or photocatalysis (i.e., mainly via surface reactivity based on catalyst activation by the UV light). With its relatively long wavelength, fewer pollutants directly absorb UV-A and thus it is generally less effective than using the same wavelengths with a photocatalyst designed to operate by UV-A absorption [1; 2]. Photocatalysis is commonly facilitated on surfaces coated with nanosized titanium dioxide (TiO\({}_{2}\)), which is considered reasonably durable and cost-efficient [3; 4; 5].  
Selected publications report developing and testing UV treatment of selected odorous gases on a lab-scale for both UV-A [1; 6; 7; 8; 9; 10; 11] and UV-C [12; 13; 14]. In the lab-scale experiments, the percent reduction varied depending on the coating's thickness, the coating material, temperature, relative humidity, dust accumulation and the UV wavelength. Statistically significant mitigation of NH\({}_{3}\), H\({}_{2}\)S, N\({}_{2}\)O, O\({}_{3}\) and VOCs was shown [1; 6; 7; 8; 9; 10; 11; 12; 13; 14]. Pilot-scale studies with UV-A photocatalysis showed effective mitigation of measured odor (-63%), \(p\)-cresol (-49%), skatole (-49%), indole (-66%), H\({}_{2}\)S (-40%), butan-1-ol (-41%), O\({}_{3}\) (-100%), N\({}_{2}\)O (-14%) and NH\({}_{3}\) (-11%) in the swine and poultry barn [2; 15; 16; 17; 18; 19].  
Only two studies (published in 2008 and 2012) have been conducted at a farm-scale [20; 21] for evaluating the mitigation of NH\({}_{3}\), CH\({}_{4}\), CO\({}_{2}\) and PM concentrations inside swine nurseries by utilizing UV-A. While these pioneering tests conducted in Italy showed auspicious results, it is still necessary to test whether UV-A photocatalysis is effective for other swine housing types and management systems farm conditions. We have been scaling up the UV-A technology to farm-scale trials to provide the necessary data on the performance (e.g., the percent reduction) and treatment economics.  
[PERSON] et al., (2021) designed, built and tested a UV mobile laboratory for treating up to 1.25 m\({}^{3}\cdot\)s\({}^{-1}\) of air with UV-A and TiO\({}_{2}\) photocatalyst [18]. Then, we tested UV-A photocatalysis to mitigate fast-moving gases emitted from swine manure using the mobile laboratory [19]. Significant percent reduction for measured odor (-63%), \(p\)-cresol (-41%), indole (-20%), butyric acid (-48%), propionic acid (-51%), butan-1-ol (-41%), N\({}_{2}\)O (-14%) and NH\({}_{3}\) (-11%) were reported.  
Thus, the next logical step was to test the UV mobile lab at a farm-scale. We used TiO\({}_{2}\)-based UV photocatalysis by connecting the mobile lab to one of the continuous fans that remove gaseous emissions from stored manure pit under slatted-floor swine barn. We aimed to evaluate the on-farm-scale efficacy of UV photocatalysis performance in mitigating odorous gaseous emissions using swine barn exhaust air. The effects of several variables were tested: (a) UV dose, (b) different wavelengths (UV-A and UV-C), (c) effect of suspended PM and (d) preliminary economic analyses.  
The results are needed to notify the design of farm trials and applications, where the interior barn walls are sprayed with the photocatalyst, and the foil indoor air will be passively treated as it moves through the barn.