## 3 Results and Discussion
### Gas Concentrations
#### 3.2.3 No\({}_{\rm x}\)  
NO\({}_{\rm x}\) represents the total combination of NO and NO\({}_{2}\), which were both measured during this study. In this study, NO was found to be the predominant component of NO\({}_{\rm x}\) (Table 2), with average concentrations (33.4 \(\pm\) 3.2 \(\mu\)g m\({}^{-3}\)) four-and-a-half times greater than those of NO\({}_{2}\) (7.3 \(\pm\) 0.8 \(\mu\)g m\({}^{-3}\)). Unfortunately, the NO\({}_{\rm x}\) concentration data were contaminated after 4 July 2020, due to a build-up of condensation in the sampling tube, meaning that NO\({}_{\rm x}\) data for the final 12 days of the study were not used. Weekday (34 \(\pm\) 4.1 \(\mu\)g m\({}^{-3}\)) and night (32 \(\pm\) 5.4 \(\mu\)g m\({}^{-3}\)) concentrations of NO were similar, and weekend daytime concentrations were slightly lower (28 \(\pm\) 6.6 \(\mu\)g m\({}^{-3}\)). Average NO  
Figure 8: Correlation analysis of NH\({}_{3}\) and SO\({}_{2}\) concentrations; evidence of a strong positive association during emission events. Figure 7: Comparative analysis of SO\({}_{2}\), NH\({}_{3}\), and NO concentrations around a manure facility, showing patterns of emission peaks during agitation activities and weekend variability. concentrations were greatest on weekend nights (49.7 \(\pm\) 13.6 \(\upmu\)g m\({}^{-3}\)); however, these difference were not found to be statistically significant (\(p<\) 0.05). Similar to NH\({}_{3}\) and SO\({}_{2}\), NO concentrations recorded increases during manure agitation (Figure 7); however, NO concentrations at the weekends appeared to display an approximately inverse pattern to NH\({}_{3}\) and SO\({}_{2}\). That is, when NH\({}_{3}\) and SO\({}_{2}\) concentrations were elevated during the weekend daytime, NO concentrations were depleted, and this situation was reversed during weekend nights. NO is produced as a result of nitrification and denitrification processes during composting [17; 31]. Similar to the increased concentrations of NH\({}_{3}\) and SO\({}_{2}\) during agitation, NO concentrations may have been increased as a result of manure turning, by exposing more manure to the air, increasing the potential for diffusion [17]. The lower concentrations of NO at weekend daytimes may be explained through the inhibition of nitrobacteria activity by high temperatures [17; 19], with greater concentrations of NO overnight when temperatures were lower. [PERSON] [18] reported an inverse relationship between NH\({}_{3}\) emissions and NO emissions, with greater NH\({}_{3}\) emissions in well-aerated and higher-temperature conditions, while NO emissions increased during manure storage. Previous research has found that NO emissions substantially increase only later in the composting process (beyond 15-30 days), after the thermophilic phase, when mesophilic nitrifying bacteria are able to grow [33; 34]. Unlike NO, concentrations of NO\({}_{2}\) displayed a pattern more similar to NH\({}_{3}\), with elevated concentrations during weekdays and weekend daytimes, and lower concentrations at night (Table 2). Internal NO\({}_{2}\) concentrations were not correlated with ambient regional NO\({}_{2}\) concentrations (Table 3), suggesting that the main source of NO\({}_{2}\) in the facility was the composting manure. However, analysis showed that NO\({}_{2}\) concentrations had a strong negative correlation with relative humidity (r = -0.6, \(p<\) 0.001) (Figure 9, Table 3), and a moderate positive correlation with temperature (r = 0.476, \(p<\) 0.001), although the latter is likely to reflect only the relationship between temperature and humidity. It is possible that greater humidity could have contributed to the indirect relationship between NO\({}_{2}\) and NO concentrations by providing water for the reaction from NO\({}_{2}\) to nitric acid and NO\({}_{x}\) (Equation (2)), thus also explaining the negative correlation with humidity.