A decade of global volcanic SO2 emissions measured from space.

The global flux of sulfur dioxide (SO2) emitted by passive volcanic degassing is a key parameter that constrains the fluxes of other volcanic gases (including carbon dioxide, CO2) and toxic trace metals (e.g., mercury). It is also a required input for atmospheric chemistry and climate models, since it impacts the tropospheric burden of sulfate aerosol, a major climate-forcing species. Despite its significance, an inventory of passive volcanic degassing is very difficult to produce, due largely to the patchy spatial and temporal coverage of ground-based SO2 measurements. We report here the first volcanic SO2 emissions inventory derived from global, coincident satellite measurements, made by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite in 2005-2015. The OMI measurements permit estimation of SO2 emissions from over 90 volcanoes, including new constraints on fluxes from Indonesia, Papua New Guinea, the Aleutian Islands, the Kuril Islands and Kamchatka. On average over the past decade, the volcanic SO2 sources consistently detected from space have discharged a total of ~63 kt/day SO2 during passive degassing, or ~23 ± 2 Tg/yr. We find that ~30% of the sources show significant decadal trends in SO2 emissions, with positive trends observed at multiple volcanoes in some regions including Vanuatu, southern Japan, Peru and Chile.

Estimated ultraviolet exposure levels for a sufficient vitamin D status in North America.

Solar UV radiation is a major provider of vitamin D for humans. This study examines the distribution of solar UV radiation weighted according to the vitamin D action spectrum over the USA and Canada. Hourly and daily doses of spectrally integrated UV irradiance using the vitamin D action spectrum were estimated using a statistical relationship between UV irradiance and global solar irradiance, total ozone, and dew point temperature for 45 sites in Canada and 52 in the USA. Brewer spectrophotometer measurements at 12 sites in Canada and 21 sites in the USA were used to validate the obtained results. Different characteristics of the vitamin D action spectrum-weighted UV irradiance distribution over North America are presented in the form of monthly maps and as a data file. The time required to obtain standard vitamin D dose is also calculated for six types of skin.

On the relationship between erythemal and vitamin D action spectrum weighted ultraviolet radiation.

Erythemally weighted solar ultraviolet (UV) radiation is often used to characterize the production of vitamin D in a human body. However, the vitamin D production action spectrum is different than that for erythemal UV. The vitamin D action spectrum weighted UV is more sensitive to UV-B, while the erythemal UV action spectrum has higher weighting coefficients than the vitamin D action spectrum in the UV-A part of the spectrum. Therefore, by using the erythemal UV as an estimate for the vitamin D action spectrum weighted UV can give results that differ by up to a factor of 5. This study examines the relationship between erythemal and vitamin D action spectrum weighted UV radiation using measurements of spectral UV at the surface by Brewer spectrophotometers that are part of the US and Canadian observational networks. It is shown that the ratio of vitamin D action spectrum weighted UV to erythemal UV is nearly constant for high levels of UV (UV Index greater than 5.5) and therefore vitamin D action spectrum weighted UV can be described in terms of erythemal UV. For lower levels of UV though this relationship should not be used. A simple formula that calculates vitamin D action spectrum weighted UV from UV Index is developed. An empirical formula that expresses the ratio of vitamin D action spectrum weighted UV to erythemal UV as a function of the solar zenith angle and column ozone is also suggested. The geographical distributions of vitamin D action spectrum weighted UV in the US and Canada are discussed.