The atmospheric chemistry of sulphuryl fluoride, SO₂F₂

Abstract. The atmospheric chemistry of sulphuryl fluoride, SO₂F₂, was investigated in a series of laboratory studies. A competitive rate method, using pulsed laser photolysis (PLP) to generate O(¹D) coupled to detection of OH by laser induced fluorescence (LIF), was used to determine the overall rate coefficient for the reaction O(¹D) + SO₂F₂ → products (R1) of k₁ (220–300 K) = (1.3 ± 0.2) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Monitoring the O(³P) product (R1a) enabled the contribution (α) of the physical quenching process (in which SO₂F₂ is not consumed) to be determined as α (225–296 K)=(0.55 ± 0.04). Separate, relative rate measurements at 298 K provided a rate coefficient for reactive loss of O(¹D), k_1b, of (5.8 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ in good agreement with the value calculated from (1−α) × k₁=(5.9 ± 1.0) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Upper limits for the rate coefficients for reaction of SO₂F₂ with OH (R2, using PLP-LIF), and with O₃ (R3, static reactor) were determined as k₂ (294 K)<1 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ and k₃ (294 K)<1 × 10⁻²³ cm³ molecule⁻¹ s⁻¹. In experiments using the wetted-wall flow tube technique, no loss of SO₂F₂ onto aqueous surfaces was observed, allowing an upper limit for the uptake coefficient of γ(pH 2–12)<1 × 10⁻⁷ to be determined. These results indicate that SO₂F₂ has no significant loss processes in the troposphere, and a very long stratospheric lifetime. Integrated band intensities for SO₂F₂ infrared absorption features between 6 and 19 μm were obtained, and indicate a significant global warming potential for this molecule. In the course of this work, ambient temperature rate coefficients for the reactions O(¹D) with several important atmospheric species were determined. The results (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, k_{(O¹D + N2)}=(0.33 ± 0.06); k_{(O¹D + N2O)}=(1.47 ± 0.2) and k_{(O¹D + H2O)}=(1.94 ± 0.5) were in good agreement with other recent determinations.