Average marine particles

We will illustrate the necessity of including solute from CCN by a simple calculation, recalling that pH = 5.6 is the supposed equilibrium value for water in contact with 300 ppm of CO2. (That calculation will appear later.) In clean, marine air, the concentration of submicrometer aerosol particles (by far the most numerous) is small, say 0.25 pg m . It is known from measurements that the molecular form is often NH4HSO4, and we assume it is all dissolved in 0.125 g/m of liquid water in a cloud - which is typical for fair-weather marine clouds. Thus the average concentration of sulfate ion [SO4 ], mol/L, is... 

Similar data for sulfate have been reported in many studies. Figure 9.36, for example, shows overall average sulfate distributions measured in marine areas as well as at continental sites (Milford and Davidson, 1987). The marine data show two modes, a coarse mode associated with sea salt and a fine mode associated with gas-to-particle conversion. Sulfate in seawater, formed, for example, by the oxidation of sulfur-containing organics such as dimethyl sulfide, can be carried into the atmosphere during the formation of sea salt particles by processes described earlier and hence are found in larger particles. The continental data show only the fine particle mode, as expected for formation from the atmospheric oxidation of the S02 precursors. 

FIGURE 9.36 Average size distributions for sulfate in continental and marine aerosol. AM M, is the fraction of the total mass of sulfate (Mr) found in each particle size range (adapted from Milford and Davidson, 1987). 

FIGURE 14.46 Average cloud droplet number concentration as a function of subcloud aerosol particle concentration (0.05-1.5 fj.m) in marine ( ) and continental ( ) air masses (adapted from Martin et al., 1994). 

Figure 5.1. Effect of particle size and the slurry standing time on the recover/ of /4s compared to the certified value, (a) 36 gm, ( ) 50 gm and (a) 77 gm. (A) Slurry of marine sediment, (B) aqueous phase of the sediment slurry, (C) slurry from a coal, (D) aqueous phase of the coal slurry. All data points are the averages of four independent experiments. (Reproduced with permission of Elsevier, Ref. [16].)...

The amount of primary production carried out in the oceans each year has been estimated from ocean color satellite data and shipboard incubations to be 140 g C m for a total of 50-60 Pg C (4-5 Pmol C) hxed in the surface ocean each year (Shuskina, 1985 Martin et al, 1987 Field et al, 1998). This represents roughly half of the global annual 105 Pg C hxed each year (Field etal., 1998), despite the fact that marine phytoplankton comprise less than 1 % of the total photosynthehc biomass on Earth. Extrapolahon from Redheld ratios suggests the incorporation 0.6-0.8 Pmol N, 40-50 Tmol P into biogenic particles each year in associahon with marine primary production. From the proportion of primary production carried out by diatoms and the average Si C raho of diatoms, silica production rates may be calculated to be 200-280 Tmol Si yr (Nelson et al, 1995 Treguer et al, 1995). 

Marin et al I ref. 31] analyzed the data of Dumez and Froment in terms of the Bethe-tree network model outlined above. For instantaneous growth of coke to a size sufficient to block the mesopores but not the macropores, Beeckman and Froment [ref. 20 derived the following equation for the average coke content of the particle ... 

Fig. 7-2. Model size distributions of the marine background aerosol (a) particle number density, (b) surface area, (c) volume. The contribution of sea salt to the volume distribution is indicated by the shaded area, and arrows indicate the appropriate scale. By integration one obtains a total number density N =290 particles/cm3, a total surface area A = 5.8 x 10 7 cm2/cm3, and a total volume V= 1.1 x 10 " cm3/cm3. For an average density of 103 kg/m3, the mass concentration is 11 pig/m3 (5 pig/m3 of sea salt). The dashed curve gives the distribution of the surface area that is effective in collisions with gas molecules. For larger particles the collision rate is lowered by the rate of diffusion.

Figures 8.15 and 8.16 show number and volume aerosol distributions in clean maritime air measured by several investigators (Meszaros and Vissy 1974 Hoppel et al. 1989 Haaf and Jaenicke 1980 De Leeuw 1986) and a model marine aerosol size distribution. The distributions of Hoppel et al. (1989) and De Leeuw (1986) were obtained at windspeeds of less than 5 m s 1 in the subtropical and North Atlantic, respectively. The distribution of Meszaros and Vissy (1974) is an average of spectra obtained in the South Atlantic and Indian Oceans during periods when the average windspeed was 12 m s-1. It is difficult to determine the extent to which the differences in these size distributions are the result of differences in sampling location and meteorological conditions such as windspeed (which affects the concentrations of the larger particles), or to uncertainties inherent in the different measurement methods.

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