太阳光谱仪的定标技术与渤海海域的光学测量

本文以太阳光谱仪为基础介绍了根据仪器测量的电信号数据反演气溶胶光学厚度的基本原理以及依据Langley方法的定标技术。通过两次测量试验对比,提出了一种比较实用的仪器定标方法,即在海洋上空对仪器进行定标并且取得了满意的结果。利用该仪器于2003年8月对渤海海域上空的大气光学特性进行了大面积调查,分析了当时海域上空各种大气参数(气溶胶光学厚度、臭氧浓度以及水汽含量等)的空间分布情况,为我国近海海域二类水体水色遥感反演中大气校正模式的建立提供了必要的数据参考。     

衡水湖地区气溶胶分布特征的航测研究

利用飞机机载粒子测量系统(PMS)对河北省衡水湖自然保护区上空的大气气溶胶粒子进行观测研究。观测结果表明:下垫面、天气条件、逆温等对气溶胶的分布存在较大的影响;衡水湖上空不同高度的气溶胶平均谱分布均呈现出单峰分布;细粒子谱分布在0.28μm左右处出现峰值;多阶Γ函数对气溶胶粒子谱有较好的拟合效果。     

用于反应堆安全壳内氟-18探测器的校准及影响因素

安装于核反应堆安全壳内的大气辐射监测仪的氟-18探测器采用γ-γ符合测量原理,连续监测气溶胶中氟-18的活度水平。其主要计量特性为活度响应及其非线性,采用氟-18参考源进行校准,活度响应以探测器γ-γ符合计数率与氟-18参考源的活度之比表示。在5.5～25 kBq的活度范围内,非线性可忽略,氟-18参考源中氟-18核素分布均匀性影响活度响应测量的复现性;立体角的变化是影响活度响应校准结果的主要因素。     

气溶胶对远红外激光辐射的衰减规律研究

计算分析了10.6μm波长远红外激光辐射在不同能见度条件下的大气气溶胶中水平传输的衰减系数、有效传输距离以及斜程传输时的透过率变化规律,对比分析了远红外激光辐射在1.0g/m3的高浓度酸雾和油雾气溶胶中的传输能力。根据Mie理论计算了直径为0.5～40μm的水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光的散射效率因子、吸收效率因子和消光效率因子。结果表明:气溶胶的消光系数越大、大气能见度越低,大气气溶胶对远红外激光辐射的衰减越严重;在1.0g/m3的高浓度酸雾和油雾气溶胶中远红外激光辐射的有效传输距离只有20～50m。水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光辐射的衰减机理基本相同,其中散射作用居于主导地位并且平均直径大于5μm的气溶胶粒子对10.6μm远红外激光辐射具有显著的衰减作用。     

应用圆二色光谱研究真空对超氧化物歧化酶二级结构的影响

超氧化物歧化酶经真空处理不同时间,利用圆二色光谱研究不同真空时间对超氧化物歧化酶二级结构的影响.结果表明:在3～15 min范围,不同真空处理时间对超氧化物歧化酶的α-螺旋、β-折叠、β-转角及无规卷曲相对含量的影响程度不同.与对照组相比,处理组的α-螺旋、β-转角和无规卷曲含量降低,降幅范围分别为26.1%～41.3%、52.1%～68.8%和2.1%～3.8%;β-折叠增加,增幅范围分别为6.5%～9.2%,表明真空作用使超氧化物歧化酶的二级结构中α-螺旋、β-转角及无规卷曲向β-折叠转化.     

