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MISR research-aerosol-algorithm refinements for dark water retrievals
摘要： We explore systematically the cumulative effect of many assumptions made in the Multi-angle Imaging SpectroRadiometer (MISR) research aerosol retrieval algorithm with the aim of quantifying the main sources of uncertainty over ocean, and correcting them to the extent possible. A total of 1129 coincident, surface-based sun photometer spectral aerosol optical depth (AOD) measurements are used for validation. Based on comparisons between these data and our baseline case (similar to the MISR standard algorithm, but without the “modified linear mixing” approximation), for 558 nm AOD < 0.10, a high bias of 0.024 is reduced by about one-third when (1) ocean surface under-light is included and the assumed whitecap reflectance at 672 nm is increased, (2) physically based adjustments in particle microphysical properties and mixtures are made, (3) an adaptive pixel selection method is used, (4) spectral reflectance uncertainty is estimated from vicarious calibration, and (5) minor radiometric calibration changes are made for the 672 and 866 nm channels. Applying (6) more stringent cloud screening (setting the maximum fraction not-clear to 0.50) brings all median spectral biases to about 0.01. When all adjustments except more stringent cloud screening are applied, and a modified acceptance criterion is used, the Root-Mean-Square-Error (RMSE) decreases for all wavelengths by 8–27 % for the research algorithm relative to the baseline, and is 12–36 % lower than the RMSE for the Version 22 MISR standard algorithm (SA, with no adjustments applied). At 558 nm, 87 % of AOD data falls within the greater of 0.05 or 20 % of validation values; 62 % of the 446 nm AOD data, and > 68 % of 558, 672, and 866 nm AOD values fall within the greater of 0.03 or 10 %. For the ?ngstr?m exponent (ANG), 67 % of 1119 validation cases for AOD > 0.01 fall within 0.275 of the sun photometer values, compared to 49 % for the SA. ANG RMSE decreases by 17 % compared to the SA, and the median absolute error drops by 36 %.
关键词： AOD,aerosol retrieval,MISR,dark water,?ngstr?m exponent
更新于2025-09-23 15:21:01
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Evaluating the influence of laser wavelength and detection stage geometry on optical detection efficiency in a single-particle mass spectrometer
摘要： Single-particle mass spectrometry (SPMS) is a useful tool for the online study of aerosols with the ability to measure size-resolved chemical composition with a temporal resolution relevant to atmospheric processes. In SPMS, optical particle detection is used for the effective temporal alignment of an ablation laser pulse with the presence of a particle in the ion source, and it gives the option of aerodynamic sizing by measuring the offset of particle arrival times between two detection stages. The efficiency of the optical detection stage has a strong influence on the overall instrument performance. A custom detection laser system consisting of a high-powered fibre-coupled Nd:YAG solid-state laser with a collimated beam was implemented in the detection stage of a laser ablation aerosol particle time-of-flight (LAAP-TOF) single-particle mass spectrometer without major modifications to instrument geometry. The use of a collimated laser beam permitted the construction of a numerical model that predicts the effects of detection laser wavelength, output power, beam focussing characteristics, light collection angle, particle size, and refractive index on the effective detection radius (R) of the detection laser beam. We compare the model predictions with an ambient data set acquired during the Ice in Clouds Experiment – Dust (ICE-D) project. The new laser system resulted in an order-of-magnitude improvement in instrument sensitivity to spherical particles in the size range 500–800 nm compared to a focussed 405 nm laser diode system. The model demonstrates that the limit of detection in terms of particle size is determined by the scattering cross section (Csca) as predicted by Mie theory. In addition, if light is collected over a narrow collection angle, oscillations in the magnitude of Csca with respect to particle diameter result in a variation in R, resulting in large particle-size-dependent variation in detection efficiency across the particle transmission range. This detection bias is imposed on the aerodynamic size distributions measured by the instrument and accounts for some of the detection bias towards sea salt particles in the ambient data set.
