Depositional fluxes

Dry Deposition. Dry deposition occurs in two steps the transport of pollutants to the earth s surface, and the physical and chemical interaction between the surface and the pollutant. The first is a fluid mechanical process (see Fluid mechanics), the second is primarily a chemical process, and neither is completely characterized at the present time. The problem is confounded by the interaction between the pollutants and biogenic surfaces where pollutant uptake is enhanced or retarded by plant activity that varies with time (47,48). It is very difficult to measure the depositional flux of pollutants from the atmosphere, though significant advances were made during the 1980s and early 1990s (49,50). 

HONO the mean flux was an emission of 1 ng Nm s but this includes periods both of emission and deposition. On several occasions, no concentration gradients were detected. The direction of the flux was dependent on NOj concentration, with emission observed only when NOj concentration was less than 10 ppb. The process of HONO exchange appears to be regulated by the net result of small deposition flux to the surface and a surface chemistry production of HONO from NOj. Fluxes of PAN deposition were measured using a chamber technique " and were small (less than 0.5ng Nm s ). 

It is important to note tlmt tlic deposition rate is a strong function of particle dimneter tluough the term v, wliich appears twice in tlic deposition flux equation. Equation (9.7.10) must be modified to treat process gas streams discliarging particles of a given size distribution. The suggested procedure is somewhat simihu to tlial for calculating overall collection efficiencies for particulate control equipment (12). For this condition, the overall rale is given by... 

PEM (Pollution Episodic Model) is an urban scale air pollution model capable of predicting short-term average surface concentrations and deposition fluxes of two gaseous or particulate pollutants. 

We begin our analysis by comparing the surface fluxes. According to the indicated partitioning factors, 74% of the 11 Mg DMS-S/m /h emitted from the ocean surface should be returned as nss-SO in rain. This leads to a predicted wet deposition flux of nss-SO of 8.1 Mg S/(m /h), which is 37% lower than the measured flux of 13 Mg S/(m /h). Since the estimated accuracy of the DMS emission flux is 50% (Andreae, 1986), this is about as good agreement as can be expected. It indicates that our "closed system" assumption is at least a reasonable first approximation. (A more sophisticated treatment would consider sulfur oxida-... 

Settle, D. M. and Patterson, C. C. (1982). Magnetites and sources of precipitation and dry deposition fluxes of industrial and natural leads to the North Pacific at Enewetak. /. Geophys. Res. 87, 8857-8869. 

Impurities travel from atmosphere to ice sheet surface either attached to snowflakes or as independent aerosols. These two modes are called wet and dry deposition, respectively. The simplest plausible model for impurity deposition describes the net flux of impurity to ice sheet (which is directly calculated from ice cores as the product of impurity concentration in the ice, Ci, and accumulation rate, a) as the sum of dry and wet deposition fluxes which are both linear functions of atmospheric impurity concentration Ca (Legrand, 1987) ... 

The presence of both single gold atoms and gold clusters, evident in Figure 3(b), indicates that the deposition flux is largely atomic or very small clusters as expected from the process gas pressure. 

The total wet deposition flux consists of 2 contributory factors. The first derives from the continuous transfer of Hg to cloud water, described by chemistry models. There are 2 limiting factors 1) the uptake of gas phase Hg(0), which is regulated by the Hemy s corrstant and 2) the subsequent oxidation of Hg(0) to Hg(ll), which is governed by reaction rate constants and the irritial concentratiorrs of the oxidant species. The total flirx depends on the hquid water content of the cloud and the percentage of the droplets in the cloud that reach the Earth s surface. 

FIG. 45. (a) The ratio of the ion flux to the deposition flux. Rj. and (b) the ratio of the energy flux to the deposition flux. max. as a function of power delivered to the SiHa-Ar discharge at an excitation frequency of 50 MHz and a pressure of 0.4 mbar. (Compiled from E. A. G. Hamers. Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands. 1998.)... 

Thomson J, Higgs NC, Clayton T (1995) A geochemical criterion for the recognition of Heinrich events and estimation of their depositional fluxes by the ( °Thexcess)° profiling method. Earth Planet Sci Lett 135 41-56... 

