Global to microscale evolution of the Pinatubo volcanic aerosol derived from diverse measurements and analyses
Global to microscale evolution of the Pinatubo volcanic aerosol derived from diverse measurements and analyses
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来自不同测量和分析的皮纳图博火山气溶胶的全球到微观演化
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
R. Bergstrom
中科院分区：
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作者：
P. Russell;J. Livingston;R. Pueschel;J. J. Bauman;J. Pollack;S. Brooks;P. Hamill;L. Thomason;L. Stowe;T. Deshler;E. Dutton;R. Bergstrom
我们收集的皮纳图博气溶胶从空间，空气和地面测量数据，开发一个复合图片，并评估测量和检索技术的一致性和不确定性。卫星红外光谱、粒子形态和蒸发温度测量结果与理论计算结果一致，显示出H2SO 4-H2O混合物的主要成分，在大多数平流层温度和湿度下，H2SO 4的重量分数为65-80%。重要的例外是：（1）火山灰，至少在1992年3月之前存在于对流层顶上方的所有高度;（2）在高纬度冬季和热带对流层顶的低温下，H2SO 4含量要小得多。实验室光谱学和计算产生了H2SO 4-H2O液滴的波长和温度依赖的折射率。这些允许从测量的光学深度光谱中导出粒度信息，用于与撞击器和光学计数器测量进行比较。所有这三种技术都描绘了Reff（有效半径）演变的大致一致的画面。在爆发后的第一个月，虽然粒子数量大大增加，但热带核心外的Reff与爆发前的值相似，为0.1至0.2 μm，因为小粒子（r < 0.2 μm）和大粒子（r > 0.6 μm）的数量都增加了。在接下来的3-6个月内，extramore Reff增加到<0.5 μm，反映了颗粒通过冷凝和凝聚而生长。大多数数据表明，Reff在爆发后持续增加了101年。在0.6-0.8 μm以上的Reff值与1992年中后期甚至更晚的0.38-1 μm光学深度谱一致。然而，在这一时期，从现场测量的值有点少，差异可能反映在现场采样的最大的颗粒很少，最小的颗粒，光学深度谱的不敏感性，或平坦的光谱无法放置一个上限的颗粒大小。需要延伸到波长λ > 1 μm的光学深度谱来更好地约束Reff，特别是对于Reff > 0.4 μm。根据原位粒度分布计算的消光光谱与光学深度测量结果一致;两者均显示初始光谱λmax ≤ 0.42 μm，此后增加至0.78 ≤ λmax ≤ 1 μm。直到1993年，光谱开始显示出明显的返回到λmax ≤ 0.42 μm的抢占特征。大Reff（>0.3 μm）和相对平坦的消光光谱（0.4-1 μm）的双重特征是皮纳图博火山影响的最长寿命指标之一。它们在数量、质量、表面积和光学深度的峰值之后持续存在数年，在所有波长≤1 μm处。颗粒尺寸分布和光学深度谱的这种耦合演变有助于解释从高级甚高分辨率辐射计和平流层气溶胶和气体实验卫星传感器获得的0.5和1.0 μm光学深度全球图之间的关系。然而，高级甚高分辨率辐射计和SAGE中可见光光学厚度产品之间有重要的差别。我们讨论了这些差异的可能原因以及如何解决这些差异。
We assemble data on the Pinatubo aerosol from space, air, and ground measurements, develop a composite picture, and assess the consistency and uncertainties of measurement and retrieval techniques. Satellite infrared spectroscopy, particle morphology, and evaporation temperature measurements agree with theoretical calculations in showing a dominant composition of H2SO4‐H2O mixture, with H2SO4 weight fraction of 65–80% for most stratospheric temperatures and humidities. Important exceptions are (1) volcanic ash, present at all heights initially and just above the tropopause until at least March 1992, and (2) much smaller H2SO4 fractions at the low temperatures of high‐latitude winters and the tropical tropopause. Laboratory spectroscopy and calculations yield wavelength‐ and temperature‐dependent refractive indices for the H2SO4‐H2O droplets. These permit derivation of particle size information from measured optical depth spectra, for comparison to impactor and optical‐counter measurements. All three techniques paint a generally consistent picture of the evolution of Reff, the effective radius. In the first month after the eruption, although particle numbers increased greatly, Reff outside the tropical core was similar to preeruption values of ∼0.1 to 0.2 μm, because numbers of both small (r < 0.2 μm) and large (r > 0.6 μm) particles increased. In the next 3–6 months, extracore Reff increased to ∼0.5 μm, reflecting particle growth through condensation and coagulation. Most data show that Reff continued to increase for ∼1 year after the eruption. Reff values up to 0.6–0.8 μm or more are consistent with 0.38–1 μm optical depth spectra in middle to late 1992 and even later. However, in this period, values from in situ measurements are somewhat less. The difference might reflect in situ undersampling of the very few largest particles, insensitivity of optical depth spectra to the smallest particles, or the inability of flat spectra to place an upper limit on particle size. Optical depth spectra extending to wavelengths λ > 1 μm are required to better constrain Reff, especially for Reff > 0.4 μm. Extinction spectra computed from in situ size distributions are consistent with optical depth measurements; both show initial spectra with λmax ≤ 0.42 μm, thereafter increasing to 0.78 ≤ λmax ≤ 1 μm. Not until 1993 do spectra begin to show a clear return to the preemption signature of λmax ≤ 0.42 μm. The twin signatures of large Reff (>0.3 μm) and relatively flat extinction spectra (0.4–1 μm) are among the longest‐lived indicators of Pinatubo volcanic influence. They persist for years after the peaks in number, mass, surface area, and optical depth at all wavelengths ≤1 μm. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between global maps of 0.5‐ and 1.0‐μm optical depth derived from the Advanced Very High Resolution Radiometer (AVHRR) and Stratospheric Aerosol and Gas Experiment (SAGE) satellite sensors. However, there are important differences between the AVHRR and SAGE midvisible optical thickness products. We discuss possible reasons for these differences and how they might be resolved.