关键词： LAAP-TOF,aerosol,single-particle mass spectrometry,Mie theory,laser wavelength,detection stage geometry,optical detection efficiency
更新于2025-09-23 15:19:57
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Development of a coupled aerosol lidar data quality assurance and control scheme with Monte Carlo analysis and bilateral filtering
摘要： Mie-scatter lidar can capture the vertical distribution of aerosols, and a high degree of quantification of lidar data would be capable of coupling with a chemical transport model (CTM). Thus, we develop a data quality assurance and control scheme for aerosol lidar (TRANSFER) that mainly includes a Monte Carlo uncertainty analysis (MCA) and bilateral filtering (BF). The AErosol RObotic NETwork (AERONET) aerosol optical depth (AOD) is utilized as the ground truth to evaluate the validity of TRANSFER, and the result exhibits a sharp 41% (0.36) decrease in root mean square error (RMSE), elucidating an acceptable overall performance of TRANSFER. The maximum removal of uncertainties appears in MCA with an RMSE of 0.08 km-1, followed by denoising (DN) with 50% of MCA in RMSE. BF can smooth interior data without destroying the edge of the structure. The most noteworthy correction occurs in summer with an RMSE of 0.15 km-1 and Pearson correlation coefficient of 0.8, and the least correction occurs in winter with values of 0.07 km-1 and 0.93, respectively. Overestimations of raw data are mostly identified, and representative values occur with weak southerly winds, low visibility, high relative humidity (RH) and high concentrations of both ground fine particulate matter (PM2.5) and ozone. Apart from long-term variations, the intuitional variation in a typical overestimated pollution episode, especially represented by vertical profiles, shows a favorable performance of TRANSFER during stages of transport and local accumulation, as verified by backward trajectories. Few underestimation cases are mainly attributed to BF smoothing data with a sudden decrease. The main limitation of TRANSFER is the zigzag profiles found in a few cases with very small extinction coefficients. As a supplement to the research community of aerosol lidar and an exploration under complicated pollution in China, TRANSFER can aid in the preprocessing of lidar data-powered applications.
关键词： Aerosol Lidar,Bilateral filtering,North China Plain,Monte Carlo,data quality control
更新于2025-09-23 15:19:57
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Outstanding Photocurrent Density and IPCE of Liquida??State NiO Perovskitea??Sensitized Solar Cells
摘要： The efficiency and photocurrent density reported for a p-type sensitized solar cells up to now are still lagging behind that of the n-type counterparts, limiting the successful development of p-n tandem cells. To circumvent this issue, NiO thin film is fabricated by aerosol-assisted chemical vapour deposition (AACVD) technique and employed in p-type solar cells. A systematic study is conducted to comprehend the correlation between the NiO thickness and the power conversion efficiency (PCE) of liquid-state NiO-based sensitized solar cells. By carefully designing the cell components, this type of device demonstrates the highest photocurrent density (Jsc) exceeding 18 mA cm-2 when using iodine/triiodide as redox shuttle matching the one produced by TiO2 counterpart. This is accomplished by (1)using AACVD technique for one-step deposition of compact and mesoporous NiO electrodes, (2)optimizing the thickness of NiO layer through controlling the deposition time and (3)adopting methylammonium lead iodide (CH3NH3PbI3) as a light harvester prepared via a sequential deposition method.
关键词： aerosol-assisted chemical vapour deposition,photovoltaics,NiO,perovskite
更新于2025-09-23 15:19:57
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Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets
摘要： The mass accommodation coefficient, αM, describes the liquid?vapor evaporation and condensation kinetics at interface. In spite of numerous experimental efforts, reliable values of αM are still not available for many substances. Here, we present a novel experimental technique, photothermal single-particle spectroscopy (PSPS), that allows for a robust retrieval of mass accommodation coefficients from three simultaneous independent measurements. PSPS combines resonant photoacoustic absorption spectroscopy with modulated Mie scattering measurements on single particles. We study the mass transport of water on organic aerosol droplets that are optically trapped using counter-propagating tweezers. We find the mass accommodation coefficient of water on a pure model organic that is fully miscible with water to be 0.021 at 296 K and to decrease by more than an order of magnitude when the temperature increases to 309 K. The experimentally observed temperature dependence of αM shows an Arrhenius behavior. Furthermore, the water content of the droplets is found to have a profound effect on αM is observed at low water concentrations, while at elevated water concentrations, we observe a 5-fold increase in αM. The technique presented in this work has the potential to become a reliable method for the retrieval of αM values at liquid?vapor interfaces, which are essential for accurate global climate and pharmaceutical aerosol inhalation modeling, to mention but a few.
