ASSIGNMENT

Gaussian Dispersion Problem and Surface Water Pollution



Gaussian Dispersion Problem and Surface Water Pollution

Part 01: Gaussian Dispersion Problem

The report is based on the analysis of the problem statement, Two typical 1950s Toowoomba town houses A and B are situated on a 5° slope and are separated by approximately 5m. Unfortunately, the height of house A's chimney is insufficient (below council regulations), and due to sloping ground, the chimney height on the lower house A is about the same height as eaves on house B.

Discussion

Firstly, it is estimated that the contaminated gas stream typical source strength (14 g/s) for the smoke emitted from the chimney of House A. In principle, the emissions of different pollutants from a given source come in constant proportions, and are independent of the location of the source. Since the impact linearly depend on the emission strength, considering another pollutant (as long as it is conservative and does not undergo any chemical transformation, for example, or is subject to gravitational settling) is the same as changing the emission strength or scenario. This, however, might change the degree of impact, but not the ranking between alternative locations. Therefore, the results of the analysis should be independent of the pollutant chosen.

The basic Gaussian diffusion equations assumes that

atmospheric stability and all other meteorological parameters are uniform and constant throughout the layer into which the pollutants is discharged, and in particular that wind speed and direction are uniform and constant in the domain;

turbulent diffusion is a random activity and therefor the dilution of the pollutant can be described in both horizontal and vertical directions by the Gaussian or normal distribution;

the pollutant is released at a height above the ground that is given by the physical stack height and the rise of the plume due to its momentum and buoyancy (together forming the effective stack height);

the degree of dilution is inversely proportional to the wind speed;

pollutant material reaching the ground level is reflected back into the atmosphere;

the pollutant is conservative, i.e., not undergoing any chemical reactions, transformation or decay.

One calls the chimney of House A the picture representing the dispersion of a pollutant in given region. We can use a model to compute a short-term or a long-term average plume. The short-term representation depends on the particular weather conditions, in particular the wind direction and speed, the temperature and the humidity. The long-term average is influenced by the distribution of different weather conditions over a long period, typically a year. The wind rose is a graphical representation of the frequencies of the different wind directions (Figure above).

We show in Figure shows the average air pollution plume resulting from NO2 emissions by a waste incinerator of capacity 120 000 t/yr.

To see the average air pollution plume resulting from NOx emissions by a waste incinerator of capacity 120 000 t/yr, you can run the ISC3 long-term model. The default parameters describe a 30 m stack with a 60 cm diameter, an exit temperature of 80 degrees Centigrade and an exit velocity of 1 ...