# VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO\({}_{2}\) Photocatalysis
## 2 Results and Discussion
### UV Treatment of Odorous VOCs in Synthetic Mixture
#### 2.1.3 Effect of Relative Humidity and Air Temperature on UV Treatment  
The effects of relative humidity (RH, 0 to 90%; at fixed T = 25 \({}^{\circ}\)C) and air temperature (from 5 to 40 \({}^{\circ}\)C; at fixed RH = 30%) were tested. Results were reproducible, i.e., associated with low relative humidity (RH, 0 to 90%).  
Figure 4: Total odor reduction (expressed as odor detection thresholds (ODT)) as a function of measured UV energy dosage at 254 nm (obtained at different treatment time). The ODT of each air sample was assessed by at least 4 trained panelists using a forced-choice dynamic-dilution olfactometer at Iowa State University.  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \multirow{2}{*}{**Compound Name**} & \multirow{2}{*}{**UV\({}_{185+254}\)**} & \multicolumn{3}{c}{**UV\({}_{185+254}\)**} & \multicolumn{3}{c}{**UV\({}_{254}\)**} \\  & & \multicolumn{3}{c}{**No Catalyst**} & & \multicolumn{3}{c}{**No Catalyst**} \\ \cline{2-9}  & **ng J\({}^{-1}\)** & **nmole J\({}^{-1}\)** & **ng J\({}^{-1}\)** & **nmole J\({}^{-1}\)** & **ng J\({}^{-1}\)** & **nmole J\({}^{-1}\)** & **ng J\({}^{-1}\)** & **nmole J\({}^{-1}\)** \\ \hline Methyl mercaptan & 4.72 & 0.100 & 5.23 & 0.111 & 4.43 & 0.0943 & 1.20 & 0.0255 \\ Ethyl mercaptan & 14.6 & 0.236 & 15.6 & 0.252 & 13.6 & 0.219 & 4.04 & 0.0652 \\ Dimethyl sulfide & 4.94 & 0.0796 & 4.49 & 0.0724 & 4.32 & 0.0697 & 1.48 & 0.0239 \\ Butyl mercaptan & 8.68 & 0.0965 & 9.37 & 0.104 & 9.46 & 0.105 & 3.76 & 0.0418 \\ Acetic acid & 11.6 & 0.193 & \(-\)12.0 & \(-\)0.200 & 11.3 & 0.188 & \(-\)3.61 & \(-\)0.0601 \\ Propanoic acid & 8.65 & 0.117 & \(-\)0.326 & \(-\)0.00440 & 8.41 & 0.114 & \(-\)1.38 & \(-\)0.0186 \\ Butyric acid & 15.7 & 0.179 & 1.25 & 0.0142 & 16.2 & 0.184 & \(-\)0.299 & \(-\)0.00340 \\ Isovalicylic acid & 49.2 & 0.482 & 9.99 & 0.0979 & 49.9 & 0.489 & 12.0 & 0.1174 \\ \(p\)-Cresol & 78.8 & 0.730 & 98.0 & 0.907 & 111 & 1.03 & 94.0 & 0.870 \\ \hline \multicolumn{9}{c}{Experimental conditions: 25 mg TiO\({}_{2}\) for treatment with a catalyst; 300 mL min\({}^{-1}\) airflow (equivalent to treatment time of 1.9 min); T = 25 \({}^{\circ}\)C; dry air. Measured light intensity.} \\ \end{tabular}
\end{table}
Table 2: Summary of mass removal rates per unit of input UV energy (ng J\({}^{-1}\); nmole J\({}^{-1}\)).  
standard deviations (RSDs, Tables S7 and S8). The effect of RH is summarized in Figures S1-S4. The UV treatment effectiveness followed the same general pattern as reported in Figures 1 and 2, i.e., UV\({}_{185+254}\) + TiO\({}_{2}\)\(>\) UV\({}_{254}\) + TiO\({}_{2}\)\(>\) UV\({}_{185+254}\), no catalyst \(>\) UV\({}_{254}\), no catalyst. No apparent effects of RH on \(R\) were observed (Figures S1A-S4A). However, a significant decrease in VOC mass converted was observed with high RH (Figures S1A-S4A). This is consistent with [PERSON] et al. [45] reporting on the excess moisture that could lead to slowing down the reaction rate due to the competitive adsorption of water with reactants on the TiO\({}_{2}\) surface.  
No apparent effect of temperature on \(R\) was observed for \(p\)-cresol and most of the VFAs (Figures S5A-S8A). An apparent increase of both \(R\) and mass converted was observed for mercaptans with a temperature increase to 25 \({}^{\circ}\)C. Further temperature above 25 \({}^{\circ}\)C did not have any significant trend/effect on \(R\) or mass converted (Figures S5-S8).