Heikes, BrianLee, MeehyeJacob, DanielTalbot, RobertBradshaw, JohnSingh, HanwantBlake, DonaldAnderson, BruceFuelberg, HenryThompson, Anne M.2024-07-262024-07-261996-10-01Heikes, Brian, Meehye Lee, Daniel Jacob, Robert Talbot, John Bradshaw, Hanwant Singh, Donald Blake, Bruce Anderson, Henry Fuelberg, and Anne M. Thompson. “Ozone, Hydroperoxides, Oxides of Nitrogen, and Hydrocarbon Budgets in the Marine Boundary Layer over the South Atlantic.” Journal of Geophysical Research: Atmospheres 101, no. D19 (1996): 24221–34. https://doi.org/10.1029/95JD03631.https://doi.org/10.1029/95JD03631http://hdl.handle.net/11603/34907The NASA GTE TRACE A mission sampled air over the South Atlantic and western Indian Oceans. Thirteen flight legs were flown within the marine boundary layer (MBL). The MBL was typically the cleanest air sampled (e.g., CH₄ < 1680 ppb, CO < 70 ppb, C₂H₆ < 400 ppt, C₃H₈ < 40 ppt, NOx < 15 ppt, and midday NO < 5 ppt) but was overlain by polluted air. The photochemistry of the MBL was influenced by oceanic emissions, surface deposition, and entrainment of pollutants from aloft. Chemical budgets were constructed for several species in the MBL in order to investigate these effects and are presented for ethane, ethylene, propane, propylene, n-butane, formic acid (HFo), methylhydroperoxide (CH₃OOH), oxides of nitrogen (i.e., NO, NO₂, PAN, HNO₃), hydrogen peroxide (H₂O₂), and ozone (O₃). A photochemical point model was used to evaluate local chemical production and loss. An entrainment model was used to assess material exchange between the lower free troposphere (FT) and the MBL and a resistance deposition model was used to evaluate material exchange across the air-sea interface. The results suggested the ocean to be the source of measured alkenes in the MBL and to be the most likely source of the shorter-lived alkanes: propane and n-butane. Ethane was the only hydrocarbon for which input from aloft may have exceeded its photochemical destruction. The estimated hydrocarbon sources from the ocean were in agreement with prior analyses. Transport from the lower FT together with surface loss could not account for measured concentrations of CH₂O, HFo, and HNO₃. The transport of peroxyacetylnitrate (PAN) from the FT to the MBL exceeded the rate of HNO₃ production and was more than sufficient to maintain observed NOx levels without having to invoke an oceanic source for NO. The flux of NOx, PAN, and HNO₃ was in balance with the surface deposition flux of HNO₃. However, the predicted rates of HNO₃ formation from the oxidation of NO₂ and HNO₃ entrainment from aloft were inadequate to maintain observed levels of HNO₃ unless HNO₃ was partitioned between the gas phase and a more slowly depositing aerosol phase. The estimated dry deposition flux of HNO₃ to the South Atlantic during TRACE A, 2–4 × 10⁹ molecules cm⁻² s⁻¹, was about 10 times the annual average estimate for this region. The destruction of O₃ within the MBL was found to be exceeded by transport into the MBL from aloft, 6 ± 2 × 10¹⁰ compared to 11 ± 10 × 10¹⁰ molecules cm⁻² s⁻¹. The principal O₃ destruction process was mediated by the formation and surface deposition of H₂O₂ and CH₃OOH, 4 ± 4 × 10¹⁰ and 1.1 ± 0.5 × 10¹⁰ molecules cm⁻² s⁻¹. The direct loss of O₃ to the sea surface was estimated to be 1.7 ± 0.2 × 10¹⁰ molecules cm⁻² s⁻¹. CH₃OOH was lost to the sea and transported into the FT from the MBL. Its first-order loss rate was estimated to be 7 × 10⁻⁶ s⁻¹ for a mean MBL height of 700 m. H₂O₂ and CH₂O losses from the MBL were estimated at rates of 1.3 × 10⁻⁵ s⁻¹ for both species. The inclusion of surface deposition improved the agreement between predicted and measured concentrations of HNO₃, CH₃OOH, H₂O₂, and CH₂O. However, model CH₂O remained significantly greater than that measured in the MBL.14 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domainhttps://creativecommons.org/publicdomain/mark/1.0/Text