Lorem Ipsum Dolor 1

Final assessment – Evaluating the risk from the

release of a toxic pollutant by solving the

advection equation.

The problem to be solved: You are a consultant working for a company that deals with exposure risk from factory fires. You are employed by a regional authority to work on a project in which a new factory is being built that manufactures a dangerous chemical known as ‘Purest Green’. The company that runs the factory predicts that in the worst-case scenario, an explosion would lead to release of a plume with a Gaussian profile given by the following scalar field:

f (x, y) = 900*exp −1 x

20

“$#

%’&

2

+

y

20

“$#

%’&

” 2

$$#

%”&

“$$#

%”& Where 900 is the maximum concentration in parts per billion [ppb] and the ‘x’ and ‘y’ variables refer to distance in km away from the epicenter. There is a town located in a region between 40-50km east of the factory and 30-50km north. It is your job to assess the variable pollutant levels that might reach this town using knowledge about typical wind speeds and directions by solving the advection equation. This information can then be used by the council to approve/reject or alter plans for the factory to be built. It would generate local job opportunities if approved. You are told to work with the following information:

• You should plan your assessment using a grid that runs, relatively, from -10 to 60km

from west to east and from -70 to 70 km south to north, using the factory as the origin

(0,0). Your grid will have a spacing of 5km.

• Whilst you have been told the eastward wind speed can be safely assumed to be 10

m/s, you are also told that the northward wind speed varies between 8-12 m/s.

Lorem Ipsum Dolor 2 Run a simulation using four different wind speed combinations to assess how average concentrations vary in the town’s domain. This information should be used to quantify a time from pollutant release at which levels become hazardous. This hazardous level for ‘Purest Green’ is set at 100ppb and the authority should derive appropriate response tactics in the eventuality that the factory is built. Your report should help to refine such tactics.

The mechanisms for solving the problem: Download the spreadsheet from todays blackboard page. In the spreadsheet you will find that an initial domain has already been set up. It stretches from -10 to 60 along the top row, and 70 to -70 along the column. Both represent east-west and north-south respectively. You should first create the pollutant field at time t=0. For this we need to implement the equation given above. You should have done similar in last week’s practice session. If you haven’t, you should spend time reading and implementing the instructions in that sheet.

Solving the advection equation. Temperature, as well as other things like water vapour, clouds and pollutants are moved around by the winds by a process known as advection. Pure advection means that as the property (temperature, water vapour, cloud, …) moves with the wind its is conserved (i.e. if you let a pocket of pollutant, concentration P, advect with the wind at point ‘a’ its concentration at point ‘b’ will be, P). The advection equation in 1D can be represented by the following expression:

∂P

∂t

= −u

∂P

∂x This is a partial differential equation which describes the advection of a quantity ‘P’. We haven’t covered partial differential equations, apart from partial differentiation, in our course, but they are used to relate changes in a given property as a function of more than one variable. In this case, we want to know how a variable changes with both time and space. Whilst we haven’t studied these, you have practiced methods that we need to use to solve them. In 2 dimensions we can write the advection equation as:

∂P

∂t

= −u

∂P

∂x

− v

∂P

∂y

Lorem Ipsum Dolor 3 where ‘y’ is the north-south direction and ‘x’ is the west-east direction.

Computing the advection equation The advection equation does not have a general analytical solution. But it can be ‘solved’ approximately on a computer. The equation demonstrates that the rate of change of quantity ‘P’ is equal to some gradients in the scalar field multiplied by the wind speed at any given point:

Pt

+1,x,y − Pt,x,y

Δt

= − u

x,y

Pt

,x,y − P t,x−Δx,y

Δx

+ v

x,y

Pt

,x,y − Pt,x,y−Δy

Δy

⎛⎜⎝

⎞⎟⎠ where ‘t’ denotes the time-level, ‘x’ denotes the distance along the west-east direction and ‘y’ denotes the distance along the north-south direction. So you can see that the gradients are defined in a discrete sense. It might seem a little daunting, but we can in fact re-arrange this equation to arrive a solution we can use in Excel. Ultimately we want our new variable

Pt

+1,x,y on its own. So, we can actually re-arrange the above to arrive at the following expression:

