A Review of Aerosol Optical Properties and Radiative Effects

Atmospheric aerosols influence the earth's radiative balance directly through scattering and absorbing solar radiation, and indirectly through affecting cloud properties. An understanding of aerosol optical properties is fundamental to studies of aerosol effects on climate. Although many such studies have been undertaken, large uncertainties in describing aerosol optical characteristics remain, especially regarding the absorption properties of different aerosols. Aerosol radiative effects are considered as either positive or negative perturbations to the radiation balance, and they include direct, indirect (albedo effect and cloud lifetime effect), and semi-direct effects. The total direct effect of anthropogenic aerosols is negative (cooling), although some components may contribute a positive effect (warming). Both the albedo effect and cloud lifetime effect cool the atmosphere by increasing cloud optical depth and cloud cover, respectively. Absorbing aerosols, such as carbonaceous aerosols and dust, exert a positive forcing at the top of atmosphere and a negative forcing at the surface, and they can directly warm the atmosphere. Internally mixed black carbon aerosols produce a stronger warming effect than externally mixed black carbon particles do. The semi-direct effect of absorbing aerosols could amplify this warming effect. Based on observational (ground-and satellite-based) and simulation studies, this paper reviews current progress in research regarding the optical properties and radiative effects of aerosols and also discusses several important issues to be addressed in future studies.     

关于硝酸盐气溶胶光学特征和辐射强迫的研究进展

在过去的20多年里,中外对硫酸盐气溶胶做了大量的研究,对它在大气中的排放、含量、光学特征和辐射强迫有了深入的认识;由于硝酸盐气溶胶在大气中平均含量比硫酸盐低很多,因此过去人们对硝酸盐的研究没有给予重视。然而,近年来的研究表明,硝酸盐气溶胶的散射性质在某些波段甚至强于硫酸盐;同时,由于未来对人为硫酸盐前体物的减排,硫酸盐气溶胶排放会大幅度减少,而硝酸盐气溶胶的排放却增长迅速,其在人为气溶胶中所占的比重越来越高,将会导致其在未来造成的辐射强迫有可能超过硫酸盐,使得其在地区范围内和季节尺度上成为重要的辐射强迫和气候影响因子。中国是硝酸盐气溶胶排放量较大的地区,硝酸盐对未来中国气候和气候变化的影响显得越来越重要。因此,就近年来有关硝酸盐气溶胶的排放和在大气中的浓度变化、光学厚度分布特征及其辐射强迫的研究进展做了回顾和介绍,并对其未来的研究做了展望。     

大气气溶胶研究的前沿问题

从4个方面对大气气溶胶研究的前沿问题作了总结和分析：气溶胶的基本特征、气溶胶的气候效应、沙尘气溶胶以及气溶胶对健康环境的影响。介绍了当前国际上有关的大气气溶胶研究计划,讨论了未来大气气溶胶研究的主要领域及研究方向。     

A Modeling Study of the Effects of Direct Radiative Forcing Due to Carbonaceous Aerosol on the Climate in East Asia

The study investigated the effects of global direct radiative forcing due to carbonaceous aerosol on the climate in East Asia, using the CAM3 developed by NCAR. The results showed that carbonaceous aerosols cause negative forcing at the top of the atmosphere (TOA) and surface under clear sky conditions, but positive forcing at the TOA and weak negative forcing at the surface under all sky conditions. Hence, clouds could change the sign of the direct radiative forcing at the TOA, and weaken the forcing at the surface. Carbonaceous aerosols have distinct effects on the summer climate in East Asia. In southern China and India, it caused the surface temperature to increase, but the total cloud cover and precipitation to decrease. However, the opposite effects are caused for most of northern China and Bangladesh. Given the changes in temperature, vertical velocity, and surface streamflow caused by carbonaceous aerosol in this simulation, carbonaceous aerosol could also induce summer precipitation to decrease in southern China but increase in northern China.     

大气气溶胶变化对农业影响的研究进展

随着工业化和城市化的迅速发展,大气气溶胶含量和种类明显增加,它们通过直接吸收和反射太阳辐射以及改变其它辐射强迫因子(云、臭氧)的大小间接影响地气系统的能量收支,从而影响气候。气溶胶变化对气候的影响已有较多的研究,而对植被(农业)的影响是一个相对较新的研究领域,文章简要概述了大气气溶胶辐射强迫效应和大气气溶胶对农业的影响研究现状及国内外主要研究成果,并对气溶胶监测方法及模式评估方面可能存在的问题作了简单的分析。     

平流层气溶胶的辐射强迫及其气候响应的水平二维分析

利用比较先进的辐射模式计算了平流层气溶胶的辐射强迫,并对之进行了参数化。结果发现平流层气溶胶的辐射强迫的水平分布不仅与其本身的水平变化有关,而且与下垫面的反照率有很大的关系。利用近期开发的二维能量平衡模式模拟了皮纳图博火山气溶胶对地面平衡温度的影响,结果表明:皮纳图博火山至喷发后1年半左右降温达最大,至喷发后第5年降温已很小。     

硫酸盐气溶胶辐射强迫的数值模拟研究

利用IAP/LASG GOALS 4.0海气耦合模式,"显式"考虑了硫酸盐气溶胶的直接作用,并且引入德国马普气象研究所的三维浓度分布资料,模拟计算了硫酸盐气溶胶的辐射强迫.主要结果为:全球气溶胶年平均的辐射强迫为-0.29 W m-2,在IPCC TAR给定的范围内,空间分布上具有明显的地域性,几个大值地区分别为东亚、西欧和北美,它们的中心值均超过-1.5 W m-2,南美、澳大利亚以及非洲南部的辐射强迫介于-0.2～-0.4 W m-2之间,而海洋和偏远的大陆地区,则基本上不受人为硫酸盐气溶胶的影响;计算的东亚地区硫酸盐气溶胶的平均辐射强迫为-0.75 W m-2,约为全球平均的2.5倍,为北半球平均的1.6倍.文中还讨论了全球硫酸盐气溶胶对温室气体辐射强迫的减缓作用.     

温室气体和硫酸盐气溶胶的辐射强迫作用

对GOALS4 .0海 陆 气耦合模式的相关部分进行了改进 ,主要改进包括温室气体的扩充和硫酸盐气溶胶“显式”方案的引入 ,并引入 2 0世纪温室气体的实际浓度变化以及硫循环模式模拟的硫酸盐气溶胶的三维全球浓度分布 ,模拟了温室气体和硫酸盐气溶胶造成的辐射强迫的空间分布和时间变化。全球平均的温室气体和硫酸盐气溶胶的辐射强迫分别为 2 .17W /m2 和 - 0 .2 9W /m2 ;温室气体造成的辐射强迫在空间上呈现明显的纬向结构 ,最大值 (大于 2 .5W/m2 )和最小值 (小于 1W /m2 )分别位于副热带和两极地区 ,在北半球主要工业区硫酸盐气溶胶的辐射强迫绝对值接近温室气体的辐射强迫值 (大于 - 2 .0W /m2 )。     

Model analysis of influences of aerosol mixing state upon its optical properties in East Asia

The air quality model system RAMS (Regional Atmospheric Modeling System)-CMAQ (Models-3 Community Multi-scale Air Quality) coupled with an aerosol optical/radiative module was applied to investigate the impact of different aerosol mixing states (i.e., externally mixed, half externally and half internally mixed, and internally mixed) on radiative forcing in East Asia. The simulation results show that the aerosol optical depth (AOD) generally increased when the aerosol mixing state changed from externally mixed to internally mixed, while the single scattering albedo (SSA) decreased. Therefore, the scattering and absorption properties of aerosols can be significantly affected by the change of aerosol mixing states. Comparison of simulated and observed SSAs at five AERONET (Aerosol Robotic Network) sites suggests that SSA could be better estimated by considering aerosol particles to be internally mixed. Model analysis indicates that the impact of aerosol mixing state upon aerosol direct radiative forcing (DRF) is complex. Generally, the cooling effect of aerosols over East Asia are enhanced in the northern part of East Asia (Northern China, Korean peninsula, and the surrounding area of Japan) and are reduced in the southern part of East Asia (Sichuan Basin and Southeast China) by internal mixing process, and the variation range can reach 5 W m－2. The analysis shows that the internal mixing between inorganic salt and dust is likely the main reason that the cooling effect strengthens. Conversely, the internal mixture of anthropogenic aerosols, including sulfate, nitrate, ammonium, black carbon, and organic carbon, could obviously weaken the cooling effect.     

Direct Radiative Forcing of Anthropogenic Aerosols over Oceans from Satellite Observations

Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth (AOD) and its accompanying shortwave radiative forcing (RF) are usually simulated by nu- merical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System (CERES/SSF) experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were -1.03±0.48 W m-2 and -0.34 ±0.16 W m-2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases.     

Assessment of Individual Direct Radiative Effects of Major Aerosol Species in East Asia

To assess individual direct radiative effects of diverse aerosol species on a regional scale,the air quality modeling system RAMS-CMAQ(Regional Atmospheric Modeling System and Community Multiscale Air Quality) coupled with an aerosol optical properties/radiative transfer module was used to simulate the temporal and spatial distributions of their optical and radiative properties over East Asia throughout 2005.Annual and seasonal averaged aerosol direct radiative forcing(ADRF) of all important aerosols and individual components,such as sulfate,nitrate,ammonium,black carbon(BC),organic carbon(OC),and dust at top-of-atmosphere(TOA) in clear sky are analyzed.Analysis of the model results shows that the annual average ADRF of all important aerosols was in the range of 0 to-18 W m?2,with the maximum values mainly distributed over the Sichuan Basin.The direct radiative effects of sulfate,nitrate,and ammonium make up most of the total ADRF in East Asia,being concentrated mainly over North and Southeast China.The model domain is also divided into seven regions based on different administrative regions or countries to investigate detailed information about regional ADRF variations over East Asia.The model results show that the ADRFs of sulfate,ammonium,BC,and OC were stronger in summer and weaker in winter over most regions of East Asia,except over Southeast Asia.The seasonal variation in the ADRF of nitrate exhibited the opposite trend.A strong ADRF of dust mainly appeared in spring over Northwest China and Mongolia.     

人为气溶胶的直接辐射效应及其对南亚冬季风的影响

运用区域气候模式RegCM4.0(Regional Climate Model Verson 4.0)耦合入一个化学过程,对硫酸盐、黑碳、有机碳这3种人为气溶胶的时空分布特征和直接辐射效应进行了数值模拟,进而研究了气溶胶对南亚冬季风的影响。结果表明:光学厚度和地表短波辐射强迫的时空变化可能主要受硫酸盐气溶胶的影响。在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,大气层顶和地表的负短波辐射强迫分布与气溶胶分布基本一致,地表辐射强迫强度绝对值比大气层顶辐射强迫强度绝对值大得多。相关分析和合成分析表明:在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,南亚人为气溶胶主要分布区中的气溶胶柱浓度含量与南亚冬季风的建立和强度有反相关关系。这与气溶胶吸收太阳辐射,从而引起气温和位势高度的变化有关。     

中国地区气溶胶的辐射强迫及其气候响应试验

根据国内测定的排放因子数据和国家、部委及各省市统计年鉴公布的排放源数据,得到的中国大陆的1°×1°网格精度的SO2的排放分布,计算了中国地区人为扰动气溶胶的辐射强迫。应用近期开发的二维能量平衡模式计算了由该种气溶胶所引起的中国地区地面温度变化。模式结果表明,最大辐射强迫和最大地面温度变化都集中在中国的沿海和四川地区。最大辐射强迫达3 W/m2。     

近十年北京气溶胶光学特性及直接辐射强迫研究

利用SBDART（Santa Barbara DISORT Atmospheric Radiative Transfer）辐射传输模式,结合AERONET（Aerosol Robotic Network）北京站观测的气溶胶光学特性数据,评估北京地区近十年气溶胶以及黑碳气溶胶的辐射强迫,主要研究结果如下:北京近十年气溶胶平均光学厚度（aerosol optical depth, AOD_440nm）为0.61±0.56,?ngstr?m波长指数均值为1.09,单次散射反照率（single scattering albedo, SSA_440nm）的均值为0.888±0.045;AOD呈现下降趋势,SSA呈上升趋势,表明该区域气溶胶污染有所改善。晴空条件下,大气层顶、地面和大气的气溶胶直接辐射强迫多年均值分别为?24.91±19.80 W m?2、?65.52±43.78 W m?2、40.61±28.62 W m?2,即气溶胶对大气层顶和地表为冷却效应,对大气产生加热作用。气溶胶和黑碳气溶胶的直接辐射强迫绝对值的年际变化表现为微弱的下降趋势,季节变化特征为春夏季高,冬季低,这与AOD的变化规律一致。并且黑碳气溶胶的直接辐射强迫下降趋势与SSA的上升趋势呈现较好的反位相关系。     

Future impact of anthropogenic sulfate aerosol on North Atlantic climate

We examine the simulated future change of the North Atlantic winter climate influenced by anthropogenic greenhouses gases and sulfate aerosol. Two simulations performed with the climate model ECHAM4/OPYC3 are investigated: a simulation forced by greenhouse gases and a simulation forced by greenhouse gases and sulfate aerosol. Only the direct aerosol effect on the clear-sky radiative fluxes is considered. The sulfate aerosol has a significant impact on temperature, radiative quantities, precipitation and atmospheric dynamics. Generally, we find a similar, but weaker future climate response if sulfate aerosol is considered additionally. Due to the induced negative top-of-the-atmosphere radiative forcing, the future warming is attenuated. We find no significant future trends in North Atlantic Oscillation (NAO) index in both simulations. However, the aerosol seems to have a balancing effect on the occurence of extreme NAO events. The simulated correlation patterns of the NAO index with temperature and precipitation, respectively, agree well with observations up to the present. The extent of the regions influenced by the NAO tends to be reduced under strong greenhouse gas forcing. If sulfate is included and the warming is smaller, this tendency is reversed. Also, the future decrease in baroclinicity is smaller due to the aerosols’ cooling effect and the poleward shift in track density is partly offset. Our findings imply that in simulations where aerosol cooling is neglected, the magnitude of the future warming over the North Atlantic region is overestimated, and correlation patterns differ from those based on the future simulation including aerosols.     

