Emissions inventories are tools to assess the quantities of pollutants released into the air from various sources.  One set of pollutants that the Environmental Protection Agency (EPA) regulates comprises criteria pollutants and precursors to ozone formation; these pollutants are regulated based on their health and/or environmental effects, and include:

Inventories summarize emissions from point, area, biogenic, and mobile sources within Clark County.

A second set of pollutants regulated by DAQ are hazardous air pollutants (HAPs).  HAPs are chemicals or chemical classes widely considered to be toxic and to cause adverse health effects. Currently, 187 chemicals are outlined on the HAP list.

Point sources are stationary, commercial, or industrial sources, and are typically included in the State Implementation Plan (SIP). These comprise major sources that emit more than 100 tons per year of any criteria pollutant, 15 tons per year of any HAP, or 25 tons per year of combined HAPs. The inventory information is used to track SIP progress, calculate operating permit program emission fees, fulfill annual reporting requirements to EPA, and supply information to the general public. 

Area sources are stationary sources that are too small or too numerous to be treated as individual point sources. The area source inventory is determined from local demographic information, state energy and agricultural statistical data, and specific information surveys. 

Biogenic sources comprise the natural (non-anthropogenic) component of VOC and NOx emissions, such as forests, vegetation and soils.

The mobile source inventory includes both on-road and nonroad sources. Highway vehicles such as cars, light duty trucks, heavy-duty trucks, and motorcycles using gasoline and diesel fuels are referred to as on-road mobile sources. Nonroad mobile sources include a wide variety of internal combustion engines not associated with highway vehicles, such as locomotives, airplanes, and small residential, recreational, and commercial engines. The emissions are calculated from vehicle miles traveled (VMT), emission factors for highway vehicle classes obtained from EPA's MOVES model, and other EPA-derived factors.

DAQ submits annual emission inventories for Clark County to EPA. In addition, several research projects have been completed to more accurately reflect the emissions in Clark County.  The completed projects are listed below:

DAQ performs a wide variety of computer modeling, including demonstration of NAAQS and Increment compliance of stationary sources, air quality management of hydrographic basins, and SIP modeling for attainment and maintenance demonstrations.