Processing categories: area, mobile, point

An emission inventory is built and reported for a variety of compounds or chemical classes such as CO, NO_x, VOC, PM₁₀, and SO₂. However, AQM photochemical mechanisms (e.g., CB4, RADM2) contain a simplified set of equations that use representative “model species” to represent atmospheric chemistry. Therefore, factors are needed to convert the emissions from the chemical classes in the emission inventory to the species in the intended photochemical mechanism. The Spcmat program produces matrices that contain the factors for performing this conversion.

The speciation factors are provided to Spcmat using "speciation profiles", which are applied to the inventory's sources using a "speciation cross-reference". For inventories that contain VOC mass, an additional factor is needed that converts the VOC mass to Total Organic Gases (TOG) mass, since the profiles used for VOC are actually computed based on TOG. The TOG profiles are used (instead of VOC profiles) since some of the TOG mass gets assigned to model species. Using VOC-only profiles would underestimate the volatile mass being emitted. Historically in SMOKE, the VOC-to-TOG conversion factors have been assigned by SCC or FIPS and SCC. Starting with SMOKE version 2.3, however, these factors can optionally be assigned by speciation profile ID codes. In fact, since the VOC-to-TOG factors come directly from the raw data used to create speciation profiles factors (such as the SPECIATE4.0 database), the most consistent way to assign these factors is actually by speciation profile ID. SMOKE version 2.3 is backward compatible with existing GSCNV file formats.

Spcmat outputs both mass-based and mole-based speciation factors for all sources. Previous systems have assumed that the average molecular weight of the model species was sufficient to represent the molecular weight of a species emitted by a specific source. In fact, the actual molecular weight of a model species is different for different types of emission processes. To represent the mass values more accurately, the mass and mole factors are input, applied, and output separately by Spcmat.

The speciation cross-reference file input to Spcmat specifies the speciation profile to be used for transforming the inventory pollutants to the model species for each source or type of source. Spcmat permits profiles to be assigned based on the country, state, and county code, the SCC, and other source characteristics. In the hierarchical system used to apply the profiles, the most specific assignments are applied first, followed by the next most specific, and so on. This system ensures that the most-specific matches override the less-specific ones.

For stationary area/nonpoint sources, the available combinations and their order are the following, starting with the most specific. “Left x of SCC” refers to an 8- or 10-digit SCC with all digits except the first x set to 0. “Left 2 of SIC code” refers to a 4-digit SIC code with the third and fourth digits set to 0.

For nonroad sources, the available combinations and their order are:

For mobile sources, the available combinations and their order are:

For point sources, the available combinations depend on the source definition. A header in the speciation cross-reference file format allows you to indicate the source definition. (The header is required for IDA inventories). For IDA-formatted inventories, a source is defined as the unique combination of country/state/county code, plant ID, point ID, stack ID, segment, and SCC. For point sources, the available combinations and their order are: