An evaporative cooling pad system was installed upwind of exhaust fans and downwind of pigs in a tunnel ventilated finishing building to determine effectiveness in reducing dust, ammonia, and odours. The system reduced dust and odour levels in exhaust airflow but air cleaning efficiencies were reduced as airflow rate increased, as expected. The system reduced total dust levels by as much as 65% at a relatively low ventilation rates, but less than 20% at high airflow rates typical of maximum, hot weather ventilation. Indoor ammonia was 5 ppm or less and was reduced across the washing wall at the lowest ventilation rate but not at the higher ventilation rates. Odour levels appear to be strongly linked to dust levels, i.e. reductions in odour intensity, irritation intensity, and odour concentration occurred with dust reductions. Phenol and mercaptan concentrations were measured using HPLC from dust samples collected in the building and were similar to levels reported by other researchers.