus. We present directly measured Above Cloud Aerosol Optical Depth (ACAOD) from the recent ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) airborne field campaign during August and September 2016. In our analysis, we use data from the Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) instrument and found an average ACAOD of 0.32 at 501 nm, with an average Ångström exponent (AE) of 1.71. The AE is much lower at 1.25 for the full column (including below cloud level aerosol), indicating the presence of large aerosol particles, likely marine aerosol, embedded within the vertical column. ACAOD is observed to be highest near coast at about 12°S, whereas its variability is largest at the southern edge of the average aerosol plume, as indicated by 12 years of MODIS observations. In comparison to MODIS derived ACAOD and long term fine-mode plume-average AOD, the directly-measured ACAOD from 4STAR is slightly lower than the ACAOD product from MODIS. The peak ACAOD expected from long term retrievals is measured to be closer to coast in 2016 at about 1.5°-4°
Light, Energy and the Environment, 2016
NASA’s ORACLES campaign aims to understand key parameters and processes driving the interactions ... more NASA’s ORACLES campaign aims to understand key parameters and processes driving the interactions of biomass burning aerosols with clouds over the South Atlantic. We describe first results from two hyperspectral instruments deployed in ORACLES-2016.
Journal of Geophysical Research: Atmospheres, 2013
Cirrus clouds are important modulators of the Earth radiation budget and continue to be one of th... more Cirrus clouds are important modulators of the Earth radiation budget and continue to be one of the most uncertain components in weather and climate modeling. Sun photometers are widely accepted as one of the most accurate platforms for measuring clear sky aerosol optical depth (AOD). However, interpretation of their measurements is ambiguous in the presence of cirrus. Derivation of a valid AOD under cirrus conditions was focused previously on correction factors, rather than on derivation of cirrus cloud optical thickness (COT). In the present work, we propose a new approach that uses the total measured irradiance to derive cirrus COT and ice particle effective diameter (D eff). For this approach, we generate lookup tables (LUTs) of total transmittance for the Sun photometer field of view (FOV) due to the direct and scattered irradiance over the spectral range of 400-2200 nm, for a range of cirrus COT (0-4), and a range of ice cloud effective diameters (10-120 mm) by using explicit cirrus optical property models for (a) cirrus only and (b) a two-component model including cirrus and aerosols. The new approach is tested on two cases (airborne and ground-based) using measured transmittances from the 14-channel NASA Ames Airborne Tracking Sun photometer. We find that relative uncertainties in COT are much smaller than those for D eff. This study shows that for optically thin cirrus cases (COT < 1.0), the aerosol layer between the instrument and the cloud plays an important role, especially in derivation of D eff. Additionally, the choice of the cirrus model may introduce large differences in derived D eff .
Journal of Geophysical Research-Atmospheres, 2013
The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral air... more The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral airborne Sun photometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two‐Column Aerosol Project. Root‐mean‐square differences from Aerosol Robotic Network ground‐based observations were 0.01 at wavelengths between 500–1020 nm, 0.02 at 380 and 1640 nm, and 0.03 at 440 nm in four clear‐sky fly‐over events, and similar in ground side‐by‐side comparisons. Changes in the above‐aircraft AOD across 3 km deep spirals were typically consistent with integrals of coincident in situ (on Department of Energy Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, and 0.02 at 355, 450, 532, 550, 700, and 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350 and 1660 nm, excluding strong water vapor and oxygen absorption bands, estimated uncertainties were ~0.01 and dominated by (then) unpredictable throughput changes, up to ±0.8%, of the fiber optic rotary joint. The favorable intercomparisons herald 4STAR's spatially resolved high‐frequency hyperspectral products as a reliable tool for climate studies and satellite validation.