宽频超声衰减法测量河流泥沙粒径分布

为了研究宽频超声波通过河流泥沙悬浊液的声衰减谱中包含泥沙的颗粒粒度信息,采用超声耦合相模型和散射模型的叠加描述河流泥沙悬浊液中超声衰减行为,宽频超声换能器测量得到2～7.5MHz间泥沙悬浊液声衰减谱,结合独立模式的最优正则化反演算法,获得了相同体积浓度、不同粒径分布下和相同粒径分布、不同体积浓度下泥沙的颗粒粒径分布。结果表明,宽频超声衰减法能较好地区分3种不同粒径分布的泥沙,并且在体积浓为3.8%～8.5%范围间,测量得到的平均粒径受浓度变化影响较小。将超声法测量结果与显微镜图像法测量结果相比较,两种方法得到的粒径分布趋势较为一致,平均粒径较为吻合。     

光腔光谱方法气溶胶消光系数比对测量

搭建了非相干宽带腔增强吸收光谱(IBBCEAS)实验装置,旨在实现大气气溶胶宽波段消光系数的在线测量。为评估IBBCEAS系统测量大气气溶胶消光系数的稳定性和准确性,联用单波长腔衰减相位移反照率监测仪(CAPS-ALB)在复旦大学环境科学楼开展比对测量研究。比对结果显示,两台装置在532nm波长处测量的气溶胶消光系数变化趋势基本一致,相关系数为0.974,说明IBBCEAS装置具有与通过计量检测认证的高精准度仪器相似的稳定性和可靠性。通过CAPS-ALB仪器的比对校准,IBBCEAS装置的测量平均偏差由7.08Mm^-1降低到2.4Mm^-1,测量准确性得到显著提升。另外发现,宽波段光谱测量对研究气溶胶消光系数的波长依赖性具有重要意义。     

北京地区冬季气溶胶分级化学成分及来源分析

在北京城区进行冬季大气气溶胶采样,样品采用PIXE方法进行分析,得到大气气溶胶中20种元素的质量浓度。结果表明:元素Mg、Fe、Si这3种元素均呈粗粒模态单峰型分布,且峰值出现在2～4μm,表明它们来自土壤尘;S、Cl、K等3种元素谱分布呈细粒单峰型分布,峰值都出现在0.25～0.5μm范围内,表明这3种元素主要来自燃煤;Cu、Zn、As、Br、Pb等5种元素谱分布呈双峰型谱分布;Ni、Cu、Zn、As、Se、Br、Pb等元素的粗、细模态的富集因子都较大,尤其是细粒模态,表明这些元素更容易在细粒模态上富集,进一步说明这些元素主要来自人为污染源。因子分析结果表明:土壤尘、煤烟尘、工业源和汽车尾气排放源对北京冬季气溶胶有主要贡献。     

河北地区秋季大气气溶胶物理特征分析

利用2005年10月20日在河北省石家庄和邯郸地区进行的一次飞机探测资料,初步分析了石家庄和邯郸上空的气溶胶粒子数浓度、粒径、粒子谱垂直分布特征,对石家庄与邯郸之间的水平飞行气溶胶粒子数浓度资料进行分析,并对石家庄、邯郸的气溶胶粒子谱进行函数拟合。结果表明:各高度层气溶胶粒子数浓度基本上都是石家庄高于邯郸,各高度层粒子平均直径基本上都是石家庄低于邯郸。两地气溶胶粒子数浓度、粒子平均直径随高度的分布有不同特点。石家庄、邯郸气溶胶粒子谱谱型,低层相似,基本都是单调下降,高层粒子谱谱型为多峰型。3100m高度层粒子数浓度在水平方向上分布不均匀,城市附近上空气溶胶粒子数浓度相对较大,郊县气溶胶粒子数浓度相对较小。随着高度增加,粒子数浓度减小,水平方向的绝对变化越来越小。利用幂函数N(D)=AD-B可以对不同高度气溶胶粒子谱进行较好的拟合。     

气溶胶光热干涉测量系统激发参数研究

气溶胶吸收直接影响光在大气中的传播造成光的衰减。本文采用折返式Jamin偏振干涉结构建立了气溶胶光热干涉实验系统,提出并实验研究了在激光照射(加热)和降温两个阶段分别测量吸收系数的方法,确定了两种方法测量气溶胶吸收系数的激发激光功率,为进一步开展气溶胶吸收系数的实验研究提供了参数支持。     

