# Isoprene Emissions, Oxidation Chemistry and Environmental Impacts
## 6 Measurements of Isoprene and Model Validation  
The short lifetime (typically from minutes to hours [105]) results in isoprene concentrations being localized to emission regions, thus increasing the spatial and temporal range of measurements, which is important for better understanding its sources, sinks, and atmospheric impacts on local, regional, and global scales. However, _in-situ_ measurements of isoprene are sparse and limited due to logistical difficulties. Early studies most commonly utilized a technique where isoprene was collected in cartridges, and these field samples were transported outside of Amazonia to be analyzed by gas chromatography techniques, e.g., Gas Chromatography-Flame Ionization Detection (GC-FID), Gas Chromatography-Mass Spectrometry (GC-MS) [106]. Whilst the development of new sampling approaches (e.g., use of drones) and more advanced analytical tools (proton-transfer-reaction mass spectrometry (PTR-MS), comparative reactivity method, photoionization detector (PID), semi-volatile thermal desorption aerosol gas chromatography) has meant that the emission of isoprene has been more easily measured on site in recent years. Table 2 shows a summary of isoprene's measurement techniques, measurement location, and measured as well as modeled mixing ratios for different campaigns. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Location** & **Time** & **Lat, Lon** & **Measurement Technique** & **Measured Isoprene** & **Modeled Isoprene** \\  & & & & **Mixing Ratio (ppb)** & **Mixing Ratio (ppb)** \\ \hline Canada, Egbert [107] & Jul & 44, \(-\)79 & GC-FID & 0.5 & 0.18 \\ \hline Canada, Kejzhnijk [107] & Jul & 45, \(-\)65 & GC-FID & 2.0 & 0.13 \\ \hline Canada, Frasserdale [108] & Jul-Aug & 50, \(-\)82 & GC-FID & 0.5–5 & 0.20 \\ \hline Alabama, USA [109] & Jun-Jul & 32, \(-\)88 & GC-FID & 3.8 & 1.61 \\ \hline Michigan, USA \(-\)801 m [110] & Aug & 45, \(-\)85 & GC-MS & 1.36 \({}^{*}\) & 0.18 \\ \hline Colorado, USA \(-\)280 m [111] & Jun-Aug & 39, \(-\)105 & GC-FID & 0.15 \(\pm\) 0.10 \({}^{*}\) & 0.06 \\ \hline North Carolina, USA \(-\)101 m [112] & Jun-Jul & 36, \(-\)82 & GC-MS/FID & 0.74 \(\pm\) 0.58 \({}^{*}\) & 0.38 \\ \hline Nevada, USA \(-\)1315 m [113] & Jun-Sep & 38, \(-\)120 & GC-FID & 0.397 \(\pm\) 0.558 \({}^{*}\) & 0.06 \\ \hline Amazon Basin, Brazil [114] & Jul & \(-\)2, \(-\)60 & GC-FID/FID & 2.2 (1.2-3.2) & 2.55 \\ \hline Amazon Basin, Brazil [115] & Annual & \(-\)2, \(-\)60 & GC-FID & 2.4 (1.0-5.2) & 2.13 \\ \hline Amazon Basin, Brazil [116] & Jul-Aug & \(-\)2, \(-\)60 & GC-FID & 2.0 (1.2-2.7) & 2.53 \\ \hline Central Amazonia, Brazil [117] & Dec-Jan & \(-\)2, \(-\)60 & PTR-MS & 1.66 \(\pm\) 0.9 & 2.00 \\ \hline Central Amazonia, Brazil [121] & Sep-Oct & \(-\)2, \(-\)60 & PTR-MS & 2.68 \(\pm\) 0.9 & 1.45 \\ \hline Babinna, Central Amazonia, Brazil [118] & Apr & \(-\)1, \(-\)59 & GC-MS & 6.55 \(\pm\) 1.26 & 2.29 \\ \hline Manus-Amazons, Brazil [64] & Sep & \(-\)2, \(-\)60 & PTR-MS & 7.8 \(\pm\) 3.7 & 1.64 \\ \hline Manus-Amazons, Brazil -1200 m [45] & Sep & \(-\)2, \(-\)60 & GC-MS & \(5.5\pm 2.6\) & 0.72 \\ \hline Manus-Amazons, Brazil [119] & Sep & \(-\)2, \(-\)60 & PTR-MS & \(5.2\pm 1.5\) & 1.64 \\ \hline Manus-Amazons, Brazil [119] & Feb-Mar & \(-\)2, \(-\)60 & PTR-MS & \(1.5\pm 0.78\) & 1.95 \\ \hline Manus-Amazons, Brazil [120] & Jul & \(-\)2, \(-\)60 & GC-FID & \(3.4\pm 1.8\) & 2.55 \\ \hline Central Amazonia, Brazil [121] & Sep-Nov & \(-\)2, \(-\)60 & PTR-MS & \(5.9\pm 1.3\) & 1.34 \\ \hline Central Amazonia, Brazil [121] & Dec-Feb & \(-\)2, \(-\)60 & PTR-MS & \(5.2\pm 1.5\) & 1.93 \\ \hline Central Amazonia, Brazil [121] & Mar-May & \(-\)2, \(-\)60 & PTR-MS & \(4.1\pm 0.7\) & 2.61 \\ \hline Central Amazonia, Brazil [121] & Jun-Jul & \(-\)2, \(-\)60 & PTR-MS & \(3.4\pm 0.2\) & 2.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured isoprene mixing ratios, measurement techniques, and the modeled isoprene mixing ratios at different locations.