Atmospheric transport processes

Reiter, E. R. Transport in the planetary boundaiy layer, pp. 127-182. In Atmospheric Transport Processes. Part 3 Hydrodynamic Traces. AEC Critical Review ries. TID-25731. Oak Ridge, Tenn. U.S. Atomic Energy Commission, 1972. 

As PAHs are widespread contaminants produced as a result of natural cycles (e.g., forest fires, plant decomposition and petrogenesis), as well as industrial activities, identification of anthropogenic PAHs contaminant sources is a challenge, particularly as atmospheric emissions are subject to long-range atmospheric transportation processes (Lockhart et al., 1992 ... 

Atmospheric transport processes provide an effective mechanism by which mineral aerosol is transported over the entire globe. 

Atmospheric Transport Processes. If an atmospheric constituent is not removed, then it will be transported by the winds, which vary greatly in time and space. The vertical dimension is particularly important, not only because transport speeds increase with height but because the probability of encountering clouds increases with height and the likelihood of being trapped by a ground-based... 

E. R. Reiter, Atmospheric Transport Processes, Part 1 -Energy Transfers and Transformations, AEC Critical Review series (1969). 

In the case of the GRG coupled system, both the IFS and the CTM simulate atmospheric transport processes. Different advection schemes or spatial and temporal resolutions may lead to different concentration fields in the IFS and the CTM. Thus, the applied CTM tendencies can be inconsistent with the concentration fields in the IFS. The most annoying consequence would be negative concentration values in the IFS, due to un-balanced loss processes. 

The preceding section describes the thermodynamics associated with determining whether a reaction can proceed spontaneously at a given temperature. The next question one might wish to pose is how fast such a reaction will occur. That is the concern of chemical kinetics. The concentrations of almost all atmospheric chemical species depend critically on reaction kinetics, which determines the rates at which these constituents are produced or destroyed. The observed density of most chemical species in the atmosphere is dependent on the balance between the rates of photochemical production and destruction, and the rate of atmospheric transport processes. The rate at which a chemical reaction occurs varies considerably from one reaction to another and must be determined in the laboratory. For a reaction between species A, B, C,... 

Figure 5.23. Photochemical lifetimes of water vapor and molecular hydrogen, and the time constants for atmospheric transport processes in the middle atmosphere.

A changing climate influences atmospheric chemistry through not only temperature and precipitation changes but also changes in atmospheric transport processes, changes in the... 

Benarie (1987) discusses errors in Gaussian and other atmospheric dispersion models for neutral or positive buoyancy releases. He highlights the randomness of atmospheric transport processes and the importance of averaging time. The American Meteorological Society (1978) has stated that the precision of models based on observation is closely tied to the scatter of that data. At present the scatter of meteorological data is irreducible and dispersion estimates can approximate this degree of scatter only in the most ideal circumstances. 

Transport processes describe movement of the pesticide from one location to another or from one phase to another. Transport processes include both downward leaching, surface mnoff, volatilization from the soil to the atmosphere, as weU as upward movement by capillary water to the soil surface. Transport processes do not affect the total amount of pesticide in the environment however, they can move the pesticide to sites that have different potentials for degradation. Transport processes also redistribute the pesticide in the environment, possibly contaminating sites away from the site of apphcation such as surface and groundwater and the atmosphere. Transport of pesticides is a function of both retention and transport processes. 

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... 

This chapter focuses on types of models used to describe the functioning of biogeochemical cycles, i.e., reservoir or box models. Certain fundamental concepts are introduced and some examples are given of applications to biogeochemical cycles. Further examples can be found in the chapters devoted to the various cycles. The chapter also contains a brief discussion of the nature and mathematical description of exchange and transport processes that occur in the oceans and in the atmosphere. This chapter assumes familiarity with the definitions and basic concepts listed in Section 1.5 of the introduction such as reservoir, flux, cycle, etc. 

The advent of fast computers and the availability of detailed data on the occurrence of certain chemical species have made it possible to construct meaningful cycle models with a much smaller and faster spatial and temporal resolution. These spatial and time scales correspond to those in weather forecast models, i.e. down to 100 km and 1 h. Transport processes (e.g., for CO2 and sulfur compounds) in the oceans and atmosphere can be explicitly described in such models. These are often referred to as "tracer transport models." This type of model will also be discussed briefly in this chapter. 

Under some circumstances transport processes other than fluid motion and molecular diffusion are important. One important example is sedimentation due to gravity acting on particulate matter submerged in a fluid, e.g., removal of dissolved sulfur from the atmosphere by precipitation scavenging, or transport of organic carbon from the surface waters to the deep... 

Hunt, E. R. Jr., Piper, S. C., Nemani, R., Keeling, C. D., Otto, R. D. and Running, S. W. (1996). Global net carbon exchange and intra-annual atmospheric CO2 concentrations predicted by an ecosystem process model and three-dimensional atmospheric transport model. Global Biogeochem. Cycles 10, 431-456. 

The concentration of small ions in the atmosphere is determined by 1) the rate of ion-pair production by the cosmic rays and radioactive decay due to natural radioactive substances, 2) recombination with negative ions, 3) attachment to condensation nuclei, 4) precipitation scavenging, and 5) transport processes including convection, advection, eddy diffusion, sedimentation, and ion migration under the influence of electric fields. A detailed differential equation for the concentration of short-lived Rn-222 daughter ions including these terms as well as those pertaining to the rate of formation of the... 

The first row describes the condition if 1000 kg/h is emitted into the air. The result is similar to the Level II calculation with 19700 kg in air, 57 kg in water, 24 kg in soil and only 0.2 kg in sediment. It can be concluded that benzene discharged to the atmosphere has very little potential to enter other media. The rates of transfer from air to water and air to soil are both only about 0.4 kg/h. Even if the transfer coefficients were increased by a factor of 10, the rates would remain negligible. The reason for this is the value of the mass transfer coefficients which control this transport process. The overall residence time is 19.8 hours, similar to Level II. 

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