HR: 1340h
AN: A53C-0903    [Abstracts]
TI: Absorption Cross Sections of Formaldehyde in the Ultraviolet Spectral Region of 28100-28500 cm$^{-1}$ (351-356 nm) at 0.04 cm$^{-1}$ (0.0005 nm) Resolution: Implications for {\it in Situ} Laser-Induced Fluorescence Detection
AU: * Co, D T
EM: co@fas.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138 United States
AU: Keutsch, F N
EM: frank@huarp.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138 United States
AU: Anderson, J G
EM: anderson@huarp.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138 United States
AB: Formaldehyde (HCHO) is the principal intermediate in the oxidation of hydrocarbons in the troposphere. Because HCHO has a diurnally-averaged lifetime in the upper troposphere (UT) of about 8-12 hours, it can serve as a tracer for recent convection and a proxy for volatile organic compounds (VOCs) emitted. Model studies have shown that convectively injected acetone [(CH$_{3}$)$_{2}$CO], hydrogen peroxide (H$_{2}$O$_{2}$), and methyl hydroperoxide (CH$_{3}$OOH) can be significant sources of HOx in the UT, producing HCHO as an intermediate. Thus, a measurement of HCHO is important for the understanding of HOx chemistry and ozone production, especially in the tropical transition layer (TTL). The absence of fast, precise, and accurate measurements of acetone and peroxides make {\it in situ} HCHO measurements even more important. Simultaneous measurement of HCHO along with OH, HO$_{2}$, and other species involved with ozone and HOx chemistry will provide insight into the question of convection's impact on ozone production in the TTL and the stratospheric budget of convectively transported organic pollutants. Accurate absolute absorption cross sections of HCHO are not only needed in satellite-based remote sensing experiments using differential optical absorption spectroscopy but also in laser-induced fluorescence (LIF) HCHO flight platforms for {\it in situ} measurements. LIF provides a high sensitivity technique that takes advantage of the high absorption cross sections of the narrow single rotational lines of HCHO. However, previous measurements of the absorption spectrum of HCHO in the UV region have never been rotationally resolved. In this study, we obtained rotationally resolved absolute cross sections of HCHO in the spectral region of 28100-28500 cm$^{-1}$ (351-356 nm) at 0.04 cm$^{-1}$ (0.0005 nm at 353.5 nm) resolution using Fourier transform spectroscopy. HCHO concentration was determined by condensed-phase iodometric titration, and gaseous HCHO generation was performed using a novel micro-injector technology. Spectra were acquired with high wavenumber accuracy, and the pressure and temperature dependences of the cross sections were also studied. High-resolution spectra are useful as they can be readily degraded to confirm low-resolution measurements, and our resulting HCHO absorption spectra were compared to existing literature at lower resolutions.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting