Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p33d..01d&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P33D-01
Mathematics
Logic
0305 Aerosols And Particles (0345, 4801, 4906), 0325 Evolution Of The Atmosphere (1610, 8125)
Scientific paper
Recent attempts to resolve the faint young sun paradox have focused on an early Earth atmosphere containing elevated levels of the greenhouse gases methane (CH4) and carbon dioxide (CO2) to provide adequate warming to the Earth's surface. However, the photolysis of CH4 and CO2 in equal ratios in the laboratory has been shown to produce significant aerosol mass, equivalent to or greater than the aerosol mass produced in Titan simulations. The haze layer generated by these aerosols could offset the warming by scattering incoming solar radiation, creating an antigreenhouse effect. The amount of CH4 in the prebiotic Earth's atmosphere could have been significantly less than the amount of CO2. Additionally, high amounts of H2 may have been present in the prebiotic Earth's atmosphere, and could affect the haze chemistry. In this work we examine haze formation in an early Earth atmosphere composed of CO2, H2, N2, and CH4, with a CO2/CH4 ratio of 10. Haze particles were generated using different concentrations of H2, with levels up to 15 percent by volume H2. To initiate aerosol formation a broad-spectrum ultraviolet (UV) energy source with emission at Lyman-α was used to simulate the solar spectrum. Aerosol composition and total aerosol mass produced as a function of reagent gas were measured using an Aerosol Mass Spectrometer (AMS). A Scanning Mobility Particle Sizer (SMPS) was also used to measure the aerosol mass, as well as the size distribution of the particles. Results show an order of magnitude decrease in haze production with the addition of H2, with no significant change in the chemical composition of the haze. We calculate that such a haze would not have a significant antigreenhouse effect. Further, the highly oxidized particles formed could be more biologically interesting than a Titan-like hydrocarbon haze. The presence of H2 on the early Earth could thus favor warmer surface temperatures while still allowing photochemical haze formation to deliver complex organic species to the early Earth's surface.
Aiken Allison C.
Dewitt L.
Hasenkopf Christa A.
Jimenez Jose L.
McKay Chris P.
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