Ppb

The International Organization for Standardization (ISO)² does not accept the common use of parts per billion (ppb) for two reasons: the meaning of billion is ambiguous, and parts is also ambiguous because it could refer to volume, mass, number, or some other measure.

. Therefore, Great River Energy expects ozone and NO concentrations associated with the Project to be negligible, and well below all federal standards (nitrogen dioxide (NO2) – 100 parts per billion (ppb) as one-hour average, 53 ppb as annual average; ozone 70 ppb as 8-hour average).