HR: 0800h
AN: A51C-0084    [Abstracts]
TI: HCO Cross Sections and Radical Yields From the Photolysis of Saturated Aldehydes
AU: * Flad, J E
EM: jonathan.e.flad@noaa.gov
AF: NOAA Aeronomy Lab, 325 Broadway, Boulder, CO 80305 United States
AU: Brown, S S
EM: steven.s.brown@noaa.gov
AF: NOAA Aeronomy Lab, 325 Broadway, Boulder, CO 80305 United States
AU: Burkholder, J B
EM: james.b.burkholder@noaa.gov
AF: NOAA Aeronomy Lab, 325 Broadway, Boulder, CO 80305 United States
AU: Ravishankara, A R
EM: a.r.ravishankara@noaa.gov
AF: NOAA Aeronomy Lab, 325 Broadway, Boulder, CO 80305 United States
AB: Aldehydes are a major component of oxygenated volatile organic compounds (OVOC) in the atmosphere. They are removed from the atmosphere primarily by reaction with OH or by photodissociation from ultraviolet (< 350 nm) light. The photolysis of aldehydes proceeds via two major channels, one of which is a significant source of atmospheric free radicals. Determination of the radical yields from aldehyde photolysis as a function of temperature, pressure and wavelength has important implications for the HOx budget, particularly in the upper troposphere. Photolysis of formaldehyde and acetaldehyde has been studied extensively in the laboratory, although current parameterizations for radical yields are based in part on studies that have used indirect methods. A sensitive and direct method of measuring these radical yields is therefore of substantial interest. A new instrument has been developed to measure formyl (HCO) radical yields from the photodissociation of aldehydes. A pulsed, tunable ultraviolet laser is used to photolyze the aldehyde between 290 and 350 nm, and a second tunable laser is used to detect the HCO radicals using cavity ring-down spectroscopy on the A-X system (613 - 617 nm). The photolysis and probe lasers copropagate along the axis of the ring-down cell to maximize the overlap of the two laser beams for sensitive HCO detection. The absorption cross section of HCO has been determined by measuring the HCO product from the reaction of atomic chlorine with formaldehyde relative to the NO ₃ product from the reaction of atomic chlorine with chlorine nitrate. Atomic chlorine was generated by photolysis of Cl ₂ at 335 nm. The HCO quantum yield from the photolysis of acetaldehyde and formaldehyde and its dependence on photolysis wavelength, temperature, and pressure is being studied.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005