## 4 Discussion
### Summary of the UV-A Photocatalysis
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Reference**} & \multirow{3}{*}{**Targeted Gas**} & \multirow{3}{*}{**UV Dose**} & \multicolumn{3}{c}{**Target Gas Emission**} & \multicolumn{1}{c}{**Cost 1**} \\  & & **(\(\mathbf{m}\)/cm\({}^{2}\))** & \multicolumn{1}{c}{**(\(\mathbf{E}\), mg/min,**} & \multicolumn{1}{c}{**(USD/kg for NH\({}_{\mathbf{x}}\),**} \\  & & **(\(\mathbf{m}\)/cm\({}^{2}\))** & **Odor, O\(\mathbf{U}\)\(\mathbf{e}\)/min)** & **USD/g for butan-1-ol, N\({}_{2}\)O,** \\ \cline{3-6}  & & & **Control** & **UV Treatment** & **O\({}_{3}\) USD/ton of O\(\mathbf{U}\)\(\mathbf{e}\) for (Odor)** \\ \hline \multirow{3}{*}{[13] (pilot-scale treating standard gases)} & \multirow{3}{*}{NH\({}_{3}\)} & 3.9 & 746 & 676 & 53.4 \\  & & NH\({}_{3}\) & 5.8 & 763 & 676 & 62.5 \\ \cline{2-6}  & & 2.5 & 31.5 & 25.3 & 442 \\ \cline{2-6}  & & 3.9 & 30.9 & 20.3 & 352 \\ \cline{2-6}  & & 5.8 & 32.9 & 19.4 & 403 \\ \hline \multirow{3}{*}{This study (pilot-scale treating emissions)} & NH\({}_{3}\) & 5.8 & 64.2 & 60.2 & 1260 \\  & N\({}_{2}\)O & 3.9 & 8.14 & 7.79 & 10.6 \\ \cline{1-1}  & N\({}_{2}\)O & 5.8 & 8.06 & 6.92 & 4.72 \\ \cline{1-1}  & O\({}_{3}\) & 1.3 & 0.01 & 0.00 & 18.9 \\ \cline{1-1}  & O\({}_{3}\) & 5.8 & 0.01 & 0.00 & 60.0 \\ \cline{1-1}  & & 3.9 & 9200 & 3910 & 0.71 \\ \cline{1-1}  & & 5.8 & 9200 & 3430 & 0.94 \\ \hline \hline \end{tabular} Note: 1 electric energy needed for UV treatment to mitigate a unit mass of pollutants in the air (USD/g).  
\end{table} 
Table 13: Techno-economic analysis of mitigating target gases with UV-A photocatalysis. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Reference**} & \multirow{3}{*}{**Targeted Gas**} & \multicolumn{3}{c}{**Target Gas Concentration**} \\  & & **UV Dose** & \multicolumn{3}{c}{**(\(\mathbf{p}\)pm, O\({}_{3}\) = ppb,**} \\  & & **(\(\mathbf{m}\)/cm\({}^{2}\))** & **Odor = O\(\mathbf{U}\)\(\mathbf{e}\)/m\({}^{2}\))** & **\% Reduction** \\ \cline{3-6}  & & & **Control** & **UV Treatment** & \\ \hline \multirow{3}{*}{[13]} & NH\({}_{3}\) & 3.9 & 67.4 \(\pm\) 0.36 & 61.1 \(\pm\) 0.30 & **9** \\  & & 5.8 & 68.9 \(\pm\) 0.68 & 61.1 \(\pm\) 0.70 & **11** \\ \cline{2-6}  & & 2.5 & 0.66 \(\pm\) 0.02 & 0.53 \(\pm\) 0.06 & **19** \\ standard gases) & Butan-1-ol & 3.9 & 0.65 \(\pm\) 0.03 & 0.43 \(\pm\) 0.04 & **34** \\  & & 5.8 & 0.69 \(\pm\) 0.02 & 0.41 \(\pm\) 0.07 & **41** \\ \hline \multirow{3}{*}{} & NH\({}_{3}\) & 5.8 & 5.98 \(\pm\) 0.28 & 5.62 \(\pm\) 0.34 & **6** \\  & N\({}_{2}\)O & 3.9 & 0.29 \(\pm\) 0.01 & 0.28 \(\pm\) 0.00 & **4** \\ \cline{1-1}  & N\({}_{2}\)O & 5.8 & 0.29 \(\pm\) 0.00 & 0.25 \(\pm\) 0.01 & **14** \\ \cline{1-1}  & O\({}_{3}\) & 1.3 & 0.34 \(\pm\) 0.03 & 0 & **100** \\ \cline{1-1}  & O\({}_{3}\) & 5.8 & 0.31 \(\pm\) 0.02 & 0 & **100** \\ \hline \multirow{3}{*}{This study (pilot-scale with same manure)} & \multirow{3}{*}{2.5} & N/A & N/A & **PA(51),** & **BA(45),** \\ \cline{1-1}  & & & & & **p-Cresol(41)** \\ \cline{1-1}  & & & & & **AA(49),** \\ \cline{1-1}  & & & & & **BA(53),** \\ \cline{1-1}  & & & & & **p-Cresol(67),** \\ \cline{1-1}  & & & & & **Indole(32)** \\ \cline{1-1}  & & & & & **AA(51),** \\ \cline{1-1}  & & & & & **BA(48),** \\ \cline{1-1}  & & & & & **Indole(20)** \\ \hline \multirow{3}{*}{Odor} & \multirow{3}{*}{2.5} & 352 \(\pm\) 7.98 & 239 \(\pm\) 24.4 & **32** \\ \cline{1-1}  & & 3.9 & 653 \(\pm\) 32.1 & 277 \(\pm\) 21.7 & **58** \\ \cline{1-1}  & & 5.8 & 653 \(\pm\) 9.25 & 243 \(\pm\) 64.4 & **63** \\ \hline \hline \end{tabular} Note: DMDS = dimethyl disulfide, acetic acid = AA, propanoic acid = PA, isobutyric acid = IA, and butanoic acid = BA, N/A = not available.  
\end{table} 
Table 12: Summary and comparison of the % reduction of targeted gases with UV-A photocatalysis. Bold signifies statistical significance. techno-economic assessment of UV-A cost. Farm-scale trials with the UV-A photocatalysis installed inside barns to mitigate indoor air quality and the pathogen load are warranted.