HR: 1340h
AN: A43C-0083    [Abstracts]
TI: Actinic Flux Measurements for the Central California Ozone Study
AU: * Stockwell, W R
EM: William.Stockwell@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Goliff, W S
EM: Wendy.Goliff@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AB: The formation rates and lifetimes of many tropospheric chemical species depend on the photolysis rate parameters of nitrogen dioxide, ozone, formaldehyde and other compounds. A compound's photolysis rate parameter depends on its wavelength dependent absorption coefficients, its quantum yields and the spherically integrated solar radiation, also know as actinic flux. However in many field studies actinic flux is estimated from models or flat plate radiometer measurements. A major goal of this project was to determine the importance of measuring actinic flux as part of a major field study. Measurements of actinic flux were made during the summer of 2000 as part of the Central California Ozone Study (CCOS). Spectral-radiometers with hemispherical integrating collectors were located at the University of California at Davis (UC-Davis), Sunol, California, and the Desert Research Institute in Reno, Nevada. This study focused on comparing actinic flux measurements made during two high ozone episodes occurring at the end of July and during mid-September. The measured actinic flux was compared with total horizontal flux data from shadowband radiometers co-located at UC-Davis. Although actinic flux and total horizontal flux are different quantities, at lower wavelengths comparisons are reasonable due to the greater scattering of radiation. The agreement between the total horizontal flux and actinic flux measurements was close for wavelengths below 332 nm and was within 7 x $^{12}$ photons cm$^{-3}$ s$^{-1}$ while above this wavelength they diverged to differences of 3.7 x 10$^{14}$ photons cm$^{-3}$ s$^{-1}$ or greater. The measured actinic flux and the actinic flux calculated from models including the delta-Eddington approach and the standard Peterson flux agreed better for the September episode then for the July episode.
DE: 0345 Pollution--urban and regional (0305)
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting