## 3 Results
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 S2. A surrogate abundance of indole is represented by (PAC), i.e., peak area counts for indole in the headspace above manure measured by SPME and analyzed by GC-MS. PACs are arbitrary units of M.S. detector response. (Figure 4), \(\sim\)\(-\)40-31% in p-cresol (Figure 5), \(\sim\)53-66% in 4-ethyl phenol (Figure 6) without statistical significance. However, bi-weekly 2 kg/m\({}^{2}\) reapplication treatment showed significantly (_p_ < 0.05) reduced phenol, p-cresol, and 4-ethyl phenol by 89%, 74%, and 87%, respectively (Table 1). Figure 4: Mitigation of phenol 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 S4. A surrogate abundance of indole is represented by (PAC), i.e., peak area counts for indole in the headspace above manure measured by SPME and analyzed by GC-MS. PACs are arbitrary units of M.S. detector response. Figure 3: Mitigation of indole 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 S3. A surrogate abundance of indole is represented by (PAC), i.e., peak area counts for indole in the headspace above manure measured by solid-phase microextraction (SPME) and analyzed by GC-MS. PACs are arbitrary units of an MS detector response. In the case of odor (Table 1, Figure S1), no significant mitigation impact was observed. The 2 kg/m\({}^{2}\) bi-weekly reapplication treatment reduced the odor concentration by 22%, whereas 2 kg/m\({}^{2}\) and 4 kg/m\({}^{2}\) showed 11% and 4.2% reductions, respectively (Table 1). All three treatments did not show statistical impacts on odor and GHGs (Figures S2-S4). Figure 5: Mitigation of \(p\)-cresol (4-methyl phenol) 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 S5. A surrogate abundance of indole is represented by (PAC), i.e., peak area counts for indole in the headspace above manure, sampled by SPME and analyzed by GC-MS. PACs are arbitrary units of M.S. detector response. Figure 6: Mitigation of 4-ethyl phenol 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 S6. A surrogate abundance of indole is represented by (PAC), i.e., peak area counts for indole in the headspace above manure measured by SPME and analyzed by GC-MS. PACs are arbitrary units of M.S. detector response. The treatments showed no significant impact of CO\({}_{2}\) (\(-\)1.4\(-\)1.7%) and N\({}_{2}\)O (\(-\)2.4-4.4%). Interestingly, the HAP biochar showed the generation of CH\({}_{4}\) emission with the range of \(-\)46 to \(-\)15%, without statistical significance. These findings are consistent with [PERSON] et al. [18] and [PERSON] et al.