Journal of Geophysical Research: Atmospheres, 2014
Total columnar water vapor (CWV), nitrogen dioxide (NO 2), and ozone (O 3) are derived from a new... more Total columnar water vapor (CWV), nitrogen dioxide (NO 2), and ozone (O 3) are derived from a newly developed, hyperspectral airborne Sun-sky spectrometer (4STAR) for the first time during the two intensive phases of the Two-Column Aerosol Project (TCAP) in summer 2012 and winter 2013 aboard the DOE G-1 aircraft. We compare results with coincident measurements. We find 0.045 g/cm 2 (4.2%) negative bias and 0.28 g/cm 2 (26.3%) root-mean-square difference (RMSD) in water vapor layer comparison with an in situ hygrometer and an overall RMSD of 1.28 g/m 3 (38%) water vapor amount in profile by profile comparisons, with differences distributed evenly around zero. RMSD for O 3 columns average to 3%, with a 1% negative bias for 4STAR compared with the Ozone Measuring Instrument along aircraft flight tracks for 14 flights during both TCAP phases. Ground-based comparisons with Pandora spectrometers at the Goddard Space Flight Center, Greenbelt, Maryland, showed excellent agreement between the instruments for both O 3 (1% RMSD and 0.1% bias) and NO 2 (17.5% RMSD and À8% bias). We apply clustering analysis of the retrieved products as a case study during the TCAP summer campaign to identify variations in atmospheric composition of elevated pollution layers and demonstrate that combined total column measurements of trace gas and aerosols can be used to define different pollution layer sources, by comparing our results with trajectory analysis and in situ airborne miniSPLAT (single-particle mass spectrometer) measurements. Our analysis represents a first step in linking sparse but intense in situ measurements from suborbital campaigns with total column observations from space. However, in many ground-based and airborne applications such concurrent measurements are not available. For example, ground-based (e.g., Aerosol Robotic Network (AERONET)) and airborne Sun photometers measure SEGAL-ROSENHEIMER ET AL.
Light Scattering Reviews 9, 2014
The direct and indirect radiative effects of aerosols suspended in the atmosphere above clouds (A... more The direct and indirect radiative effects of aerosols suspended in the atmosphere above clouds (ACA) are a highly uncertain component of both regional and global climate. Much of this uncertainty is observational in nature most orbital remote sensing algorithms were not designed to simultaneously retrieve aerosol and cloud optical properties in the same vertical column.
The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) concept combines air... more The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) concept combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) and AERONET-like sky scanning capability with state-of-the-art monolithic spectrometry. The overall science goal for the 4STAR is to improve knowledge of atmospheric constituents and their links to climate. The moderate-resolution spectral capability will improve retrievals of gas constituents (e.g., H2O, O3, and NO2) and thereby improve determination of aerosol properties as residual components of the total optical depth. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sun photometry alone. 4STAR also carries the potential for improved cloud retrievals by combining its zenith sky radiance measurements with surface albedo estimates (in analogy to the recentl...
Journal of Quantitative Spectroscopy and Radiative Transfer, 2018
The paper discusses certain limitations on applicability of Spectral Deconvolution Algorithm (SDA... more The paper discusses certain limitations on applicability of Spectral Deconvolution Algorithm (SDA) to aerosol optical depth spectral measurements contaminated by cirrus clouds. Analysis of the synthetic data demonstrates that application of SDA to cloud contaminated measurements can produce significant errors in the apparent optical depth fine mode retrievals. Such application can produce results that just look reasonable and physically admissible but in fact can be relatively far from the truth and therefore can be misleading.
Advanced Environmental, Chemical, and Biological Sensing Technologies VII, 2010
In recent years open-path FTIR systems (active and passive) have demonstrated great potential and... more In recent years open-path FTIR systems (active and passive) have demonstrated great potential and success for monitoring air pollution, industrial stack emissions, and trace gas constituents in the atmosphere. However, most of the studies were focused mainly on monitoring gaseous species and very few studies have investigated the feasibility of detecting bio-aerosols and dust by passive open-path FTIR measurements. The
Journal of Geophysical Research-Atmospheres, 2014
ABSTRACT The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspe... more ABSTRACT The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral airborne Sun photometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two‐Column Aerosol Project. Root‐mean‐square differences from Aerosol Robotic Network ground‐based observations were 0.01 at wavelengths between 500–1020 nm, 0.02 at 380 and 1640 nm, and 0.03 at 440 nm in four clear‐sky fly‐over events, and similar in ground side‐by‐side comparisons. Changes in the above‐aircraft AOD across 3 km deep spirals were typically consistent with integrals of coincident in situ (on Department of Energy Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, and 0.02 at 355, 450, 532, 550, 700, and 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350 and 1660 nm, excluding strong water vapor and oxygen absorption bands, estimated uncertainties were ~0.01 and dominated by (then) unpredictable throughput changes, up to ±0.8%, of the fiber optic rotary joint. The favorable intercomparisons herald 4STAR's spatially resolved high‐frequency hyperspectral products as a reliable tool for climate studies and satellite validation.
Journal of Physical Chemistry C, 2007
Cypermethrin is a synthetic pyrethroid that has become one of the most important insecticides in ... more Cypermethrin is a synthetic pyrethroid that has become one of the most important insecticides in wide-scale use both indoors and outdoors. Although cypermethrin is likely to become adsorbed (following its application) on aerosols and upon stagnant outdoor and indoor surfaces, its atmospheric degradation processes are not well understood yet. Here, we have quantitatively investigated the oxidation of cypermethrin by gaseous ozone, including kinetic analysis and identification of volatile and nonvolatile products. The investigation was done using a novel apparatus, combining two FTIR setups for the parallel analysis of both condensed and gas phases. The nonintrusive analysis method enabled one to follow the reaction in real time without any alteration that may affect the process. The proposed reaction mechanism involves both an ozonide formation and an ester cleavage process that occur due to secondary radical chain reactions. It was found to follow a Langmuir-Hinshelwood mechanism with a half-life time of cypermethrin in relation to average atmospheric ozone level of 50 ppb of about 21 days. These results indicate that the heterogeneous oxidation of cypermethrin by ozone cannot be neglected in the overall environmental fate cycle for this material. Furthermore, several of the yielded condensed products are toxic and more polar than the parent molecule, a fact that makes them possible contaminators of groundwater in contrast to the parent molecule. Gaseous phosgene, a known nerve gas, was found to be generated during the ozonolysis reaction, which may increase the hazard in the use of cypermethrin as an indoor insecticide.
Phys. Chem. Chem. Phys., 2011
Evaluation of pesticides' fate in the atmosphere is important in terms of environmental effects o... more Evaluation of pesticides' fate in the atmosphere is important in terms of environmental effects on non-target areas and risk assessments analysis. This evaluation is usually done in the laboratory using analytical grade materials and is then extrapolated to more realistic conditions. To assess the effect of the pesticide purity level (i.e. analytical vs. technical) and state (i.e. sorbed film vs. airborne particles), we have investigated the oxidation rates and products of technical grade cypermethrin as thin film and in its airborne form, and compared it with our former results for analytical grade material. Technical grade thin film kinetics for both ozone and OH radicals revealed reaction rates similar to the analytical material, implying that for these processes, the analytical grade can be used as a good proxy. Oxidation products, however, were slightly different with two additional condensed phase products: formanilide, N-phenyl and 2-biphenyl carboxylic acid, which were seen with the technical grade material only. OH experiments revealed spectral changes that suggest the immediate formation of surface products containing OH functionalities. For the ozonolysis studies of airborne material, a novel setup was used, which included a long-path FTIR cell in conjugation with a Scanning Mobility Particle Sizer (SMPS) system. This setup allowed monitoring of real-time reaction kinetics and product formation (gas and condensed phases) together with aerosol size distribution measurements. Similar condensed phase products were observed for airborne and thin film technical grade cypermethrin after ozonolysis. Additionally, CO, CO 2 and possibly acetaldehyde were identified as gaseous oxidation products in the aerosols experiments only. A kinetic model fitted to our experimental system enabled the identification of both primary and secondary products as well as extraction of a formation rate constant. Kinetic calculations (based on gaseous products formation rate) have revealed values similar to that of the thin film experiments. Interestingly, heterogeneous oxidation of cypermethrin was also found to generate ultra fine secondary organic aerosols. Again, no significant difference was observed between analytical and technical grade materials. However, particle size distribution was much broader when films were exposed to OH and ozone than to ozone alone.
Optical Sensors and Sensing Congress (ES, FTS, HISE, Sensors), 2019
To realize the potential of spectrometers for airborne sunphotometry, a hybrid instrument incorpo... more To realize the potential of spectrometers for airborne sunphotometry, a hybrid instrument incorporating radiometers and miniature spectrometers is being built. This brings with it several challenges in amplifier design, thermal management and stray-light control.
The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements ... more The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements of spectral aerosol optical depth (AOD), precipitable water and spectral sky radiance, which can be inverted to retrieve aerosol microphysical properties that are critical to assessments of aerosol-climate interactions. Because of data quality criteria and sampling constraints, there are significant limitations to the temporal and spatial coverage of AERONET data and their representativeness for global aerosol conditions.The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument, jointly developed by NASA Ames and PNNL (Pacific Northwest National Laboratory) with NASA Goddard collaboration, combines airborne sun tracking and AERONET-like sky scanning with spectroscopic detection. Being an airborne instrument, 4STAR has the potential to fill gaps in the AERONET data set. The 4STAR instrument operated successfully in the SEAC4RS (Studies of Emissions and Atmosp...
Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles... more Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for global climate change scenarios. Our understanding of aerosol-cloud interactions in the SE Atlantic is hindered both by the lack of knowledge on aerosol and cloud properties, as well as the lack of knowledge about detailed physical pro...
The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements ... more The AERONET (AErosol RObotic NETwork) ground-based suite of sunphotometers provides measurements of spectral aerosol optical depth (AOD), precipitable water and spectral sky radiance, which can be inverted to retrieve aerosol microphysical properties that are critical to assessments of aerosol-climate interactions. Because of data quality criteria and sampling constraints, there are significant limitations to the temporal and spatial coverage of AERONET data and their representativeness for global aerosol conditions. The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument, jointly developed by NASA Ames and PNNL with NASA Goddard collaboration, combines airborne sun tracking and AERONET-like sky scanning with spectroscopic detection. Being an airborne instrument, 4STAR has the potential to fill gaps in the AERONET data set. Dunagan et al. [2013] present results establishing the performance of the instrument, along with calibration, engineering flight ...
To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate th... more To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate that daytime aerosol optical depth over low-level clouds is similar to that in neighboring clear skies at the same heights. Based on recent airborne lidar and sun photometer observations above the southeast Atlantic, the mean aerosol optical depth (AOD) difference at 532 nm is between 0 and −0.01, when comparing the cloudy and clear sides, each up to 20 km wide, of cloud edges. The difference is not statistically significant according to a paired t test. Systematic differences in the wavelength dependence of AOD and in situ single scattering albedo are also minuscule. These results hold regardless of the vertical distance between cloud top and aerosol layer bottom. AOD aggregated over ∼ 2 • grid boxes for each of September 2016, August 2017 and October 2018 also shows little correlation with the presence of low-level clouds. We posit that a satellite retrieval artifact is entirely responsible for a previous finding of generally smaller AOD over clouds (Chung et al., 2016), at least for the region and time of our study. Our results also suggest that the same values can be assumed for the intensive properties of free-tropospheric biomass-burning aerosol regardless of whether clouds are present below.
Atmospheric Chemistry and Physics Discussions, 2019
The SouthEast Atlantic (SEA) is host to a climatologically significant biomass burning aerosol la... more The SouthEast Atlantic (SEA) is host to a climatologically significant biomass burning aerosol layer overlying marine stratocumulus. We present directly measured Above Cloud Aerosol Optical Depth (ACAOD) from the recent ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) airborne field campaign during August and September 2016. In our analysis, we use data from the Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) instrument and found an average ACAOD of 0.32 at 501 nm, with an average Ångström exponent (AE) of 1.71. The AE is much lower at 1.25 for the full column (including below cloud level aerosol), indicating the presence of large aerosol particles, likely marine aerosol, embedded within the vertical column. ACAOD is observed to be highest near coast at about 12°S, whereas its variability is largest at the southern edge of the average aerosol plume, as indicated by 12 years of MODIS observations. In comparison to MODIS derived ACAOD and long term fine-mode plume-average AOD, the directly-measured ACAOD from 4STAR is slightly lower than the ACAOD product from MODIS. The peak ACAOD expected from long term retrievals is measured to be closer to coast in 2016 at about 1.5°-4°
Light, Energy and the Environment, 2016
NASA’s ORACLES campaign aims to understand key parameters and processes driving the interactions ... more NASA’s ORACLES campaign aims to understand key parameters and processes driving the interactions of biomass burning aerosols with clouds over the South Atlantic. We describe first results from two hyperspectral instruments deployed in ORACLES-2016.
