Air quality at low outdoor temperatures in Norwegian horse stables

The aim of this study was to investigate the variation in air quality on days with low outdoor air temperatures in Norwegian horse stables. A total of 19 insulated, mechanically-ventilated stables with horses kept inside during the night were included in the study. In almost all of the stables (n=18) ventilation fans were operated during the night. In eleven of the stables the exhaust fans had a manual step by step regulation whereas in the remaining eight stables the exhaust fans were regulated by a temperature-setpoint thermostat. Fresh air inlets however, were highly variable in design and management leading to potential for ineffectiveness of ventilation functions. In four of the stables there were no specific air inlet systems, in five stables the exit door was used as the only air inlet. Mean outside air temperature was 0.0 ± 0.8 °C and mean indoor air temperature was 7.5 ± 0.5 °C. Mean level of CO₂ was 1800 ppm and only in one stable CO₂ exceeded 3000 ppm. Mean inside ammonia (NH₃) was 1.3 ppm and only in one stable the level of NH₃ exceeded 5 ppm. The total dust concentration was 0.69 ± 0.19 mg/m³ and in two stables the dust concentration exceeded 1.0 mg/m³. Half of the stables visited had a lower calculated air exchange rate than recommended. Still, the majority of the stables maintained acceptable air quality, with ammonia and dust levels within recommended levels.