Dry depositional fluxes

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. 

U. Shahin, S.-M. Yi, R. D. Paode, and T. M. Holsen, Long-Term Elemental Dry Deposition Fluxes Measured Around Lake Michigan, Environ. Sci. 

The size distribution of air particles not only influences the distribution and partitioning dynamics of POPs, but also determines dry and wet deposition flux of POPs. An interesting phenomenon was observed for relationship among atmospheric PAHs, particle size distribution, and the levels of PAHs in soil (Kim, 2004). For urban sites, the composition pattern and absolute concentrations of PAHs in soil were well correlated with those in air where the atmospheric particles size was distributed evenly among seasons with predominant amount of fine particles < 3 pm. Dry deposition flux of PAHs followed seasonal variation in atmospheric concentration in urban site. However, at a suburban site with large seasonal variation in particle size distribution, dry deposition flux and soil residue did not reflect the seasonal variation of atmospheric PAHs. From this result, site-specificity in atmospheric particle distribution may also influence the distribution and residues in the underlying soil. 

There are nine known radioactive isotopes and six are listed in Table 2. Sulfur-35 has the longest half-life and is produced by cosmogenic synthesis in the upper atmosphere cosmogenic S-35 (Tanaka and Turekian, 1991) is sufficiently long lived to be useful in determining overall removal and transformation rates of SO2 from the atmosphere and an estimated dry deposition flux to total flux ratio is —0.20 in the eastern US (Turekian and Tanaka, 1992). 

Values are means standard errors for 2 years of data. Numbers of observations range from 15 (HNO3) to 26 (particles) to 128 (precipitation) to 730(802). In comparing these deposition rates it must be recalled that any such estimates are subject to considerable uncertainty. The standard errors given provide only a measure of uncertainty in the calculated sample means relative to the population means hence additional uncertainties in analytical results, hydrologic measurements, scaling factors, and deposition velocities must be included. The overall uncertainty for wet deposition fluxes is about 20% and that for dry deposition fluxes is approximately 50% for SOj", Ca ", K", and approximately 75% for NOj" and... 

It is interesting to note that the surface used most widely in the United States is the Aerochem-Metrics bucket Since 1982, the buckets have been deployed at over 100 sites nationwide as part of the National Atmospheric Deposition Program (NADP) (8). This monitoring program has resulted in a sizeable dry deposition flux data base for numerous trace element and ionic species (12). 

The surrogate surfaces summarized in Table 2 have been used to measure dry deposition fluxes for a number of species. In many cases, airborne... 

Dry gaseous deposition is a complex process which depends on the physical-chemical properties of the PCBs, characteristics of the adsorbing surface, and environmental conditions (e.g., windspeed). In the ambient atmosphere, dry particulate deposition is predominantly in the form of fine aerosols (<1 pm), which deposit on surfaces by rapid, vibratory (Brownian) diffusion (Holsen and Noll 1992). However, in urban areas, PCBs are associated with course aerosols (>1 pm), and these particulates represent the majority of the dry deposition flux even though PCBs are largely in the vapor phase (Holsen et al. 1991). 

Because the processes by which a molecule, or particle, is transported to the surface of the earth and absorbed by the surface are quite complex, the dry deposition process is represented by an overall transfer coefficient. It is generally assumed that the dry deposition flux is proportional to the local pollutant concentration [at a known reference height (zr), typically 10 m], resulting in the expression F = — vdC, where F represents the dry deposition flux (the amount of pollutant depositing to a unit surface area per unit time) and C is the local pollutant concentration at the reference height. The proportionality constant, vd, has units of length per unit time and is known as the deposition velocity. 

Noll K, Yuen P and Fang K (1990), Atmospheric coarse particulate concentrations and dry deposition fluxes for ten metals in two urban environments. 

The dry deposition of gases and small particles can be estimated by atmospheric flux dry deposition flux [pg m s ] = dry deposition velocity [m s ] x air concentration of compound [pgm ] (Hbfken etal. 1988, Schwela 1977). 

Spruce and fir trees have a larger filtering biomass than pine and deciduous trees. For example, in coniferous stands the dry deposition fluxes of sulfur are about 2.5-fold... 

Baeyens W, Dehairs P and Dedeurwaerder H (1990) Wet and dry deposition fluxes above the North Sea. Atmos Environ 24A 1693-1703. 

It is generally impractical, in terms of the atmospheric models within which such a description is to be embedded, to simulate, in explicit detail, the microphysical pathways by which gases and particles travel from the bulk atmosphere to individual surface elements where they adhere. In the universally used formulation for dry deposition, it is assumed that the dry deposition flux is directly proportional to the local concentration C of the depositing species, at some reference height above the surface (e.g., 10 m or less)... 

Kramm, G., Dlugi, R., and Muller, H. (1993) On the determination of dry deposition fluxes of ozone, nitric oxide and nitrogen dioxide, EUROTRAC Newslett., 11/93, 2-9. 

Table 3.8. Average concentrations (pg/m ) and dry deposition fluxes of nutrient elements in the SYS (Wan et al., 2003) (With permission from Wan XF)...

In summer the flows are from southern China and Japan, Pacific maritime conditions. In addition, summer is the wettest season and rain scavenging also contributes to the summer minimums. It tends to be the minimum in the summer time. Nitrate also shows a similar cycle. According to the concentrations of nutrients and sulphate described above, the dry deposition fluxes can be obtained in each season. The seasonal variability of dry deposition fluxes is similar to that of its concentration. The dry deposition flux of nitrate in the southern YS is at a maximum in spring and reaches a minimum in summer. Other nutrient elements in the southern YS have similar seasonal cycles to that of nitrate. 

From the concentrations in precipitation and monthly rainfall data in Table 3.10, we can easily conclude the monthly average wet deposition fluxes in the southern YS (Table 3.10, Wan et al., 2003). The seasonal variability of wet deposition fluxes in the southern YS is contrary to that of dry deposition fluxes. It tends to reach a maximum in summer and a minimum in winter. Though the concentrations are relatively low in summer, the wet deposition fluxes are still the greatest in the whole year due to enormous rainfall. By comparing dry and wet deposition fluxes, it can also be found that the wet... 

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