## Appendix A  
The following tables summarize the studies that evaluated FTIR comparing them with reference values. The following terminology applies:  
* Year: Year of the study (published). The studies are given in chronological order; separately for laboratory and portable systems. * Instrument: Manufacturer and model of the FTIR (as given in the study). In italics in case the FTIR was portable (and the letter \"P\" is added). * Difference: Difference of FTIR from the reference value. If many points were available, the mean and the range (in brackets) is given. * Slope: Linear regression analysis slope. * \(R^{2}\): Coefficient of determination of linear regression. * Range: Concentration or emissions range (from plots or tables of the studies). * Points: Number of points that the mean or the slope and R2 were calculated. * Comment: Particularities of the tests and additional information: CNG = compressed natural gas; D = diesel; E = ethanol; FFV = flex-fuel vehicle; G = gasoline; M = methanol; x = number of cars; y = years. * Ref: Citation of study. For each study, the following subdivisions were made whenever data were available:
* FTIR measuring cylinder (calibration gas). * FTIR and reference, both sampling from the dilution tunnel. * FTIR and reference, both sampling from the tailpipe. * FTIR sampling from the tailpipe, reference from the dilution tunnel. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Year** & **Instrument 1** & **Difference** & **Slope** & **R2** & **Range** & **Points** & **Comment** & **Ref.** \\ \hline  & & & & FTIR measuring cylinder & & & & \\
2010 & MSS MultiGas 2020 & \(-\)10.5\% & - & - & 12\% & 1 & mix with CO, NO, C\({}_{3}\)H\({}_{6}\) & [99] \\
2010 & AVL Season & & 1.01 & - & 1-14\% & 10 & [99] \\
2019 & AVL Season & \(<\)1\% & - & - & 1500 and 15,000 rpm & 2 & [99] \\
2005 & P- Tured Gamnet Ck2000 & \(-\)4\% & - & - & 145\% & 1 & [110] \\
2005 & P- Tured Gamnet Ck2000 & \(-\)5\% & - & - & 10.0\% & 1 & mix with CO & [110] \\
2015 & P- Spectrum 2, ProfileTime & 0.4\% (-\%,-4\%) & 1.02 & 1.00 & 0.2\% & 17 & [181] \\  & & & & & & & \\
1990 & Nicolet Season & \(-\)0.6\% & - & - & 300-70\% /mi & means & G, D,2 & [164] \\
1990 & Mutsen Isorth & 0.92 & 0.99 & 0.4\%-2\% & 25 & G, Grab N9S & [112] \\
1993 & Matton RA & 13.7\% (-\)0.8\% & 27\% & 1.05 & 0.98 & 0.2\%-1\% & 280 & 25.9 [G, CNO] & [207] \\
1993 & Nicolet RECA & 3.0\% (-\)13\%,18\% & 0.93 & 0.97 & 0.2\%-1\% & 268 & 25.7 [G, CNO] & [207] \\
1994 & Nicolet RECA & -2.8\% (-\%,-5\%) & 0.96 & 0.89 & 0.4\%-6\% & 12 & [99] \\
1994 & Nicolet RECA & 7.000 & 2.1\% & - & 0.4\% & 1 & G, Hud MSS & [171] \\ \hline  & & & & & & & \\
1990 & Nicolet Season & \(-\)1.3\% & - & - & 300-270\% /mi & means & G, D,2 & [164] \\
2010 & AVL Season & -5\% & - & - & 600-26\% /mi & 28 & G, Hello & [123] \\
2011 & AVL Season & -2.2\% & - & - & 14.2\% & 9 & G, D, CNG, moved, motion, & [135] \\
2015 & P- Tured Gamnet Ck2000 & 3.1\% & - & - & 12.8\% & engine & [110] \\
2005 & P- Tured Gamnet Ck2000 & \(-\)12\% & - & - & 400 \% /mi & 1 & G & [110] \\
2006 & P- Tured Gamnet Ck2000 & -12\% & 1.02 & 0.96 & 8.1\% & cycle & G & [164] \\
2020 & P- Walker Matrix MC3 2  & - & 0.99 & 0.99 & -43\% & cycle & D & [102] \\
1995 & Prototype & & & & & & & \\
1998 & WV Season & 1.01 & 0.36 & 300-30\% /mi & 80 & G & [164] \\
2013 & MEX-400F1 & 10\% (+\)1\% & - & - & 200 \% /mi & 6 & Gaz (B0-10), M15-30 & [179] \\
2017 & Gamnet Ck2000 & 1.06 & 0.97 & 140-20\% /mi & 20 & D,G, GZ, CNG & [197] \\
2018 & AVL Season & \(+\)4\% & - & - & 110-190\% /mi & 11 & [101] \\
2020 & AVL Season & 1.01 & 0.90 & 200-40\%/mi & 9 & D & [99] \\
2021 & AVL Season & 0.2\% (+0.8\%) & - & - & 140-40\% /mi & 37 & G & [199] \\
2020 & P- Tured Gamnet Ck2000 & \(-\)21\% (+0.8\%) & - & - & 180-20\% /mi & 11 & G & [140] \\
20218 & P- Tured Gamnet Ck2000 & \(-\)21\% (+0.8\%) & 0.96 & 0.70 & 85-300\% /mi & 18 & D, CNG & [99] \\ \hline  & & & & & & & & \\ \end{tabular}
\end{table} 
Table 1: Comparisons of FTIR with CO\({}_{2}\) analyzes (all NDIR).