14. PGPLUME

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General introduction

The PGPLUME model is a far-field plume dispersion model for passive dispersion.
The high-momentum jet models AEROPLUME and HFPLUME are quite suitable to model near-field plume dispersion, but the entrainment relations used in these models will not accurately describe the (far-field) dispersion behaviour when the jet momentum no longer dominates the entrainment process. That is why AEROPLUME/HFPLUME will automatically make a transition to the PGPLUME passive dispersion model when this is necessary.
PGPLUME is a Gaussian plume model using well-known standard (Pasquill-Gifford) correlations to find the standard deviations.

PGPLUME will almost always be run after the near-field jet models (AEROPLUME and HFPLUME) have been used.

The downwind location where AEROPLUME/HFPLUME make a transition to PGPLUME is also indicated by the location of the 'matching' plane.

Range of applications and limitations

PGPLUME applies to passive dispersion: momentum and density excess with respect to the ambient atmosphere must be small. It assumes that the influence of chemical reactions (HF) has become negligible. It is not suitable for dense plumes: HEGADAS should be used for those cases.

Guidance for use

Normally the jet models AEROPLUME and HFPLUME decide to what far-field model a transition, if any, should be made. The user can use the link files prepared by AEROPLUME or HFPLUME to run PGPLUME.

If PGPLUME results have to be used later by the PROFILE program, then the averaging time AVTIMC in the DISP input block must be set to 18.75 s or less. In other words, PGPLUME must calculate 'instantaneous' results.

PGPLUME INPUT PARAMETERS

A description of all the input parameters that can occur in an PGPLUME input file will be given.

The PGPLUME input file has the DOS filename 'casename.PGI' where 'casename' is the user-supplied name of the problem.

In the following, actual keywords are given in capitals and in bold. The descriptions of less important parameters or parameters that need not normally be set by the user, are given in a smaller font.
All parameters, except TITLE, occur in blocks preceded by a specific block keyword. For PGPLUME these block keywords are: GEOMETRY, GASDATA, STATE, AMBIENT, DISP and TERMINAT.

The TITLE keyword does not occur in a parameter block.

TITLE The title of the current problem to be run with PGPLUME.
  At most 50 alphanumeric characters.
  Optional, no default.

The GEOMETRY block gives the plume geometry at the transition point.

DXPLUME Horizontal downwind distance of transition location (m).
  0 <= DXPLUME <= 104 (10 km).
  Mandatory.
  Actual source is assumed to be at 0 m downwind.
ZPLUME Plume centroid height at transition location (m)
  0 <= ZPLUME <= 500.
  Mandatory.
  ZPLUME can be less than DPLUME/2 for a touch-down or slumped plume.
DPLUME Plume effective diameter at transition location (m)
  0.1 <= DPLUME <= 500.
  Mandatory.
  Valid for airborne, touch-down or slumped plumes.
PHIPLUME Plume inclination (relative to horizontal) at transition location (°)
  -10 <= PHIPLUME <= 10.
  Mandatory.
  PHIPLUME should, by definition of a 'passive' plume, be small.

GASDATA block contains the gas composition and thermodynamic data. The released gas is assumed to consist of water and a (dry) pollutant.

CPGAS Specific heat at constant pressure of the dry gas (J/(mole K)).
  5 <=CPGAS<= 300.
  Mandatory.
MWGAS Molar mass of dry gas (kg/kmole).
  2 <= MWGAS<= 200.
  Mandatory.
WATGAS Mole fraction of water in released gas at release point (-).
  0 <= WATGAS <= 1
  Optional, default is 0.
GASFRAC Mole fraction of dry component in released gas at release point (-).
  0 <=GASFRAC<= 1
  Optional, default is 1.

The STATE input block contains parameters describing the plume dynamic and thermodynamic state at the transition point.

UREL Plume excess velocity at transition point (m/s).
  -2 <=UREL <= 2
  Mandatory.
  Excess velocity is difference between the ambient wind-speed and the plume speed, both at plume centroid height. Must necessarily be small for a passive plume.
RREL Plume excess density at transition point (kg/m3).
  -1 <= RREL <= 1
  Mandatory.
  Excess density is difference between the ambient density and the plume density, both at plume centroid height. Must necessarily be small for a passive plume.
CMASS Concentration of released plume gas at transition point (kg/m3).
  10-15<= CMASS <= 1
  Mandatory.
DURATION Release duration (s).
  -106 <= DURATION <= 106
  Optional, default is steady-state release (DURATION < 0).
  Negative for steady-state releases, positive for finite-duration, constant releases. Using a positive value invokes finite-duration correction in PGPLUME.

The AMBIENT block contains parameters describing the conditions of the ambient atmosphere at plume centroid height at the transition point.

DENSITY Ambient density at centroid height (kg/m3).
  0.5 < DENSITY <= 2.0.
  Mandatory.
UATM Ambient wind velocity at centroid height (m/s).
  1.0 < UATM <= 20.
  Mandatory.
AIRTEMP Ambient air temperature at centroid height (C).
  -50 <= AIRTEMP <= 50.
  Mandatory.
AIRPRESS Ambient air pressure (atm).
  0.7 <=AIRPRESS<= 1.1.
  Optional, default is 1.0 atm.
RHPERC Relative air humidity at centroid height (%).
  0.0 <= RHPERC <= 100.
  Mandatory.

The DISP block contains parameters describing the dispersion characteristics.

ZR Land surface roughness (m).
  10-5 <=ZR <= 1.
  Mandatory.
PQSTAB Pasquill/Gifford stability class.
  PQSTAB = A, B, C, D, E or F (character).
  Mandatory.
AVTIMC Concentration measurement averaging time (s).
  18.75 <= AVTIMC <= 3600.
  Mandatory.
  'Instantaneous' limit is 18.75 s.
  Note: If the PROFILE program will be using results of a PGPLUME run, then AVTIMC must be 18.75 s or less in the PGPLUME calculations. In other words, PROFILE expects PGPLUME to have calculated results for an 'instantaneous' plume.

The TERMINAT block sets PGPLUME calculation termination criteria.

XFIRST First output distance (m).
  0 <=XFIRST <= 104 (10 km).
  Mandatory.
  XFIRST must exceed the downwind position of the transition point.
STEP Arithmetic progression step-size (m).
  0 <= STEP <= 5 x 104 (50 km).
  Mandatory.
  Output is at distance XFIRST and then at (arithmetic) intervals of STEP , until NSTEP steps have been taken or until XLAST has been reached or if gas concentration drops below VFLAST.
NSTEP Maximum number of arithmetic steps to be taken (-).
  0 <= NSTEP <= 500.
  Mandatory.
  See description STEP. XLAST will never be exceeded
FACTOR Geometric progression scale factor (-).
  1 < FACTOR <= 100.
  Mandatory.
  Output is generated at distances (XFIRST+ ISTEP x STEP) x FACTOR, where ISTEP goes from 1 to NSTEP. After this the distances are multiplied per output step by FACTOR until XLAST has been reached. FACTOR must be greater than 1.0 to be effective.
XLAST Last output distance (m).
  0 <= XLAST <= 5 x 104(50 km).
  Mandatory.
  XLAST must exceed XFIRST.
VFLAST Last required mole fraction gas (ppm).
  10-5 <=VFLAST<= 5 x 104.
  Mandatory.
  PGPLUME will halt if concentration of gas falls below VFLAST.

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