6.6. Laypoint

6.6.1. Description
6.6.2. Processing Order
6.6.3. Files and Environment Variables

6.6.1. Description

Processing categories: point

The Laypoint program uses the SMOKE point-source inventory file with gridded and hourly meteorology data to compute hourly plume rise for all point sources. The plume rise is expressed in terms of layer fractions for each source.

Laypoint is run only for the MAQSIP and CMAQ styles of processing, in which all of the plume rise calculations are done prior to input to the AQM. In Laypoint, meteorological data are used to calculate the plume rise for all point sources. Then, the plume is distributed into the vertical layers that the plume intersects based on the pressure in each layer. Only these fractions are stored (not the emissions in each layer), until the SMOKE merge step (Smkmerge). Therefore, the plume rise calculations do not need to be repeated for each control strategy or grid. The Laypoint program calculates the plume rise for all days of each meteorological scenario. Plume rise calculation for fires

Regardless whether the heat flux for wildfires is precomputed or internally computed, the Pouliot-Godowitch plume rise algorithm ( http://www.epa.gov/ttn/chief/conference/ei14/session12/pouliot.pdf ) converts the heat flux (Q) to a bouyancy flux (F) for use in the plume rise calculation (Equation 1). Hourly heat flux (Q) can be estimated based upon daily area burned, fuel loading, material burned and a constant default heat content (8000 BTU/lb). See more detail information in Section 4.4.18, “Plume Rise Calculation for Fires”.

To account for a smoldering fraction of the fire emissions, fire plumes are distributed into both the model layers below the plume bottom and into the model layers between the plume top and bottom. The smoldering fraction of the total fire emissions is distributed into the model layer below the plume bottom. The remaining part of emissions are distributed into the model layers between the plume bottom and top.

Equation 2 estimates the plume bouyant efficiency (BE) which is the portion of heat release from a fire that produces bouyancy, using the fire size in acres. The smoldering fraction (Sfraction) of the fire plume is calculated from the BE (Equation 3). All the fire emissions are allocated to the model layers using a weighting based on the hourly sigma-pressure vertical coordinate. These equations are is used in Laypoint when the variable FIRE_PLUME_YN is set to Y. More information about processing fire emissions is in Section 4.4.18, “Plume Rise Calculation for Fires”.

Fire-specific plume rise equations are following:

  1. F = 0.00000258 x Q

  2. BEsize = 0.0703 x ln( acres ) + 0.3

  3. Sfraction = 1 - BEsize


  • F = Bouyancy flux (m4/s3)
  • Q = Heat flux for fires (BTU/hr)
  • BEsize = bouyanct efficiency
  • acres = fire size in acres
  • Sfraction = smoldering fration