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Ship-borne aerosol profiling with lidar over the Atlantic Ocean: From pure marine conditions to complex dust-smoke mixtures
摘要： The multiwavelength Raman lidar PollyXT has been regularly operated aboard the research vessel Polarstern on expeditions across the Atlantic Ocean from North to South and vice versa. The lidar measurements of the Polarstern cruises PS95 from Bremerhaven to Cape Town (November 2015) and PS98 from Punta Arenas to Bremerhaven (April/May 2016) are presented and analysed in detail. The latest setup of PollyXT allows improved coverage of the marine boundary layer (MBL) due to an additional near-range receiver. Three case studies provide an overview of the detected aerosol over the Atlantic Ocean. In the first case, marine conditions were observed near South Africa on the autumn cruise PS95. Values of optical properties (depolarisation ratios close to zero, lidar ratios of 23 sr at 355 nm and 532 nm) within the MBL indicate pure marine aerosol. A layer of dried marine aerosol, indicated by an increase of the particle depolarisation ratio to about 10% at both wavelengths and thus confirming the non-sphericity of these particles, could be detected on the top of the MBL. On the same cruise, an almost pure Saharan dust plume was observed near the Canary Islands, presented in the second case. The third case deals with several layers of Saharan dust partly mixed with biomass-burning smoke measured on PS98 near the Cape Verde Islands. While the MBL was partly mixed with dust in the pure Saharan dust case, an almost marine MBL was observed in the third case. A statistical analysis showed latitudinal differences in the optical properties within the MBL, caused by the down-mixing of dust in the tropics and anthropogenic influences in the northern latitudes whereas the optical properties of the MBL in the southern hemisphere correlate with typical marine values. The particle depolarisation ratio of dried marine layers ranged between 4–9%. Night measurements from PS95 and PS98 were used to illustrate the potential of aerosol classification using lidar ratio, particle depolarisation ratio and ?ngstr?m exponent. Lidar ratio and particle depolarisation ratio have been found to be the main indicator for the particle type, whereas the ?ngstr?m exponent is rather variable.
关键词： PollyXT,Atlantic Ocean,depolarisation,marine boundary layer,Polarstern,lidar,aerosol
更新于2025-09-23 15:23:52
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Night-Time Oxidation of a Monolayer Model for the Air–Water Interface of Marine Aerosols—A Study by Simultaneous Neutron Reflectometry and in Situ Infra-Red Reflection Absorption Spectroscopy (IRRAS)
摘要： This paper describes experiments on the ageing of a monolayer model for the air–water interface of marine aerosols composed of a typical glycolipid, galactocerebroside (GCB). Lipopolysaccharides have been observed in marine aerosols, and GCB is used as a proxy for these more complex lipopolysaccharides. GCB monolayers are investigated as pure films, as mixed films with palmitic acid, which is abundant in marine aerosols and forms a stable attractively mixed film with GCB, particularly with divalent salts present in the subphase, and as mixed films with palmitoleic acid, an unsaturated analogue of palmitic acid. Such mixed films are more realistic models of atmospheric aerosols than simpler single-component systems. Neutron reflectometry (NR) has been combined in situ with Fourier transform infra-red reflection absorption spectroscopy (IRRAS) in a pioneering analysis and reaction setup designed by us specifically to study mixed organic monolayers at the air–water interface. The two techniques in combination allow for more sophisticated observation of multi-component monolayers than has previously been possible. The structure at the air–water interface was also investigated by complementary Brewster angle microscopy (BAM). This study looks specifically at the oxidation of the organic films by nitrate radicals (NO3?), the key atmospheric oxidant present at night. We conclude that NO3? oxidation cannot fully remove a cerebroside monolayer from the surface on atmospherically relevant timescales, leaving its saturated tail at the interface. This is true for pure and salt water subphases, as well as for single- and two-component films. The behaviour of the unsaturated tail section of the molecule is more variable and is affected by interactions with co-deposited species. Most surprisingly, we found that the presence of CaCl2 in the subphase extends the lifetime of the unsaturated tail substantially—a new explanation for longer residence times of materials in the atmosphere compared to lifetimes based on laboratory studies of simplified model systems. It is thus likely that aerosols produced from the sea-surface microlayer at night will remain covered in surfactant molecules on atmospherically relevant timescales with impact on the droplet’s surface tension and on the transport of chemical species across the air–water interface.
