Multi-decade measurements of the long-term trends of atmospheric species by high-spectral-resolution infrared solar absorption spectroscopy

Solar absorption spectra were recorded for the first time in 5 years with the McMath Fourier transform spectrometer at the US National Solar Observatory on Kitt Peak in southern Arizona, USA (31.91°N latitude, 111.61°W longitude, 2.09 km altitude). The solar absorption spectra cover 750-1300 and 1850-5000 cm⁻¹ and were recorded on 20 days during March-June 2009. The measurements mark the continuation of a long-term record of atmospheric chemical composition measurements that have been used to quantify seasonal cycles and long-term trends of both tropospheric and stratospheric species from observations that began in 1977. Fits to the measured spectra have been performed, and they indicate the spectra obtained since return to operational status are nearly free of channeling and the instrument line shape function is well reproduced taking into account the measurement parameters. We report updated time series measurements of total columns for six atmospheric species and their analysis for seasonal cycles and long-term trends. As an example, the time series fit shows a decrease in the annual increase rate in Montreal-Protocol-regulated chlorofluorocarbon CCl₂F₂ from 1.51±0.38% yr⁻¹ at the beginning of the time span to −1.54±1.28% yr⁻¹ at the end of the time span, 1 sigma, and hence provides evidence for the impact of those regulations on the trend.     

Response to “Toward unified satellite climatology of aerosol properties. 3. MODIS versus MISR versus AERONET”

A recent paper by Mishchenko et al. compares near-coincident MISR, MODIS, and AERONET aerosol optical depth (AOD), and gives a much less favorable impression of the utility of the satellite products than that presented by the instrument teams and other groups. We trace the reasons for the differing pictures to whether known and previously documented limitations of the products are taken into account in the assessments. Specifically, the analysis approaches differ primarily in (1) the treatment of outliers, (2) the application of absolute vs. relative criteria for testing agreement, and (3) the ways in which seasonally varying spatial distributions of coincident retrievals are taken into account. Mishchenko et al. also do not distinguish between observational sampling differences and retrieval algorithm error. We assess the implications of the different analysis approaches, and cite examples demonstrating how the MISR and MODIS aerosol products have been applied successfully to a range of scientific investigations.     

Improvements for ground-based remote sensing of atmospheric aerosol properties by additional polarimetric measurements

We discuss the improvements in the aerosol properties characterization resulting from the additional multi-wavelength polarization measurements measured by a new CIMEL polarized sun/sky-photometer, CE318-DP. In order to process direct-sun, sky and polarization measurements in a wide spectral range (340–1640 nm), we developed new calibration methods and strategies, e.g. using the Langley plot method to calibrate both direct-sun irradiance and sky radiance, as well as combining laboratory facilities with a vicarious method to calibrate the polarized sky measurements. For studying the impact of new polarimetric measurements on the retrievals of aerosol properties, we have processed an extensive record of field measurements using an updated Dubovik and King retrieval algorithm [Dubovik O, Sinyuk A, Lapyonok T, Holben BN, Mishchenko MI, et al. Application of spheroid models to account for aerosol particle nonsphericity in remote sensing of desert dust. J Geophys Res 2006;111:D11208.]. A preliminary analysis shows that adding polarization in the inversion can reduce possible errors (notably for about 30% of our field cases) in the fine mode size distribution, real part of refractive index and particle shape parameter retrievals, especially for small particles.     

An improved high-resolution solar reference spectrum for earth's atmosphere measurements in the ultraviolet, visible, and near infrared

We have developed an improved solar reference spectrum for use in the analysis of atmospheric spectra from vacuum wavelengths of 200.07 through 1000.99 nm. The spectrum is developed by combining high spectral resolution ground-based and balloon-based solar measurements with lower spectral resolution but higher accuracy irradiance information. The new reference spectrum replaces our previous reference spectrum, and its derivatives, for use in a number of physical applications for analysis of atmospheric spectra, including: wavelength calibration; determination of instrument transfer (slit) functions; Ring effect (Raman scattering) correction; and correction for spectral undersampling of atmospheric spectra, particularly those that are dilute in absorbers. The applicability includes measurements from the GOME, SCIAMACHY, OMI, and OMPS satellite instruments as well as aircraft-, balloon-, and ground-based measurements.     