两种方法测量大气气溶胶折射率的对比分析

针对气溶胶折射率在分析大气气溶胶光学特性中的重要性,介绍两种综合利用黑碳仪、浊度计、光学粒子计数器和微脉冲激光雷达测量大气气溶胶折射率的新方法。两种方法都是根据球形粒子的Mie散射理论计算大气气溶胶的折射率,使用以上两种方法对厦门地区气溶胶折射率进行了计算和对比分析,证明了它们的合理性,分析了它们的测量精度和误差来源。     

Retrieval and monitoring of aerosol optical thickness over an urban area by spaceborne and ground-based remote sensing

We used an instrumental synergy of both ground-based (sunphotometer) and spaceborne [POLDER (polarization and directionality of the Earth's reflectances) and Meteosat] passive remote-sensing devices to determine the aerosol optical thickness over the suburban area of Thessaloniki, Greece, from April 1996 to June 1997. The POLDER spaceborne instrument measures the degree of polarization of the solar radiance reflected by the Earth-atmosphere system. Aerosol optical thickness (AOT) retrieval needs an accurate estimate of the contribution of the ground surface to the top of atmosphere's polarized radiance. We tested existing surface reflectance models and fitted their parameters to find the best model for the Thessaloniki area. The model was constrained and validated by use of independent data sets of coincident sunphotometer and POLDER measurements. The comparison indicated that the urban AOT over Thessaloniki was retrieved by the POLDER instrument with an accuracy of +/-0.05. From analysis of Meteosat data we found that approximately 40% of the days with high AOT (>0.18) are associated with African dust transport events, all observed in the period March-July. Excluding dust events, the 15-month AOT averages 0.12 +/- 0.04. During the 15-month period that the study was conducted, we observed aerosol pollution peaks with an AOT of >0.24 on 15 of the 164 days on which measurements were possible.     

Approach to photorealistic halo simulations

A multiple-scattering Monte Carlo model that can produce near-photographic quality images is developed and used to simulate several dramatic halo displays. The model atmosphere contains an absorbing ozone layer plus two clear, molecular air layers with Rayleigh scattering surrounding a cloud layer and an atmospheric boundary layer with aerosol particles subject to Lorentz-Mie scattering. Halos are produced by right hexagonal or pyramidal crystals that reflect and refract according to geometric optics without diffraction, although "junk" crystals with a pronounced forward-scattering peak but no halo peaks may be included to simulate typical, faint halos. Model parameters include ozone height and content, surface and cloud pressure, cloud optical thickness, crystal shapes, orientations and abundances, atmospheric turbidity, aerosol radius, and albedo. Beams for each wavelength are sorted into small bins as halo beams if they have been scattered once only by a single crystal and otherwise as sky beams, which are smoothed and combined with the halo beams to produce images. Multiple scattering generally vitiates halos, but extremely rare halos, such as Kern's arc, can be produced if a significant fraction of crystals in optically thick clouds have identical shapes and are highly oriented. Albedo is a model by-product with potential value in climate studies.     

Ozone and water-vapor measurements by Raman lidar in the planetary boundary layer: error sources and field measurements

A new lidar instrument has been developed to measure tropospheric ozone and water vapor at low altitude. The lidar uses Raman scattering of an UV beam from atmospheric nitrogen, oxygen, and water vapor to retrieve ozone and water-vapor vertical profiles. By numerical simulation we investigate the sensitivity of the method to both atmospheric and device perturbations. The aerosol optical effect in the planetary boundary layer, ozone interference in water-vapor retrieval, statistical error, optical cross talk between Raman-shifted channels, and optical cross talk between an elastically backscattered signal in Raman-shifted signals and an afterpulse effect are studied in detail. In support of the main conclusions of this model study, time series of ozone and water vapor obtained at the Swiss Federal Institute of Technology in Lausanne and during a field campaign in Crete are presented. They are compared with point monitor and balloon sounding measurements for daytime and nighttime conditions.     