关键词： palmitic acid,monolayer,neutron,nitrate radical,palmitoleic acid,reflectivity,aerosol,infra-red,cerebroside,Brewster angle microscopy
更新于2025-09-23 15:23:52
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Dust Detection and Aerosol Properties Over Arabian Sea Using MODIS Data
摘要： The present study deals with the use of Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared bands in the dust detection. Eight dust storm cases over the Arabian Sea have been selected (four TERRA and four AQUA) during the year 2002–2008. The brightness temperature (BT) difference method has been applied on MODIS thermal bands 29 (8 μm), 31 (11 μm) and 32 (12 μm) to detect dust storms over the Arabian Sea. The performance assessment of BT differences (BT29–BT31 and BT31–BT32) has shown that BT31–BT32 has performed better to BT29–BT31. We suggest that BT31–BT32 is an effective combination of MODIS bands for dust detection over oceans and sea. The maximum (Dmax) and minimum dust (Dmin) intensity locations have also been identified in all the eight dust storm cases. The aerosol properties (aerosol optical thickness, τ; asymmetry factor g and Angstrom exponent α) over Dmax and Dmin have been studied using MODIS Level 2 data. In AQUA dust storms cases τ values (Dmax) were higher than TERRA dust cases, whereas g values were nearly same. The α was always positive in case of TERRA dust cases; however in AQUA negative α was also reported. Afternoon dust storms are more intense compared to forenoon dust storms and dust particles are also coarser.
关键词： BT difference,Arabian Sea,Dust detection,MODIS,Dust aerosol properties
更新于2025-09-23 15:23:52
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An improved algorithm for retrieving the fine-mode fraction of aerosol optical thickness. Part 2: Application and validation in Asia
摘要： Since small aerosol particles are mostly anthropogenic, the fine-mode aerosol optical thickness (fAOT) can be used to infer PM2.5 amounts. However, satellite-based fAOT products such as those from the Moderate Resolution Imaging Spectroradiometer (MODIS) are highly uncertain over land. An improved fAOT retrieval method called the look-up table–spectral deconvolution algorithm (LUT-SDA) was tested and improved using data from Asia. The improvement is achieved by accounting for seasonal changes instead of using constant annual mean values of the aerosol parameters used in the LUT-SDA derived from the Aerosol Robotic Network (AERONET) data from 2010 to 2014. Compared with the previous version of the LUT-SDA developed for Beijing, Hong Kong, and Osaka, the updated LUT-SDA generates more accurate fine-mode fractions (FMFs) with the total mean root-mean-square error (RMSE) decreasing from 0.24 to 0.18. The updated LUT-SDA was then applied to retrieve fAOT and was validated by retrievals from 45 AERONET sites over the period 2015 to 2016. A good accuracy was achieved by this method with 31% of the validation sites having > 50% of retrievals falling within the estimated error (EE) envelope ± (0.05 + 0.15 × AERONET fAOT) and 42% of the validation sites having 40–50% of retrievals falling within the EE envelope. In the total validation and comparison with the MODIS Collection 6 fAOT, the fAOT retrievals from the LUT-SDA agreed more closely with AERONET retrievals, showing a low bias. About 48% of the LUT-SDA-based fAOT retrievals fell within the EE envelope (RMSE = 0.29), while ~22% of the MODIS-based fAOT retrievals fell within the EE envelope (RMSE = 0.42). The fAOT was significantly underestimated by the MODIS algorithm in most areas of Asia with many values of zero. This study demonstrates that the refined LUT-SDA method is valid for the large-scale estimation of fAOT from satellite images.
关键词： MODIS,Aerosol optical thickness,Fine-mode fraction
更新于2025-09-23 15:23:52
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A 10-year record of aerosol optical properties and radiative forcing over three environmentally distinct AERONET sites in Kenya, East Africa
摘要： In the framework of Aerosol Robotic Network (AERONET), the aerosol optical, microphysical and radiative properties were investigated over three sites (CRPSM_Malindi, Nairobi, and ICIPE_Mbita) in Kenya, East Africa (EA) during 2006-2015. The annual mean (±σ) aerosol optical depth at 440 nm (AOD440) was found high at Mbita (0.27±0.09) followed by Malindi (0.26±0.07), and low at Nairobi (0.19±0.04). Whereas, the seasonal mean AOD440 noticed high (low) values during the local dry (wet) seasons. The aerosol optical properties: AOD, single scattering albedo (SSA), asymmetry parameter (ASY), and complex aerosol refractive index (RI) exhibited significant temporal and spectral heterogeneities illustrating the complexity of aerosol types with an abundance of fine-mode aerosols during the local dry (JJA) season. Characterization of major aerosol types revealed the dominance of mixed-type followed by biomass burning aerosols. The aerosol volume size distribution revealed that the coarse- over fine-mode aerosols showed a significant contribution to the total volume particle concentration, especially at high (> 0.3) AOD440. Further, the aerosol columnar number size distribution (CSD) retrieved from the King’s inversion of spectral AOD exhibited a power law distribution affirming multiplicity of aerosol sources. The direct aerosol radiative forcing values simulated in the shortwave region using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model showed good correlation (r=>0.85) with the AERONET derived ones at the top-of-atmosphere (TOA), bottom-of-atmosphere (BOA) and within the atmosphere (ATM). The annual mean (±σ) TOA, BOA, and ATM forcing values were found in the range from -8.10±3.75 to -13.23±4.87, -34.54±4.86 to -46.11±10.27, and 26.63±6.43 to 36.24±7.26 Wm-2, respectively, with an atmospheric heating rate (AHR) of 0.74±0.12–1.02±0.20 K day-1. The SBDART-derived DARF exhibited significant temporal heterogeneity with high (low) during the local dry (wet) seasons. Results derived from the present study forms a basis for regional climate change studies and could increase the accuracy of climate models over this unexplored region of Africa.
关键词： Aerosol radiative forcing,Aerosol optical depth,Size distribution,East Africa,AERONET,Single scattering albedo
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 21st International Multi-Topic Conference (INMIC) - Karachi, Pakistan (2018.11.1-2018.11.2)] 2018 IEEE 21st International Multi-Topic Conference (INMIC) - Silica Nano-Particulate Coating Having Self-Cleaning and Antireflective Properties for PV Modules
摘要： In this research, silica nanoparticles are coated over the solar PV module glass to acquire super hydrophilic, antireflective and highly transparent surface. Silane precursor mixed with air sprayed on the substrate by aerosol deposition method. Pressure difference between the plasma chamber and the substrate is tuned by the introduction of helium gas, which results in good control over layer thickness and refractive indices. Due to the porous nature and graded index of coated film, the transmittance of glass substrate is increased from 91% to 99.2%. Surface topology of coated film is studied by AFM shows excellent antifogging and super-hydrophilic nature attributed to roughness and nano-porosity of coated film. Moreover, the super-hydrophilic nature endows these coatings with self-cleaning properties, which further enhances the overall efficiency of solar PV modules.
关键词： Antireflective coatings,Super-hydrophilic,Silica nanoparticles,Thin films,solar PV,Aerosol deposition,Nano-porous
更新于2025-09-23 15:22:29
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Single Image Defogging Based on Illumination Decomposition for Visual Maritime Surveillance
摘要： Single image fog removal is important for surveillance applications and many defogging methods have been proposed, recently. Due to the adverse atmospheric conditions, the scattering properties of foggy images depend on not only the depth information of scene, but also the atmospheric aerosol model, which has more prominent influence on illumination in a fog scene than that in a haze scene. However, recent defogging methods confuse haze and fog, and they fail to consider fully about the scattering properties. Thus, these methods are not sufficient to remove fog effects, especially for images in maritime surveillance. Therefore, this paper proposes a single image defogging method for visual maritime surveillance. Firstly, a comprehensive scattering model is proposed to formulate a fog image in the glow-shaped environmental illumination. Then, an illumination decomposition algorithm is proposed to eliminate the glow effect on the airlight radiance and recover a fog layer, in which objects at the infinite distance have uniform luminance. Secondly, a transmission-map estimation based on the non-local haze-lines prior is utilized to constrain the transmission map into a reasonable range for the input fog image. Finally, the proposed illumination compensation algorithm enables the defogging image to preserve the natural illumination information of the input image. In addition, a fog image dataset is established for visual maritime surveillance. The experimental results based on the established dataset demonstrate that the proposed method can outperform the state-of-the-art methods in terms of both the subjective and objective evaluation criteria. Moreover, the proposed method can effectively remove fog and maintain naturalness for fog images.
