NUMPAR v emission rate

[dean.paini]

Hi all

I am trying to figure out how NUMPAR and emission rate interact. NUMPAR is the number of particles to be released per cycle, while emission rate is the "mass units released each hour".
1. How long is a cycle? Can this be adjusted by the user?
2. Is emission rate the number of units (particles) released each hour, or rather, the total mass of units (particles) released per hour?
3. I could imagine entering values into both these parameters that might contradict each other. Does one take precedence over the other, or is there some more complex set of rules describing the relationship between the two?

Thanks

Dean Paini

[ariel.stein]

The number of particles released per cycle NUMPAR (2500) would be the maximum number of particles or puffs released over the duration of the emission. NUMPAR has a different meaning for puff and particle simulations. In a full puff simulation (INITD = 1 or 2), only one puff per time step is released, regardless of the value of NUMPAR. In a particle or mixed particle-puff simulation (INITD = 0, 3, 4), NUMPAR represents the total number of particles that are released during one release cycle. Multiple release cycles cannot produce more than MAXPAR number of particles. For a mixed simulation (particle-puff), NUMPAR should be greater than one but does not need to be anything close to what is required for a full 3D particle simulation.

To simplify certain simulations when a constant particle number release rate is required, specifying a negative value for NUMPAR will over-ride the particle number release rate calculations (in terms of the number of sources, hours emission, and pollutants) and force the particle release rate to be |NUMPAR| particles per hour for each source and pollutant.

The maximum number of particles MAXPAR (10000) is the maximum number permitted to be carried at any time during a simulation. In all simulation types, particle or puffs are only emitted if the particle count is less than MAXPAR. Note that there are situations where NUMPAR can (and should) exceed MAXPAR because the actual particle release rate is computed by dividing NUMPAR by the number of sources, pollutants, and release hours.

The maximum particle duration KHMAX (9999) is the number of hours after release that a particle is dropped from the simulation. For simulations using regional meteorological grids, particles are dropped when the reach the grid boundary. However, when using global meteorological data, it may be computationally prudent to drop particles after they are no longer over the region of interest.

[dean.paini]

Thanks ariel.stein

My work is focusing on particle simulations not puff and much of what you said about NUMPAR makes sense, but what i don't understand is that emission rate, which is generated in the CONTROL file and is defined as number of particles per hour, appears to be similar to NUMPAR, which is generated in the setup.cfg file and is defined as you have described.

To illustrate. For a simulation in which emission is running for 4 hours from one location. If i set NUMPAR at 1,000 and emission rate at 1000, what would the actual number of particles emitted per hour be? Using NUMPAR would mean 250 particles per hour emitted, but using emission rate would mean 1,000 particles per hour emitted. Does one of these parameters take precedence? Or is there some other kind of interaction, such as 1,000 particles are released per hour (to match emission rate) until NUMPAR is achieved (in this case the emission would only last 1 hour instead of the 4 hours in this example)?

[alicec]

The emission rate determines how much mass is released while numpar determines how many computational particles are released.
For example suppose you define an emission rate of 1000 (kg/hour) and you release 1000 computational particles in an hour. Then each computational particle has a mass of 100(kg/hour) / 100(particles/hour) = 1 kg/particle.

You can use the MESSAGE file to check what you are getting. Here is an example in which the emission rate was set to 1(unit mass/hour). Numpar was set to 100 particles/hour. And below is part of a MESSAGE file.

The second to last column (in bold and underlined) shows the number of computational particles. Here, you see the initial time step is 15 minutes. Each 15 minute time step, 25 computational particles are emitted until after an hour, you have 100 computational particles in the simulation.
The last column (number after the bold number) shows the total mass being carried in the simulation.
The total amount of mass emitted after an hour is 1 (or close enough). So each computational particle has 1(unit mass)/100 (particles) = 0.01 unit mass/particle.

NOTICE advrng: (kg ,xyr,xy1) - 1 10 10 147 52
NOTICE main: Initial time step (min) 15
NOTICE emspnt: emissions started
NOTICE main: 1 59620335 25 0.25000003
NOTICE main: 1 59620350 50 0.49999979
NOTICE main: 1 59620365 75 0.74999958
NOTICE main: 1 59620380 100 0.99999934
NOTICE parout: 13 5 11 1 0 Num= 100

Hope this helps.
Alice

[dean.paini]

Thanks Alice

That makes a lot of sense. The scales have fallen from my eyes!

Dean