Transmission of radiation through an aerosol medium

The properties of radiation through an aerosol medium have been achieved. This has been done by employing Mie scattering theory to calculate the radiation transfer scattering parameters in the form of extinction, absorption and scattering efficiencies. The equation of radiative transfer for the heat flux through a plane parallel atmosphere of aerosol has been solved. The aerosol size distributions are found in practical systems. Average efficiencies over size distribution for spherical particles of complex refractive index are calculated. Therefore, the radiative properties of stratospheric aerosols have been done. The obtained results found to be in a good agreement with the previous work.     

地表反射太阳辐射的参数化计算方法

 从能量守恒定律出发,建立了朗伯地表对下行辐射的反射作用引起天空亮度变化的解析计算模型。利用射线追踪原理,提出了地表与大气之间多次反射作用的理论模型。引入了一个多次散射的影响因子,并对附加的天空亮度进行了修正。利用混合修正的d-Eddington近似和互易性原理计算了大气的透射率、反照率以及半球平均反照率。最后计算了地表反照率分别为0.15,0.25和0.35情形下的天空亮度增量,实验测量数据证实了这些结果。结果表明：当地表的反照率不为0时,存在“临边增亮”效应,并且随着地表反照率的增大,这种效应更加明显。     

Long-term trends of tropospheric carbon monoxide and hydrogen cyanide from analysis of high resolution infrared solar spectra

Long-term trend and seasonal variation of the mean free tropospheric volume mixing ratios of carbon monoxide (CO) and hydrogen cyanide (HCN) have been derived from analysis of a time series of solar absorption spectra recorded from the US National Solar Observatory on Kitt Peak (31.9°N, 111.6°W, 2.09 km altitude) spanning almost three decades. The results of a fit to the CO 258 daily averages from May 1977 to April 2005 as a function of time with a model that assumes a sinusoidal seasonal cycle and a linear long-term trend with time yield a mean volume mixing ratio of 102±3) parts per billion (10^-9 per unit volume) below 10 km altitude, 1 sigma. The CO measurements show a seasonal cycle with a maximum in March and a minimum in September with an amplitude of (22.3±1.5)% relative to the mean. The best-fit corresponds to a long-term CO trend of , 1 sigma, relative to the mean. To quantify the possible impact of periods of intense fires, the CO measurements have been compared with the measurements of HCN, a well-documented emission product of biomass burning with a lifetime of ∼5 months. The best fit to the full HCN time series of 208 daily averages from May 1978 to April 2005 results in a mean volume mixing ratio of below 10 km altitude with a similar seasonal cycle, though with a lower relative amplitude than for CO. Although same-day enhancements up to a factor of 1.87 for HCN and 1.24 for CO were measured relative to values predicted by a fit to the time series that accounts for the seasonal cycles and trends of both molecules, excluding time periods of elevated fire emissions has no significant impact on the best-fit long-term free tropospheric CO and HCN trends. Our result of no long-term CO trend since the late 1970s suggests that the global average long-term decline reported from 1990 through 1995 measurements has not continued in the free troposphere. Similarly, a fit to the full time series of 208 HCN free tropospheric daily averages with the same model yields an average 2.09-10 km mixing ratio of 0.219 ppbv and a long-term trend of , 1 sigma, relative to the mean since 1978, also indicating no significant long-term trend above the lower mid-latitude continental US Kitt Peak station. The results for both molecules suggest the site was not significantly impacted by summer boreal fires during the time span of the measurements that in some years cause widespread pollution above northern higher latitude sites.     

Modeling single-scattering properties of small cirrus particles by use of a size-shape distribution of ice spheroids and cylinders

In this study, we model single-scattering properties of small cirrus crystals using mixtures of polydisperse, randomly oriented spheroids and cylinders with varying aspect ratios and with a refractive index representative of water ice at a wavelength of 1.88 μm. The Stokes scattering matrix elements averaged over wide shape distributions of spheroids and cylinders are compared with those computed for polydisperse surface-equivalent spheres. The shape-averaged phase function for a mixture of oblate and prolate spheroids is smooth, featureless, and nearly flat at side-scattering angles and closely resembles those typically measured for cirrus. Compared with the ensemble-averaged phase function for spheroids, that for a shape distribution of cylinders shows a relatively deeper minimum at side-scattering angles. This may indicate that light scattering from realistic cirrus crystals can be better represented by a shape mixture of ice spheroids. Interestingly, the single-scattering properties of shape-averaged oblate and prolate cylinders are very similar to those of compact cylinders with a diameter-to-length ratio of unity. The differences in the optical cross sections, single-scattering albedo, and asymmetry parameter between the spherical and the nonspherical particles studied appear to be relatively small. This may suggest that for a given optical thickness, the influence of particle shape on the radiative forcing caused by a cloud composed of small ice crystals can be negligible.     

