Once the Met4moves meteorology preprocessor and the MOVES model processing that results in the SMOKE-formatted emissions factor lookup tables are completed, we address the remaining major component of the SMOKE-MOVES tool: the SMOKE model processing step. The goals of this step are (1) to estimate emissions from on-road mobile sources based on MOVES-based emissions lookup tables and meteorology data, (2) to create hourly gridded speciated air quality model-ready input files, and (3) to produce various types of reports for the user.
As some readers are aware, MOBILE6 and MOVES are both vehicle emissions modeling systems used with SMOKE. However, they differ in their approaches to calculating off-network evaporative emissions. In MOBILE6, off-network emissions processes are calculated as emission factors in grams/mile, which is related to VMT. MOVES, on the other hand, uses the source (vehicle) type population (VPOP) to calculate start and off-network evaporative emissions, which are assigned to off-network emissions processes; these processes are hour-dependent due to VPOP (activity) assumptions built into the MOVES model. Thus, compared to the SMOKE-MOBILE6 approach, the SMOKE-MOVES approach requires additional vehicle population inventory data as input for estimating mobile-source emissions from off-network emissions processes. This requirement is reflected in the discussion below.
When processing mobile-source emissions from MOVES, SMOKE performs the following basic steps.
The way the MOVES-generated emissions factor lookup tables are used varies according to whether SMOKE is modeling on-roadway emission processes or off-network emissions processes.
On-roadway emission processes: When estimates of on-roadway emission processes (e.g., exhaust running, on-road evaporative, tire and brake wear) are needed, SMOKE requires county-total VMT and average hourly speed (SPEED) inventory data as inputs to a new SMOKE postprocessor called Movesmrg which is part of the SMOKE-MOVES tool. Movesmrg uses the MOVES RatePerDistance (RPD) table (SMOKE format) to estimate on-road sources emission. The key lookup fields for the factors are gridded hourly temperature and average hourly speed from the avgSpeedBinID field. SMOKE interpolates in the RPD table (in unit of grams/mile) based on gridded hourly temperature and average speed. Figure 2a shows processing steps for on-roadway emissions processes in the SMOKE system using VMT and SPEED inventory input data.
Off-network emission processes: When estimates are needed for off-network emissions processes, including the off-network vapor venting emissions process, SMOKE uses county-total VPOP by vehicle type as input to Movesmrg together with the RatePerVehicle (RPV) and RatePerProfile (RPP) lookup tables Figure 2.14, “MOVES mobile RatePerVehicle and RatPerProfile (off-network) processing steps”. A significant difference in the processing steps between the on-roadway emissions processes (RPD table) and the off-network emissions processes (RPV and RPP tables) is that off-network emissions processing does not require the Temporal program step because vehicle population (VPOP) does not need to be temporally allocated. In the RPV table, gridded hourly temperature and hour of the day are the key lookup fields SMOKE uses to estimate hourly off-network emissions in unit of grams/vehicle/hour. For the evaporative fuel off-network vapor venting emissions process only, Movesmrg uses the RPP lookup table to estimate the emission rates based on the minimum and maximum temperatures computed by Met4moves.
For all three emission rate lookup tables (RPD, RPV, RPP), SMOKE performs linear interpolation when using them.