In natural ventilation system-enabled dairy buildings (NVDB), achieving accurate gas emission values is highly complicated. The external weather affects measurements of the gas concentration of pollutants ($c_P$) and volume flow rate (Q) due to the open-sided design. Previous research shows that increasing the number of sensors at the side opening is not cost-effective. However, accurate measurements can be achieved with fewer sensors if an optimal sampling position is identified. Therefore, this study attempted to calibrate the outlet of an NVDB for the direct emission measurement method. Our objective was to investigate the $c_P$ gradients, in particular, for ammonia ($c_{N{H}_3}$), carbon dioxide ($c_{C{O}_2}$), and methane ($c_{C{H}_4}$) considering the wind speed (v) and their mixing ratios ([$\overline{{\mathrm{c}}_{{\mathrm{CH}}_4}/{\mathrm{c}}_{{\mathrm{NH}}_3}}$]) at the outlet, and assess the effect of sampling height (H). The deviations in each $c_P$ at six vertical sampling points were recorded using a Fourier-transform infrared (FTIR) spectrometer. Additionally, wind direction and speed were recorded at the gable height (10 m) by an ultrasonic anemometer. The results indicated that, at varied heights, the average $c_{N{H}_3}$ (p < 0.001), $c_{C{O}_2}$ (p < 0.001), and (p < 0.001) were significantly different and mostly concentrated at the top (H = 2.7). Wind flow speed information revealed drastic deviations in $c_P$, for example up to $+105.1\%$ higher $c_{N{H}_3}$ at the top (H = 2.7) compared to the baseline (H = 0.6), especially during low wind speed (v < 3 m s${}^{-1}$) events. Furthermore, [$\overline{{\mathrm{c}}_{{\mathrm{CH}}_4}/{\mathrm{c}}_{{\mathrm{NH}}_3}}$] exhibited significant variation with height, demonstrating instability below 1.5 m, which aligns with the average height of a cow. In conclusion, the average $c_{C{O}_2}$, $c_{C{H}_4}$, and $c_{N{H}_3}$ measured at the barn’s outlet are spatially dispersed vertically which indicates a possibility of systematic error due to the sensor positioning effect. The outcomes of this study will be advantageous to locate a representative gas sampling position when measurements are limited to one constant height, for example using open-path lasers or low-cost devices.

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.