Multiple-scattering effect on ozone retrieval from space-based differential absorption lidar measurements

Single-scattering and multiple-scattering lidar signals are calculated for a spaceborne differential absorption lidar system for global ozone measurements at the on and off wavelength pair at 305 and 315 nm. The effect of multiple scattering is found to be negligible on stratospheric and tropospheric ozone retrieval under background stratospheric aerosol. Under low-visibility conditions in the planetary boundary layer the presence of multiple scattering causes an overestimation in maritime aerosol and an underestimation in urban as well as in rural aerosol. This effect is also examined in three cirrus models. The multiple scattering does not permit accurate ozone retrieval within cirrus; however, below it the solution recovers somewhat with generally an underestimation depending on the type and density of cirrus. The effect of aerosol and Rayleigh extinction on the ozone retrieval is also discussed.     

Case study of modeled aerosol optical properties during the SAFARI 2000 campaign

We present modeled aerosol optical properties (single scattering albedo, asymmetry parameter, and lidar ratio) in two layers with different aerosol loadings and particle sizes, observed during the Southern African Regional Science Initiative 2,000 (SAFARI 2,000) campaign. The optical properties were calculated from aerosol size distributions retrieved from aerosol layer optical thickness spectra, measured using the NASA Ames airborne tracking 14-channel sunphotometer (AATS-14) and the refractive index based on the available information on aerosol chemical composition. The study focuses on sensitivity of modeled optical properties in the 0.3-1.5 microm wavelength range to assumptions regarding the mixing scenario. We considered two models for the mixture of absorbing and nonabsorbing aerosol components commonly used to model optical properties of biomass burning aerosol: a layered sphere with absorbing core and nonabsorbing shell and the Maxwell-Garnett effective medium model. In addition, comparisons of modeled optical properties with the measurements are discussed. We also estimated the radiative effect of the difference in aerosol absorption implied by the large difference between the single scattering albedo values (approximately 0.1 at midvisible wavelengths) obtained from different measurement methods for the case with a high amount of biomass burning particles. For that purpose, the volume fraction of black carbon was varied to obtain a range of single scattering albedo values (0.81-0.91 at lambda=0.50 microm). The difference in absorption resulted in a significant difference in the instantaneous radiative forcing at the surface and the top of the atmosphere (TOA) and can result in a change of the sign of the aerosol forcing at TOA from negative to positive.     

卫星遥感气溶胶光学厚度的双通道方法

本文提出了一种利用ＮＯＡＡ－１４极轨卫星甚高分辨率辐射计可见光和近红外两个通道的反射率资料遥感晴空条件下，均匀下垫面上整层大气气溶胶光学厚度的双通道方法。该方法利用气溶胶散射的波长关系，把基于大气辐射传输方程近红外通道的光学厚度均值引入可见通道，使单个通道中地表反射率和大气因子参数化的误差得以抵消，极大地提高遥感精度。     

沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性。分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数。分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响。在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异。     

Lifetimes and time scales in atmospheric chemistry

Atmospheric composition is controlled by the emission, photochemistry and transport of many trace gases. Understanding the time scale as well as the chemical and spatial patterns of perturbations to trace gases is needed to evaluate possible environmental damage (e.g. stratospheric ozone depletion or climate change) caused by anthropogenic emissions. This paper reviews lessons learned from treating global atmospheric chemistry as a linearized system and analysing it in terms of eigenvalues.The results give insight into how emissions of one trace species cause perturbations to another and how transport and chemistry can alter the time scale of the overall perturbation. Further, the eigenvectors describe the fundamental chemical modes, or patterns, of the atmosphere's chemical response to perturbations.