## 3 Results and Discussion
### Plastic Bag Extraction  
The average \(\pm\) standard deviation of the blank plastic bag extracts (\(n=12\)) was \(55\pm 61\) pg g\({}^{-1}\), and all of the recovery yields determined hereafter were blank-corrected. The extraction tests exhibited no significant loss of the trapping solution (see subsection S2 in the Supplementary Materials) and no significant dependency of the recovery yields on the tested inversed aqua regia concentrations. However, it is worth noting that the preliminary tests showed that the use of 5% inversed aqua regia required 7 days to achieve 90% recovery yields. Moreover, there was the slight dependency of the recovery yields on the extraction time (Table 2): the recovery yields were 100% when the extraction time was 24 h, but slightly decreased and varied when the extraction time was shorter than 24 h. The stable mercury isotope measurements of the extracts showed that, overall, the differences from the reference values were in the range of -0.03% to 0.02% for \(\delta^{199}\)Hg, -0.04% to 0.11% for \(\delta^{200}\)Hg, -0.06% to 0.18% for \(\delta^{201}\)Hg, -0.07% to 0.23% for \(\delta^{202}\)Hg, and -0.12% to 0.33% for \(\delta^{204}\)Hg (Table 2). Ninety percent of the measured isotope ratios agreed with the reference values within 1\(\sigma\) confidence interval and 96% within 2\(\sigma\) confidence intervals. However, the precision of the samples with a 3 h extraction time was slightly poorer than that of the other extraction times. Overall, we conclude that the extraction time of 24 h with an inversed aqua regia concentration between 20% and 40% gave the best results and is recommended for plastic bag extraction. Comparison with the other extraction methods demonstrates that our method gave comparable results with those by the reported methods (Table 3). The advantages here are: the use of inversed aqua regia does not require a quenching reagent for oxidants, which is required when other strong oxidizing solutions, such as KMnO4 and BrCl, are used and slowly reduces Hg\({}^{2+}\), causing unintentional loss of Hg\({}^{2+}\) and: a number of sample extracts can be prepared in a day when TGM samples collected by the BAuTs were already preconcentrated.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Sampling** & **Flow Rate** & **Total Volume** & **Hg in Backup** & **Collection** \\  & **Duration (h)** & **(L min\({}^{-1}\))** & **(m\({}^{3}\))** & **BAuT (pg)** & **Efficiency\({}^{\ddagger}\) (\%)** \\ \hline Laboratory air & 6 & 100 & 36 & 7 & 99.99 \\ Clean room air & 24 & 100 & 144 & 115 & 99.86 \\ Reactor air & 1.3 & 20 & 1.5 & 74.8 & 99.93 \\ \hline \hline \end{tabular} \({}^{\dagger}\) Collection efficiency was determined based on the trapped TGM in the backup and primary BAuTs.  
\end{table}
Table 1: Results of the total gaseous mercury (TGM) breakthrough test.  
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**n**} & **Spiked Hg** & **Extraction** & **Recovery** & \(\delta^{199}\)Hg \(\delta^{1}\) & \(\delta^{200}\)Hg \(\delta^{1}\) & \(\delta^{201}\)Hg \(\delta^{1}\) & \(\delta^{202}\)Hg \(\delta^{1}\) & \(\delta^{204}\)Hg \(\delta^{1}\) \\  & & **(ng)** & **(h)** & **Yield (\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline Reference \(\delta^{1}\)Hg & & & N.A. \({}^{\ddagger}\) & N.A. \({}^{\ddagger}\) & N.A. \({}^{\ddagger}\) & \(-0.17\pm 0.01\) & \(-0.27\pm 0.01\) & \(-0.46\pm 0.02\) & \(-0.56\pm 0.03\) & \(-0.82\pm 0.07\) \\  & 40\% inversed & 6 & 103 \(\pm\) 2 & 24 & 102 \(\pm\) 5 & \(-0.19\pm 0.05\) & \(-0.30\pm 0.06\) & \(-0.51\pm 0.06\) & \(-0.62\pm 0.09\) & \(-0.91\pm 0.07\) \\  & aqua regia & & & & & & & & \\  & aqua regia & & & & & & & & \\  & 20\% inversed & 3 & 103 \(\pm\) 2 & 24 & 103 \(\pm\) 3 & \(-0.10\pm 0.02\) & \(-0.18\pm 0.03\) & \(-0.40\pm 0.03\) & \(-0.45\pm 0.06\) & \(-0.67\pm 0.06\) \\  & aqu