在火山喷发过程中排放出的二氧化硫被氧化成硫酸盐，并可进而形成硫酸盐气溶胶，后者能影响地球的辐射平衡。Bao等人利用对保存在岩石记录中的大气硫酸盐进行硫和三氧同位素测量，来研究硫酸盐形成的特定氧化通道。生物谷启用新域名www.bioon.net
他们发现，在新生代中期（距今3400万至700万年前）在北美洲高平原北部，曾经发生7次与喷发相关的硫酸盐气溶胶沉降事件。
在这些沉积物中所发现的在同位素上不相关联的硫酸盐可能只是在碱性云水中产生的，这种云水有利于在对流层中形成一个由臭氧支配的二氧化硫氧化通道。
这表明，与今天的弱酸性条件不同的是，那个地区的云水在新生代中期经常是碱性的。 (生物谷Bioon.net)
生物谷推荐原文出处：
Nature doi:10.1038/nature09100
Massive volcanic SO2 oxidation and sulphate aerosol deposition in Cenozoic North America
Huiming Bao, Shaocai Yu & Daniel Q. Tong
Volcanic eruptions release a large amount of sulphur dioxide (SO2) into the atmosphere1, 2. SO2 is oxidized to sulphate and can subsequently form sulphate aerosol3, which can affect the Earth's radiation balance, biologic productivity and high-altitude ozone concentrations, as is evident from recent volcanic eruptions4. SO2 oxidation can occur via several different pathways that depend on its flux and the atmospheric conditions3. An investigation into how SO2 is oxidized to sulphate—the oxidation product preserved in the rock record—can therefore shed light on past volcanic eruptions and atmospheric conditions. Here we use sulphur and triple oxygen isotope measurements of atmospheric sulphate extracted from tuffaceous deposits to investigate the specific oxidation pathways from which the sulphate was formed. We find that seven eruption-related sulphate aerosol deposition events have occurred during the mid-Cenozoic era (34 to 7 million years ago) in the northern High Plains, North America. Two extensively sampled ash beds display a similar sulphate mixing pattern that has two distinct atmospheric secondary sulphates. A three-dimensional atmospheric sulphur chemistry and transport model study reveals that the observed, isotopically discrete sulphates in sediments can be produced only in initially alkaline cloudwater that favours an ozone-dominated SO2 oxidation pathway in the troposphere. Our finding suggests that, in contrast to the weakly acidic conditions today5, cloudwater in the northern High Plains may frequently have been alkaline during the mid-Cenozoic era. We propose that atmospheric secondary sulphate preserved in continental deposits represents an unexploited geological archive for atmospheric SO2 oxidation chemistry linked to volcanism and atmospheric conditions in the past.
