A commercial ozone generation system was evaluated in a tunnel ventilated, 1000 head, pig finishing building under full ventilation (80,000 c.f.m.). Ozone levels increased along the length of the house from 0.0 ppm at the entrance to 0.10 ppm in the middle of the building to 0.15 ppm at the exhaust. Dust, odour, and ammonia were characterized in both the treatment and an adjacent control building. These results indicated that the dust level decreased by 63% total mass in the ozonated building. Optical particle size analysis of data from the ozonated house found that particles between 0.3 and 0.5 micro m decreased 8% (P<0.025) from entrance to exhaust. Particle counts between particles of 0.5-0.7 micro m increased 18% (P<0.01) from the entrance of the building to the middle of the building and decreased 14% (P<0.025) from middle of the building to the exhaust. For particles larger than 0.7 micro m the particle counts increased from entrance to the middle of the building and remained constant from the middle of the building to the exhaust. In the control building all optical particle counts increased from entrance to the middle of the building and remained constant from the middle of the building to the exhaust. Ammonia levels were 58% (P<0.01) lower in the ozonated building compared to the control building, 1.3 ppm compared to 3.1 ppm. A trained odour panel found that air samples from the ozonated building were statistically more odorous, irritable, and unpleasant than air samples from the control building (P<0.05). This result contradicted the observations of all field personnel and is being further investigated.