Abstract
Pollution from vehicles is a serious concern for the environment and human health. Vehicle emission regulations worldwide have limits for pollutants such as hydrocarbons, CO, and NOx. The measurements are typically conducted at engine dynamometers (heavy-duty engines) sampling from the tailpipe or at chassis dynamometers (light-duty vehicles) sampling from the dilution tunnel. The latest regulations focused on the actual emissions of the vehicles on the road. Greenhouse gases (GHG) (such as CO2, CH4, N2O), and NH3 have also been the subject of some regulations. One instrument that can measure many gaseous compounds simultaneously is the Fourier transform infrared (FTIR) spectrometer. In this review the studies that assessed FTIRs since the 1980s are summarized. Studies with calibration gases or vehicle exhaust gas in comparison with well-established techniques were included. The main conclusion is that FTIRs, even when used at the tailpipe and not at the dilution tunnel, provide comparable results with other well-established techniques for CO2, CO, NOx, while for hydrocarbons, higher deviations were noticed. The introduction of FTIRs in the regulation needs a careful description of the technical requirements, especially interference tests. Although the limited results of prototype portable FTIRs for on-road measurement are promising, their performance at the wide range of environmental conditions (temperature, pressure, vibrations) needs further studies.
Highlights
Vehicle emissions are regulated since the 1970s [1]
The main conclusion is that Fourier transform infrared (FTIR), even when used at the tailpipe and not at the dilution tunnel, provide comparable results with other well-established techniques for CO2, Carbon Monoxide (CO), NOx, while for hydrocarbons, higher deviations were noticed
The following sections summarize the results of the studies that assessed FTIRs against calibration gases or reference instruments
Summary
Vehicle emissions are regulated since the 1970s [1]. The measurements are conducted on chassis dynamometers (light-duty vehicles) or in engine test cells (heavy-duty engines).The instruments described in the regulations are sampling from the full dilution tunnel, where the whole exhaust gas is diluted, or directly from the tailpipe (undiluted exhaust).The control of the regulated pollutants (e.g., CO, NOx ) with advanced aftertreatment devices [2] has led in some cases to increased emission of non-regulated pollutants (e.g., N2 O, NH3 ). Vehicle emissions are regulated since the 1970s [1]. The measurement techniques for regulated pollutants are well-defined in the regulation (e.g., non-dispersive infrared (NDIR) for CO and CO2 ). For non-regulated pollutants, only recently, a Global Technical Regulation for light-duty vehicles (GTR 15) prescribes possible measurement techniques. One method that can measure many compounds is FTIR (Fourier transform infrared) spectroscopy (= study of the interaction between light with matter) [3]. Many compounds absorb infrared energy at an intrinsic wave number (or wavelength) proportionally to their concentration. In an FTIR spectrometer, some of the infrared (IR) radiation is absorbed by the sample, and some of it is passed through (transmitted). FTIR, compared to other IR techniques, can measure many components in real-time due to the use of an interferometer that allows the collection of a broad range of wavelengths. NDIR analyzers measure one compound due to the use of an optical filter that allows the selection of a narrow wavelength area, specific to the compound of interest
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