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- Title
Sensitivity of tropospheric chemical composition to halogen-radical chemistry using a fully coupled size-resolved multiphase chemistry/global climate system -- Part 1: Halogen distributions, aerosol composition, and sensitivity of climate-relevant gases.
- Authors
Long, M. S.; Keene, W. C.; Easter, R. C.; Sander, R.; Liu, X.; Kerkweg, A.; Erickson, D.
- Abstract
Observations and model studies suggest a significant but highly non-linear role for halogens, primarily Cl and Br, in multiphase atmospheric processes relevant to tropo-spheric chemistry and composition, aerosol evolution, radiative transfer, weather, and climate. The sensitivity of global atmospheric chemistry to the production of marine aerosol and the associated activation and cycling of inorganic Cl and Br was tested using a size-resolved multiphase coupled chemistry/global climate model (National Center for Atmospheric Research's Community Atmosphere Model (CAM); v3.6.33). Simulation results showed strong meridional and vertical gradients in Cl and Br species. The simulation reproduced most available observations with reasonable confidence permitting the formulation of potential mechanisms for several previously unexplained halogen phenomena including the enrichment of Br- in submicron aerosol, and the presence of a BrO maximum in the polar free troposphere. However, simulated total volatile Br mixing ratios were generally high in the troposphere. Br in the stratosphere was lower than observed due to the lack of long-lived organobromine species in the simulation. Comparing simulations using chemical mechanisms with and without reactive Cl and Br species demonstrated a significant temporal and spatial sensitivity of primary atmospheric oxidants (O3, HOx, NOx), CH4, and non-methane hydrocarbons (NMHC's) to halogen cycling. Simulated O3 and NOx were globally lower (65% and 35%, respectively, less in the planetary boundary layer based on median values) in simulations that included halogens. Globally, little impact was seen in SO2 and non-sea-salt SO2-4 processing due to halogens. Significant regional differences were evident: the lifetime of nss-SO2-4 was extended downwind of large sources of SO2. The burden and lifetime of DMS (and its oxidation products) were lower by a factor of 5 in simulations that included halogens, versus those without, leading to a 20% reduction in nss-SO2-4 in the Southern Hemisphere planetary boundary layer based on median values.
- Subjects
TROPOSPHERIC chemistry; SENSITIVITY analysis; ATMOSPHERIC models; HALOGENS; RADICALS (Chemistry); MULTIPHASE flow; ATMOSPHERIC aerosols; STRATOSPHERE
- Publication
Atmospheric Chemistry & Physics Discussions, 2013, Vol 13, Issue 3, p6067
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acpd-13-6067-2013