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### The difference between two type of spacing in concentration modeling

Posted: **February 24th, 2018, 8:18 am**

by **Mahdiye Mirzai**

Hi

I have two plot with same source and pollutant, one of them has 0.1 0.1 spacing and another one has 0.5 0.5, could some one explain me why the Results are different and The difference between The sum releases is at least 10 times?

### Re: The difference between two type of spacing in concentration modeling

Posted: **February 27th, 2018, 9:59 am**

by **glenn.rolph**

Because the calculation of concentration is mass/volume and since your grid cell is larger in the first one, hence a larger volume, and therefore the concentration will be less assuming the mass is approximately the same in the grid box. Similarly for deposition, the calculation is mass/area and since your area is larger for the first one, the mass per area is less assuming a similar mass being deposited in the area. You need to scale the grid size to the area of interest as well as the resolution of the meteorological data (it doesn't make sense to have a very fine concentration grid when the meteorology grid resolution is very large). But, you should also not make it so small that only a few particles are available within the grid cell to represent the distribution of real particles (you can always increase the number of particles in the simulation at the expense of slowing the run time of the model.)

### Re: The difference between two type of spacing in concentration modeling

Posted: **February 27th, 2018, 12:06 pm**

by **Mahdiye Mirzai**

I appreciate for your attention and response