【作者】 巩崇水；

【导师】 王式功； 辛金元；

【作者基本信息】 兰州大学 ， 气象学， 2014， 博士

【摘要】 影响气候变化的诸多因素之中气溶胶是科学界关注的焦点之一,原因是它对气候变化的影响存在着较大的不确定性。虽然气溶胶气候效应的研究起步较早,但进展相对缓慢,现在普遍认为由此引起的全球平均辐射强迫和温室气体产生的辐射强迫量级相当,而其性质与作用却相反。气溶胶引起的温度降低效应(阳伞效应)区域差异很明显,在局部区域内有可能抵消由温室气体引起的升温作用。中国大陆地形复杂,气候多样,是对全球气候变化响应最敏感的地区之一,同时也是气溶胶类型众多、数量庞大的地区之一。气溶胶对中国大陆地区气候变化的影响如何?还仍然是个没有被完全解开的迷。因此,本文采用了2004年起建立的中国大陆地区太阳分光观测网(CSHNET,the Chinese Sun Hazemeter Network,2004年时设有观测站点23个,后逐步拓展至35个)获得的地基气溶胶光学参数资料,结合MODIS(moderate-resolution imaging spectroradiometer)卫星观测资料对气溶胶单次散射反照率(single scattering albedo, SSA)和气溶胶的直接辐射强迫(aerosol radiative forcing at the top of atmosphere, TOA)进行了相关反演和计算。使用地基与空基观测资料相结合的反演思路,通过比较1998年由美国加利福尼亚大学研发的SBDART(Santa Barbara DISORT Atmospheric Radiative Transfer)辐射传输模式基于地面实测资料和多组理论参数得到的气溶胶辐射通量(path radiance)结果与MODIS的对应波段观测值之间的百分比均方根误差(RMSD, root mean square difference),当该误差最低时,认为当前的SSA、不平衡系数(Asymmetry parameter)和消光系数等参数最为接近大气的实际情况。而后利用SBDART辐射传输模式,计算了晴空条件下相关的气溶胶直接辐射强迫结果。其中单次散射反照率是衡量气溶胶吸收强弱的重要光学参数,当气溶胶粒子吸收性越强,SSA则越小；一般而言,当气溶胶的SSA从0.9降低至0.8的过程中,气溶胶直接辐射强迫的值将出现从负值到正值的转变,对应的气候效应则从冷却效应转变为加热效应。气溶胶的直接辐射强迫则表明了地-气系统入射和出射的辐射平衡关系,当TOA>0(此处向地面方向为正)时,地面和对流层将整体变暖。基于之前关于中国大陆地区太阳分光观测网(CSHNET)的联网观测研究中,不同生态区域气溶胶的光学厚度和波长指数存在较大的时空分布差异的重要发现,本文侧重于人类活动和自然条件各自对气候变化产生影响的量化计算和分析研究,进而阐明它们所产生的气溶胶直接辐射强迫的气候效应。SSA(单次散射反照率)结果表明,在中国大陆,人类活动影响强烈的区域,特别是中东部地区、华南地区和东部沿海地区,气溶胶主要呈现出受人为源影响显著,即工业排放和机动车尾气等造成的硫酸性气溶胶,其散射性较强,平均SSA大于0.90,表现出可能会产生冷却效应的特征。而在东北以农业为主的区域,以及植被较好,受人为源影响较小的地区,SSA呈现出以沙尘源为主,表现为吸收性,平均值在0.80-0.85的范围内。在西北和青藏高原地区,地表以沙漠、戈壁等为主,或者高寒草甸、植被稀疏,其诸观测站呈现出矿物性气溶胶特征,吸收性较强,SSA一般低于0.80,表现出可能会产生加热效应的特征。即便如此,在西部局部工业较为集中的地区,如兰州和阜康等,人为工业源影响较大,在某些季节也显露出硫酸性气溶胶(通常产生冷却效应)的影响特征,SSA平均值在0.80-0.85。此外,三亚观测站位于海南岛南端,地理位置特殊,且工业气溶胶影响很少,表现为海盐性气溶胶特征,SSA平均为0.87,与受人为源影响较大的山东胶州湾、上海等沿海测站的硫酸性气溶胶特征截然不同。与上述地区相对应的TOA(气溶胶的直接辐射强迫)表现出与SSA基本一致的结果,即在东部、南部人为源排放较多的地区,受人为源散射性气溶胶的影响,TOA基本呈现出冷却效应；而在自然沙尘／矿物源占主导地位的地区,TOA则呈现出不同程度的加热效应。在西北荒漠、青藏高原与东北农业区气溶胶直接辐射强迫对地-气系统加热效应显著,大气层顶年均辐射强迫约为+10W/m2；在中东部、华北与华南地区气溶胶对地-气辐射系统冷却效应显著,年均辐射强迫约为-11W/m2。在四川省盐亭站,受人为气溶胶的大量排放和盆地地理位置限制,其冷却效应在所有站点里表现为最强(-21.1W/m2),内蒙古的鄂尔多斯则因为邻靠沙漠和荒漠化草原,矿物性气溶胶影响特征明显,其加热效应最高(16.7W/m2)。就TOA而言,它首先与当地自然源气溶胶的类型密切相关,其次受局地人为源的影响也很大。此外,季节因素也是不容忽视的影响因子之一,例如东北地区在冬季会有长期的供暖期,煤烟造成的烟尘性气溶胶一般为细模态且呈现吸收性,此时当地会因为大面积的积雪覆盖使得沙尘性气溶胶含量明显降低,导致该地冬季与其它季节相比呈现出不同的辐射特征。另一方面,春季由于长距离沙尘输送带到东部的沙尘／矿物性气溶胶也往往会对北方地区产生较大的影响。总之,大气中的气溶胶,无论是将太阳辐射吸收还是反射回宇宙空间,在所有观测站点的近地面辐射强迫,均呈现出地面接收的太阳辐射能减少的现象,从而侧面证实了“阳伞效应”在不同的气溶胶类型下均成立。所不同的是,依据气溶胶本身对太阳辐射吸收性和散射性的不同,对大气的直接辐射强迫加热效应呈现出差异,从而导致整个地-气系统产生了加热或者冷却的地域性差别。如华北平原、华南地区和东南沿海地区(特别是京津冀、珠三角和长三角地区),气溶胶对地-气系统的影响以冷却效应为主,在其他区域则表现为不同程度的加热效应,这样的差异可能会对局地大气的热力状况和环流特征产生进一步的影响。此外,本文研究结果还表明,使用维护方便、易于操作的便携式LED太阳分光光度计和MICROTOPS Ⅱ光度计进行联网观测,基于统一的观测技术与改进的反演方法,进一步得到的不同生态系统的单次散射反照率和气溶胶直接辐射强迫,并以此衡量气溶胶的气候效应,结果同样具有较高的精度和价值,填补了中国大陆地区单次散射反照率和辐射强迫时空分布研究方面的空白并首次得到不同生态地区气溶胶气候效应的季节差异结果。尤其是我国西藏地区气候条件恶劣,难以进行精密仪器的长期运行和维护工作,故此,本项研究也为条件恶劣地区光学数据的获取和气候效应的评估提供了一条新的便捷途径。更多还原