Pt

+1,x,y = Pt,x,y + Δt *− ux,yPt,x,y − P t,x−Δx,yΔx+ vx,yPt,x,y − Pt,x,y−ΔyΔy⎛⎜⎝⎞⎟⎠ You will need to implement this equation in excel using the same procedures you came across in lecture 7.Performing one time-step then many time-steps Once you have the scalar field set and the wind field set you are ready to perform one timestep in order to predict what will happen 100 seconds into the future. To do this, apply the above equation in the spreadsheet at every point except the west most and north most boundaries, which are always set to the initial values. For this problem you should calculate the gradient for 60 time-steps, always with a resolution of 100 seconds. If you have set the model up correctly with absolute and relative cell references you should be able to do this by copying and pasting.Lorem Ipsum Dolor 4Your assessment report Download the template of the report and following the section headings and activities. To summarise what we are looking for:- Contextuliase your problem by plotting the initial condition and describing the problem at hand. Do not simply copy and paste the text from this PDF, but give the reader a feel for the layout of your report.- Use equation editor to describe any equations in full- Describe the methodology in full.- Demonstrate how average concentrations of the pollutant in the town’s domain change as a function of time. Describe how you have arrived at an average.- Summarize your results and recommendations We are using Turni

Use this template to construct your report. Text included in grey areas can be deleted and are simply there to act as a guide in writing your report. All other information can be found in the project PDF and lecture slides. The report should be no larger than 4 pages, not including any bibliography that you feel necessary to include.

title

Your name.

Introduction:

Here you must introduce the problem you are solving. Contextualize your problem by introducing the scalar field that is used to model the pollutant release. Plot the initial condition and describe the problem at hand. Present any equations using the equation editor. Then give the reader a feel for the layout of your report with regards to what they can expect as they read through.

Methodology:

Discuss the methodology used to arrive at your recommendations. Again, present any equations using the equation editor. Do not assume a reader will understand all terms presented.

Results :

Following on from the methodology, present the results of your simulations. You may wish to help the reader understand any graphs with a discussion in the text. For example :’Graph x demonstrates that at time T, pollutant levels breach the 100ppb limit’. Use at least one plot of how simulations have evolved with time over the 2D domain and how average concentration vary in the town with time.

Recommendations:

Consider how the results of your simulations might be used by a local authority to design appropriate mitigation strategies. Also consider how these simulations might be improved.

Bibliography

This is simple an example of a bilbiography

Lim, S. S.; Vos, T.; Flaxman, A. D.; Danaei, G.; Shibuya, K.; Adair-Rohani, H.; AlMazroa, M. A.; Amann, M.; Anderson, H. R.; Andrews, K. G.; Aryee, M.; et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet, 2012, 380, 2224-60.

Beelen, R.; Raaschou-Nielsen, O.; Stafoggia, M.; Andersen, Z.J.; Weinmayr, G.; Hoffmann, B.; Wolf, K.; Samoli, E.; Fischer, P.; Nieuwenhuijsen, M.; Vineis, P.; Xun, W.W.; Katsouyanni, K.; Dimakopoulou, K.; Oudin, A.; Forsberg, B.; Modig, L.; Havulinna, A.S.; Lanki, T.; Turunen, A.; Oftedal, B.; Nystad, W.; Nafstad, P.; De Faire, U.; Pedersen, N. L.; Östenson, C. G.; Fratiglioni, L.; Penell, J.; Korek, M.; Pershagen, G.; Eriksen, K. T.; Overvad, K.; Ellermann, T.; Eeftens, M.; Peeters, P. H.; Meliefste, K.; Wang, M.; Bueno-de-Mesquita, B.; Sugiri, D.; Krämer, U.; Heinrich, J.; de Hoogh, K.; Key, T.; Peters, A.; Hampel, R.; Concin, H.; Nagel, G.; Ineichen, A.; Schaffner, E.; Probst-Hensch, N.; Künzli, N.; Schindler, C.; Schikowski, T.; Adam, M.; Phuleria, H.; Vilier, A.; Clavel-Chapelon, F.; Declercq, C.; Grioni, S.; Krogh, V.; Tsai, M. Y.; Ricceri, F.; Sacerdote, C.; Galassi, C.; Migliore, E.; Ranzi, A.; Cesaroni, G.; Badaloni, C.; Forastiere, F.; Tamayo, I.; Amiano, P.; Dorronsoro, M.; Katsoulis, M.; Trichopoulou, A.; Brunekreef, B.; Hoek, G. Effects of long-term exposure to air pollution on natural-cause mortality: an analysis of 22 European cohorts within the multicentre ESCAPE project. Lancet, 2014, 383, 785−795.

Janssen, N. A.; Hoek, G.; Simic-Lawson, M.; Fischer, P.; van Bree, L.; ten Brink, H.; Keuken, M.; Atkinson, R. W.; Anderson, H. R.; Brunekreef, B.; Cassee, F. R. Black carbon as an additional indicator of the adverse health effects of airborne particles compared with PM10 and PM2.5. Environ. Health Perspect. 2011, 119, 1691−1699.

tin for this. The report must be no more than 4 pages long, not including any references you may want to use.Additional points to consider:- The reader might not be an expert and have much time to make a decision.- Can the regional authority be helped by referencing current pollutant exposure guidelines?- Your simulations might not be ideal and you might want to consider how you would improve it in the future. This includes increasing the accuracy of your simulation.