EGU2020-10457
https://doi.org/10.5194/egusphere-egu2020-10457
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Meteor Ablated Phosphorus as a Source of Bioavailable P to the Terrestrial Planets

Kevin Douglas1, Thomas Mangan1, Jaun Diego Carrillo-Sanchez1, David Bones1, Wuhu Feng1,2, Mark Blitz1,2, and John Plane1
Kevin Douglas et al.
  • 1School of Chemistry, University of Leeds, Leeds, LS7 9JT, United Kingdom
  • 2National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, United Kingdom

             Phosphorus, P, is a key biological element with major roles in replication, information transfer, and metabolism. Interplanetary dust particles (IDPs) contain ~0.8 % P by elemental abundance, and meteoric ablation in a planetary atmosphere is a significant source of atomic P. Orthophosphate (oxidation state +5) is the dominant form of inorganic P at the Earth’s surface, however, due to their low water solubility and reactivity, such P(V) salts have a poor bio-availability. Less oxidised forms of P (oxidation state ≤ +3) are however far more bio-available. Previous studies have focused on the direct delivery of P to the surface in meteorites. In contrast, the atmospheric chemistry of P has so far been ignored.

            The vaporized P atoms entering the upper atmospheres of the terrestrial planets will undergo chemical processing to form a variety of compounds in which P may exist in different oxidation states due to the presence of both oxidizing and reducing agents. Initial oxidation of P will proceed to produce PO2. From PO2, an exothermic route to phosphoric acid (H3PO4) exists via the formation of HOPO2; however, the bio-available compound phosphonic acid (H3PO3) should also form via HPO2.

            Using a combination of both experiment and theory, rate coefficients for the reactions of meteor ablated P have been determined. Using a pulsed laser photolysis-laser induced fluorescence (LIF) technique, the reactions of P, PO, and PO2 with atmospherically relevant species have been studied as a function of temperature for the first time. Rate coefficients for the subsequent reactions of PO2 leading onto to phosphoric and phosphonic acid were calculated from high-level electronic structure calculations.

            In addition to understanding the reaction kinetics, the delivery of P to the upper atmospheres of Earth, Mars, and Venus via the ablation of IDPs has also been investigated. Using a meteor ablation simulator, micron-size particles were flash heated, and the ablation of PO and Ca recorded simultaneously by LIF. These ablation profiles were used to validate the output of a Chemical Ablation Model (CABMOD), a thermodynamic model that predicts the ablation rates of different elements from IDPs. By combining CABMOD with an astronomical model of dust sources, the global injection rates of P into the atmospheres of Earth, Mars, and Venus has been estimated to be 0.017, 1.15×10-3, and 0.024 t d-1 (tonnes per Earth day) respectively.

            The results from the kinetics experiments, together with the P injection rates from CABMOD, have been input into a global chemistry-climate model of the Earth’s atmosphere (WACCM). Using WACCM, the relative amounts of phosphoric and phosphonic acid produced from meteor ablated P in the Earth’s atmosphere can be assessed. Preliminary results indicated that both H3PO4, and the bio-available H3PO3 are formed, with around a third of the ablated P ending up as H3PO3. Further work is also underway to determine where on the Earth’s surface H3PO3 will be deposited, to understand how accretion rates would have differed on the early Earth, and to input the P chemical scheme into a Mars atmospheric model.

How to cite: Douglas, K., Mangan, T., Carrillo-Sanchez, J. D., Bones, D., Feng, W., Blitz, M., and Plane, J.: Meteor Ablated Phosphorus as a Source of Bioavailable P to the Terrestrial Planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10457, https://doi.org/10.5194/egusphere-egu2020-10457, 2020

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