A model analysis of the tropical South Atlantic Ocean tropospheric ozone maximum: The interaction of transport and chemistry

Abstract

Abstract. The meteorological and photochemical nature of the South Atlantic Ocean tropospheric column ozone maximum is examined by analyzing the Geophysical Fluid Dynamics Laboratory (GFDL) Global Chemical Transport Model (GCTM) simulation during the Southern Hemisphere late winter. An ozone maximum of greater than 40 Dobson units is produced by the GCTM over the South Atlantic Ocean. The model is evaluated against available meteorological and ozone data and found to be in good qualitative agreement with observed wind fields, satellite measurements of tropospheric column ozone, tropospheric column ozone produced from ozonesonde data, and vertical profiles from ozonesondes. A quantitative analysis is performed over an area of the South Atlantic Ocean essentially devoid of local NO x sources and for a time, September, when the regional tropospheric ozone mass is at a maximum. The tropospheric mass of reactive nitrogen transported into the region is a result of source contributions from lightning (49%), biomass burning (36%), and 15% from the remaining NO x sources (fossil fuel plus biogenic plus stratosphere plus aircraft). Even with the removal of biomass burning NO x from the ozone photochemical system, the GCTM still produces an oceanic tropospheric column ozone maximum, suggesting the ozone phenomenon existed before agricultural burning by humans. The structure of clean air CO/CH 4 net chemistry consists of ozone production in the upper troposphere (+2.2 Tg/month), weak destruction in the middle troposphere (-1.8 Tg/month), and strong destruction in the lower troposphere (-4.2 Tg/month). Through photochemistry, the two largest NO x sources help control the vertical profile of ozone with lightning dominating in the upper troposphere, while the relative importance of biomass burning is virtually constant throughout the troposphere. A mass budget analysis of ozone over the tropospheric South Atlantic Ocean reveals that net mass transport of ozone into the domain is nearly balanced by net chemical destruction and deposition and that the mass transport into and out of the region are comparable to the chemical production and destruction terms. The three-dimensional circulation governing the ozone vertical structure is one of horizontal mass convergence and net chemical production supplying ozone to the upper troposphere which is fluxed downward by subsidence and removed in the boundary layer by net chemical destruction, deposition, and horizontal mass divergence.

The zonal structure of tropical O<sub>3</sub> and CO as observed by the Tropospheric Emission Spectrometer in November 2004 – Part 2: Impact of surface emissions on O<sub>3</sub> and its precursors

“…This pervasive zonal ozone distribution has been observed from satellites, in particular from the total ozone mapping spectrometer (TOMS) using a tropospheric ozone residual technique (Fishman and Larsen, 1987;Fishman et al, 1991Fishman et al, , 2003. This distribution is due in part to the recirculation of ozone and ozone precursors between South America and sub-equatorial Africa over the Atlantic (Krishnamurti et al, 1996;Thompson et al, 1996;Sinha et al, 2004;Moxim and Levy, 2000;Martin et al, 2002;Sauvage et al, 2005;Jenkins and Ryu, 2004b;Chatfield et al, 2004;Edwards et al, 2003;Wang et al, 2006). In addition, a high pressure system centered over Australia seen from the NCEP reanalysis (not shown, but available at http://www.cdc.noaa.gov/HistData/), low monthly averaged cloud optical depths from the International Satellite Cloud Climatology Project (ISCCP) (Rossow and Schiffer, 1991;Rossow et al, 1993) (available at http://isccp.giss.nasa.gov/), and relatively high biomass burning (van der Werf et al, 2006) indicate conditions favorable to ozone formation.…”

“…These emissions can produce ozone near the surface which can in turn be convectively lofted into the upper troposphere (Chatfield and Delany, 1990). However, NO x from lightning is directly emitted into the upper troposphere and can play a dominant role in the production of tropical ozone downwind (Pickering et al, 1998;Sauvage et al, 2007a;Martin et al, 2007;Boersma et al, 2005;Moxim and Levy, 2000). The Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) estimates lightning flash counts by means of a high speed CCD imaging sensor (3-6 km horizontal resolution) in conjunction with a narrow band (λ=777 nm) filter.…”

Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production

“…Other studies estimated O 3 budget (without sources differentiation) over the South Atlantic using global models (Moxim and Levy, 2000) or measurements (Jacob et al, 1996). They estimated net O 3 production rates of 1.5-2.1 ppbv/day in the UT over the south Atlantic.…”

Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model

“…They show a predominantly zonal asymmetry in all seasons with maximum TCO values in the Atlantic and minimum in the Pacific region. The origin of wave 1 in TCO has been attributed mostly to upper tropospheric ozone production from lightning NO x and biomass burning coupled with the large-scale Walker Circulation [Moxim and Levy, 2000;Martin et al, 2002]. The seasonal contrast is greatest in the Atlantic with maximum values during austral spring over the southern tropical Atlantic.…”