Solar System Abundances and Condensation Temperatures of the Halogens Fluorine, Chlorine, Bromine, and IodineOPEN ACCESS
Katharina Lodders, Bruce Fegley Jr
Submitted to Chemie der Erde/Geochemistry October 2020, revised December 2022
Update (9 February 2023): LINK
Geochemistry, In Press, Journal Pre-proof, Available online 9 February 2023
“We review a large body of available meteoritic and stellar halogen data in the literature used for solar system abundances (i.e., representative abundances of the solar system at the time of its formation) and associated analytical problems. Claims of lower solar system chlorine, bromine and iodine abundances from recent analyses of CI-chondrites are untenable because of incompatibility of such low values with nuclear abundance systematics and independent measurements of halogens in the sun and other stars. We suspect analytical problems associated with these peculiar rock types have led to lower analytical results in several studies. We review available analytical procedures and concentrations of halogens in chondrites. Our recommended values are close to previously accepted values. Average concentrations by mass for CI-chondrites are F = 92 ± 20 ppm, Cl = 717 ± 110 ppm, Br = 3.77 ± 0.90 ppm, and I = 0.77 ± 0.31 ppm. The meteoritic abundances on the atomic scale normalized to N(Si) =106 are N(F) = 1270 ± 270, N(Cl) = 5290 ± 810, N(Br) = 12.3 ± 2.9, and N(I) = 1.59 ± 0.64. The meteoritic logarithmic abundances scaled to present-day photospheric abundances with log N(H) = 12 are A(F) = 4.61 ± 0.09, A(Cl) = 5.23 ± 0.06, A(Br) = 2.60 ± 0.09, and A(I) = 1.71 ± 0.15. These are our recommended present-day solar system abundances. These are compared to the present-day solar values derived from sunspots of N(F) = 776 ± 260, A(F) = 4.40 ± 0.25, and N(Cl) = 5500 ± 810, A(Cl) = 5.25 ± 0.12. The recommended solar system abundances based on meteorites are consistent with F and Cl abundance ratios measured independently in other stars and other astronomical environments. The recently determined chlorine abundance of 776 ± 21 ppm by Yokoyama et al. (2022) for the CI-chondrite-like asteroid Ryugu is consistent with the chlorine abundance evaluated for CI-chondrites here. Historically, the halogen abundances have been quite uncertain and unfortunately remain so. We still need reliable measurements from large, representative, and well-homogenized CI-chondrite samples. The analysis of F, Br, and I in Ryugu samples should also help to obtain more reliable halogen abundances. Updated equilibrium 50 % condensation temperatures from our previous work (Lodders, 2003; Fegley and Schaefer, 2010; Fegley and Lodders, 2018) are 713 K(F), 427 K (Cl), 392 K (Br) and 312 K (I) at a total pressure of 10−4 bar for a solar composition gas. We give condensation temperatures considering solid-solution as well as kinetic inhibition effects. Condensation temperatures computed with lower halogen abundances do not represent the correct condensation temperatures from a solar composition gas.”
