Soda Ash Emission Factors

An emission factor is a value developed from available and reliable data that represents the quantity of a pollutant released into the atmosphere relevant to specific inputs and processes. An emission factor is derived from the weight of a pollutant divided by the unit rate, volume, distance, or duration of the emission. For soda ash, the emission factor relevant to carbon dioxide emissions is .097 metric tons of CO2 per metric ton of trona ore, which is the input to the rotary kiln calcination process producing soda ash. Emission factors are used to estimate source-specific emissions for area-wide inventories, such as greenhouse gas inventories, when actual data are unavailable. Emission factors are not used to set limits in permits or other regulatory standards.

General Information

• Emission factors are estimated averages from various source data of acceptable quality. They assume long-term averages for all facilities within a specific source category. The equation used to develop emission factors is Emissions = Activity Rate multiplied by the Emission Factor multiplied by (1 minus the value of Emission Reduction / 100). The value for emission reduction is derived from the ability of control devices to destroy a contaminant before it reaches the atmosphere or the removal efficiency of control equipment in conjunction with the capture efficiency of the control device, with the assumption that, once captured, the contaminant will be contained or destroyed. Emission factors are reflective of typical not advanced control equipment. In contrast, a mass balance equation is more effective at estimating emissions from processes when a lot of material is lost to the atmosphere.

Ratings

• Emission factors are rated A through E, depending on the reliability of the emission data used to develop the factor and the data quality evaluation. Basically, a higher rating represents the factor's ability to represent national contributions for each source activity. Rating A is regarded as excellent; there was enough data available and it was adequately validated. Rating B is regarded as above average, but the data lacks detail. Rating C is average because the data lacks background information. Rating D is below average because unacceptable methodologies were used, but the factor can be used to provide an order of magnitude values for the source. Rating E is poor because it does not contain a representative sample and there is a lot of variability among source processes.

Soda Ash Emission Factors

• In regards to greenhouse gas inventories, soda ash emission factors are based upon the calcination process whereby CO2 and water are generated when trona is calcined in rotary kilns to transform it chemically into crude soda ash, but the formula relies upon the amount of trona ore mined. As such, CO2 emissions are equal to the emission factor multiplied by the amount of trona ore mined, .0974 multiplied by 16.7 million metric tons of trona ore mined in the United States in 2006 as determined by the USGS, which equals 1,626 gigagrams of CO2 emissions from soda ash production. (Note: Trona ore mined decreased to 14.50 million metric tons in 2008.) Although no letter rating is available for the EPA's emission factor for greenhouse gas reporting, one report states that although reliable and accurate sources are available for process data, no data is available for soda ash end use processes that include the production of glass and the manufacturing of soap products.