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 Vog-free view of Mauna Loa Volcano Photograph by S.R. Brantley on March 2, 1988 |
 Vog obscures view of Mauna Loa Volcano Photograph by C.C. Heliker on December 2, 1994 |
| A layer of vog (bottom photo) trapped against the southwest flank of Mauna Loa Volcano obscures the view from the USGS Hawaiian Volcano Observatory. When the usually strong northeast trade winds are interrupted, east Hawai`i and the Hawai`i Volcanoes National Park often experience vog conditions. The Environmental Protection Agency (EPA) primary standard for sulfur dioxide gas says that a person's exposure should not exceed 0.139 parts per million averaged over a 24-hour period, more than once each calendar year. Between 1987 and 1997, the concentration of SO2 exceeded the standard about 70 times in Hawai`i Volcanoes National Park. |
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