Journal of Geophysical Research: Atmospheres, 2013
Cirrus clouds are important modulators of the Earth radiation budget and continue to be one of th... more Cirrus clouds are important modulators of the Earth radiation budget and continue to be one of the most uncertain components in weather and climate modeling. Sun photometers are widely accepted as one of the most accurate platforms for measuring clear sky aerosol optical depth (AOD). However, interpretation of their measurements is ambiguous in the presence of cirrus. Derivation of a valid AOD under cirrus conditions was focused previously on correction factors, rather than on derivation of cirrus cloud optical thickness (COT). In the present work, we propose a new approach that uses the total measured irradiance to derive cirrus COT and ice particle effective diameter (D eff). For this approach, we generate lookup tables (LUTs) of total transmittance for the Sun photometer field of view (FOV) due to the direct and scattered irradiance over the spectral range of 400-2200 nm, for a range of cirrus COT (0-4), and a range of ice cloud effective diameters (10-120 mm) by using explicit cirrus optical property models for (a) cirrus only and (b) a two-component model including cirrus and aerosols. The new approach is tested on two cases (airborne and ground-based) using measured transmittances from the 14-channel NASA Ames Airborne Tracking Sun photometer. We find that relative uncertainties in COT are much smaller than those for D eff. This study shows that for optically thin cirrus cases (COT < 1.0), the aerosol layer between the instrument and the cloud plays an important role, especially in derivation of D eff. Additionally, the choice of the cirrus model may introduce large differences in derived D eff .
Journal of Geophysical Research-Atmospheres, 2013
The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral air... more The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral airborne Sun photometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two‐Column Aerosol Project. Root‐mean‐square differences from Aerosol Robotic Network ground‐based observations were 0.01 at wavelengths between 500–1020 nm, 0.02 at 380 and 1640 nm, and 0.03 at 440 nm in four clear‐sky fly‐over events, and similar in ground side‐by‐side comparisons. Changes in the above‐aircraft AOD across 3 km deep spirals were typically consistent with integrals of coincident in situ (on Department of Energy Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, and 0.02 at 355, 450, 532, 550, 700, and 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350 and 1660 nm, excluding strong water vapor and oxygen absorption bands, estimated uncertainties were ~0.01 and dominated by (then) unpredictable throughput changes, up to ±0.8%, of the fiber optic rotary joint. The favorable intercomparisons herald 4STAR's spatially resolved high‐frequency hyperspectral products as a reliable tool for climate studies and satellite validation.
Journal of Geophysical Research: Atmospheres, 2014
Total columnar water vapor (CWV), nitrogen dioxide (NO 2), and ozone (O 3) are derived from a new... more Total columnar water vapor (CWV), nitrogen dioxide (NO 2), and ozone (O 3) are derived from a newly developed, hyperspectral airborne Sun-sky spectrometer (4STAR) for the first time during the two intensive phases of the Two-Column Aerosol Project (TCAP) in summer 2012 and winter 2013 aboard the DOE G-1 aircraft. We compare results with coincident measurements. We find 0.045 g/cm 2 (4.2%) negative bias and 0.28 g/cm 2 (26.3%) root-mean-square difference (RMSD) in water vapor layer comparison with an in situ hygrometer and an overall RMSD of 1.28 g/m 3 (38%) water vapor amount in profile by profile comparisons, with differences distributed evenly around zero. RMSD for O 3 columns average to 3%, with a 1% negative bias for 4STAR compared with the Ozone Measuring Instrument along aircraft flight tracks for 14 flights during both TCAP phases. Ground-based comparisons with Pandora spectrometers at the Goddard Space Flight Center, Greenbelt, Maryland, showed excellent agreement between the instruments for both O 3 (1% RMSD and 0.1% bias) and NO 2 (17.5% RMSD and À8% bias). We apply clustering analysis of the retrieved products as a case study during the TCAP summer campaign to identify variations in atmospheric composition of elevated pollution layers and demonstrate that combined total column measurements of trace gas and aerosols can be used to define different pollution layer sources, by comparing our results with trajectory analysis and in situ airborne miniSPLAT (single-particle mass spectrometer) measurements. Our analysis represents a first step in linking sparse but intense in situ measurements from suborbital campaigns with total column observations from space. However, in many ground-based and airborne applications such concurrent measurements are not available. For example, ground-based (e.g., Aerosol Robotic Network (AERONET)) and airborne Sun photometers measure SEGAL-ROSENHEIMER ET AL.
Light Scattering Reviews 9, 2014
The direct and indirect radiative effects of aerosols suspended in the atmosphere above clouds (A... more The direct and indirect radiative effects of aerosols suspended in the atmosphere above clouds (ACA) are a highly uncertain component of both regional and global climate. Much of this uncertainty is observational in nature most orbital remote sensing algorithms were not designed to simultaneously retrieve aerosol and cloud optical properties in the same vertical column.
