## 3 Results  
The 8-weeks of performance of biochar on mitigation of gaseous emissions (evaluated as the percentage reduction) are summarized in Table 1 for the one-time application (Treatments 1 and 2, 2 and 4 kg/m\({}^{2}\)) and bi-weekly reapplication (Treatment 3, 2 kg/m\({}^{2}\)). The one-time biochar treatment could significantly reduce NH\({}_{3}\) (up to 33%) and skatole (up to 48%) emissions. There were no significant impacts of biochar on the mitigation of odor and GHGs. However, there was a clear advantage to biochar reapplication. The percentage reduction of NH\({}_{3}\) and skatole emissions improved to 53% and 80%, respectively. In addition, the emissions of all other targeted VOCs (indole, phenol, p-cresol, 4-ethyl phenol) were significantly reduced (78%, 89%, 74%, 87%). However, still, no statistically significant impacts were found on the mitigation of odor and GHGs. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Targeted Gases**} & \multicolumn{3}{c}{**\% Reduction (\(p\)-Value)**} \\ \cline{2-4}  & **2 kg/m\({}^{2}\)** & **4 kg/m\({}^{2}\)** & **2 kg/m\({}^{2}\)** \\  & **One-Time Application** & **One-Time Application** & **Bi-Weekly Reapplication** \\  & **(Treatment 1)** & **(Treatment 2)** & **(Treatment 3)** \\ \hline \multirow{2}{*}{NH\({}_{3}\)} & **33** & **25** & **53** \\  & **(0.008)** & **(0.0152)** & **(0.0001)** \\ \hline \multirow{2}{*}{Skatole} & **42** & **48** & **80** \\  & **(0.0442)** & **(0.0119)** & **(0.0001)** \\ \hline \multirow{2}{*}{Indole} & 38 & 36 & 78 \\  & (0.4715) & (0.5153) & **(0.0184)** \\ \hline \multirow{2}{*}{Phenol} & 28 & 49 & 89 \\  & (0.7054) & (0.1686) & **(0.0049)** \\ \hline \multirow{2}{*}{P-cresol} & 31 & \(-\)40 & 74 \\  & (0.8619) & (0.7653) & **(0.0282)** \\ \hline \multirow{2}{*}{4-Ethyl phenol} & 66 & 53 & 87 \\  & (0.4445) & (0.9664) & **(0.0074)** \\ \hline \multirow{2}{*}{Odor} & 11 & 4.2 & 22 \\  & (0.8806) & (0.9923) & (0.4733) \\ \hline \multirow{2}{*}{CO\({}_{2}\)} & \(-\)1.4\% & 1.7 & \(-\)0.3 \\  & (0.9916) & (0.9842) & (0.9999) \\ \hline \multirow{2}{*}{CH\({}_{4}\)} & \(-\)15 & \(-\)16 & \(-\)46 \\  & (0.9536) & (0.9435) & (0.3588) \\ \hline \multirow{2}{*}{N\({}_{2}\)O} & \(-\)2 & 2.3 & 4.4 \\  & (0.9963) & (0.9947) & (0.964) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mitigation of gaseous emissions with highly alkaline and porous (HAP) biochar treatments. Effects of the dose (biochar mass/manure surface area) and bi-weekly reapplication. Statistically significant percentage reduction (Control vs. Treatment) of emissions are in bold. Negative percentage reduction signifies gas generation. In case of NH\({}_{3}\) (Table 1, Figure 1), both one-time biochar treatments (2 kg/m\({}^{2}\) and 4 kg/m\({}^{2}\)) significantly (\(p<0.05\)) reduced emissions by 33% and 25%, respectively; the 2 kg/m\({}^{2}\) with reapplication treatment showed significant (\(p<0.05\)) reduction by 53%. In case of skatole (Table 1, Figure 2), both one-time biochar treatments (2 kg/m\({}^{2}\) and 4 kg/m\({}^{2}\)) significantly (\(p<0.05\)) reduced emissions by 25% and 48%; the 2 kg/m\({}^{2}\) with reapplication treatment showed significant (\(p<0.05\)) reduction by 80%. In case of other targeted odorous VOCs (Table 1), the one-time 2 kg/m\({}^{2}\) and 4 kg/m\({}^{2}\) biochar treatments showed \(\sim\)36-38% reduction in indole (Figure 3), \(\sim\)28-49% in phenol  
Figure 1: Mitigation of NH\({}_{3}\) emissions from swine manure treated with biochar—effects of one-time dose (2 and 4 kg/m\({}^{2}\)) and 2 kg/m\({}^{2}\) bi-weekly reapplication. Vertical arrows represent the application or reapplication of biochar and manure to storage simulators. Each data point represents the mean of (\(n=3\)) measurements. Detailed statistical analysis is provided in Table S1. Figure 2: Mitigation of skatole emissions from swine manure treated with biochar—effects of one-time dose (2 and 4 kg/m\({}^{2}\)) and 2 kg/m\({}^{2}\) bi-weekly reapplication.