关键词： temperature dependence,photoacoustic absorption spectroscopy,optical trapping,water transport,organic aerosol droplets,modulated Mie scattering,mass accommodation coefficient,Arrhenius behavior,PSPS,photothermal single-particle spectroscopy
更新于2025-09-23 15:19:57
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Increase of the particle hit rate in a laser single-particle mass spectrometer by pulse delayed extraction technology
摘要： A single-particle mass spectrometer (SPMS) can provide a wealth of valuable information on chemical and physical parameters of individual particles in real time. One of the main performance criteria of the instrument is efficiency of particle detection (hit rate). Most SPMS instruments use constant electrical field (DC) extraction, where stationary high voltage is applied to the extraction electrodes. As the aerosol particles initially carry a certain charge, those with a high amount to charge can be deflected by this electric field and lost, thus decreasing the hit rate. We realized that the delayed extraction technique can eliminate the stochastic dispersion of the particle beam caused by their deflection in the stationary electric field. As the result, the hit rate of the instrument can be significantly improved. Also, as the effect of the deflection in the electric field is mass dependent, it can cause distortion of the measured size distribution of the particles. Hence, the delayed extraction technique can bring the recorded distribution closer to the actual one. We found that the delayed extraction technique provides a mass resolution improvement as well as increases the hit rate. The gain in the hit rate depends on the type of particles. It can be 2 orders of magnitude for model particles and up to 2–4 times for ambient particles. In the present work we report experiments and results showing the effect of the delayed extraction on the beam divergence caused by particle charge, the hit rate improvement, and the effect of the delayed extraction on the measured particle size distribution.
关键词： hit rate,particle charge,aerosol particles,delayed extraction,single-particle mass spectrometer
更新于2025-09-23 15:19:57
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Benefit of depolarization ratio at λ = 1064 nm for the retrieval of the aerosol microphysics from lidar measurements
摘要： A better quantification of aerosol properties is required for improving the modelling of aerosol effects on weather and climate. This task is methodologically demanding due to the diversity of the microphysical properties of aerosols and the complex relation between their microphysical and optical properties. Advanced lidar systems provide spatially and temporally resolved information on the aerosol optical properties that is sufficient for the retrieval of important aerosol microphysical properties. Recently, the mass concentration of transported volcanic ash, which is relevant for the flight safety of aeroplanes, was retrieved from measurements of such lidar systems in southern Germany. The relative uncertainty of the retrieved mass concentration was on the order of ±50 %. The present study investigates improvements of the retrieval accuracy when the capability of measuring the linear depolarization ratio at 1064 nm is added to the lidar setup. The lidar setups under investigation are based on those of MULIS and POLIS of the Ludwig-Maximilians-Universit?t in Munich (Germany) which measure the linear depolarization ratio at 355 and 532 nm with high accuracy. The improvements are determined by comparing uncertainties from retrievals applied to simulated measurements of this lidar setup with uncertainties obtained when the depolarization at 1064 nm is added to this setup. The simulated measurements are based on real lidar measurements of transported Eyjafjallaj?kull volcano ash. It is found that additional 1064 nm depolarization measurements significantly reduce the uncertainty of the retrieved mass concentration and effective particle size. This significant improvement in accuracy is the result of the increased sensitivity of the lidar setup to larger particles. The size dependence of the depolarization does not vary strongly with refractive index, thus we expect similar benefits for the retrieval in case of measurements of other volcanic ash compositions and also for transported desert dust. For the retrieval of the single scattering albedo, which is relevant to the radiative transfer in aerosol layers, no significant improvements were found.
