The Model 205 Dual Beam Ozone Monitor™ was designed for even higher precision and faster response time than our popular Model 202. Data may be output as frequently as every 2 s, making it ideal for vertical profiling using balloons or aircraft measurements where high temporal resolution is required. For a given averaging time, the Model 205 has a higher precision (better than 1 ppb for 10 s averaging) and a more stable baseline than the Model 202. The Model 205 has all of the features of the Model 202 single beam instrument, including a real time clock; averaging times of 10 s, 1 min, 5 min and 1 h; an internal data logger; serial and analog data outputs; and a backup air pump to protect against data loss in the field. The Model 205 Ozone Monitor has been designated as a Federal Equivalent Method (FEM) by the EPA.