Aerosol Optical Properties and Radiative Impacts in the Pearl River Delta Region of China during the Dry Season

Aerosol optical properties and direct radiative effects on surface irradiance were examined using seven years(2006–2012)of Cimel sunphotometer data collected at Panyu—the main atmospheric composition monitoring station in the Pearl River Delta(PRD) region of China. During the dry season(October to February), mean values of the aerosol optical depth(AOD)at 550 nm, the ?ngstr?m exponent, and the single scattering albedo at 440 nm(SSA) were 0.54, 1.33 and 0.87, respectively.About 90% of aerosols were dominated by fine-mode strongly absorbing particles. The size distribution was bimodal, with fine-mode particles dominating. The fine mode showed a peak at a radius of 0.12 μm in February and October(~0.10μm~3μm~(-2)). The mean diurnal shortwave direct radiative forcing at the surface, inside the atmosphere(FATM), and at the top of the atmosphere, was-33.4 ± 7.0, 26.1 ± 5.6 and-7.3 ± 2.7 W m~(-2), respectively. The corresponding mean values of aerosol direct shortwave radiative forcing per AOD were-60.0 ± 7.8, 47.3 ± 8.3 and-12.8 ± 3.1 W m~(-2), respectively. Moreover,during the study period, FATMshowed a significant decreasing trend(p 0.01) and SSA increased from 0.87 in 2006 to 0.91 in 2012, suggesting a decreasing trend of absorbing particles being released into the atmosphere. Optical properties and radiative impacts of the absorbing particles can be used to improve the accuracy of inversion algorithms for satellite-based aerosol retrievals in the PRD region and to better constrain the climate effect of aerosols in climate models.     

青藏高原地区气溶胶直接辐射强迫的数值模拟研究

通过比较EMAC模式模拟结果和卫星观测结果证实了模式的可信性,进而利用模拟结果分析研究了2010～2012年青藏高原上空气溶胶光学厚度及其直接辐射强迫的时空分布规律。结果表明:所有气溶胶组分中,沙尘、水溶性气溶胶和气溶胶中液态水是高原的主要消光物质,三者年平均消光占比分别为0.27、0.20和0.49。2011年夏季纳布罗火山爆发,高空气溶胶消光在海拔14 km以上显著增强。青藏高原气溶胶在大气顶和地表的直接辐射强迫分布总体上由北向南递减,沙尘气溶胶在高原北部边缘大气顶产生正辐射强迫,气溶胶大气层直接辐射强迫对大气有增温效应,主要出现在沙尘含量高的地区。此外,受纳布罗火山爆发的影响,平流层气溶胶在2011年秋、冬季产生了明显较强的负辐射强迫,相比于无火山爆发的2010年和 2012年,青藏高原上空平流层气溶胶负辐射强迫在2011年秋季和冬季分别增加了55.50%和52.38%。     

Why Is the Climate Forcing of Sulfate Aerosols So Uncertain?

l. IntroductionAlthough the aerosol has been recognized as an important factor which has innuence onthe past, present and future climate for a long time, it still has much uncertainty in assessingits climate forcing. The direct radiative forcing of sulfate aerosols has been estimated rangingfrom --0.3 W/ m2 to --0.9 W/ m2 in recent publications (Charlson et al., l992, Kiehl andBriegleb l993; Taylor and Penner 1994, Boucher and Anderson l995, Kieh1 and Rodhe l995;Chuang et al., l997, Penne…     

Aerosol optical properties and its radiative forcing over Yulin,China in 2001 and 2002

The aerosol optical properties and direct radiative forcing over the Mu Us desert of northern China, acquired through a CE318 sunphotometer of the ground-based Aerosol Robotic Network (AERONET), are analyzed. The seasonal variations in the aerosol optical properties are examined. The effect of meteorological elements (pressure, temperature, water vapor pressure, relative humidity and wind speed) on the aerosol optical properties is also studied. Then, the sources and optical properties under two different cases, a dust event and a pollution event, are compared. The results show that the high aerosol optical depth (AOD) found in Yulin was mostly attributed to the occurrence of dust events in spring from the Mu Us desert and deserts of West China and Mongolia, as well as the impacts of anthropogenic pollutant particles from the middle part of China in the other seasons. The seasonal variation and the probability distribution of the radiative forcing and the radiative forcing efficiency at the surface and the top of the atmosphere are analyzed and regressed using the linear and Gaussian regression methods.