关键词： depolarization ratio,volcanic ash,aerosol properties,microphysical retrieval,lidar measurements
更新于2025-09-23 15:19:57
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Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe
摘要： Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (DAOT ? ±0.05 ± 0.15(cid:3)AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5% and 1.2% per year in AOT, based on daily averaging, were found for the southwestern Baltic Sea from MODIS c051 and c061, respectively. This is in line with a decrease of 1.2% per year in AOT at the AERONET station Hamburg. For the western Gotland Basin area, Sweden, negative trends of 1.5%, 1.1% and 1.6% per year in AOT have been found for MODIS c051, MODIS c061 and AERONET GDT, respectively. The strongest trend of –1.8% per year in AOT was found for AERONET Belsk, Poland, which can be compared to –1.5% per day obtained from MODIS c051 over central Poland. The trends in MODIS and AERONET AOT are nearly all statistically significant at the 95% confidence level. The strongest aerosol sources are suggested to be located southwest, south and southeast of the investigation area, although the highest prevalence of pollution events is associated with air mass transport from southwest.
关键词： satellite observations,atmospheric transport,aerosol optical thickness,anthropogenic aerosol
更新于2025-09-19 17:15:36
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Retrieval of the Fine-Mode Aerosol Optical Depth over East China Using a Grouped Residual Error Sorting (GRES) Method from Multi-Angle and Polarized Satellite Data
摘要： The ?ne-mode aerosol optical depth (AODf) is an important parameter for the environment and climate change study, which mainly represents the anthropogenic aerosols component. The Polarization and Anisotropy of Re?ectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL) instrument can detect polarized signal from multi-angle observation and the polarized signal mainly comes from the radiation contribution of the ?ne-mode aerosols, which provides an opportunity to obtain AODf directly. However, the currently operational algorithm of Laboratoire d’Optique Atmosphérique (LOA) has a poor AODf retrieval accuracy over East China on high aerosol loading days. This study focused on solving this issue and proposed a grouped residual error sorting (GRES) method to determine the optimal aerosol model in AODf retrieval using the traditional look-up table (LUT) approach and then the AODf retrieval accuracy over East China was improved. The comparisons between the GRES retrieved and the Aerosol Robotic Network (AERONET) ground-based AODf at Beijing, Xianghe, Taihu and Hong_Kong_PolyU sites produced high correlation coef?cients (r) of 0.900, 0.933, 0.957 and 0.968, respectively. The comparisons of the GRES retrieved AODf and PARASOL AODf product with those of the AERONET observations produced a mean absolute error (MAE) of 0.054 versus 0.104 on high aerosol loading days (AERONET mean AODf at 865 nm = 0.283). An application using the GRES method for total AOD (AODt) retrieval also showed a good expandability for multi-angle aerosol retrieval of this method.
关键词： multi-angular remote sensing,?ne-mode aerosol optical depth,optimal aerosol model determination,PARASOL,polarized remote sensing
更新于2025-09-19 17:15:36
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Hematite films by aerosol pyrolysis: influence of substrate and photocorrosion suppression by TiO2 capping
摘要： Sn-doped hematite (Fe2O3) films were prepared by aerosol pyrolysis (AP) on fluorine doped tin oxide (FTO), titanium and stainless steel. Photoactive electrodes were obtained in all cases and the photosensitivity had an onset around 650 nm. Maximum incident photon to electron conversion efficiency (IPCE) was 0.3 at 300 nm for samples deposited on FTO. The Faradaic efficiency of the photocorrosion reaction was found to be 0.47 % for an unprotected FTO/hematite electrode in H2SO4. The Faradaic efficiency of this dissolution reaction decreased to 0.3 % for a hematite electrode covered with a 65 nm thick dip coated layer of TiO2, and to 0.17 % for a sample with a spray coated TiO2 layer, thus proving the beneficial role of TiO2 in protecting hematite against photocorrosion.
关键词： photocorrosion,aerosol pyrolysis,α-Fe2O3 / TiO2 electrodes
更新于2025-09-19 17:15:36