关键词： Illumination Decomposition,Haze-Lines Prior,Image Defogging,Atmospheric Aerosol Model,Visual Maritime Surveillance
更新于2025-09-23 15:22:29
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Application of Aerosol Jet 3D Printing with Conductive and Non-Conductive Inks for Manufacturing mm-Wave Circuits
摘要： In this paper, an application of Aerosol Jet 3D printing with conductive and non-conductive inks for the realization of mm-wave circuits well above 30 GHz is presented and investigated. The Optomec 5X aerosol jet 3D printing system is used together with polyimide and silver inks to fully-additive manufacture various microstrip circuits. A section of microstrip transmission line with a transition to a via-less conductor backed coplanar waveguide was designed together with a T-junction and a branch-line coupler. These circuits were designed to operate within the Ka and V frequency bands. The measured thickness of the polyimide dielectric substrate is 20.7 ± 1.35 μm while the silver traces are 2.6 ± 1.35 μm. A section of the transmission line with the developed transitions was measured up to the W-band, exhibiting a total loss of 0.65 dB/mm at 100 GHz. The T-junction power divider yielded a total loss at its center frequency of 34 GHz of 0.55 dB. The 3-dB branch line coupler yielded a loss at its center frequency at 42 GHz of 1.1 dB. The experimental results demonstrate the application of this approach for fast and high-resolution mm-wave circuit fabrication.
关键词： circuit fabrication,additive manufacturing,mm-wave circuits,aerosol jet printing,3D printing
更新于2025-09-23 15:22:29
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Inversion of Aerosol Optical Depth Based on the CCD and IRS Sensors on the HJ-1 Satellites
摘要： To perform a high-resolution aerosol optical depth (AOD) inversion from the HJ-1 satellites, a dark pixel algorithm utilizing the HJ-1 satellite data was developed based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) algorithm. By analyzing the relationship between the apparent reflectance from the 1.65 μm and 2.1 μm channels of MODIS, a method for estimating albedo using the 1.65 μm channel data of the HJ-1 satellites was established, and a high-resolution AOD inversion in the Chengdu region based on the HJ-1 satellite was completed. A comparison of the inversion results with CE318 measured data produced a correlation of 0.957, respectively, with an absolute error of 0.106. An analysis of the AOD inversion results from different aerosol models showed that the rural aerosol model was suitable as a general model for establishing an aerosol inversion look-up table for the Chengdu region.
关键词： dark pixel,albedo,aerosol optical depth,HJ-1 satellite
更新于2025-09-23 15:22:29
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CALIPSO lidar level?3 aerosol profile product: version?3 algorithm design
摘要： The CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) level 3 aerosol profile product reports globally gridded, quality-screened, monthly mean aerosol extinction profiles retrieved by CALIOP (the Cloud-Aerosol Lidar with Orthogonal Polarization). This paper describes the quality screening and averaging methods used to generate the version 3 product. The fundamental input data are CALIOP level 2 aerosol extinction profiles and layer classification information (aerosol, cloud, and clear-air). Prior to aggregation, the extinction profiles are quality-screened by a series of filters to reduce the impact of layer detection errors, layer classification errors, extinction retrieval errors, and biases due to an intermittent signal anomaly at the surface. The relative influence of these filters are compared in terms of sample rejection frequency, mean extinction, and mean aerosol optical depth (AOD). The 'extinction QC flag' filter is the most influential in preventing high-biases in level 3 mean extinction, while the 'misclassified cirrus fringe' filter is most aggressive at rejecting cirrus misclassified as aerosol. The impact of quality screening on monthly mean aerosol extinction is investigated globally and regionally. After applying quality filters, the level 3 algorithm calculates monthly mean AOD by vertically integrating the monthly mean quality-screened aerosol extinction profile. Calculating monthly mean AOD by integrating the monthly mean extinction profile prevents a low bias that would result from alternately integrating the set of extinction profiles first and then averaging the resultant AOD values together. Ultimately, the quality filters reduce level 3 mean AOD by -24 and -31 % for global ocean and global land, respectively, indicating the importance of quality screening.
关键词： version 3,aerosol,lidar,optical depth,CALIPSO,quality screening,extinction
更新于2025-09-23 15:22:29