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Atmospheric Dispersion, Transport, and Deposition
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Reference was made to the average lifetimes or residence times of various atmospheric pollutants in Chapter 2. All gas-phase and particulate-phase pollutants have a life history in the atmosphere before they are ultimately removed. By averaging the life histories of all molecules of a substance, or all particles of a particular type or size, one can determine their average residence or lifetime. Residence time can also be described in the context of a pollutant’s half-life, that is, the time required to reduce its concentration by 50% of its initial value.
Transport within and between Compartments
Published in J. Mark Parnis, Donald Mackay, Multimedia Environmental Models, 2020
Having obtained the fugacities, all process rates can be deduced as Df, and a steady-state mass balance may be then stated in which the total inputs to each medium equal the outputs. The amounts and concentrations can be calculated from such expressions. An overall residence time can be calculated as the sum of the amounts present divided by the total input (or output) rate. A reaction residence time can be calculated as the amount divided by the total reaction rate, and a corresponding advection residence time can also be deduced. Doubling emissions simply doubles fugacities, masses, and concentrations, but the residence times are unchanged.
Water and the Hydrogeology of Watersheds
Published in Daniel T. Rogers, Urban Watersheds, 2020
The residence time of water as groundwater can range from days to thousands of years, and is a function of several variables. The dominant influence is depth, manifested by the strong correlation between increasing groundwater depth and residence time. Other factors influencing residence time include: The composition of the aquifer materialEffective porosityHydraulic gradientDistance to point of discharge
Conceptual model of regional groundwater flow based on hydrogeochemistry (Montérégie Est, Québec, Canada)
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2018
Châtelaine Beaudry, René Lefebvre, Christine Rivard, Vincent Cloutier
Isotopic indicators of residence time can also help in inferring groundwater origin and evolution of the water groups found in Montérégie Est and their interrelations. Tritium and radiocarbon can provide such indications of groundwater residence time, for young water (less than about 50 years for tritium) and older water (up to 50,000 years for 14C), respectively (Clark and Fritz 1997). Overall, 42 samples were analyzed for tritium and 43 for radiocarbon, with 28 samples subjected to both analyses. Figure 8B relates tritium and uncorrected radiocarbon ages. Samples analyzed for only one of those two parameters are also represented, in the left and bottom margins of the graph. Ranges of values obtained for tritium and radiocarbon data for each water group are provided in Table 3.
Computational fluid dynamic (CFD) modelling in anaerobic digestion: General application and recent advances
Published in Critical Reviews in Environmental Science and Technology, 2018
Constanza Sadino-Riquelme, Robert E. Hayes, David Jeison, Andrés Donoso-Bravo
Mixing behaviour has traditionally been studied by means of tracer methods, which can be used to evaluate residence time distribution curves (RTD). Such studies have identified that in some digesters dead zones can account for a high fraction of total volume, reducing effective hydraulic retention and treatment capacity (Monteith and Stephenson, 1981; Capela et al., 2009). However, tracer studies provide only limited information on what is actually occurring inside of the reactor. A convenient tool to study mixing in more detail is computational fluid dynamics (CFD). CFD has been widely used to evaluate and analyze hydraulic and mixing behaviour of anaerobic digesters, and it is expected to play an important role in the use of modelling to study AD (Batstone et al., 2015).
Reference conditions and threshold values for nitrate-nitrogen in New Zealand groundwaters
Published in Journal of the Royal Society of New Zealand, 2023
Christopher J. Daughney, Uwe Morgenstern, Magali Moreau, Richard W. McDowell
Groundwater age describes the residence time of a parcel of groundwater within an aquifer system, i.e. the time elapsed since recharge. Due to convergence of flow paths of different length and recharge source, mainly at the sampled discharge points such as wells and springs, any groundwater sample contains a mixture of different ages (Maloszewski and Zuber 1996). The groundwater age distribution within a particular sample can be described by measures of its central tendency (e.g. mean age) and distributional shape (e.g. age mixing model), which in turn can be estimated by fitting a lumped parameter model (LPM) to measured concentrations of age tracers in the groundwater sample (Zuber et al. 2005; Daughney et al. 2010; Morgenstern and Daughney 2012).