Synthesis of different gold nanostructures by solar radiation and their SERS spectroscopy

In this article, a simple and novel photochemical synthesis of different gold nanostructures is proposed using solar radiation. This method is rapid, convenient and of low cost, and can be performed under ambient conditions. By adjusting the concentration of sodium acetate (NaAc), different morphologies of the products can be easily obtained. Without NaAc, the products obtained are mainly polyhedral gold particles; lower concentration of NaAc (0.05 and 0.1 M) accelerates the formation of flowerlike gold nanostructures; while higher concentration of NaAc (0.5 M) facilitates the formation of a variety of gold nanowires and nanobelts. It is found that the morphology change of gold nanaostructures is the result of the synergistic effect of poly(diallyl dimethylammonium) chloride (PDDA), Ac⁻ ions, and the pH value. In addition, the different gold nanostructures thus obtained were used as substrates for surface‐enhanced Raman scattering (SERS) with p‐aminothiophenol (p‐ATP) as the probe molecule. In comparison, the flowerlike gold nanostructures show stronger SERS effect than the other gold nanostructures, which is associated with their unique geometrical shapes providing highly localized electromagnetic (EM) field for the optical enhancement to the probe molecules. These gold nanostructures, with different geometrical shapes, might have potential applications in the areas of photonics, optoelectronics and optical sensing. Copyright © 2009 John Wiley & Sons, Ltd.     

Attenuation of solar radiation by a water mist from the ultraviolet to the infrared range

A model is developed for the hemispherical transmittance of direct and scattered solar radiation from a cloudless atmosphere by a mist layer of water droplets in order to investigate the potential of water misting systems to serve as a protection from solar irradiation with particular emphasis on harmful UV radiation. The proposed model is based on published spectral experimental data for solar irradiation, Mie theory for interaction of the radiation with single spherical droplets, and radiative transfer theory. Known limiting solutions are employed to simplify the Mie calculations. The modified two-flux approximation is used to account for both direct and diffuse irradiation in lieu of a numerical solution for the full radiative transfer equation in anisotropically scattering media. The role of the governing parameters of a disperse water curtain of water droplets, water content, and droplet size for sample conditions is studied in some detail, particularly in the near-ultraviolet part of the spectrum where radiation can result in human tissue damage.     

大气气溶胶偏振遥感研究进展

POLDER-1是国际上第一个可以获取偏振光观测的星载对地探测器, 随着POLDER/PARASOL等偏振仪器的应用, 偏振遥感在国际上已成为一个快速发展的研究领域, 并在大气气溶胶监测等方面发挥了重要的作用, 取得了一系列研究成果。从POLDER/PARASOL,APS(aerosol polarimetry sensor)和航空偏振相机、地基偏振观测平台三个方面综述了大气气溶胶偏振遥感近20年(1993-2013)的研究进展, 重点介绍: (1)POLDER/PARASOL陆地上空和海洋上空气溶胶参数反演算法; POLDER/PARASOL气溶胶光学厚度(AOD)产品精度验证、应用以及与MODIS等卫星AOD产品的对比分析。(2)MICROPOL,RSP和APS陆地上空和海洋上空气溶胶参数反演算法; 国产多角度航空偏振相机(directional polarimetric camera, DPC)的气溶胶参数反演算法。(3)CE318-2和CE318-DP的气溶胶地基偏振反演算法。其中卫星、航空和地面气溶胶参数反演的结果包括总的AOD、细粒子AOD、粗粒子AOD、粒子谱分布、粒子形状、复折射指数、单次散射反射率、散射相函数、偏振相函数以及云顶AOD。在以上研究基础上, 提出了大气气溶胶偏振遥感研究存在的问题及展望, 为大气气溶胶偏振遥感研究提供有价值的参考。     

