Persistence Factor Sample Clauses

Persistence Factor. To derive an 8-hour CO concentration from the modeled 1-hour CO concentration, a persistence factor was applied to the modeled 1-hour concentration. The persistence factor accounts for variability in traffic and meteorological conditions between the 1-hour time frame and the 8-hour time frame. The persistence factor is the ratio between the maximum 1-hour CO concentration and the resulting maximum 8-hour concentration in the 8-hour time frame containing the maximum 1-hour concentration. For a local area, EPA recommends using the average of the highest 10 non-overlapping 8-hour CO concentrations from the previous three years as the persistence factor. Where representative monitoring data is not available EPA recommends the use of a persistence factor of 0.7. For this study, the EPA recommended persistence factor of 0.7 was used because the study was on the national scale. Examination of state air quality monitoring data may yield a persistence factor different than the national default value of 0.7. This could result in a different set of project conditions and types that would be covered under the PA. A state-specific persistence factor can be easily incorporated into a state PA since the results reported in section 4.7 Summary of Modeled Results are all in terms of the one-hour concentration. Thus, simply multiplying the one-hour concentration by the state-specific persistence factor would provide the 8-hour CO concentration.

Persistence Factor. In order to compare results to the 8-hour CO standard, the total CO concentration for a given scenario is obtained by multiplying the 1-hour modeled project contribution CO concentration by the persistence factor and then adding the 8-hour CO background concentration: 8 − ℎ = 1 − ℎ + 8 − ℎ The persistence factor accounts for variability in traffic (i.e., less traffic during off peak hours) and meteorological conditions (i.e., changes in wind speed, wind direction, and temperature) between the 1-hour time frame and the 8-hour time frame. The persistence factor is the ratio between the maximum 1-hour concentration and the resulting maximum 8-hour concentration in the 8-hour time frame containing the maximum 1-hour concentration. The persistence factor recommended by EPA for a local area is derived from the average of the highest 10 non-overlapping 8-hour CO concentrations over the previous three years. Where representative monitoring data are not available, EPA recommends the use of a persistence factor of 0.7, which was applied for this analysis17.