CH and formaldehyde structures in partially-premixed methane/air coflow flames

CH and CH2O inner cone structures in partially premixed methane/air Bunsen flames are examined with 2-D laser-induced fluorescence (LIF) imaging for stoichiometries 1.36 less than or equal to Phi less than or equal to 3.0. Chosen LIF excitation strategies minimize the temperature dependent partition function variation for CH2O, and maintain CH signal strength while eliminating Rayleigh scattering background. The formaldehyde structure appears inside CH in the inner flame cone for moderately fuel rich stoichiometries typical of appliance flames. CH LIF becomes too weak to distinguish from background at richer stoichiometries (Phi=2.7). A distinct formaldehyde inner cone structure persists even for very rich Phi, with an increasing width. A simple I-D model replicates the variation in the relative concentrations of CH and formaldehyde in the inner cone, Predicted absolute CH agrees within a factor of two with the measured value. Exhaust probe measurements show that metal inserts reduce NO and increase CO emissions. LIF images of CH and CH2O taken for these perturbed flames reveal the CH2O structures are spatially expanded by the inserts

Laser-induced fluorescence of formaldehyde hot bands in flames (vol 39, pg 3712, 2000)

No abstract

Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation

The most important chemical cleaning agent of the atmosphere is the hydroxyl radical, OH. It determines the oxidizing power of the atmosphere, and thereby controls the removal of nearly all gaseous atmospheric pollutants. The atmospheric supply of OH is limited, however, and could be overcome by consumption due to increasing pollution and climate change, with detrimental feedback effects. To date, the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species. Here we present and analyse long-term measurements of atmospheric OH concentrations, which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany. We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period, despite the fact that OH concentrations are influenced by thousands of reactants. A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH, but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry. As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe, we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set