The reflection and polarization properties of non-spherical aerosol particles

In this paper, we investigate the capability of multi-angle TOA reflectance and polarized reflectance for the retrieval of aerosol properties including aerosol mode (fine mode and coarse mode), aerosol shape (sphere and non-spherical), and aerosol optical thickness. Single-scattering parameters and phase-matrix elements were computed for randomly oriented non-spherical aerosol particles. Sensitivity indices were introduced to quantify the sensitivity of the TOA total reflectance and polarized reflectance to aerosol parameters. Finally, on the basis of the sensitivity study, this paper presents a conceptual approach toward the remote sensing of non-spherical aerosol three parameters (aerosol mode, aerosol shape, and aerosol optical thickness) using the TOA total reflectance and TOA polarized reflectance for the 0.865 μm spectral bands measured at multiple viewing angles.     

基于反射太阳光反演气溶胶光学厚度和有效半径

根据太阳光的极化特性,提出了一种利用单波长太阳光遥感反演球形水凝物气溶胶光学厚度和有效半径的方法.根据矢量辐射传输理论,利用累加法,计算了λ=0.75μm(可见光)和3.3μm(近红外)两种波长太阳光入射时气溶胶的反射矩阵.气溶胶的有效半径为0.01—1.5μm,光学厚度为0.05—1.利用计算机模拟了反演过程,结果表明,当粒子的有效半径小于0.4μm时可以利用可见光波段进行反演;当粒子有效半径大于1.0μm时可以利用近红外波段反演;在0.4—1.0μm之间,利用这两个波段均可以得到精确性很 关键词： 光学厚度 有效半径 极化 反演     

A new concept of white light generation using a nano-waveguide for the solar radiation collection use

We propose a novel system of a nano-waveguide that can be used to generate the continuous optical spectrum, i.e. white light. A system consists of two micro-ring resonators and a nano-ring resonator that can be integrated into a single system. The large bandwidth signal is generated using a soliton pulse propagating within a Kerr-type nonlinear medium, whereas the continuous bandwidth or wavelength of light signal can be performed. Results obtained have shown the potential of using such a system for white light source generation and amplification, which is discussed. The amplified pulse can be stored within a nano-waveguide, which is allowed to form the continuous spectrum after amplification. Alternatively, the low-level solar radiation can be amplified, and the bandwidth signals can also be enlarged.     

The use of nuclear track detectors as an environmental solar ultraviolet radiation dosimeter

Investigation of using CR-39 nuclear track detectors as solar ultraviolet radiation (SUVR) dosimeter was studied. The nuclear track detectors were irradiated with Cf-252 (alpha and fission fragments) before exposure to sun light. The exposure of nuclear track detectors to SUVR were carried out under two different conditions (i) the detector was mounted on a solar tracker mechanism which always rotate towards the sun, and (ii) fixed on a horizontal surface. The measurements were performed for different periods extended from one to eight weeks continuously at Dhahran - Saudi Arabia. The period extended from the middle of July to middle of September: the hottest months in Saudi Arabia. The weekly integrated SUVR measured by Eppley sensor was ranged from 2400 W. h. m⁻² for one week up to 21000 W.h.m⁻² for eight weeks. The results indicate linear correlation between both the track diameters of alphas and fission fragments and the total exposure to SUVR. The results clearly demonstrate that it is possible to use the nuclear track detectors as an environmental and personal SUVR dosimeters.     

Retrieval of aerosol physical and chemical properties from mid-infrared extinction spectra

We report several results that validate the accuracy of a retrieval method for the determination of a number of aerosol particle properties from their mid infrared (600-6000 cm⁻¹) extinction spectra. These properties include the number density, chemical composition, phase, size distribution, and to some extent, shape. The approach is based on information obtained in laboratory studies of micron-sized particles using the aerosol flow tube (AFT) technique. We report here experiments in which our method is used to measure a variety of aerosols including SiO₂ micro-spheres as well as solid NaCl, (NH₄)₂SO₄, ice and liquid water particles. The uncertainties in the retrieved aerosol properties associated with the particle shapes (spheres, spheroids, cylinders, hexagonal and rectangular prisms) as well as the effect of variations in the spectral range were evaluated. To assess the accuracy of the retrieved size distributions and particle shapes, the properties calculated from infrared spectra were compared with corresponding properties determined using alternative methods. We used scanning electron microscopy (SEM) for solid (NH₄)₂SO₄ and NaCl aerosols and direct particle imaging with an optical microscope assembly for liquid water aerosols. On the basis of the validation results, we discuss the boundaries of applicability of the most popular spectral model, single scattering by spherical, homogeneous aerosol particles.     

Long-term evolution in the tropospheric concentration of chlorofluorocarbon 12 (CCl2F2) derived from high-spectral resolution infrared solar absorption spectra: retrieval and comparison with in situ surface measurements

The average tropospheric volume mixing ratios of chlorofluorocarbon 12 (CCl₂F₂) have been retrieved from high-spectral resolution ground-based infrared solar-absorption spectra recorded from March 1982 to October 2003 with the McMath Fourier transform spectrometer at the US National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude). The retrievals are based on fits to the unresolved ν₈ band Q-branches near using the SFIT2 retrieval algorithm. The annual increase rate was equal to (16.88±1.37) parts per trillion (10^-12) by volume at the beginning of the time series, March 1982, or (4.77±0.04)%, 1 sigma, declining progressively to (2.49±1.24) parts per trillion, by volume at the end, October 2003, or (0.46±0.24)%, 1 sigma. Average tropospheric mixing ratios from the solar spectra have been compared with average surface flask and in situ sampling measurements from the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, CO, (USA) (40.0°N, 105.5°W, 3013 m altitude). The average ratio and standard deviation of the monthly means of the retrieved tropospheric mixing ratios relative to the CMDL surface mixing ratios is (1.01±0.03) for the overlapping time period. Both datasets demonstrate the progressive impact of the Montreal protocol and its strengthening amendments on the trend of CCl₂F₂, though a tropospheric decrease has yet to be observed.     

甲胺分子的同步辐射光电离解离质谱

在超声射流冷却条件下,利用同步辐射光源,结合飞行时间质谱对CH3NH2分子在60—140nm波长范围内的光电离解离进行了研究.主要动力学过程为母体离子的解离过程.CH2NH2+和CH3+由CH3NH2+在高能量时解离生成,而CH2NH2+的1,1脱H2过程则产生其他离子.CH3NH2分子的电离势(IP)为916±001eV,和分子轨道能量计算的理论值符合得非常好,并获得CH3NH2+和CH2NH2+的生成热分别为860±05kJmol和7541kJmol. 关键词： 同步辐射光电离 飞行时间质谱 电离势 生成热     

偏振光在非球形气溶胶中传输特性的Monte Carlo仿真

非球形气溶胶是影响辐射传输的重要因素. 系统给出了矢量辐射传输Monte Carlo模型, 并验证了其准确度; 考虑入射光偏振态, 讨论了不同方向漫射光Stokes矢量对气溶胶形状的敏感性; 分析了气溶胶形状、入射光偏振状态对光波退偏振度、透过率及反射率的影响. 模拟仿真结果表明, 对于不同偏振态的入射光, 不同方向的Stokes矢量对气溶胶形状变化的灵敏程度并不一致, 而在天顶角0°方向区域,Q, U及V分量对形状的灵敏程度普遍不高; 气溶胶形状对反射漫射光退偏程度的影响强于透射漫射光, 入射光偏振态不同, 漫射光退偏程度也存在较大差异. 气溶胶形状对光波整体透过率与反射率影响显著, 且该影响随传播距离增大而增大; 入射光偏振态对透过率与反射率影响相对较小, 与自然光相比, 水平偏振光透过率略偏小, 反射率略偏大, 垂直偏振光反之, 圆偏振光与自然光的模拟结果相当.     

青藏高原对流层气溶胶的激光雷达监测与研究

运用激光雷达方程和Fernald方法,对西藏那曲地区和北京地区对流层气溶胶的微脉冲激光雷达(MPL)探测数据进行时空反演和比较,结果表明:气溶胶散射比廓线有着较为相似的结构分布,分层锯齿结构非常明显,主要包括贴地层、气溶胶混合层和气溶胶对流层。那曲测站上空气溶胶散射比在无云条件下最大值基本上保持在2.0左右;在测站上空均存在密度较大且较厚的积云;夏季的混合层或残留层(浅蓝色部分)高度抬高;夏季对流层低层积云的云量和积云出现的概率较冬季要少。