【Abstract】 Aerosol plays a more and more important role in climate change and has a big uncertainty on climate effect. Aerosol radiative forcing (ARF) can be the measurement of the influence of aerosols on the climate. Related research started relatively early and now it is widely believed that aerosol can offset the rise of global temperatures caused by greenhouse gases to some extent. In China, different aerosol types will cause different aerosol radiative forcing. It is important to quantize the uncertainty of aerosol on the climate effect. The aerosol climate effect is still unknown in this area.We retrieved the single scattering albedo (SSA) and aerosol radiative forcing by using the aerosol optical parameters observed by the Chinese Sun Hazemeter Network from2004and MODIS aerosol product. Based on previous studies, there are big differences in spatial and temporal distribution of aerosol optical depth (AOD) and Angstrom exponents among different ecosystems by using CSHNET. Further work had been done in this paper, climate effect made by human activities and natural conditions had been calculated and analyzed. Reflected radiances at the top of the atmosphere as measured by a spaceborne spectroradiometer are sensitive to both AOT and SSA. On the basis of extensive radiative transfer simulations, it is demonstrated that the combined use of the two measurements allows for the retrieval of SSA at a reasonable accuracy under moderate to heavy aerosol loadings. And the aerosol radiative forcing were calculated by SBDART radiative transfer code in order to assess the aerosol climate effect under the clear sky.The results shows that, central and eastern regions, east coastal area and south China have strong human activities, especially the sulfate aerosols with strong scattering, the single scattering albedo (SSA) are greater than0.90in these areas. Because of the better vegetation and less human activities in agriculture ecosystem in northeast China, SSA shows an absorption feature and the values are between0.80to0.85. The surface is mostly desert and gobi in northwest China and Tibet Plateau, and lack of vegetation in this region, SSA shows a strong absorption feature and the values are less than0.80. However, in some developing industrial cities in northwest China, such as Lanzhou and Fukang, aerosols are composed with mineral and sulfate aerosol, SSAs are between0.80to0.85. In addition, Sanya Bay is located in Hainan where less industrial aerosols exist, sea-salt aerosol is the chief component, the annual averaged SSA is0.87.The aerosol radiative forcing at the top of atmosphere (TOA) is consistent with SSA. The TOA in the regions affected by anthropogenic source aerosols in east and south China presents a cooling effect. And TOA presents a warming effect in the regions where exist more dust or mineral aerosols. Because of a mass emissions of anthropogenic aerosols and the morphologic basin, the cooling effect in Yanting is largest. The warming effect in Erdos is the strongest due to the mineral aerosols from desert and desertification grassland.The located natural aerosol type, anthropogenic aerosol and seasonal factors are the main influence factors of TOA. In winter, there is a long term heating period which would provide much soot aerosols in north China and make the radiative forcing effect appear different feature. The long distance transportation of dust/mineral aerosols in spring will make big impact around north China.In addition, aerosols in atmosphere will absorb the radiance or reflect the radiance into Universe. The radiative forcing near the surface are all cooling down in all the stations and all the aerosol types. The difference is the absorbed aerosols warming the earth-atmosphere system and the scattering aerosols cooling it. Considering the differences of aerosol radiative forcing in different regions, local atmospheric thermal condition and regional circulation form will change in the future.The results also shows that, based on an unified observation network which has been built by using low cost and easy operate LED sun hazemeter, we can get the further results of single scattering albedo and aerosol direct radiation force in different ecological systems. The results which have higher accuracy and value can used to measure the climate effect. Especially in Tibet region, because of the villainous climate conditions, it’s hard to use precision instruments for long-term operation and maintenance work. Therefore, this study also provide a new and convenient way for optical data acquisition and aerosol climate effect estimation in rough terrain.更多还原