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Simultaneous Airborne Measurements of Inorganic Halogens and Ozone Depletion in the Tropics

This study focuses on the airborne simultaneous measurements of BrO, HOBr, BrCl, and Br2 in the tropical region, utilizing Chemical Ionization Mass Spectrometry (CIMS) for high-sensitivity detection. The research outlines the instrumental setup, data coverage, and results, indicating that modeled concentrations of BrO and other inorganic halogens are underestimated. Additionally, we discuss the implications of inorganic halogen photolysis and its significant contribution (up to 20%) to ozone depletion in the Tropical Marine Boundary Layer (TMBL).

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Simultaneous Airborne Measurements of Inorganic Halogens and Ozone Depletion in the Tropics

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  1. Simultaneous Airborne Measurements of BrO, HOBr, BrCl and Br2 in the Tropics: Inorganic Halogens and Subsequent O3 Depletion Michael Le Breton, Jennifer Muller, Kimberley Leather, Thomas Bannan, Steve Andrews, Shallcross, AsanBacak & Carl Percival

  2. Outline • Instrumental setup - CIMS • Data coverage • Data results • Modelling vs measured • SS O3 depletion

  3. Data coverage

  4. Chemical Ionisation • Soft ionisation • High sensitivity • Flexible ionization • Detect both + and – ions • ppt, LODs A-+ B  B-+ A reagention molecule to detect I- + HCOOH →[HCOOH].I-

  5. Manchester CIMS 22 Torr 0.24Torr 10-3 Torr 10-4 Torr

  6. CIMS measurements BrCl- I-.HOBr.H2O

  7. BrO calibration • HOBr , BrCl and Br2 all calibrated on FT • 1. BrCl – Cl2 and Br2 gas mixture equilibrate • 2. HOBr – AgNO3 (liberates Br) • Mix with CCl4 (Removes Br2) • Quantify with H+ and Br- • 3. Br2 – gas mixture and perm tube NO

  8. Time series example

  9. B823 transit

  10. BrO and O3 data

  11. Altitude profiles

  12. Model

  13. O3 loss reactions 1. Br + O3→ BrO + O3 2. Br + DMS → products 3. BrO + HO2 → HOBr 4. BrO + DMS → Br + DMSO 5. HOBr + hν → OH + Br 11. O3 + HO2 → OH + 2O2 12 O3 + hν → O(1D) + O2 13a O(1D) + N2 → O(3P) + N2 13b O(1D) + O2 → O(3P) + O2 13c O(1D) + H2O → OH + OH 14 BrO + CH3O2 → HOBr + CH2OO 15a CH2OO → OH + HO2 15b CH2OO + H2O → HCOOH + H2O 6. Br2 + hν → Br + Br 7. BrCl + hν → Br + Cl 8. HOBr (wet deposition)→ 9. BrCl (wet deposition)→ 10. Br2 (wet deposition)→

  14. O3 loss reactions Consider the four loss reactions O3+ HO2 → OH + 2O2 O3 + OH → HO2 + O2 12 O3 + hν → O(1D) + O2 13c O(1D) + H2O → OH + OH 1. Br + O3→ BrO+ O3 O3HO2+O3 = k11[HO2][O3] O3OH+O3 = k16[OH][O3] O3O1D = F1*J12[O3] F1 =k13C[H2O] / k13a[N2] + k13b[O2] + k13C[H2O] O3Br+O3 = k1[Br][O3]

  15. SS approx for HO2 [HOBr] = k3[BrO][HO2] / J5 + J8] SS1 [HO2] = J5[HOBr] / K3[BrO] SS2 We don’t know the wet deposition rate underestimate of HO2or lower limit. [HO2] = J5 [HOBr] / K3[BrO] SS3

  16. BrO Altitude profiles

  17. CIMS case studies

  18. Summary and further work • A suite of inorganics simultaneously measured in tropics on aircraft • Also have measurements of formic, butanoic, nitric, HCN, ClNO2and N2O5 • CIMS measurements indicate model underestimates BrO by a factor of 3/4 • Other inorganic halogens underestimated by similar factor • Free Br dominated by inorganic photolysis • Inorganic halogen photolysis responsible for up to 20% O3 loss in TMBL

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