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In 2011, the European Commission introduced a limit for nonvolatile particle number (PN) emissions >23 nm from light-duty (LD) vehicles and the stated intent is to implement similar legislation for on-road heavy-duty (HD) engines at the next legislative stage. This paper reviews the recent literature regarding the operation-dependent emission of PN from LD vehicles and HD engines, and the measurement procedure used for regulatory purposes. The repeatability of the PN method is of the order of 5% and higher scatter of the results can easily be explained by the effect of the vehicles or the aftertreatment devices on the PN emissions (e.g., the fill state of the diesel particulate filters). Reproducibility remains an issue since it may exceed 30%. These high-variability levels are mainly associated with calibration uncertainties of the PN instruments. Correlation measurements between the full-flow dilution tunnels (constant-volume samplers, CVS) and the proportional partial-flow dilution systems (PFDS) showed agreement within 15% for the PN method down to 1 × 10 11 p/kWh. At lower concentrations, the PN background of the CVS and/or the PFDS can result in larger inconsistencies. The filter-based particulate matter (PM) mass and the PN emissions correlate well down to 1-2 mg/km for LD vehicles and to 2-3 mg/kWh for HD applications. The correlation improves when only elemental carbon mass is considered: it is relatively good down to 0.1-0.3 mg/km or mg/kWh. ACRONYMS AND ABBREVIATIONS ACEA Association des Constructeurs Européens d'Auto mobiles (European Automobile Manufacturers' Association) AM Accumulation mode APC AVL particle counter

The Raman line shape of the symmetric C = O stretching band at 1710 cm−1 has been measured in liquid acetone as a function of pressure from 1 bar to 4 kbar over the temperature range from −25 to 50 °C. The experimental data obtained show several unusual features. First, there is a frequency difference 〈δν〉 of about 7 cm−1 between the polarized and depolarized components. Sceond, the isotropic linewidth Γiso decreases with increasing density, in contrast to the opposite trend usually found in other liquids. Third, the second moment M2(V) of the isotropic band appears to decrease with increasing density. The consideration of the experimental linewidth and frequency data leads to a conclusion that intermolecular dipole–dipole coupling between polar acetone molecules are responsible for the observed unusual behavior of 〈δν〉, Γiso, and M2(V).

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The Raman band of the ring vibration (ν5) and the Fermi resonance between the carbonyl stretching (ν2) and the first overtone of the ring breathing vibration (2ν7) have been studied in liquid ethylene carbonate in the pressure range between 1 and 3000 bar and at temperatures from 40 to 160 °C. The relative changes of the transition dipole moments of both bands in resonance are estimated from the measurements of their intensity ratios. The knowledge of these parameters enables a comparison of the experimental frequency noncoincidence effect between isotropic and anisotropic components of the bands and the theory based on strong dipole moment coupling. The noncoincidence effect for the ν5 vibration are also explained in terms of this theory. The pressure induced frequency shifts of the bands are interpreted qualitatively by the permanent dipole–dipole coupling model.

The Raman line shapes and frequencies of the ν4 asymmetric (C=CH2) stretching mode at 1657 cm−1 and the ν9 symmetric (C–CH3) stretching mode at 805 cm−1 (both of symmetry A1) have been measured in dilute solutions of isobutylene in several polar and nonpolar solvents. The frequency shifts in the different solutions can be interpreted in terms of repulsion, dispersion, induction, and dipolar forces between molecular bonds. The induction and dipolar forces play only a minor role. The blue shift due to the repulsion forces and the red shift due to the attractive dispersion forces are nearly equal for ν9, while the dispersion forces are much more important for ν4. Analogous behavior has already been described in our earlier work dealing with pure compressed isobutylene. The frequency shift and the linewidth are connected via the first and second spectral moments, and the order of magnitude of the width can be predicted from the frequency shifts. However, quantitative calculations are more difficult for linewidths than for shifts. Qualitatively, the linewidth behavior is consistent with the result for the vibrational frequencies concerning the relative importance of the repulsive and attractive energies.

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