Using airborne observations to improve estimates of short-lived halocarbon emissions during summer from Southern Ocean

Abstract. We present observations of CHBr 3 , CH 2 Br 2 , CH 3 I, CHClBr 2 , and CHBrCl 2 from the Trace Gas Organic Analyzer (TOGA) during the O 2 /N 2 Ratio and CO 2 Airborne Southern Ocean (ORCAS) study and the 2nd Atmospheric Tomography mission (ATom-2), in January and February of 2016 and 2017. We also use CH 3 Br from the University of Miami Advanced Whole Air Sampler (AWAS) on ORCAS and from the UC Irvine Whole Air Sampler (WAS) on ATom-2. We compare our observations with simulations from the Community Atmosphere Model with Chemistry (CAM-Chem). We report regional enrichment ratios of CHBr 3 and CH 2 Br 2 to O 2 of 0.19 ± 0.01, and 0.07 ± 0.004 pmol : mol, poleward of 60° S between 180° W and 55° W, and of 0.32 ± 0.02, 0.07 ± 0.004 pmol : mol over the Patagonian Shelf, between 40° S and 55° S and between 70° W and 55° W where we also report enrichment ratios of CH 3 I to O 2 of 0.38 ± 0.03 pmol : mol and of CH 2 ClBr 2 to O 2 of 0.19 ± 0.04 pmol: mol. Using the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model, we use correlations between halogenated hydrocarbon mixing ratios and the upwind influences of chlorophyll a, sea ice, solar radiation, and dissolved organic material to investigate previously hypothesized sources of halogenated volatile organic compounds (HVOCs) in the southern high latitudes. Our results are consistent with a biogenic regional source of CHBr 3 , and both non-biological and biological sources of CH 3 I over these regions, but do not corroborate a regional sea-ice source of HVOCs in January and February. Based on these relationships, we estimate the average two-month (Jan.-Feb.) emissions poleward of 60° S between 180° W and 55° W of CHBr 3 , CH 2 Br 2 , CH 3 I, and CHClBr 2 to be 91 ± 8, 31 ± 17, 35 ± 29, and 11 ± 4 pmol m −2 hr −1 , and regional emissions of these gases over the Patagonian Shelf to be 329 ± 23, 69 ± 5, 392 ± 32, 24 ± 4 pmol m −2 hr −1 respectively.