Sections 17.1 and 17.2 summarize the issues for preparing emission inventories. Section

17.3 describes the needs for ancillary data. Section 17.4 summarizes the emissions modeling

steps. Section 17.5 and Section 17.6 summarizes the issues associated with modeling of future

year emissions data. Finally, Section 17.7 provides guidance on emissions to be used for local

area primary PM2.5 modeling.

17.1 What Emission Inventory Data are Needed to Support Air Quality Models?

Air quality models require hourly emissions for each grid cell and model layer in the

modeling domain. Depending on the application, models may be run for episodic periods or for

36 2002 is the recommended inventory year for the baseline modeling (the starting point

for future year projections). Other years may be modeled for the base case modeling (for

performance evaluation) if episodes are chosen from years other than 2002. If all of the episodes

are from 2002, then the base case and baseline inventories will be for the same year. See Section

14.1 for more details on selecting modeling time periods.

up to a full year or multiple years. The emissions need to be allocated to the chemical species

required for the chemical mechanism and version of the model being used. The speciated

emissions of VOC and PM2.5 depend on the air quality model and chemical mechanism being

used. For primary PM2.5 emissions, the models typically divide the PM into (at a minimum)

organic carbon, elemental carbon, primary sulfate, primary nitrate, and “all other” PM2.5

emissions. Calculating the speciated emissions is part of the emission modeling step, described

in Section 17.4 based on data described in Section 17.3.

Emission inventory data from five general categories are needed to support air quality

modeling: stationary point-source emissions, stationary area-source emissions (also called nonpoint),

mobile emissions for on-road sources, mobile emissions for nonroad sources (including

aircraft, railroad, and marine vessels), and biogenic/geogenic emissions. The emission inventory

development and emissions modeling steps can be different for each of these categories.


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