1999 Alaska Air Toxics Emission Inventory Background
Beginning in spring 2000, the Alaska Department of Environmental Conservation (DEC) started compiling information to be used in an Air Toxics Emission Inventory. Information was gathered for area, point, and mobile sources for the three largest cities: Anchorage, Fairbanks, and Juneau. Resource constraints kept DEC from developing a statewide inventory.
To begin addressing air quality concerns in smaller communities, DEC identified pollutant-emitting activities and gathered their emission factors. This information could be used by villages to help develop inventories for their communities.
There are limitations to the inventory. The following lists the primary concerns with the inventory:
- Scope of Inventory - Juneau, Fairbanks, and Anchorage are the only communities in the inventory. Any future versions should address sources in Village Alaska.
- Uncertainty in Emission Estimate Calculations - Hazardous air pollutant emissions are estimated by relating an emission factor (pounds of pollutant released per gallon fuel burned) to activity data (gallons of fuel burned per year) for a specific source (e.g. power generator). EPA estimates emission factors by testing emissions from source types. The tests may occur with limited source models, within a narrow age range, and in climates milder than Alaska. There is a lot of uncertainty surrounding the applicability of emission factors to Alaska.
- Mass Does Not Equal Concentration - Inventoried emissions are reported in tons per year. The tons of pollutant emitted in the atmosphere do not necessarily relate to the concentration of pollutant a person inhales. Concentration is the mass of pollutant for a given volume of air, like milligrams per cubic meter. Chemical characteristics, sunlight, weather, and other forces affect pollutant concentration in air.
- Accuracy of Reported Mass Emissions - For some pollutants, mass per year emissions are reported to a thousandth of a ton, which is 2 pounds. The use of three decimal places allows us to acknowledge small quantities of pollutants rather than showing the emission rate as zero, but should not be considered accurate.