Atmospheric deposition, measurement methods

Frescholtz 2002). Although ongoing and new planned field and laboratory studies are designed to further test this hypothesis, we feel that it is warranted at this time to develop a pilot-scale network of aimual ecosystem fluxes of THg in TF and LF as indicators of total atmospheric deposition. These fluxes can then be compared with measured wet plus modeled diy deposition based on both inferential and regional-scale models to develop independent estimates of total atmospheric deposition for forested catchments. We also believe that this approach could eventually be applied to a national network, such as the MDN. Although this method is best aimed at forested sites, ongoing research will address methods appropriate for other ecosystems. 

Several integral measurement methods were evaluated in the early stages of this program. The wet-chemistry bubbler system deployed in Europe for remote measurement purposes cannot distinguish different chemical species. Since the deposition velocity is very species dependent, clear distinction among different chemical species is required to derive dry deposition rates. Filterpack methods have limitations as well. At the 1982 Technical Committee meeting of the National Atmospheric Deposition Program, conducted in St. Louis, a... 

Monitoring of changes in the radioecological situation around each radiation-hazardous enterprise is the main methodic principle of information survey. Measurements, which frequency and scope depend on location and specific condition of every environmental contamination source, are conducted as follows monitoring of seawater, aerosols - every day dry land, atmospheric depositions - every week drinking water - every month coastal and marine vegetation, fish, benthos - once a year. 

This chapter begins with a definition of the different transfer processes involved in chemical transport in the atmosphere-canopy-soil surface system. A qualitative description of each process is followed by an example of how the relevance of the different processes changes with the physical chemical properties of the chemical. Then, a theoretical framework is presented for the two processes for which this is available, namely dry gaseous deposition and dry particle-bound deposition. This is accompanied by a description of the measurement methods available to quantify these processes. The last section is devoted to summarizing the available correlations and presenting several example calculations of mass transfer coefficients. 

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

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... 

The accuracy of the measurement of radon concentrations with bare track detectors was found to be unsatisfactory due mainly to the changes of the deposition rate of radon progeny onto the detector as a result of air turbulence. In this work, therefore, a method was developed which can correct the contributions of the deposition to the track densities by classifying the etched tracks according to their appearance, i.e. round or wedge shaped. Using this method, about 30% improvement in the error of measurements was achieved. The calibration coefficient ob tained by experiment was 0.00424 tracks/cm /h/(Bq/m ), which agreed well with the calculated value. Comparison was also made of the present method with other passive methods, charcoal and Terradex, as to their performance under the same atmosphere. 

Dosimetric Studies. The main objective of Rn-d dosimetry is to enable the assessment of the observed dose from Rn-d deposited in the respiratory tract from measured Rn-d concentration in the atmosphere. As a consequence of an inhomogeneous Rn-d deposition within the lung, different dosimetric concepts have been developed to describe either regional mean dose values (e.g. for tracheobronchial or pulmonary region) or microdosimetric dose calculations (e.g. for the basal cell layer). Using Monte Carlo calculation methods it is also possible to account for the random nature of cellular hits by deposited alpha particles. The results of such dosimetric calculations should provide the following information needed for Rn-d risk assessment ... 

Property measurements of fullerenes are made either on powder samples, films or single crystals. Microcrystalline C6o powder containing small amounts of residual solvent is obtained by vacuum evaporation of the solvent from the solution used in the extraction and separation steps. Pristine Cgo films used for property measurements are typically deposited onto a variety of substrates (< . , a clean silicon (100) surface to achieve lattice matching between the crystalline C60 and the substrate) by sublimation of the Cr,o powder in an inert atmosphere (e.g., Ar) or in vacuum. Single crystals can be grown either from solution using solvents such as CS and toluene, or by vacuum sublimation [16, 17, 18], The sublimation method yields solvent-free crystals, and is the method of choice. 

The first step in the application of the concept was to determine the critical load values for the different regions of eastern Canada. This was done using historical measurements of lake acidity in concert with the Integrated Assessment Model (IAM) which links atmospheric transport and deposition models with water chemistry and empirical biological response models. Details of the method are given in Jeffries and Lam (1993). 

Substances can be removed from the atmosphere by dry deposition to surfaces. A method for obtaining the parameters of dry deposition uses eddy correlation flux measurements that require chemical sensors with very fast... 

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