Cycling marine boundary layer

Marine mercury cycle. All fluxes are in units of Mmol/y. Preindustrial fluxes are in parentheses. The marine boundary layer is the iower part of the troposphere in which mercury transformations associated with the air-sea interface occur. Source After Mason, R. R, and G.-R. Sheu (2002). Global Blogeochemical Cycles 16, GB001440. 

Crutzen and co-workers (Sander and Crutzen, 1996 Vogt et al., 1996) have developed a model for chemistry in the marine boundary layer at midlatitudes, in which autocatalytic cycles involving sea salt particles generate photochemically active gases such as BrCl, Br2, and Cl2. It is likely that such chemistry also occurs in the Arctic as well. In these cycles, reactions (125) and (126) in the condensed phase,... 

Clarke, A. D., Z. Li, and M. Kitchy, Aerosol Dynamics in the Equatorial Pacific Marine Boundary Layer Microphysics, Diurnal Cycles, and Entrainment, Geophys. Res. Lett., 23, 733-736 (1996). 

The rather fast reaction rate of halomethanes with Cl atoms suggests that this process may play a primary role in the removal of halomethanes from the troposphere and results in the formation of HC1 or 1C1 molecules. These degradation pathways do not lead to bromine or iodine atoms but to relatively stable molecules, which may initiate a different bromine and iodine cycles in the marine boundary layer. The atmospheric lifetime of IC1 is probably controlled by its sunlight photodissociation to iodine and chlorine atoms. Another possible degradation pathway of IC1 may be the hydrolysis to hypoiodous acid IOH, which may further be dissolved in seawater. 

In this Chapter we discuss the distribution of DMS and H S in marine air. The discussion focuses on 1) analytical techniques used to obtain the existing data base, 2) the measurements of DMS and H2S over the oceans, and 3) modelling efforts to test current concepts of tropospheric cycling of these compounds. Results from simple box model of the marine boundary layer are presented for comparison of estimated rates of sea/air exchange and photochemical oxidation with atmospheric concentrations of DMS and H2S in the marine boundaiy layer. 

Figure 2 Global distribution of atmospheric CH4 from 1992 to May 1, 2001. Three-dimensional latitudinal distribution of CH4 in the marine boundary layer is presented. The surface represents data from the NOAA/CMDL cooperative air sampling network smoothed in time and latitude (source National Oceanic and Atmospheric Administration (NOAA), Climate Monitoring and Diagnostics Laboratory (CMDL), Carbon Cycle Greenhouse Gases). Updated versions are available on line at http //www.cmdl.noaa.gov/ccgg/gaUery/index pageType =...

Yvon S. A., Saltzman E. S., Cooper D. J., Bates T. S., and Thompson A. M. (1996) Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12 degrees S, 135 degrees W) a comparison of field data and model results 1. Dimethylsulfide. J. Geophys. Res. Atmos. 101(D3), 6899-6909. 

Fig. 13-5 The sulfur cycle in the remote marine boundary layer. Within the 2500 m boundary layer, burden units are ng S/m and flux units are ng S/m h. Fluxes within the atmospheric layer are calculated from the burden and the residence time. Dots indicate that calculations based on independent measurements are being compared. The measured wet deposition of nss-SO " (not shown) is 13 7 //g S/m /h Inputs and outputs roughly balance, suggesting that a consistent model of the remote marine sulfur cycle within the planetary boundary layer can be constructed based on biogenic DMS inputs alone. Data (1) Andreae (1986) (2) Galloway (1985) (3) Saltzman et al. (1983) (4) sulfate aerosol lifetime calculated earlier in this chapter based on marine rainwater pH the same lifetime is applied to MSA aerosol. Modified from Crutzen et al. (1983) with the permission of Kluwer Academic Publishers.

Once the importance of DMS to the global sulfur cycle was established, numerous measurements of DMS concentrations in the marine atmosphere have been conducted. The average DMS mixing ratio in the marine boundary layer (MBL) is in the range of 80-1 lOppt but can reach values as high as 1 ppb over entrophic (e.g., coastal, upwelling) waters. DMS mixing ratios fall rapidly with altitude to a few parts per trillion in the free troposphere. After transfer across the air-sea interface into the atmosphere, DMS reacts predominantly with the hydroxyl radical and also with the nitrate (N03) radical. Oxidation of DMS is the exclusive source of methane sulfonic acid (MSA) in the atmosphere, and the dominant source of S02 in the marine atmosphere. We will return to the atmospheric chemistry of DMS in Chapter 6. 

Pszeimy AAP, Moldanov J, Keene WC, Sander R, Maben JR, Martinez M, Crutzen PJ, Pemer D, Priim RG (2004) Halogen cycling and aerosol pH in the Hawaiian marine boundary layer. Atmos Chem Phys 4 147-168... 

The reactions of halogen atoms and radicals are of fundamental importance in stratospheric chemistry (see Sects. 4.4 and 8.2, 8.3, and 8.4), and the halogen cycle is also of interest in the marine boundary layer in the troposphere (see Sect. 7.5). In this section, among the atmospheric reactions of halogen atoms and radicals, fundamental homogeneous reactions of Cl atoms and CIO radicals are described, and the reactions of bromine and iodine atoms and radicals are discussed in the more phenomenological discussions in Chaps. 7 and 8. 

Pszenny AAP, Castelle AJ, Galloway JN and Duce RA,1987, A study of the sulphur cycle in the Antarctic marine boundary layer, J. Geophys. Res.,94,D7,9819-9830. 

Heintzenberg J, Leek C. Seasonal variation of the atmospheric aerosol near the top of the marine boundary layer over Spitsbergen related to the Arctic sulphur cycle. Tellus 1994 46B 52-67. 

Figure 13-5 is the box model of the remote marine sulfur cycle that results from these assumptions. Many different data sets are displayed (and compared) as follows. Each box shows a measured concentration and an estimated residence time for a particular species. Fluxes adjoining a box are calculated from these two pieces of information using the simple formula, S-M/x. The flux of DMS out of the ocean surface and of nss-SOl back to the ocean surface are also quantities estimated from measurements. These are converted from surface to volume fluxes (i.e., from /ig S/(m h) to ng S/(m h)) by assuming the effective scale height of the atmosphere is 2.5 km (which corresponds to a reasonable thickness of the marine planetary boundary layer, within which most precipitation and sulfur cycling should take place). Finally, other data are used to estimate the factors for partitioning oxidized DMS between the MSA and SO2 boxes, for SO2 between dry deposition and oxidation to sulfate, and for nss-SO4 between wet and dry deposition. 

If DMS concentrations at the surface of the ocean are presumed to be at steady state, production must balance loss. The fate of DMS is thought to be evasion across the sea surface into the marine atmospheric boundary layer. However, since rates of DMS production are unknown, it is impossible to compare production with flux to the atmosphere, which is relatively well constrained. An alternative sink for DMS in seawater is microbial consumption. The ability of bacteria to metabolize DMS in anaerobic environments is well documented (32-341. Data for aerobic metabolism of DMS are fewer (there are at present none for marine bacteria), but Sivela and Sundman (25) and de Bont et al. (25) have described non-marine aerobic bacteria which utilize DMS as their sole source of carbon. It is likely that bacterial turnover of DMS plays a major role in the DMS cycle in seawater. 

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