Radiative effects of natural aerosols: A review
Radiative effects of natural aerosols: A review
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DOI：
10.1016/j.atmosenv.2004.12.029
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发表时间：
2005-04
影响因子：
5
通讯作者：
S. Satheesh;K. Moorthy
中科院分区：
文献类型：
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作者：
S. Satheesh;K. Moorthy
近年来，人们对人为气溶胶通过直接和间接影响对气候的影响的兴趣大大增加。为评估人为气溶胶对气候的影响，开展了几项广泛的调查和协调的实地活动。然而，对天然气溶胶的研究远远少于对人为气溶胶的研究，尽管它们很重要。天然气溶胶特别重要，因为它们为气溶胶的影响提供了一种基础水平，而且与人为的气溶胶不同，对它们没有有效的控制。此外，在全球范围内，天然气溶胶的丰度是主要人为气溶胶（硫酸盐、烟尘和有机物）的数倍。主要的天然气溶胶成分是海盐、土壤尘埃、天然硫酸盐、火山气溶胶和自然森林火灾产生的气溶胶。与人为气溶胶一样，由于森林砍伐等过程，土壤尘埃等天然气溶胶的丰度也在增加，森林砍伐使更多的土地暴露出来，从而可能直接与大气相互作用，并且由于其他人类活动。由于大部分天然气溶胶（海盐和天然硫酸盐）属于非吸水性（和吸湿性），它部分抵消了温室气体和吸水性气溶胶（如烟灰）造成的变暖。在陆地和海洋上传播的矿物粉尘引起地表冷却（由于散射和吸收），同时引起低层大气加热（由于吸收）；这反过来又会加剧低空逆温，增加大气稳定性，减少对流。为了准确预测沙尘气溶胶对气候的影响，沙尘的时空分布至关重要。由于缺乏适当的数据库，对尘源功能的区域特征了解甚少。地表太阳辐射的减少将导致感热通量的减少，所有这些都将导致区域和全球气候的扰动。高风速下海盐气溶胶浓度的增加会导致凝结核增多，云滴浓度增加，云反照率随之增加。尽管海盐和天然硫酸盐造成的直接辐射影响比人为因素造成的影响小，但其间接影响（和不确定性）要大得多。由于海洋数据库不足，在海盐气溶胶辐射强迫方面存在相当大的不确定性。天然气溶胶的存在可能影响人为气溶胶的辐射影响，当它们处于混合状态时，很难区分自然气溶胶和人为气溶胶对辐射强迫的贡献。因此，有必要记录自然气溶胶的辐射效应，特别是在自然源很强的热带地区。这就是本文的主题。
In recent years, there has been a substantial increase in interest in the influence of anthropogenic aerosols on climate through both direct and indirect effects. Several extensive investigations and coordinated field campaigns have been carried out to assess the impact of anthropogenic aerosols on climate. However, there are far fewer studies on natural aerosols than on anthropogenic aerosols, despite their importance. Natural aerosols are particularly important because they provide a kind of base level to aerosol impact, and there is no effective control on them, unlike their anthropogenic counterparts. Besides, on a global scale the abundance of natural aerosols is several times greater than that of the major anthropogenic aerosols (sulphate, soot and organics). The major natural aerosol components are sea salt, soil dust, natural sulphates, volcanic aerosols, and those generated by natural forest fires. As with anthropogenic aerosols, the abundance of natural aerosols such as soil dust is also increasing, due to processes such as deforestation, which exposes more land areas which may then interact directly with the atmosphere, and due to other human activities. Since a major fraction of the natural aerosol (sea salt and natural sulphate) is of the non-absorbing type (and hygroscopic), it partly offsets the warming due to greenhouse gases as well as that due to absorbing aerosols (e.g., soot). The mineral dust transported over land and ocean causes surface cooling (due to scattering and absorption) simultaneously with lower atmospheric heating (due to absorption); this could in turn intensify a low-level inversion and increase atmospheric stability and reduce convection. To accurately predict the impact of dust aerosols on climate, the spatial and temporal distribution of dust is essential. The regional characteristics of dust source function are poorly understood due to the lack of an adequate database. The reduction of solar radiation at the surface would lead to a reduction in the sensible heat flux and all these will lead to perturbations in the regional and global climate. Enhanced concentration of sea salt aerosols at high wind speed would lead to more condensation nuclei, increase in the cloud droplet concentration and hence cloud albedo. Even though direct radiative impacts due to sea salt and natural sulphate are small compared to those due to anthropogenic counterparts, their indirect effects (and the uncertainties) are much larger. There is a considerable uncertainty in sea salt aerosol radiative forcing due to an inadequate database over oceans. The presence of natural aerosols may influence the radiative impact of anthropogenic aerosols, and it is difficult to separate the natural and anthropogenic aerosol contributions to radiative forcing when they are in a mixed state. Hence it is necessary to document the radiative effects of natural aerosols, especially in the tropics where the natural sources are strong. This is the subject matter of this review.