The higher concentrations of some heavy metals, like Zn, Cu, Ni, and Pb, in snowmelt waters in comparison with rain waters is possibly related to the elevated content of solid particles in snow. Deposition fluxes are less important in the... 

The spatial pattern of national emissions and atmospheric transport from neighboring countries causes high variability in depositions to different countries. The highest deposition flux of cadmium averaged over the country area is noted for Poland (almost 100 g/km2/yr), followed by Slovakia, Belgium, and Bulgaria. The lowest average deposition flux is in Finland and Norway. 

The spatial distribution of mercury depositions over Europe is shown in Figure 10. The highest deposition fluxes are observed in Central and Southern Europe in the countries with significant anthropogenic emissions and their neighbors. In these countries the annual mercury depositions can exceed 30 g/km2/yr. The lowest depositions were in Scandinavia and in the northern part of Russia (lower than 5 g/km2/yr). Levels of mercury deposition vary from country to country appreciably. 

Atmospheric loads to seas surrounding Europe are of great importance for environmental risk assessment. In 2002 the highest average deposition flux of lead was obtained for the Black and Azov Seas (Figure 11). This is caused by atmospheric... 

Figure 11. Averaged deposition fluxes of lead, cadmium and mercury to regional seas in 2002 (Ilyin el al., 2004).

To confirm this idea two examples are given in Figures 18(a) and (b) ecosystem-dependent depositions of lead in South Norway and in Central Spain in 2002. Depositions are split in wet and dry. Wet deposition fluxes are assumed to be the same for different types of ecosystems. Annual precipitation amounts in these regions are about 1,400 (Norway) and 510 (Spain) mm. In the Norwegian region dry deposition to forests is higher than that to arable lands. However, due to the large amount of precipitation, wet deposition prevails and total deposition (sum of wet and dry) does not differ much between forests and arable lands. 

In Spain the situation is opposite. Dry deposition to forests is higher than that to arable lands as much as 4.5 times. Moreover, unlike Norway, at this station dry deposition to forests is significantly higher than wet deposition. The total deposition fluxes to arable lands and to forests also differ almost twofold. Similar effects are also observed for cadmium and mercury. 

Variable geographical conditions and distribution of emission source causes highly uneven distribution of ecosystem-specific deposition patterns across Europe. From the viewpoint of the adverse effects it appears that the most interesting ecosystems are forests, arable lands, grasslands, and freshwaters. In Figure 19 depositions of cadmium to forests and to arable lands are exemplified. As seen, in areas where there are both forests and arable lands, deposition fluxes to forests are substantially higher than to arable lands. 

Figure 19. Deposition flux of cadmium to areas covered by forests (a) and to arable lands (b) in 2002 (Ilyin et al., 2004).

Hamilton-Taylor, J., M. Willis, and C. S. Reynolds (1984), "Depositional Fluxes of Metals and Phytoplankton in Windermere as Measured by Sediment Traps", Limnot. Oceanogr.24, 695-710. 

Paalme et al. (1990) studied the bulk deposition chemistry in the environment around the Estonian oil shale combustion area (Fig. 11 see also Kirso et al. 2002). Cations (i.e., calcium, potassium, sodium), anions (i.e., chloride, sulphate, nitrate), and - he x an e-e x t ractable PAHs were analysed in snow meltwater samples collected from 21 sampling stations in northeastern Estonia. It was found that the characteristic products of oil shale combustion, that is, Ca2+ and SC>4, accounted for over 92% of the major cations and 90% of the major anions in the snow. Correlation coefficients of r = 0.86 and 0.92 were noted for Ca2+ vs. SO - and Ca2+ vs. (SO2 - + 20 ), respectively. A high degree of correlation (r = 0.83) was also noted between Ca2+ vs. total PAHs in snow samples taken 150 km to the south of the thermal power plants. The deposition fluxes of Ca2+ and PAHs decreased with distance from the power plants. The average Ca2+ deposition flux 90 km... 

Teinemaa, E., Kirso, U., Strommen, M. R. Kamens, R. M. 2003. Deposition flux and atmospheric behavior of oil shale combustion aerosols. Oil Shale, 20, 429-440. 

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