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When we were coming in, we saw really substantial plumes of

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SO2 that the CalTech guys were measuring and we

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see signs of it in our instrument and then very sustained levels of the fine

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sulfate aerosol and this is something that they call "vog," which is sort of

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like fog, except it's from a volcano and

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the volcano is emitting a lot of SO2.

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Some volcanoes emit low levels all the time. I think Kilauea's emitting

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fairly high levels fairly often. This stuff oxidizes to make sulfuric acid and that

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then forms small droplets of sulfuric acid

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and when these guys take up water, they swell and make the real visible

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haze, the strong haze that we saw the whole time we were in Kona.

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Sulfuric acid is not good for you; this is a big part of acid rain

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and the same sort of chemistry happened in the U.S.

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that precipitated the Clean Air Act.

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So all the SO2 in that case was mostly from coal-burning,

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but we did a lot to clean that up and reduce acid rain,

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certainly an environmental crisis in the eastern U.S. probably 30 years ago.