Deposition rate emission factor

The atmospheric deposition rate in this midcontinental area, which has increased by a factor of about 3.7, suggests that natural Hg concentrations were only about 25% of modern levels. Current estimates of recent increases in global atmospheric Hg support this conclusion, and indicate that increased anthropogenic Hg emissions, rather than enhanced removal by atmospheric oxidants, are responsible for elevated Hg deposition. Moreover, the increase appears to be relatively uniform across our study area, implying regional if not global sources for the Hg falling on these remote sites. 

The environmental impact of HM, however, depends not only on their emission, but also on their deposition rates, the relative increase in HM content in soil and some other factors considered below. 

It is likely that natural ecosystems (forest, grassland) emit no or only small amounts of ammonia because normally there is a deficit of fixed nitrogen in landscapes. Reported emissions factors over forests span three orders of magnitude and are likely be influenced by re-emission of wet deposited ammonium. Older publications considerably overestimated emission by using simple models considering soil ammonium concentrations obtained from relative decomposition and nitrification rates, where Henry s law gives the equilibrium concentration of ammonia gas in the soil, and a simplified diffusion equation yields the flux to the atmosphere, for example, Dawson (1977) calculated it to be about 47 Tg N yr b... 

Clearly, the concentrations of pollutants in ambient air, and hence their impacts, are determined not only by their rates of emissions but also by the nature and efficiencies of their chemical and physical sinks, e.g., chemical transformations, as well as wet and dry deposition to the earth s surface. To a large extent, these competing processes are affected not only by direct dispersion and transport but also by such meteorological factors as temperature, sunlight intensity, and the presence of temperature inversions as well as clouds and fogs. 

For any case-study built around Equation 1, we have to consider, for model input, parameters that provide emissions or environmental concentrations, intermedia transfer factors, ingestion (or other intake) rates, body weight, exposure frequency and exposure duration. For our specific case-study below, we are interested in concentrations in surface waters due to deposition from the atmosphere. The relevant intermedia transfer factor is the bioconcentration factor for fish concentration from surface water concentrations. The intake data we need are the magnitude and range of fish ingestion in our exposed population. Because PBLx is a persistent compound that accumulates in fat tissues, we will focus for this case not on exposure frequency and duration but on long-term average daily consumption. 

SO2, NOx, and total hydrocarbons. The mass spectrometric gas analysis is on a wet basis, as water vapor is not condensed out of the gas, while the analyzers at the sample port measure a gas stream dried using a permeation tube and refrigeration-type dryers in series. In addition to the measurements described above, surface temperature measurements of the boiler skin are made to estimate radiation losses, using the skin temperature, the room temperature and tabulated heat loss factors based on the temperature difference. Particulate mass emission rate and carbon content are measured for heat and mass balance purposes. At present, material deposited within the boiler during a test is collected but not factored into the heat or mass balances, because this deposition is considered to be negligible. Data taken are used to examine the heat balance for the 20-hp system. 

These processes are not evenly distributed, since the effects observed in any locality depend upon the emission distribution pattern and transport, the rate of oxidation in the atmosphere, and the rate of deposition, which depends upon climatic factors. 

The variable emission rates and the meteorological parameters — wind velocity (dilution factor), wind direction (contribution of other sources) and the occurrence of atmospheric wet deposition - are the main parameters responsible for the variation in ambient air concentration levels with a factor of 10. 

A complicating factor in dry deposition measurements is the presence of sources of the depositing substance in the footprint of the measurement. Whereas the flux of S02 is nearly always unidirectional (downward) and the surface is a sink for S02, gases such as H2S, NH3, and NO may have surface sources. It may be possible in some cases to specify a surface emission rate. For N02, the situation appears to be even more complex than just adding a surface emission rate to the resistance model. As much as 50% of the N02 initially removed at the surface can reappear as NO as a result of surface emissions (Meyers and Baldocchi 1988). 

The surface dose rate through the nominal protective layer of skin (7 mg/cm ) from a thin uniform deposit of 1 pCi/cm is about 9 rad/hour for beta energies above about 0.6 MeV. Note that in a thin layer, the beta dose rate exceeds the gamma dose rate, for equal energies of emission, by about a factor of 100. 

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