A barn’s climate is vital for animal welfare and emissions control, including greenhouse gases like methane (CH₄) and carbon dioxide (CO${}_2$) and environmental gases like ammonia (NH${}_3$). The goal of this study was to investigate a developed low-cost online tool for monitoring barn climate and air pollutant emissions (OTICE) in naturally ventilated barns. OTICE employed a wireless sensor network with low-cost sensors for gases and climate variables, allowing scalable use across multiple barns. We evaluated the sensors for CO${}_2$, NH${}_3$, and CH₄ for accuracy, both in controlled lab conditions and in a dairy barn in Germany, where measurements were carried out continuously for a duration of 12 days. For the averaged concentration levels over the measurement period, the low-cost sensors agreed well with the reference system, with relative deviations lower than 7% for all three gases, with maximum peak deviations up to 32% for CO${}_2$, 67% for NH${}_3$, and 65% for CH${}_4$, with strong Spearman correlations for CO${}_2$ and NH${}_3$ (${\rho }_{{CO}_2}$ = 0.8, ${\rho }_{{NH}_3}$ = 0.68) and a rather weak correlation for CH₄ with ${\rho }_{{CH}_4}$ = 0.24. Further calibration and stability investigations are required, especially for CH₄ sensing. However, the overall good results for NH${}_3$ and especially CO${}_2$ measurements indicate a huge potential of the low-cost system as a valuable tool for monitoring relative NH${}_3$ emission levels and the measurement of air exchange rates in naturally ventilated barns.

Dairy housing is an important source of ammonia (NH₃) and methane (CH₄) emissions, yet site-specific emission data remain limited for Ireland. At the same time, established measurement systems are costly and difficult to deploy for long-term monitoring across commercial farms. This study quantified gaseous emissions from a naturally ventilated Irish dairy barn and evaluated the performance of a low-cost wireless sensor system (OTICE) against a photoacoustic gas analyser (PGA) during 90 days of winter housing. Concentrations of carbon dioxide (CO₂), NH₃, and CH₄ were measured at three indoor and two outdoor locations. Ventilation rates and gaseous emissions were estimated using the CO₂ mass balance method. Mean emission values derived from the reference system were 16.8 g NH₃ d⁻¹ LU⁻¹ and 227 g CH₄ d⁻¹ LU⁻¹, providing an extended dataset for naturally ventilated dairy housing under Irish winter conditions. OTICE CO₂ measurements showed strong associations with the reference measurements (r = 0.91 indoors and 0.79 outdoors), and the resulting mean ventilation rate differed by approximately 9% from the PGA-based estimate. In contrast, OTICE showed insufficient performance for absolute NH₃ and CH₄ quantification, resulting in substantial underestimation of emission values. The findings demonstrate the potential of low-cost distributed CO₂ sensing for long-term monitoring of ventilation dynamics in naturally ventilated dairy barns, while highlighting the need for field validation before low-cost gas sensors are used for absolute emission quantification.