2.15. Elevated-source processing

2.15.1. Computing layer fractions for CMAQ
2.15.2. Creating an elevated-source file for UAM and CAMX

As introduced in Section 2.5.3, “Model-ready files” and further explained in Section 2.8.5, “Point-source processing”, there are two major approaches to processing elevated point sources for air quality modeling. The first approach is to have SMOKE compute the layer assignments for the point sources; this method is used for the CMAQ model. The second approach, which is used for the UAM models and CAMX, is to select specific sources as elevated and then create a special elevated-point-source file that contains the information needed so that the AQM can compute the plume rise. In both cases, users can select elevated sources specifically (in the second approach, that selection is mandatory). Also, PinG sources can be selected in both cases.

The two approaches have some steps that are the same and some that are different. The rest of this section is split into the following two subsections, one for each elevated-point-source processing approach:

  1. Computing layer fractions for CMAQ

  2. Creating an elevated-source file for UAM and CAMX

Each subsection first overviews the steps in the approach, then gives more details on some of them.

2.15.1. Computing layer fractions for CMAQ

The CMAQ model requires the layer fractions for elevated point sources to be computed by SMOKE. To do this, SMOKE performs the following steps:

  • Uses the Smkinven program to import the annual, average-day, day-specific, and/or hour-specific emissions.

  • Optionally uses the Temporal program to calculate hourly emissions if emissions will be used as a criterion for selecting elevated sources or PinG sources. For example, you may wish to select facilities with NOx emissions greater than 100 tons/day.

  • Uses the Elevpoint program to select elevated and/or PinG sources. This step is required if modeling with PinG sources, but optional otherwise.

  • Uses the Elevpoint program to create the STACK_GROUPS file, which is needed for processing PinG sources with CMAQ.

  • Uses the Laypoint program to compute elevated plume rise for all elevated sources, and store the layer fractions for each source. This step can optionally read the output file from Elevpoint to identify the elevated sources, but otherwise will compute plume rise for all sources.

  • Uses the Smkmerge program to combine the layer fractions with the hourly emissions to generate the model-ready output files and optionally generate the PinG hourly emissions file for CMAQ.

  • Optionally uses the Smkreport program to report on elevated or PinG sources Using Elevpoint

Elevpoint can select elevated and PinG sources using multiple criteria based on emissions values, emissions rank, stack parameters, plant numbers, and an analytical plume rise calculation. The elevated criteria and PinG criteria are provided to Elevpoint using a file called PELVCONFIG. You must configure this file to contain the criteria needed to select elevated and PinG source (if these selection are needed at all). If emissions values is one of the criteria, the Elevpoint program reads all of the hourly point-source files using the PTMPLIST file. This file is a list of all PTMP files that will be evaluated to determine which sources have maximum daily emissions that exceed the specified selection criteria or to determine the emissions rank. Only the maximum daily facility-total emissions can be used by Elevpoint to select sources based on emissions.

The elevated sources and PinG sources can each be selected using different criteria. In general, there are many more elevated sources than PinG sources for typical applications of SMOKE and AQMs. Elevpoint also permits you to group PinG sources and creates the STACK_GROUPS file so that the sources are treated as a single source in the PinG rise calculation by CMAQ. Grouping is useful to reduce the total number of PinG stacks processed by CMAQ (PinG processing is a computationally expensive calculation). Using grouping makes sense when several stacks at the same plant have the same, or nearly the same, stack parameters. When that is true, the emissions from the multiple stacks can be grouped and treated as a single PinG stack. Finally, there are two SMOKE settings (SMK_ELEV_METHOD and SMK_PING_METHOD) that instruct Elevpoint and other SMOKE programs to actually use these criteria to select the elevated and PinG sources. If these settings are not set to “1” the elevated and PinG selections will not be made, and so will not affect any further processing steps. Using Laypoint

In this CMAQ approach, Laypoint uses gridded, hourly meteorological data and stack parameters to calculate the plume rise for all point-source emissions. The program’s approach is based on the Briggs algorithm, as explained in detail in Section, “Plume rise calculation”, and provides the top and bottom heights of the plume. Laypoint uses these heights to compute the plumes’ distributions into the vertical layers that the plumes intersect, using the pressure difference across each layer over the pressure difference across the entire plume as a weighting factor to make this calculation. This approach gives plume fractions by layer and source. Only these fractions are stored in the output file (PLAY) from the Laypoint program (not the emissions in each layer).

If explicit plume rise sources (e.g., wildfires with precomputed hourly plume rise) are included in the inventory, Laypoint will skip the plume rise calculation for these sources. Instead, it will use the hourly data from the SMOKE PHOUR intermediate file, which describe the fraction of emissions in layer 1 and the top and bottom of the plume. Laypoint will combine these data with the pressure weights used for all elevated point sources to compute the fraction of emissions to go into each layer. Using Smkmerge

Smkmerge applies the layer fractions from Laypoint to the elevated sources to compute the emissions in each layer. This approach has the advantage of allowing you to avoid repeating the plume rise calculations for each control strategy or grid. If the SMK_PING_METHOD setting (discussed above) indicates that the special CMAQ PinG file should be created, the Smkmerge program will also output this special file, called the PINGTS_L file. It contains the hourly, speciated emissions for each PinG source (which could be a stack group, as explained above). Optional use of Smkreport

If desired, Smkreport can apply the layer fractions and elevated or PinG statuses to the inventory to generate reports that include layer information and/or the elevated or PinG status. This reporting could be used, for example, to create a list of all PinG sources in the inventory, or to determine the elevated versus layer-1 emissions by state or SCC.