Deposition velocity, measurement

The two approaches give effectively the same results. For example, the average HNO3 deposition velocity measured by micro-meteorological methods above a forest in east Tennessee or on summer... 

Padro, J. (1996). Summary of Ozone Dry Deposition Velocity Measurements and Model Estimates over Vineyard, Cotton, Grass and Deciduous Forest in Summer. Atmos. Environ. 30(13), 2363-2369. 

FIGURE 19.4 Correlations of particle deposition velocities measured in wind tunnel for c = 1 m (Sehmel, 1980). 

Padro, J., 1996. Summary of ozone dry deposition velocity measurements and model estimates over vineyard, cotton, grass and deciduous forest in summer. Atmos. Environ. 

Yi, S., et al.. Overall elemental dry deposition velocities measured around Lake Michigan. Atmospheric Environment, 2001.35(6) 1133—1140. 

Early models used a value for that remained constant throughout the day. However, measurements show that the deposition velocity increases during the day as surface heating increases atmospheric turbulence and hence diffusion, and plant stomatal activity increases (50—52). More recent models take this variation of into account. In one approach, the first step is to estimate the upper limit for in terms of the transport processes alone. This value is then modified to account for surface interaction, because the earth s surface is not a perfect sink for all pollutants. This method has led to what is referred to as the resistance model (52,53) that represents as the analogue of an electrical conductance... 

Elicks BB, Baldocchi DD, Meyers TP, Hosker Jr RP, Matt DR. 1987. A preliminary multiple resistance routine for deriving deposition velocities from measured quantities. Water Air Soil Pollut 36 311-330. 

Scott, A.G., Radon Daughter Deposition Velocities Estimated from Field Measurements, Health Physics 45 481-485 (1983). 

Data on the rate of attachment or deposition, i.e., plate-out of radioactive particles on walls can be used to calculate the particle deposition velocity. Deposition rates can be determined experimentally by measuring the surface activity on some samples... 

This paper deals with the plate-out characteristics of a variety of materials such as metals, plastics, fabrics and powders to the decay products of radon and thoron under laboratory-controlled conditions. In a previous paper, the author reported on measurements on the attachment rate and deposition velocity of radon and thoron decay products (Bigu, 1985). In these experiments, stainless steel discs and filter paper were used. At the time, the assumption was made that the surface a-activity measured was independent of the chemical and physical nature, and conditions, of the surface on which the products were deposited. The present work was partly aimed at verifying this assumption. 

The underlying physical and/or chemical mechanisms responsible for the differences observed between the radon progeny and the thoron progeny as related to different materials are not clearly understood. Finally, it should be pointed out that the main thrust in this paper was to determine differences in surface a-activity measured on different materials with the same geometrical characteristics exposed to identical radioactive atmospheres. The calculation of deposition velocities and attachment rates, although it follows from surface a-activity measurements, was not the intent of this paper. This topic is dealt with elsewhere (Bigu, 1985). 

Porstendorfer, 1984). Knutson et al. (1983) measured similar results in their chamber investigation. The results show that the values of the deposition velocity of the free radon daughters are about 100 times those of the aerosol radon progeny. But there are no information about the effective deposition surface S of a furnished room for the calculation of the plateout rates qf and qa by means of Vg and Vg. For this reason the direct measurements of the plateout rates in rooms are necessary. Only Israeli (1983) determined the plateout rates in houses with values between qf = 3-12 h"1 and qa = 0.4-2.0 h"1, which give only a low value of the... 

The deposition velocities of the unattached daughters were calculated from the measurements in the radon chamber with the bare filter (Figure 2) and found to equal. 095+.007 cm/s for Po-218,. 085+.012 cm/s for Pb-214 and. 045+.015 cm/s for Bi-214. This decrease in deposition velocity is one of the most important sources of error in the room model. 

Environmental Fate. It can be concluded from the transport characteristics that surface water sediment will be the repository for atmospheric and aquatic thorium. Normally, thorium compounds will not transport long distances in soil. They will persist in sediment and soil. There is a lack of data on the fate and transport of thorium and its compounds in air. Data regarding measured particulate size and deposition velocity (that determines gravitational settling rates), and knowledge of the chemical forms and the lifetime of the particles in air would be useful. 

Rangarajan C, Eapen CD, Gopalakrishnan SS. 1986. Measured values of the dry deposition velocities of atmospheric aerosols carrying natural and fallout radionuclides using artificial collectors. Water Air Soil Pollut 27 305-314. 

Andersen HV, Hovmand MF, Hummelshoj P, Jensen NO (1999) Measurements of ammonia concentrations, fluxes and dry deposition velocities to a spruce forest 1991-1995. Atmos Environ 33 1367-1383... 

Measurements of activity in grass and soil in areas where no rain fell at the relevant time have been used to estimate dry deposition after the Chernobyl accident. In Denmark and in southern England, vg for137Cs was about 0.5 mm s 1 (Roed, 1987 Clark Smith, 1988). In Stockholm, however, where the Chernobyl fallout arrived several days earlier, and the particle size was larger, the dry deposition velocity of caesium was 5 mm s 1 (Persson et al., 1987). Refractory elements such as 95Zr had dry deposition velocities about 20 mm s 1. 

Inputs and outputs to the lake have been measured to calculate net retention for the pre-acidified lake. Precipitation inputs of sulfate were based on data from wet collectors (1980-1983) compiled by the National Atmospheric Deposition Program (NADP). SO2 inputs were calculated from regional ambient air concentrations (22) usinga deposition velocity of 0.5 cm/sec. Aerosol sulfate was estimated from NADP dry bucket measurements and from dry bucket and snow core measurements made in this study (22). Groundwater inputs occur largely at the southeast corner of the lake and were calculated from modeled inseepage (21) and measured sulfate concentrations in a well located in the major inseepage area. Sulfate output was estimated from mean lakewater sulfate concentration and modeled outflows. 

Although direct measurements are extremely limited, the dry component of deposition can be estimated qualitatively from data noting that the deposition rate is the product of a deposition velocity and ambient concentration observations at ground level. 

The second approach is to use the measured ambient concentrations in combination with deposition velocities reported in the literature (21-23). 

An important step towards treatment of SO2 conversion to sulfate and deposition of both species that avoids absolute uncertainties of dispersion and deposition rates was taken by Lewis and Stevens, who investigated the mathematical basis of one form of hybrid receptor modeling (.16). Their model assumes that one measures concentrations of SO2 and SO4 relative to that of some species borne by particles from the plant. They assumed that (1) dispersion, deposition and transformation of the three species (SO2, SO4 and fine primary particles) are linear or pseudo first-order processes, but may have complex dependences on time (2) dispersion affects all three pollutants identically (3) dry deposition is the only type of deposition which occurs (4) deposition velocity is the same for all fine particles, but may be different for SO2 (5) secondary sulfate is produced only by homogeneous oxidation of SO2. 

---