The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) concept combines air... more The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) concept combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) and AERONET-like sky scanning capability with state-of-the-art monolithic spectrometry. The overall science goal for the 4STAR is to improve knowledge of atmospheric constituents and their links to climate. The moderate-resolution spectral capability will improve retrievals of gas constituents (e.g., H2O, O3, and NO2) and thereby improve determination of aerosol properties as residual components of the total optical depth. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sun photometry alone. 4STAR also carries the potential for improved cloud retrievals by combining its zenith sky radiance measurements with surface albedo estimates (in analogy to the recentl...
Journal of Quantitative Spectroscopy and Radiative Transfer, 2018
The paper discusses certain limitations on applicability of Spectral Deconvolution Algorithm (SDA... more The paper discusses certain limitations on applicability of Spectral Deconvolution Algorithm (SDA) to aerosol optical depth spectral measurements contaminated by cirrus clouds. Analysis of the synthetic data demonstrates that application of SDA to cloud contaminated measurements can produce significant errors in the apparent optical depth fine mode retrievals. Such application can produce results that just look reasonable and physically admissible but in fact can be relatively far from the truth and therefore can be misleading.
Advanced Environmental, Chemical, and Biological Sensing Technologies VII, 2010
In recent years open-path FTIR systems (active and passive) have demonstrated great potential and... more In recent years open-path FTIR systems (active and passive) have demonstrated great potential and success for monitoring air pollution, industrial stack emissions, and trace gas constituents in the atmosphere. However, most of the studies were focused mainly on monitoring gaseous species and very few studies have investigated the feasibility of detecting bio-aerosols and dust by passive open-path FTIR measurements. The
Journal of Geophysical Research-Atmospheres, 2014
ABSTRACT The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspe... more ABSTRACT The 4STAR (Spectrometer for Sky‐Scanning, Sun‐Tracking Atmospheric Research), a hyperspectral airborne Sun photometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two‐Column Aerosol Project. Root‐mean‐square differences from Aerosol Robotic Network ground‐based observations were 0.01 at wavelengths between 500–1020 nm, 0.02 at 380 and 1640 nm, and 0.03 at 440 nm in four clear‐sky fly‐over events, and similar in ground side‐by‐side comparisons. Changes in the above‐aircraft AOD across 3 km deep spirals were typically consistent with integrals of coincident in situ (on Department of Energy Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, and 0.02 at 355, 450, 532, 550, 700, and 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350 and 1660 nm, excluding strong water vapor and oxygen absorption bands, estimated uncertainties were ~0.01 and dominated by (then) unpredictable throughput changes, up to ±0.8%, of the fiber optic rotary joint. The favorable intercomparisons herald 4STAR's spatially resolved high‐frequency hyperspectral products as a reliable tool for climate studies and satellite validation.
Journal of Physical Chemistry C, 2007
Cypermethrin is a synthetic pyrethroid that has become one of the most important insecticides in ... more Cypermethrin is a synthetic pyrethroid that has become one of the most important insecticides in wide-scale use both indoors and outdoors. Although cypermethrin is likely to become adsorbed (following its application) on aerosols and upon stagnant outdoor and indoor surfaces, its atmospheric degradation processes are not well understood yet. Here, we have quantitatively investigated the oxidation of cypermethrin by gaseous ozone, including kinetic analysis and identification of volatile and nonvolatile products. The investigation was done using a novel apparatus, combining two FTIR setups for the parallel analysis of both condensed and gas phases. The nonintrusive analysis method enabled one to follow the reaction in real time without any alteration that may affect the process. The proposed reaction mechanism involves both an ozonide formation and an ester cleavage process that occur due to secondary radical chain reactions. It was found to follow a Langmuir-Hinshelwood mechanism with a half-life time of cypermethrin in relation to average atmospheric ozone level of 50 ppb of about 21 days. These results indicate that the heterogeneous oxidation of cypermethrin by ozone cannot be neglected in the overall environmental fate cycle for this material. Furthermore, several of the yielded condensed products are toxic and more polar than the parent molecule, a fact that makes them possible contaminators of groundwater in contrast to the parent molecule. Gaseous phosgene, a known nerve gas, was found to be generated during the ozonolysis reaction, which may increase the hazard in the use of cypermethrin as an indoor insecticide.