HR: 0830h
AN: A31D-0065    [PDF]
TI: A new instrument to measure UV extinction profiles and photolysis frequencies in a snowpack environment
AU: * Lefer, B L
EM: lefer@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Shetter, R E
EM: shetter@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Hall, S R
EM: halls@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Riedel, E P
EM: riedel@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division 1850 Table Mesa Drive, Boulder, CO 80305 United States
AB: A new profiling irradiance spectroradiometer measured ultraviolet (UV) radiation at four to five depths in the surface snowpack during a seven-week campaign at Summit, Greenland (Summer 2003). The UV photons were collected by a small irradiance head with a Teflon diffuser and transmitted through a UV-VIS fiber optic into a scanning 1/8-meter double monochrometer and detected with a UV sensitive photomultplier. One complete scan of the UV-VIS radiation between 290-420 nm took less than 30 seconds. Five different fibers (i.e., five different depths) were serially sampled using a stepping motor and micropositioning slider to create a penetration profile every 2.5 minutes. Simultaneous atmospheric actinic flux data from a synchronized above snow scanning spectroradiometer was used to identify periods when the incident downwelling UV intensity changed during a depth profile. The UV penetration distance was calculated as an {\it e}-folding depth (the depth over which the monochromatic UV irradiance decreases by a factor of {\it e}). After measuring the angular response of the irradiance entrance optics and assuming that the in-snow radiation environment was isotropic, it is possible to scale up from irradiance to actinic flux. Fourteen different photolysis frequencies (including {\it j}NO$_{3}$$^{-}$$_{(aq)}$) were calculated from the snowpack actinic flux data. These data can then be used to add to our understanding of snowpack photolytic processes that produce gas phase NO and/or NO$_{2}$ and are speculated to result in the snowpack production of other important photochemical species (such as HONO, HCHO, HOOH, etc.) in snow-covered environments.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0394 Instruments and techniques
DE: 9315 Arctic region
DE: 9805 Instruments useful in three or more fields
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting