Output File Format: Aerosol Particle Removal Information

When an aerosol particle is introduced into the simulation it is assigned a unique ID number. This ID number will persist over time, allowing tracking of a paticular particle's evolution. If the record_removals variable in the input spec file is yes, then the every time a particle is removed from the simulation its removal will be recorded in the removal information.

The removal information written at timestep n contains information about every particle ID that is present at time (n - 1) but not present at time n.

The removal information is always written in the output files, even if no particles were removed in the previous timestep. Unfortunately, NetCDF files cannot contain arrays of length 0. In the case of no particles being removed, the aero_removed dimension will be set to 1 and aero_removed_action(1) will be 0 (AERO_INFO_NONE).

When two particles coagulate, the ID number of the combined particle will be the ID particle of the largest constituent, if possible (weighting functions can make this impossible to achieve). A given particle ID may thus be lost due to coagulation (if the resulting combined particle has a different ID), or the ID may be preserved (as the ID of the combined particle). Only if the ID is lost will the particle be recorded in the removal information, and in this case aero_removed_action(i) will be 2 (AERO_INFO_COAG) and aero_removed_other_id(i) will be the ID number of the combined particle.

The aerosol removal information NetCDF dimensions are:

• aero_removed: number of aerosol particles removed from the simulation during the previous timestep (or 1, as described above)

The aerosol removal information NetCDF variables are:

• aero_removed (dim aero_removed): dummy dimension variable (no useful value)
• aero_removed_id (dim aero_removed): the ID number of each removed particle
• aero_removed_action (dim aero_removed): the reasons for removal for each particle, with values:
  • 0 (AERO_INFO_NONE): no information (invalid entry)
  • 1 (AERO_INFO_DILUTION): particle was removed due to dilution with outside air
  • 2 (AERO_INFO_COAG): particle was removed due to coagulation
  • 3 (AERO_INFO_HALVED): particle was removed due to halving of the aerosol population
  • 4 (AERO_INFO_WEIGHT): particle was removed due to adjustments in the particle's weighting function
• aero_removed_other_id (dim aero_removed): the ID number of the combined particle formed by coagulation, if the removal reason was coagulation (2, AERO_INFO_COAG). May be 0, if the new coagulated particle was not created due to weighting.