Ozone emission factors were developed for domestic electrostatic air cleaners and photocopying machines. The air cleaners had emission rates from 0-546 µg/min. These rates will ordinarily not produce air concentrations which are >60 µg/m3 (0.030 ppm) above background. The emission rate for photocopying machines varied from 48-158 µg/copy. In small, poorly ventilated rooms these emission rates were sufficient to produce incremental steady state ozone concentrations up to 396 µg/m3 (0.202 ppm). Recent copying machine maintenance was found to reduce ozone production to less than the detectable level, 4 µg/m3 (0.002 ppm).