## 3 Results
### Hydrocarbons (HCs) and Methane (CH\({}_{4}\))  
Total hydrocarbons (THC) and methane (CH\({}_{4}\)) are typically measured with Flame Ionization Detection (FID). In FID, the sample gas is introduced into a hydrogen flame, where some of the HCs in the sample gas are ionized [154, 155]. Due to the ions, an electric current is generated at the applied electric potential, is nearly proportional to the amount of carbon atoms. For this reason, the HCs concentration is called \"THC\" and the unit is \"ppmC\". A heated FID should be used in applications such as diesel exhaust that contains significant quantities of high boiling point HCs to avoid condensation and loss of heavier HCs [128]. The FID detector temperature should be set to 113 \({}^{\circ}\)C for alcohol-fueled vehicles (instead of 190 \({}^{\circ}\)C, which is used for diesel-fueled vehicles) (USA EPA Title 40, Chapter I, Subchapter C, Part 86, Subpart B, SS86.111-94). This is based on the higher water vapor of methanol and the fact that methanol can undergo decomposition reactions if the oven is too hot [156]. The FID sensitivity for each HC is represented by a \"response factor\" that indicates the relative sensitivity compared to propane as the calibration gas. Generally, the FID haslower sensitivity to oxygenated HC components such as alcohols, aldehydes [157; 158; 159; 160] and no sensitivity to formaldehyde. For regulatory purposes, FIDs are calibrated to have a response factor of 1 for propane. Toluene and propylene have to be within 0.9 and 1.1. The FID has negligible interference from inorganic components such as CO, CO\({}_{2}\), H\({}_{2}\)O, and NO, except for O\({}_{2}\) in the sample gas. The O\({}_{2}\) concentration in the sample can affect not only FID sensitivity for HCs but also the zero point. Some THC analyzers have a compensation function for O\({}_{2}\) interference using an additional O\({}_{2}\) analyzer. The regulation allows a maximum of 1.5% oxygen interference. For measuring CH\({}_{4}\) in the engine exhaust gas with the FID analyzer, sample conditioning parts, i.e., Gas Chromatography (GC) or Non-Methane Cutter (NMC), are placed before the detector to extract or separate CH\({}_{4}\) from the other HC components. The GC-FID-based CH\({}_{4}\) analyzer is only suitable for batch measurement rather than continuous measurements. A Non-Methane Cutter (NMC) is a catalyst that selectively oxidizes HCs and only minimally CH\({}_{4}\). The regulation requires the determination of the methane conversion efficiency, which ideally should be 0%, and the ethane conversion as an approximation of the conversion efficiency of the non-methane hydrocarbons, which should be >98%. If the CH\({}_{4}\) response is <1.05, it may be omitted from the calculations of the emissions. Non-Methane Hydrocarbons (NMHCs) are calculated as the difference of THC and CH\({}_{4}\). (details in regulation, it is not a simple subtraction as conversion efficiencies need to be considered). In EU for high ethanol content fuels a different density is used to calculate THCs and NMHCs (0.934 g/L E85 vs. 0.646 g/L E10). In USA, non-methane organic gases (NMOG) include NMHCs, alcohols and carbonyls. Therefore, to measure NMOG (gasoline with ethanol > 25%), one must separately measure the principle alcohols, aldehydes, and ketones, subtract their inaccurate contribution to the FID signal, and add in their correct concentrations. Ethanol is traditionally measured by impinger collection and GC. Alternatively, the ethanol levels in diluted emissions sampled into Tedlar bags can be read directly via a photoacoustic non-dispersive infrared method [161], thus avoiding the need for off-line impinge analysis. Aldehyde measurement is via DNPH cartridge collection and off-line high-pressure liquid chromatography. Thus, ethanol and acetaldehyde are measured via batch methods, thus precluding time-resolved NMOG data. FTIR spectroscopy provides an attractive alternative because all of the species contributing to NMOG are infrared active.