Creating Source Groups
======================

After a Source Group has been added to a scenario, the **Source Group Context Menu** becomes available:

.. image:: ../_static/ContextMenu2.png
   :width: 190
   :align: center
   :alt: Source Group Context Menu

.. epigraph::

    **Clone**
        Creates a duplicate source group in the same scenario.

    **Rename**
        Changes the source group name. Must contain only letters and numbers.
        
    **Remove**
        Removes the source group from the scenario.

    **Properties**
        View and edit parameters for the source group.
        
    **Show Source Table**
        Opens a table where source properties can be viewed and edited.

Application
-----------

.. image:: ../_static/SourceGroup1.png
   :width: 624
   :align: center
   :alt: Source Group Application

A number of common application methods are included in the Application method 
menu. This is for reference only; choosing an application method does not 
populate any other dialogs. 

Application factor is set to 1 as a default value.

Calculation mode can be Prospective or Retrospective. Select **Retrospective** 
if you are modeling past applications with known emissions data, to disable
Monte Carlo parameters. If **Prospective** is selected, additional options
associated with Monte Carlo parameters are available.


Deposition
----------

.. image:: ../_static/SourceGroup2.png
   :width: 624
   :align: center
   :alt: Source Group Deposition

Modeling of dry and/or wet deposition must be enabled in the Dispersion Model 
dialog box under Scenario settings for gas deposition parameters to 
take effect. 

Physical parameters required for gas deposition modeling include diffusivity in 
air, Da [cm\ :sup:`2`/s], the diffusivity in water, Dw [cm\ :sup:`2`/s], the \
cuticular resistance to uptake by lipids for individual leaves, rcl [s/cm], and 
the Henry's Law constant, H [Pa m\ :sup:`3`/mol]. Enter values of the 
physical parameters corresponding to the modeled pollutant. 


Flux Profiles
-------------

.. image:: ../_static/SourceGroup3.png
   :width: 624
   :align: center
   :alt: Source Group Flux Profiles

Flux profiles previously defined at the Scenario level can be automatically
assigned to sources with a specific probability. All probabilities must sum to 1.

.. warning::
   If flux profiles are added/removed or probabilities are changed after adding
   sources, you must manually select the affected sources in the Source Table,
   right click, and select **Resample > Flux Profile**. All sources must be 
   assigned a flux profile for SOFEA to run.

Buffer Zones
------------

.. image:: ../_static/SourceGroup4.png
   :width: 624
   :align: center
   :alt: Source Group Buffer Zones
   
SOFEA can account for buffer zones by setting concentrations to zero at receptors
within the buffer zone of a field. The buffer zone distance and duration should 
match those applicable to the specific fumigant, the size of the fumigated
field, and the application rate. To use this option,
**Enable buffer zone processing** needs to be checked.

The **Buffer Zone** screen allows importing a prepared table of buffer zone
distances and durations based on the field size and application rate. 
A sample CSV file for methyl bromide is included in the *examples* directory of 
the application.  Alternatively, the same information can be manually entered by 
adding threshold pairs for area (ha) and application rate (kg/ha) to the table 
and then inserting buffer distance and duration for each pair of thresholds. 

When buffer zone processing is enabled, SOFEA adds a ``SO BUFRZONE`` keyword
to the AERMOD input file.  This keyword is associated with buffer zone support 
in AERMOD, which is an enhancement to the regulatory AERMOD version. For each 
source with the ``SO BUFRZONE`` keyword, any receptors located 
within the source and specified buffer zone distance from the source will not 
receive impacts associated with emissions from that field while buffer zone 
duration is in effect. The buffer zone keyword uses the following format:

.. code-block:: none

   SO BUFRZONE SrcID BZdist StartDT EndDT

``SrcID`` is the source ID; ``BZdist`` is the buffer zone distance; ``StartDT``
and ``EndDT`` are internally calculated start and end date and time based on
the application start time and a buffer zone duration.

Concentrations resulting from emissions from fields other than the one for 
which a buffer zone is in effect are calculated at the receptors within a 
buffer zone if these receptors are outside of the buffer zones of those other
fields. If the buffer zone distance is zero, impact from a fumigated field at 
receptors within that field are not calculated. 

Similar to the rings of receptors constructed around area sources, buffer 
zones are defined as quarter circles away from corners to achieve a 
constant distance away from the field. 

The buffer zone distance is based on the size of the field and the 
application rate. Based on these two parameters, SOFEA assigns buffer zones to 
sources by getting the value from the last row for which source area and 
application rate are less than the threshold values. 

.. note::
   To use a single buffer zone for all sources regardless of area and application
   rate, add one row with zero for the thresholds, and a second row with 
   large values (e.g. 999) for the thresholds.