Top Scientists Discover Major Flaw in Global Climate Models
by Red Smith
LIVERMORE, Calif. — Insights from experiments at Sandia National Laboratories has allowed an international group of researchers to discover a new major source of formic acid over the Pacific and Indian oceans.
Formic Acid is the smallest and most abundant organic acid in the global atmosphere, is a major source of rainwater acidity and lies at the end point of hydrocarbon oxidation. Global atmospheric models have significantly underpredicted the amount of formic acid present in the troposphere compared to direct measurements and calls into question current scientific understanding of hydrocarbon degradation in the atmosphere. Accurate predictions of air quality and of aerosol impacts on climate rely on a sound representation of atmospheric hydrocarbon chemistry.
Inspired by earlier work led by Sandia researcher Craig Taatjes in combustion chemistry, Sandia physical chemist David Osborn and his colleagues hypothesized that vinyl alcohol could be a chemical precursor to formic acid. However, vinyl alcohol is a metastable form, or isomer, of the common molecule acetaldehyde. Something would need to push this mixture far from its natural composition for there to be enough vinyl alcohol molecules to potentially impact formic acid concentrations.
Osborn’s team thought that photons — in particular ultraviolet light — would be an ideal tool to drive a chemical system far from equilibrium, but collisions between molecules inevitably lead to a restoration of equilibrium. For this reason, it wasn’t clear whether the approach would work at atmospheric pressure, where collision between molecules occur about 7 billion times each second. Using infrared spectroscopy to analyze the molecules after irradiation with ultraviolet light, mimicking sunlight, Osborn and his team confirmed that wavelengths can rearrange the atoms in acetaldehyde, converting it to vinyl alcohol. The process persists even at atmospheric pressure.
With the experimental and theoretical details in hand, Osborn’s collaborators could add this chemistry to local and global models of Earth’s atmosphere to see how it might alter formic acid concentrations. “This new chemistry produces about 3.4 billion tons of additional formic acid per year in the model, but this only amounts to 7 percent of formic acid in the global model,” Osborn said. “This is not enough to solve the mystery of the missing sources of formic acid that cause models to disagree with experiments.”
The project was a collaboration among Sandia, the University of New South Wales, the University of Leeds, the University of the Pacific and the University of Minnesota.
DOE/Sandia National Laboratories. “New source of formic acid discovered over Pacific, Indian oceans: Sunlight drives molecules far from equilibrium, enabling new chemical pathways.” ScienceDaily. ScienceDaily, 5 September 2018. <www.sciencedaily.com/releases/2018/09/180905131823.htm>.
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